Thomas B. Irvine, Susan L. Kevdzija, and David W. Sheldon

Glenn Research Center, Cleveland, Ohio

David A. Spera

Dynacs Engineering Company, Inc., Brook Park, Ohio

Overview of the Icing and Flow Quality

Improvements Program for the NASA

Glenn Icing Research Tunnel

NASA/TM—2001-210686

February 2001

AIAA–2001–0229
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NASA/TM—2001-210686

February 2001

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

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sponsored by the American Institute of Aeronautics and Astronautics

Reno, Nevada, January 8–11, 2001

AIAA–2001–0229

Thomas B. Irvine, Susan L. Kevdzija, and David W. Sheldon

Glenn Research Center, Cleveland, Ohio

David A. Spera

Dynacs Engineering Company, Inc., Brook Park, Ohio

Overview of the Icing and Flow Quality

Improvements Program for the NASA

Glenn Icing Research Tunnel
Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

Price Code: A03

National Technical Information Service

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Price Code: A03

Available electronically at http://gltrs.grc.nasa.gov/GLTRS
NASA/TM—2001-210686 1 

OVERVIEW OF THE ICING AND FLOW QUALITY IMPROVEMENTS PROGRAM 

FOR THE NASA-GLENN ICING RESEARCH TUNNEL 

Thomas B. Irvine, Susan L. Kevdzija, and David W. Sheldon 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

David A. Spera 

Dynacs Engineering Company, Inc. 

Brook Park, Ohio 44142 

Abstract

Major upgrades were made in 1999 to the 6-ft by 9-ft 

(1.8 m by 2.7 m) Icing Research Tunnel (IRT) at the 

NASA Glenn Research Center. These included 

replacement of the electronic controls for the variablespeed drive motor, replacement of the heat exchanger, 

complete replacement and enlargement of the leg of the 

tunnel containing the new heat-exchanger, the addition 

of flow-expanding and flow-contracting turning vanes 

upstream and downstream of the heat exchanger, 

respectively, and the addition of fan outlet guide vanes 

(OGV’s). 

This paper describes the rationale behind this latest 

program of IRT upgrades and the program’s 

requirements and goals. An overview is given of the 

scope of work undertaken by the design and 

construction contractors, the scale-model IRT (SMIRT) 

design verification program, the comprehensive reactivation test program initiated upon completion of 

construction, and the overall management approach 

followed. 

Nomenclature

A to D 1st to 4th tunnel corners 

HX heat exchanger 

IRT Icing Research Tunnel (6’ x 9’) 

OGV fan outlet guide vane 

SMIRT Scale Model Icing Research Tunnel (1/10 th 

scale) 

Introduction

Research in aircraft icing and component icing 

qualification tests have been conducted in the Icing 

Research Tunnel (IRT) at the NASA Glenn Research 

Center (GRC; previously the Lewis Research Center) 

for over fifty-five years.1

 A wide variety of civilian and 

military aircraft components and ice-protection systems 

have been tested in the IRT under icing conditions. 

Test articles are usually full-scale or nearly full-scale in 

size, because scaling laws for icing are subjects of 

current research. 

In addition to NASA, organizations sponsoring tests in 

the IRT include the FAA, the Department of Defense, 

and both large and small manufacturers of airframes 

and aircraft engines. Private organizations compensate 

NASA for the use of the IRT in accordance with formal 

agreements authorized by the Space Act of 1958. In 

recent years the IRT has been one of NASA’s busiest 

wind tunnels. The bar chart in Figure 1 shows the 

number of hours of running time in the IRT in each 

year since 1990. 

Previous Upgrades and Long-Range Plans

Although the basic structure of the IRT dates back to 

1944, many components of the facility have been 

upgraded since that time. In addition, instrumentation, 

controls, and data acquisition systems have been 

regularly upgraded to include current technology. 

Major upgrades to the IRT are listed in Table 1. The 

fan drive motor was replaced in 1986, doubling the 

available power to 5,000 horsepower. In 1992 and 

1993 the insulation on a large portion of the tunnel was 

upgraded and an external force balance was installed. 

In 1993 new fan blades were installed with pitch angles 

modified to use all the available power in the drive 

motor. This resulted in an increase in maximum tunnel 

airspeed from 305 to 420 miles per hour. 

In 1994 an IRT Long-Range Improvement Plan was 

developed, in which the following four goals were 

established: (1) Increasing the size of the uniform icing 

cloud in the test section, (2) improving and increasing 

the capability of the spray system, (3) improving the
NASA/TM—2001-210686 2 

tunnel’s aerodynamic flow quality under dry operating 

conditions, and (4) increasing the maximum airspeed in 

the tunnel. This long-range planning resulted in the 

successful advocacy for a new spraybar system 

(1996/97) 2

 and a replacement heat exchanger (1999), 

as noted in Table 1. The first three of the goals of the 

long-range plan have now been met through the 

successful completion of these latest two upgrade 

programs. It is now clear that the fourth goal, that of 

increasing the tunnel’s maximum airspeed above the 

430 mph achieved in 1994, is not achievable with the 

current drive motor. Also, the noise levels in the 

control room during operations at airspeeds above 

400 mph were found to be too high for sustained 

testing. After the new heat exchanger was installed in 

1999 there was a further reduction in maximum 

airspeed to about 390 mph under dry operating 

conditions. However, during icing sprays the tunnel 

airspeed does not decrease significantly with the 

buildup of frost on the new heat exchanger. Therefore, 

tunnel operations during icing tests continue to meet 

most customer test matrix requirements. 

Scope

This paper describes the rationale behind the 1999 

program of IRT upgrades and the program’s 

requirements and goals. An overview is given of the 

scope of work undertaken by the design and 

construction contractors, the scale-model IRT (SMIRT) 

design verification program, the comprehensive reactivation test program initiated upon completion of 

construction, and the overall management approach 

followed. 

Airflow around the IRT Loop

One of the major objectives of the 1999 program of IRT 

upgrades is to improve flow quality within the Test 

Section by reducing upstream distortions in the air 

flow, including variations in airspeed, variations in air 

temperature, flow angularity, and turbulence. For this 

reason, a brief description is in order of the flow around 

the IRT loop, entering and leaving the Test Section. 

A plan view of the original configuration of the IRT is 

shown schematically in Figure 2(a). In this plan view, 

air circulates in a counter-clockwise direction around 

the tunnel loop, which is rectangular in cross-section 

except at the drive fan where it is circular. Starting at 

the Stilling Chamber in the lower left corner, lowvelocity chilled air passes through the spray bar section 

where heated air and water droplets are sprayed into the 

stream from an array of nozzles. 

The airflow carrying a cloud of super-cooled water 

droplets is then accelerated in the Convergence Section 

and enters the Test Section, at airspeeds up to 

approximately 400 mph. In the Test Section, water 

droplets freeze on contact with a test article that is 

usually mounted on the turntable in the tunnel floor and 

rotated to the desired angle of attack. The airflow then 

exits the Test Section and begins its deceleration in the 

Diffuser, which extends through Corners A and B. 

Each of these corners contains a cascade of vanes that 

turn the flow 90 degrees with minimal losses and 

turbulence. 

Downstream of Corner B the duct shape transitions 

from rectangular to circular, and the flow enters the Fan 

Section through a radial array of fan inlet guide vanes 

(IGVs). Here the airflow is swirled clockwise (looking 

downstream), which partially counters the swirl 

imparted later by the counter-clockwise rotation of the 

fan blades and reduces flow angularity downstream. 

The total pressure in the air stream is raised by the fan, 

in the amount required to offset pressure losses that 

occur throughout the rest of the tunnel loop. Air 

temperature is also increased as a result of the heat of 

compression. This is the main source of heat that must 

be removed from the tunnel by the heat exchanger 

further downstream. 

The outflow of the fan passes through a transition duct, 

which changes in cross-sectional shape from circular to 

rectangular, and then through the Vent Tower Section. 

The movable sidewalls of the vent tower are normally 

closed, but after icing tests they can be moved inward 

to allow outside air to mix with the flow and help dry 

out the tunnel. 

From the Vent Tower the flow passes through the 

turning vanes in Corner C and then through the heat 

exchanger, where its temperature is lowered. As 

illustrated in Figures 2(b) and (c), the fin-tube panels 

of the original heat exchanger are arranged in the shape 

of a “W” laid on its side. This increases the flow areas 

of the individual panels and thereby decreases airspeeds 

over the coolant tubes to an acceptable level. The flow 

then passes through the turning vanes in Corner D and 

back to the Stilling Chamber. 

Deficiencies to be Corrected by Upgrades

In recent years, deficiencies in the operation and 

maintenance of the IRT clearly indicated that certain 

components in the supply legs of the tunnel – from the 

fan to the Stilling Chamber – needed to be replaced and 

improved. The current upgrade program was designed 

to correct the following deficiencies: 

Obsolete Electronic Controls for the Fan Motor

The 5,000-hp synchronous motor driving the IRT fan 

was installed in 1986 with a “Varichron” AC-DC-AC 

electrical system for variable-speed operation. The 

microcomputer controlling all electrical system 

operations, which was designed according to the state 
NASA/TM—2001-210686 3 

of the technology in the early 1980s, had become 

obsolete. The company that owned the Varichron 

design was phasing out technical support for this 

control system. Because of their age, the electronic 

components in the microcomputer were failing in 

increasing numbers with each passing year. 

Troubleshooting and diagnostics were becoming more 

and more difficult. Spare and replacement parts were 

very hard to locate and, when found, were extremely 

expensive. 

Deterioration of the Heat Exchanger

The Carrier Corporation installed the large copper tubecopper fin heat exchanger, with a nominal refrigeration 

capability of 2100 tons, in the IRT in 1943. After more 

than 50 years of service, the network of copper tubes 

was deteriorating to the point where the repair or 

closing-off of leaking tubes was responsible for about 

100 hours of tunnel downtime each year. Leaks were 

occurring at silver-soldered joints at the end turns of the 

tubes, which were caused by the incompatibility of the 

R-134a coolant and silver solder. 

Corrosion of the C-D Leg Floor and Ceiling

Over the years, residual water from icing tests had 

badly corroded the steel floor plates in the C-D leg. 

Rainwater had also seeped under the roofing material, 

saturating of the roof insulation and corroding the 

ceiling plates. Condensation on the outer sides of the 

steel plates also added to the corrosion. Local repairs 

were made, but it was clear that the steel structure in the 

C-D leg could not be easily modified to support a new 

heat exchanger. In addition, the existing heat 

exchanger and the surrounding steel structure were so 

closely connected that it was impractical to replace the 

heat exchanger without replacing a large portion of the 

structure as well. 

Flow Distortions from the W-Shaped Heat Exchanger 

and Motor Stand Leg Fairings

The airflow in the supply legs, from the vent tower 

section downstream of the fan through the refrigeration 

heat exchanger and into the stilling chamber has been 

shown to be unevenly distributed across duct flow 

areas. 3, 4 The two main causes of these flow distortions 

were the “W” shape of the heat exchanger and the 

presence of two large fairings around the legs of the fan 

motor support stand below the fan motor nacelle. 

These leg fairings are shown in Figure 3. The nonuniform distribution of airspeed across the heat 

exchanger produced non-uniform cooling rates, and this 

required a complicated balancing of the coolant flow 

through the various HX panels in order to achieve a 

uniform air temperature in the Test Section. 

1999 IRT Upgrade Program

Objectives

The objectives of the 1999 IRT upgrade program, in 

priority order, are as follows: 

1. Modernize the electronic controls of the fan motor 

and eliminate the excessive maintenance time and 

costs required now to keep the existing, obsolete 

Varichron microprocessor operational. 

2. Replace the aging heat exchanger and eliminate the 

excessive downtime required now for repairing 

leaks. 

3. Replace the corroded and leaking steel tunnel 

structure in the C-D leg, particularly in the floor 

and ceiling plates. 

4. Improve the quality of the airflow into the 

spraybars, removing distortions and turbulence 

caused by the “W” shape of the original heat 

exchanger. 

5. Improve the uniformity of temperature in the 

airflow into the spraybars and the Test Section. 

6. Improve the insulation on the walls and roof of the 

C-D leg and add insulation to the floor, reducing 

the thermal load on the heat exchanger. 

The goal of the program is to obtain these objectives 

without reducing the overall performance of the IRT in 

its icing environment. The various phases of the current 

upgrade program are listed in Table 2, together with the 

performing organizations, dates, and (where applicable) 

costs for each. A brief description of each phase 

follows. 

Conceptual Design Phase

Feasibility and conceptual design studies for a 

replacement heat exchanger were conducted in-house as 

early as 1994.5

 These studies helped define the overall 

scope, geometric configuration, and objectives of the 

tunnel upgrade program. The selected configuration for 

the IRT upgrades is shown schematically in Figure 4. 

The original W-shaped heat exchanger was replaced 

with a flat-faced heat exchanger in order to eliminate 

the large flow distortions caused by the corner 

structures joining the original HX panels. The new heat 

exchanger was configured as two side-by-side units, 

each with its own coolant supply and return pipes. 

Coolant flows from a supply header at an outside wall 

through parallel horizontal tubes extending to the 

middle of the tunnel and then back to a return header, in 

a single pass. 

The two HX units were offset from one another in order 

to provide access for maintenance that might be 

required on the end turns of the coolant tubes. By 
NASA/TM—2001-210686 4 

offsetting the units in the streamwise direction there is 

almost no loss of active flow area, as would be the case 

for a maintenance corridor between units that are not 

offset. 

The major disadvantage of changing to a flat heat 

exchanger is that the width of the C-D leg had to be 

increased. The “W” shape of the original heat 

exchanger (Fig. 2(c)) was selected because it provided 

almost three times the flow area of a flat heat exchanger 

of the same height, for each foot of tunnel width. In the 

original HX, the fins at the entrance face of each 

slanted panel turned the flow normal to the panel, and 

another set of curved fins on the exit face returned the 

flow to a horizontal direction. To obtain the required 

flow area with a flat HX, the width of the tunnel duct 

between Corners C and D was increased from 29.2 to 

49.2 feet (8.9 to 15.0 m), the maximum width possible 

because of an adjoining building. Even with this added 

width, airspeeds over the coolant tubes in the 

replacement HX are about 35 percent higher than in the 

original HX for the same tunnel airspeed, making drag 

losses (proportional to the square of the local airspeed) 

a significant design consideration. 

The added width in the C-D leg necessitated two new 

cascades of turning vanes in Corners C and D. Each 

cascade of vanes is 57.2 ft (17.4 m) in length. The 

selected aerodynamic design consists of 16 large vanes 

in each corner, with the cross-sections illustrated in 

Figures 5(a) and (b). These vanes were specifically 

designed to slow down the flow entering the HX and 

then speed up the flow entering the Stilling Chamber.6 

As shown in Figure 5(a), the flow expands through 

Corner C, producing an average outflow-to-inflow 

airspeed ratio of 0.59. Figure 5(b) shows that at 

Corner D the flow contracts, and the average outflowto-inflow airspeed ratio is 1.69. 

The leading edge shapes of the new vanes in Corners C 

and D are designed to be relatively insensitive to the 

angle of the incoming flow, and the advanced 

converging-diverging shape of the flow path between 

adjacent vanes changes the flow direction and speed 

with low losses. The relatively large size of these flow 

paths permits personnel access to either face of the HX, 

for inspection and repair work. 

The decision to select this major change in the 

configuration of the IRT was based in part on the 

successful use of a similar configuration in the smaller 

Boeing Research Aerodynamic Icing Tunnel (BRAIT), 

located in Seattle, Washington.7

 In the BRAIT, 

however, the expanding and contracting turning vanes 

upstream and downstream of the flat HX were formed 

from closely-spaced, curved steel plates. For both 

aerodynamic and accessibility reasons, thick cambered 

airfoils were selected for the IRT turning vanes, in 

preference to the curved steel plates. 

During the design of the steel structure of the new C-D 

leg, special attention was given to mitigating the effects 

of corrosion that had been a continuous problem with 

the original 1⁄4-inch (6.4-mm) thick plates forming the 

duct flow surfaces. The thickness of the steel plates 

forming the duct was increased by 1/16 inch (1.5 mm) 

over the thickness required for strength and stiffness. 

With this corrosion allowance, the new floor plates are 

3/8 inch (9.6 mm) thick and the wall and ceiling plates 

are 5/16 inch (8.0 mm) thick. In addition, the paint 

system was selected for maximum protection against 

corrosion, and consisted of a moisture-cure urethane 

paint containing a micaceous iron oxide (MIO) 

additive. This additive, in the form of flakes, provides 

toughness to the paint during the large temperature 

changes occurring during IRT operations. 

The conceptual design phase also defined two upgrades 

to the fan motor subsystem. These included 

replacement of the electronic controls for the variablespeed motor and the installation of outlet guide vanes 

around the fan motor housing directly downstream of 

the fan blades. Figure 6 is a block diagram of the drive 

electrical system. It was determined that the 

maintenance problems with the drive were centered in 

the obsolete microcomputer. The other hardware in the 

system worked well, without any of the deficiencies 

described earlier. Therefore, bids were requested for 

the replacement of the microcomputer alone, with 

options to replace the entire system. 

Earlier measurements of airspeed and flow angularity in 

the Vent Tower Section, downstream of the fan, 

showed that airspeed was highly variable across the 

entrance to Corner C. When the outflow of the fan was 

swirling in the direction of rotation, the two long 

fairings on the legs of the fan motor stand were found 

to concentrate the flow along the floor and near the 

inner wall, with relatively low airspeeds along the 

ceiling near the outer wall. Outlet guide vanes were 

selected as a means of removing the swirl and making 

the airspeed distribution more uniform as the flow 

enters Corner C and the heat exchanger. This was 

expected to result in a more-uniform temperature 

distribution in the flow leaving the HX. 

The selected OGV design was that of a set of cambered 

airfoils placed radially outward from the fan motor 

housing at 24-deg intervals. As shown by the crosssections in Figure 7, each OGV has a uniform chord of 

71.7 in. (1,821 mm) and a leading edge that is angled to 

the tunnel axis at approximately 45 deg inboard (at the 

fan motor housing) and 20 deg outboard (at the tunnel 

wall).8

 While there are nominally 15 OGV positions, 

the leg fairings took two of these, and the one OGV 
NASA/TM—2001-210686 5 

between the leg fairings was eliminated as both 

unnecessary and interfering with personnel access to 

the fan blades. Therefore, only 12 OGV’s were 

required. The trailing edge of one OGV was notched to 

permit opening of an access door in the fan housing. 

To avoid any structural resonance excited by the 

passing of the 12 blades of the fan up to its maximum 

speed of 460 rpm, the fundamental natural frequency of 

the OGV’s was required to be at least 100 Hz. 

Preliminary and Final Design Phases

On the basis of this series of in-house concept studies, 

approval was received to proceed with preliminary and 

final design. A design contract was awarded to Aero 

Systems Engineering, Inc. (St. Paul, Minnesota). ASE 

conducted additional concept studies, developed project 

design criteria, and produced final design drawings and 

specifications for the new C-D leg. 9, 10 Subcontractor 

specifications were also developed by ASE for the 

replacement HX, the new corner turning vanes, and the 

fan outlet guide vanes. A basement was added under 

the C-D leg, which allows the tunnel floor to be well 

insulated with easier access to piping and cabling. 

Previously, there was only a crawl space under the 

uninsulated floor of the C-D leg. 

Preliminary design of the replacement HX was 

performed by Cloudy+Britton, Inc. (Mountlake 

Terrace, Washington), with final design and fabrication 

by Frigid Coil/Imeco, Inc. (Santa Fe Springs, 

California). The two side-by-side HX units illustrated 

in Figure 4 were each fabricated in four identical 

modules, stacked vertically. Each module is 24.5 ft 

wide, 6.56 ft high, and 4.13 ft thick in the flow 

direction (7.47 m x 2.00 m x 1.26 m). R-134a coolant 

flows through 16 staggered rows of horizontal, Ushaped aluminum tubes 1.03-in. in diameter. The tube 

rows are arranged in three separate zones in the flow 

direction (with 6, 6, and 4 rows per zone), each with its 

own supply and return headers and valves for 

temperature-balancing purposes. Vertical fins in each 

module are of aluminum and have a pitch of 0.667 in. 

(16.9 mm) in the upstream and middle zones and 

0.50 in. (12.7 mm) in the downstream zone. 

Table 3 contains a summary of the HX design-point 

parameters when it is operating dry and after four hours 

of frost accumulation. The design-point operating 

conditions are a test airspeed of 300 mph (134 m/s) and 

a test temperature of – 1.4 F (- 18.6 C). 

Engineering Laboratory Design, Inc. (Lake City, 

Minnesota) created the structural designs of the 

composite airfoils for the new turning vanes and the 

OGV’s, with stress analysis support from Jordan 

Engineering (Mill Valley, California). Each turning 

vane consists of three hollow segments stacked 

vertically. Figure 8(a) shows the design configuration 

of a middle-tier segment with integral flanges for 

bolting to the lower and upper tiers of segments. The 

upper end of each vane slides into a composite socket 

bolted to the tunnel ceiling, to accommodate differential 

thermal expansion and contraction. Each segment is 

fabricated in two pieces that are bonded together at its 

leading and trailing edges. Figure 8(b) illustrates the 

laminate structure of the vane walls, composed of a 

rigid foam core between layers of glass-fiber mat and 

woven roving bonded with vinyl ester resin. The 

structural design driver was the maximum allowable 

local panel deflection of less than the chord length/ 

600, or 0.17 in. (4.4 mm). With this composite wall 

construction, design deflections were limited to 0.06 in. 

(2.1 mm). 

The air loading on the turning vanes is directed mainly 

outward along the corner diagonal. To carry two-thirds 

of this load, two horizontal tie plates of a glassreinforced composite are sandwiched between the vane 

flanges shown in Figure 8(a) and anchored to the inner 

tunnel walls. A shear connection between each vane 

and the tunnel floor and socket connections to the 

ceiling carry the other third of the airloads along the 

corner diagonal. 

Figure 9(a) shows the structural configuration of the 

OGV’s. The flange on the outboard end is bolted to the 

tunnel wall. The inboard end slides in a composite 

socket bolted to the fan motor housing, for thermal 

stress relief. Two internal webs are required for the 

structure to achieve the specified minimum natural 

frequency of 100 Hz. The additional stiffening of 

carbon-fiber fabric in the laminate was also needed, as 

shown in Figure 9(b). 

Design Verification Phase with SMIRT

The quantitative effects of the major modifications 

planned for the IRT were largely unknown at the start 

of this upgrade program. Changes such as widening the 

C-D leg, using fewer and larger turning vanes with 

novel expanding and contracting designs, adding 

OGV’s to the fan, causing larger pressure losses 

through the HX, and placing the inner and outer HX 

units in an offset position all introduced some level of 

technical risk. To reduce this risk and verify the design 

assumptions, flow quality tests were performed in a 

1/10th-scale model of the IRT, designated as the 

SMIRT, in parallel with the design effort. 11, 12, 13

Figure 10 shows the SMIRT with the two different 

configurations of the C-D leg that were tested in this 

program. Figure 10(a) is a view of the SMIRT in its 

initial configuration, modeling the original IRT loop. 

In the foreground is Corner D, with a mock-up of the 

original W-shaped heat exchanger to the left. Under the 
NASA/TM—2001-210686 6 

safety shield in the rear is a scale-model fan that is 

driven by an air turbine to produce the 350-mph 

(156-m/s) airspeed selected for the SMIRT tests. 

Figure 10(b) is a view of the SMIRT model of the new 

C-D leg, showing the new configurations of the turning 

vanes in Corners C and D and models of the inner and 

outer heat exchanger units. These HX models are 

commercially available units, and their streamwise 

thickness is somewhat larger than scale. 

Instrumentation used to measure local airspeeds, flow 

angles, turbulence, and pressure in the SMIRT 

consisted of Pitot and hot-wire probes mounted on a 

remotely controlled traversing mechanism. Data 

samples were taken along multiple horizontal and 

vertical traverses at critical sections in the tunnel loop, 

from the fan outlet to the Test Section. 

The first series of tests in the SMIRT were conducted to 

verify that flow defects measured in the SMIRT would 

quantitatively represent those in the IRT. Axial 

airspeed distributions measured across the SMIRT and 

IRT Vent Tower Sections were compared, and the flow 

distortions in each were found to very similar in both 

size and location. Figure 11(a) is a polar plot of the 

two airspeed distributions across the section, in which 

the view is downstream toward Corner C.11 Each data 

point represents axial airspeed measurements averaged 

over a 5-deg sector centered on the tunnel axis and then 

divided by the section-average airspeed. The sizes and 

positions of the IRT maximum and minimum airspeed 

ratios are both modeled almost exactly in the SMIRT, 

and the transitions between these extremes are closely 

represented. 

For quantitative comparison, the coefficient of 

variability (COV) of the SMIRT airspeed distribution in 

Figure 11(a) is 41.3 percent, compared to the actual 

IRT COV of 36.6 percent, where the COV is the ratio 

of the standard deviation of the measurements divided 

by the average of the measurements. 

The radial locations of the fairings on the North and 

South legs of the fan motor support stand are indicated 

in Figure 11(a) by the two inclined lines. Taking note 

of the direction of fan rotation, it can be seen that 

maximum airspeeds occur along the left side of the 

South leg, where the counter-clockwise swirl in the fan 

wake is blocked and would develop a higher pressure. 

Conversely, minimum airspeeds occur along the right 

side of the North leg, where swirl would develop lower 

pressure. These observations provided the rationale for 

installing OGV’s immediately downstream of the fan. 

If swirl could be eliminated from the fan wake by the 

OGV’s, the influence of the leg fairings would be 

minimized and the airspeed distribution through Corner 

C and into the HX would be made significantly more 

uniform. 

This rationale was verified by SMIRT tests in which 

OGV’s were simulated by five baffle plates placed 

around the fan motor housing. When the baffle length 

was extended downstream as far as the leg fairings (1.4 

times the fan diameter), the COV of the downstream 

airspeed distribution was reduced from the 41.3 percent 

discussed earlier to the low value of 13.9 percent.11 

During the preliminary design phase of the upgrades, 

when the geometry was defined for the new C-D leg, 

the replacement HX, and the new turning vanes in 

Corners C and D, the SMIRT was re-configured to 

model the future configuration of the IRT, as shown in 

Figure 10(b). Flow quality surveys were conducted 

across sections in the vent tower, at the inlet and outlet 

of the HX, in the wakes of the turning vanes in Corners 

C and D, at the inlet to the spraybars, and in the middle 

of the Test Section. These measurements were the 

basis for projections of the flow quality improvements 

to be expected in the IRT.12

Figure 11(b) shows an example of the SMIRT flow 

quality projections compared with equivalent data from 

the original IRT. Shown here is the vertical distribution 

of axial airspeed in the Stilling Chamber. In the 

unmodified IRT the peak-to-valley variations in the 

“W” signature are as large as the average airspeed 

itself. By contrast, airspeed measurements made in the 

modified SMIRT at this same location project a range 

of only about 10 percent of the average airspeed. 

Another example of the SMIRT test data is shown in 

Figure 5(b). The projected distribution of airspeeds 

exiting from the Corner D turning vanes is illustrated 

by the velocity vectors immediately downstream of 

vane D-5.12 These vectors are derived from flow 

measurements made with a hot-wire probe moving 

horizontally across the section shown. It can be seen 

that each vane produces a definite wake. Local 

airspeeds are higher between vanes and lower directly 

downstream of vane trailing edges. However, most of 

these speed variations are removed as the flow passes 

through the contraction section of the IRT. 

Table 4 contains a summary of flow quality parameters 

measured in the IRT before modification and 

projections from SMIRT test data for these same 

parameters after modification to the tunnel. A detailed 

comparison of these projections with actual flow 

quality measurements made in the modified IRT and a 

discussion of lessons learned from this modeling 

program is available.13 Flow quality projections from 

SMIRT data were in generally good agreement with the 

IRT data, and the SMIRT tests provided the required 

design verification for this upgrade program. 
NASA/TM—2001-210686 7 

Construction Phase

A request for bids to replace the electronic controls for 

the fan motor was released in late 1998. The vast 

majority of responses were for complete new systems, 

not just an upgrade of the electronic controls. The 

reasoning behind these broader responses was that 

interfacing a modern controller with an older electrical 

system would require significant modifications to the 

code in the controller, as well as modifications to the 

controller hardware. 

The cost of replacing all electrical and electronic 

equipment feeding the drive motor was approximately 

five times that of replacing only the electronic controls. 

Not surprisingly, a contract solely for replacement of 

the original microprocessor was awarded to the 

company owning the original Varichron design, Alstom 

Drives and Controls, Inc. (Pittsburgh, Pennsylvania), 

which had the intimate knowledge of both the old and 

new controls necessary to interface these two systems. 

The prime contract for demolishing the existing C-D 

leg, building the modified leg on new foundations and a 

basement, fabricating and installing the new turning 

vanes and OGV’s, and installing the new HX with its 

piping system was awarded to the East-West 

Construction Company (Cleveland, Ohio) in July 1997. 

Principal subcontractors were the Frigid-Coil/Imeco 

Corporation, which fabricated the replacement heat 

exchanger and delivered it to the site, and Engineering 

Laboratory Design, Inc., which designed, fabricated, 

and installed the composite turning vanes in Corners C 

and D and the outlet guide vanes (OGV’s) around the 

fan motor housing. 

Preparation of shop drawings, ordering of materials and 

parts, and other work outside the tunnel (Phase 1) 

commenced in August 1997. Demolition and 

construction work (Phase 2) began on May 10, 1999. 

The tunnel was ready for re-activation tests on 

November 23, 1999, with completion of the contract 

work on April 28, 2000. The entire duration of 

construction was 1,003 days. Figures 12 to 16 are 

views of the demolition and construction work, and the 

installation of the HX modules. 

Figures 17 to 19 show the installation of the new 

turning vanes. In Figures 17 and 18, the segmented 

construction of the turning vanes, the horizontal tie 

plates between bolted flanges, and the large sizes of the 

flow passages between vanes can be seen. In each 

corner, one lower segment of a turning vane was 

designed to be removable, to provide access to each 

side of the HX for a powered lift vehicle. The 

removable segment in Corner D can be seen in Figure 

18, at the bottom of the seventh vane from the left. 

Figure 19 is a close-up view of the outer end of a tie 

plate in Corner C. The extruded fiberglass tie plate is 

reinforced with steel plates that bear against wall 

brackets, to help carry streamwise airloads on the vane 

array. 

Figure 20 illustrates the relatively large size of the fan 

OGV’s and their installation around the motor housing. 

The view is upwind. Several of the wood fan blades 

can be seen in the background, with their leading edges 

covered by protective rubber boots. Figure 21 shows 

the socket connections to the motor housing that 

provide for differential thermal expansion and 

contraction in the radial direction. Also shown in this 

figure is the OGV with its trailing edge cut out to allow 

an access door to open in the motor housing. 

Reactivation Phase

A comprehensive series of reactivation tests was begun 

in December 1999, near the end of the construction 

phase of the upgrade program.14 The most important of 

these reactivation tests are listed in Table 2, together 

with their objectives. A detailed discussion of the 

results of these tests and some of the lessons learned 

from them is available.15 A brief overview will be 

given here. 

Reactivation of the IRT began with static and lowspeed checkouts of the new electronic controls for the 

fan motor. Motor speed was then gradually increased 

to its maximum allowable level of 460 rpm to verify 

safe and stable operation of the motor controls and the 

aero-structural integrity of components such as the fan 

blades, the new turning vanes, and the new OGV’s. 

Strain gages on the fan blades and accelerometers on 

the turning vanes and OGV’s were used to monitor 

stresses and vibrations, which were all below allowable 

limits. 

Figure 22 shows a comparison of the test airspeeds 

achievable before and after tunnel modifications, with 

an empty test section and dry, ambient air temperature 

conditions. It can be seen from this chart that the 

maximum airspeed attainable in the IRT has decreased 

from its historic high of 420 mph (188 m/s) measured 

during the 1994 qualification of new fan blades to 

approximately 390 mph (174 m/s) today. This decrease 

is attributed to an approximately 70 percent increase in 

the drag losses across the flat HX compared with the 

original W-shaped HX, and to more drag loss than 

expected at the OGV’s. 

In Figure 23, pressure drops measured across the new 

HX are compared with design pressure drops. The 

range labeled “preliminary design” is a direct 

application of pressure drops measured across the 

original W-shaped heat exchanger, where heavy frost 

doubled the pressure drop.16 In the final design of the 

replacement HX, however, frost was expected to cause 
NASA/TM—2001-210686 8 

only a small increase in the pressure drop. This is 

shown by the two final design points at the bottom of 

the range, which represent operation at a test airspeed 

of 300 mph (134 meters per second). Pressure losses 

across the new HX with or without frost were expected 

to be about the same as those with the original HX in a 

dry condition. Examination of the actual pressure drops 

measured across the new HX with and without frost 

shows that the minor effect of frost was correctly 

predicted. While the pressure losses without frost at the 

design point are about 70 percent higher than predicted, 

losses for the frosted condition are still lower than those 

for the original HX. Therefore, these additional drag 

losses at the HX are not expected to significantly affect 

tunnel operations during icing tests at moderate 

airspeeds and with test section blockage. 

Next, the new HX was brought on-line to verify the 

function of valves and controls. The coolant flows to 

each of the eight HX modules and their 24 controllable 

zones were then balanced to minimize temperature 

variations downstream. During these tests it was 

determined that the 24 remotely controlled valves in the 

system (one for each zone) were not necessary for 

obtaining a uniform air temperature output. Manual 

valves controlling the flow to each zone are sufficient 

for thermal balancing of the HX. All remotely 

controlled valves were placed in a full-open condition 

pending their removal during a future shutdown period. 

This will eliminate the drop in coolant pressure at each 

valve and increase the effectiveness of the HX. 

After both the aerodynamic and thermal subsystems of 

the IRT were determined by an independent review 

committee to be operating properly and safely, an 

Integrated System Test was conducted successfully that 

simulated a typical icing test program during a night of 

operation of the IRT. 

Figure 24 illustrates the improvements obtained in air 

temperature uniformity with the replacement HX. In 

this chart, the standard deviation of air temperature 

measured downstream of the HX, at the entrance to 

Corner D, is plotted versus the test airspeed. 

Deviations are approximately 0.6 F (0.3 C) less with the 

new HX than with the old, which is a reduction of 

approximately 50 percent at a test airspeed of 200 mph 

(94 m/s). 

Testing of the current low-temperature capability of the 

IRT was begun, but has now been postponed until the 

remotely controlled coolant valves have been removed, 

because this should improve the results of the tests. 

Figure 25 shows the preliminary low-temperature data 

obtained with the valves in place. In this chart the 

minimum static temperature attainable is plotted versus 

the test airspeed. The FAA requirement of –22 F 

(–30 C) is shown, together with the design requirement 

for the new HX (Option E) and a more ambitious 

design goal (Option F). These options represent upper 

and lower bounds on low-temperature test data 

measured in 1995 with the original W-shaped HX in 

operation. The test data shown in the figure are at an 

airspeed of 350 mph (156 m/s) with all pressure 

regulating valves in place and with and without an icing 

spray. 

A quantitative measure of the cooling performance of a 

heat exchanger is its thermal effectiveness, defined as 

the ratio of the drop in air temperature across the HX to 

the difference between the inlet air temperature and the 

internal coolant temperature. In Figure 26 some 

preliminary data on the thermal effectiveness of the 

new HX are compared with performance data for the 

original HX. As expected, the higher face (inlet) 

airspeeds in the new HX reduce its thermal 

effectiveness somewhat, compared to the W-shaped HX 

with its much lower face speed for the same test 

airspeed. However, these preliminary data still indicate 

that the performance of the new HX under icing test 

conditions will meet design requirements and may be 

close to the design goal shown in Figure 25 after the 24 

remotely control valves are removed. 

Calibration of the uniformity, droplet size, and liquid 

water content of the icing cloud was a major element of 

the activation program, consuming almost 60 percent of 

the activation operating time. Because of the major 

changes made to the quality of the airflow entering the 

spraybar section of the tunnel, hundreds of spray 

nozzles were repositioned to obtain the maximum 

uniformity of ice accretion in the Test Section.17 Icing 

uniformity was assessed by measuring the thickness of 

ice deposited on a grid of steel bars with a spacing size 

of 6 in. by 6 in. (152 mm x 152 mm). Figure 27 is a 

layout of this uniformity grid and the nomenclature 

used to record ice thickness data. Figure 28 is a typical 

contour plot of the variability of ice accretion across the 

Test Section, expressed as deviations of local thickness 

from the average thickness. 

A side benefit of the replacement heat exchanger 

project was realized when, for the first time in the IRT, 

the two different types of water spray nozzles (Standard 

and Mod-1) were installed side-by-side. The tunnel 

downtime required for the 1999 upgrade program also 

provided time for the installation of this dual spray 

nozzle system. With both nozzle sets installed, the IRT 

spray system can now cover more of the icing 

requirements in the Federal Aviation Regulation (FAR) 

Part 25, Appendix C without a time-consuming nozzle 

change-out. 

Improving the quality of the airflow entering the 

spraybars has had a small negative effect on the 

uniformity of the icing cloud. The higher turbulence 
NASA/TM—2001-210686 9 

and angularity produced by the original W-shaped heat 

exchanger actually helped to mix the water droplets into 

a more uniform cloud. 2

 The current upgrades have 

reduced the turbulence and flow angularity, and the 

water droplets from each spray nozzle tend to remain in 

a narrow stream rather than mix with droplets from 

adjacent nozzles. For this reason, icing uniformity 

appears to have degraded somewhat.17 

Aero-thermal calibration of the Test Section was 

performed, following standard procedures used earlier 

in the IRT and other wind tunnels at the Glenn 

Research Center. Airspeeds, flow angles, turbulence, 

and temperatures were measured at grid points 

spanning the middle section of the Test Section, to 

produce statistical data like that shown in Figures 29 

and 30. Detailed descriptions of these and similar 

calibration charts for the modified IRT are available.18, 

19

The final step in the activation program was a 

verification that current ice shapes agree with those 

produced in the past in the IRT, for a standardized 

airfoil model tested under standardized conditions of 

airspeed, temperature, time, and liquid-water content in 

the icing cloud. Current shapes of rime ice and glaze 

ice were found to match previous shapes within 

allowable limits.20 

Operating Time to Date

The IRT was operated for a total of 571.1 hours during 

the activation test program, without incident. As of 

November 17, 2000, the total operating time on the 

modified IRT was 978 hours. 

Conclusions

1. All of the objectives of the 1999 IRT upgrade 

program were achieved. 

2. Some reduction in the performance of the IRT 

was measured during the activation test program. 

The maximum attainable airspeed was reduced by 

about 7 percent under dry operating conditions, 

because of the higher drag losses of the 

replacement heat exchanger and the fan outlet 

guide vanes. However, drag of the new heat 

exchanger is relatively insensitive to frost 

accumulation, so airspeeds under icing conditions 

are affected less than under dry conditions. 

3. Uniformity of icing in the test section was 

reduced somewhat because of less mixing of the 

water droplets within the icing cloud as flow 

turbulence and angularity were reduced by the 

upgrades. 

4. Remote control of individual cooling zones in the 

replacement heat exchanger is not required for 

temperature uniformity downstream. Remote 

control pressure regulating valves can be removed 

from the system, reducing the coolant pressure 

drop through the heat exchanger and increasing 

maximum coolant flow rates. 

5. Preliminary test data indicate that the lowtemperature performance limit of the upgraded 

IRT will meet the design goal under dry 

conditions and the design requirement under icing 

conditions, exceeding FAA requirements. The 

complete range of low-temperature limits is not 

yet defined as a function of airspeed, blockage, 

and spray conditions. The planned facility 

performance test has been postponed until the 

remotely controlled valves in the heat exchanger 

are removed (see Conclusion 3). 

6. Operation of the modified IRT for a total of 978 

hours without incident (as of November 17, 2000) 

indicates that start-up problems have been 

successfully addressed and that the tunnel is ready 

for normal research operations. 

References

1. Soeder, R. H.; Sheldon, D. W.; Andracchio, C. 

R.; Ide, R. F.; Spera, D. A.; and Lalli, N. M.: 

NASA Lewis Icing Research Tunnel User 

Manual, NASA TM 107159. NASA Lewis 

Research Center, 1996. 

2. Irvine, T. B., Oldenburg, J. R., and Sheldon, D. 

W.: New Icing Cloud Simulation System at the 

NASA Glenn Research Center Icing Research 

Tunnel, NASA/TM-1999-208891 (also AIAA98-0143). NASA Glen Research Center, 1999.

3. Arrington, E. A.; Pickett, M. T.; Sheldon, D. W.: 

Flow Quality Studies of the NASA Lewis 

Research Center Icing Research Tunnel Circuit, 

NASA TM 106545. NASA Lewis Research 

Center, 1994. 

4. Arrington, E. A.; Gonsalez, J. C.; Kee-Bowling, 

B. K.: Flow Quality Studies of the NASA Lewis 

Research Center Icing Research Tunnel Circuit 

(1995 Tests), NASA TM 107479. NASA Lewis 

Research Center, 1998. 

5. Spera, D. A.: Comparison of Concepts for 

Improved IRT Heat Exchanger, and Analysis of 

IRT Heat Exchanger Test Data from NASA TM 

100116, Sverdrup Corporation (unpublished). 

NASA Lewis Research Center, August 1994. 

6. Sanz, J. M.: Aerodynamic Design of New 

Expanding and Contracting Turning Vanes for 

the NASA Lewis Icing Research Tunnel 
NASA/TM—2001-210686 10 

(unpublished). NASA Lewis Research Center, 

October 1996. 

7. Chintamani, S., Delcarpio, D., and Langmeyer, 

G.: Development of Boeing Research 

Aerodynamic Icing Tunnel Circuit. AGARD 

paper at “Symposium on Aerodynamics of Wind 

Tunnel Circuits and Their Components”, 

Moscow, 1996. North Atlantic Treaty 

Organization, Neuilly sur Seine, France 1996. 

8. Schmidt, J. F.: Aerodynamic Design of New Fan 

Outlet Guide Vanes for the NASA Lewis Icing 

Research Tunnel, NYMA Corporation 

(unpublished). NASA Lewis Research Center, 

October 1996. 

9. Anonymous: NASA LeRC IRT Replacement 

Heat Exchanger Concept Study, NASA LeRC 

Contract No. NAS3-27613, Phase 2, Special 

Study Report 2, Aero Systems Engineering, Inc. 

(unpublished). NASA Lewis Research Center, 

1996. 

10. Anonymous: Icing Research Tunnel Building 

No. 11 Heat Exchanger Replacement, NASA 

LeRC Contract No. NAS3-27613, Final Report, 

Vols. 1 and 2, Aero Systems Engineering, Inc. 

(unpublished). NASA Glen Research Center, 

1999. 

11. Canacci, V. A.; Gonsalez, J. C.; Spera, D. A.; 

and Weaver, H. L.: Scale Model Icing Research 

Tunnel Validation Studies, AIAA-98-0706. 

NASA Lewis Research Center 1998. 

12. Canacci, V. A.; Spera, D. A.; and Gonsalez, J. 

C.: Flow Quality Studies of the Scale Model 

Icing Research Tunnel and Projections to the 

Full-Scale Modified IRT, AIAA-99-0307. 

NASA Lewis Research Center, 1999. 

13. Canacci, V. A., Gonsalez, J. C., and Spera, D. 

A.: Use of a Scale Model Tunnel in the Design 

of Modifications to the NASA-Glenn Icing 

Research Tunnel, AIAA-2001-0230. NASAGlenn Research Center, 2001. 

14. Sheldon, D. W., and Spera, D. A.: Activation 

Plan for the Modified GRC Icing Research 

Tunnel (IRT) (unpublished). NASA Glenn 

Research Center, August 1999. 

15. Sheldon, D. W., Andracchio, C. R., Krivanek, T. 

M., Spera, D. A., and Austinson, T. A.: Lessons 

Learned and Results from the Construction 

Phase and Qualification Testing of the Icing 

Research Tunnel Upgrades, AIAA-2001-0231. 

NASA-Glenn Research Center, 2001. 

16. Olsen, W.; Van Fossen, J.; and Nussle, R: 

Measured Performance of the Heat Exchanger in 

the NASA Icing Research Tunnel Under Severe 

Icing and Dry Air Conditions, NASA TM 

100116. NASA Lewis Research Center, 1987. 

17. Ide, R. F.: Icing Cloud Calibration of the NASA 

Glenn Icing Research Tunnel, AIAA-2001-0234. 

NASA Glenn Research Center, 2001. 

18. Gonsalez, J. C., Arrington, E. A., and Curry, M. 

III: Flow Quality Surveys in the NASA Glenn 

Icing Research Tunnel (2000 Tests), AIAA2001-0232. NASA Glenn Research Center, 

2001. 

19. Gonsalez, J. C., Arrington, E. A., and Curry, M. 

III: Aero-Thermal Calibration of the NASA 

Glenn Icing Research Tunnel (2000 Tests), 

AIAA-2001-0233. NASA Glenn Research 

Center, 2001. 

20. Van Zante, J.: Correlation of Current and 

Historical Ice Accretion Shapes on an NACA 

0012 Airfoil in the NASA Glenn Icing Research 

Tunnel (unpublished). NASA Glenn Research 

Center, July 2000. 
NASA/TM—2001-210686 11 

Table 1. - Major Upgrades to the IRT 

Year Upgrade 

1999 Replace motor control electronics. Replace heat exchanger. Replace C-D leg, adding 

basement. Replace C- and D-corner turning vanes. Add fan outlet guide vanes. 

1996-7 Install new spraybar subsystem and upgrade controls, increasing number of bars from 8 to 10. 

Icing cloud size and uniformity increased approximately 100 percent. Time required to 

stabilize the icing cloud decreased 90 percent. Install cold room 3D laser scanner for 

recording ice shapes. 

1993-4 Install new insulated siding on east half of tunnel (2-in. foam core with steel face sheets). 

Install new wood fan blades with increased pitch, increasing max test airspeed from 305 mph 

to 420 mph. Increase number of spraybars, from 6 to 8. 

1992 Install new insulated siding on West half of tunnel (2-in. foam core with steel face sheets). 

Install 5-component external force balance. Install video cameras and test section lighting to 

monitor ice accretion. 

1986 Replace fan drive motor, increasing power to 5,000 hp. Upgrade controls to digital 

Varichron system. Upgrade other tunnel and refrigeration controls from analog to digital. 

Fabricate spare set of wood fan blades. 
NASA/TM—2001-210686 12 

Table 2. - Summary of Phases of IRT 1999 Upgrade Program 

Program 

Phase 

Scope of Work Dates Performing 

Organization 

Contract 

cost 

Conceptual design of HX configuration and 

layout of new C-D leg 

1994 to 

1996 

In-house: Sverdrup, 

NYMA and NASA 

NA 

Aerodynamic design of new C- and D-corner 

turning vanes and OGV’s 

10/96 In-house: NASA and 

NYMA 

NA 

Concept studies, preliminary and final designs of 

C-D leg, and HX specifications 

1996 to 

1999 

Aero Systems 

Engineering 

Preliminary design of replacement HX 1996 Cloudy + Britton 

(ASE subcontractor) 

Design 

Preliminary structural design of new turning 

vanes and OGV’s 

1996 Engineering Laboratory 

Designs (ASE subcontr.) 

$ 715 K 

1/10 th scale model of original IRT: 

Verify correlation with IRT flow quality data 

1996 to 

1997 

In-house: NYMA and 

NASA 

Design NA 

Verification 

with SMIRT 

1/10 th scale model of modified IRT: 

Estimate level of flow quality improvements to 

be obtained in IRT 

1998 In-house: NYMA NA 

Design, fabrication, and installation of 

replacement electronic controls for fan motor 

9/99 to 

12/99 

Alstom Drives and 

Controls 

$ 190 K 

Abatement of lead paint in cutting/welding areas, 

around fan motor housing, and remaining areas of 

tunnel 

5/99 $ 210 K 

Demolition of old C-D leg and construction of 

new leg with new HX and airfoils 

5/99 to 

4/00 

East-West Construction 

(Prime contractor) 

Design and fabrication of HX 

And delivery to site 

 Frigid Coil/Imeco 

(E-W subcontractor) 

Construction 

Structural design, fabrication, and installation of 

composite turning vanes and OGV’s 

 Engineering Laboratory 

Designs 

 (E-W subcontractor) 

$ 5.3 M 

($ 0.9 M) 

($ 0.4 M) 

Reactivation Checkout electronic controls for fan motor 

Verify aero-structural integrity of fan, new 

turning vanes, and OGV’s 

Verify HX stability and performance 

Conduct Integrated System Test to verify 

combined operation of all subsystems 

Conduct Facility Performance Test to measure 

operating envelope of airspeed and lowest 

temperature, with and without icing and Test 

Section blockage (postponed) 

Reposition spray nozzles for maximum 

uniformity in icing across Test Section 

Calibrate distributions of airspeed and 

temperature across Test Section 

Verify correlation of current ice shapes with 

historical ice shapes 

12/99 –

5/00 

In-house: NASA and 

Dynacs 

NA 
NASA/TM—2001-210686 13 

 Table 3. - Heat Exchanger Design-Point Parameters 

Test Conditions Design Data 

Airspeed in Test Section (mph) 300 

Air temperature entering Corner D (F) -1.4 

Modules (Coils) 

Number 8 

Approximate weight (lb) 7,145 

Refrigerant R-134a 

Cooling capacity per module (ton) 208.2 

Cooling capacity of heat exchanger (ton) 1,665.8 

Coil height 78.375 

Fin height (in.) 77.5 

Finned length of coil (in.) 294.0 

Tube sheet depth (in.) 51.0 

Top and bottom aluminum plate thickness (in.) 0.375 

Face area (sq. ft) 158.23 

Inlet connections (in.) 1 at 2.0; 2 at 1.5 

Outlet connections (in.) 2 at 6.0; 1 at 5.0 

Air side of HX Zones: Upstream Middle Downstream 

Number of rows of coolant tubes 6 6 4 

Fins per inch of tube length 1.5 1.5 2.0 

Number of coolant passes per row 2 2 2 

Total cooling surface area (sq. ft) 6,381 6,381 5,385 

Total air mass flow (lbm/s) 1,843 1,843 1,843 

Air mass flow per module (lbm/s) 230.4 230.4 230.4 

Relative humidity (%) 45.0 59.7 72.6 

Inlet dry bulb temperature (F) 11.00 5.28 1.08 

Air density (lbm/cu. ft) 0.083 0.084 0.085 

Air volume flow per module (cu. ft/m) 166,357 164,335 162,847 

Face airspeed (ft/m) 1,051 1,039 1,029 

Condensate precipitation rate (lb/h) 0.00 11.94 13.63 

Condensate accumulation in 4 hr (lb) 0.0 47.8 54.5 

Avg. frost thickness in 4 hr, at 7 lb/cu. ft (in.) 0.0000 0.0128 0.0174 

Pressure drop across zone: No frost (in. H2O) 0.31 0.31 0.28 

Pressure drop across zone: 4-h frost (in. H2O) 0.31 0.36 0.36 

Outlet dry bulb temperature (F) 5.28 1.08 -1.4 

Refrigerant side of HX 

Evaporator temperature (F) -18.0 -18.0 -18.0 

Refrigerant flow (gal/m) 21.4 17.7 11.8 

Refrigerant flow (lb/m) 243.35 207.70 138.47 

Refrigerant flow rate 1.20:1 1.37:1 1.53:1 

Feed type LRT LRT LRT 

Avg. circuit pressure drop (psi) 0.460 0.270 0.220 

Avg. circuit temperature drop (F) 1.298 0.762 0.621 

Cooling capacity (ton) 95.1 70.7 42.5 
NASA/TM—2001-210686 14 

Table 4. - Changes in Average Flow Quality Parameters from Baseline to Modified IRT, 

Estimated from SMIRT Test Data 

Station 

no. 

Section 

name 

Variation in axial 

airspeed, 

COV 

(percent) 

Axial turbulence 

intensity, 

u’/U 

(percent) 

STD of pitch 

 flow angle, 

dα

(deg) 

STD of yaw 

 flow angle, 

dβ

(deg) 

 

Actual: 

Baseline 

IRT 

Est.: 

Modified 

IRT

Actual: 

Baseline 

IRT 

Est.: 

Modified 

IRT

Actual: 

Baseline 

IRT 

Est.: 

Modified 

IRT 

Actual: 

Baseline 

IRT 

Est.: 

Modified 

IRT 

2 Vent tower: 

C-corner inlet 

36.6 13.9 23.4 21.5 6.4 1.6 5.3 1.7 

3 HX inlet 26.0 14.1 15.4 18.8 4.8 1.9 2.0 4.6 

4 HX outlet 44.5 7.0 29.0 9.0 5.1 0.6 3.6 0.6 

5 Stilling chamber: 

Spraybar inlet 

21.5 5.2 8.4 3.7 1.0 0.8 3.5 1.4 

6 

(a) 

Test mid-section: 

6-ft x 9-ft zone 0.4 0.2 --- 0.4 0.7 0.3 0.7 0.2 

6’

(a) 

Test mid-section 

4-ft x 5-ft zone 0.2 0.02 0.6 0.3 0.7 0.3 0.5 0.2 

(a) Estimates without effects of spraybars; no spraybar model in SMIRT
NASA/TM—2001-210686 15 

Figure 1. Annual running times in the 6’x 9’ Icing Research Tunnel (IRT) since 1990.

(a) Plan view of the tunnel loop. 

Figure 2. Loop configuration of the IRT before the 1999 modifications. 

( ) = No. of operating months; all others are 12 months

(6)

(9)

(8)

(10)

(5)

0

200

400

600

800

1000

1200

1400

1600

'90 '91 '92 '93 '94 '95 '96 '97 '98 '99

Year

Operating Time (hr/yr)
NASA/TM—2001-210686 16 

(b) Sectional view of the original heat exchanger. 

The flow through the W-shaped heat exchanger is shown schematically.

(c) View upstream of the original IRT heat exchanger. 

The upper layer of fin-tube panels is out of view. (C-99-1334) 

Figure 2. Loop configuration of the IRT before the 1999 modifications. 
NASA/TM—2001-210686 17 

Figure 3. View upstream of the IRT fan and motor housing. The two long fairings over the legs of the motor 

support platform cause large variations in downstream air velocities. 

Figure 4. Loop configuration of the IRT after the 1999 modifications. The width of the new C-D leg has been 

increased 69 percent to accommodate a flat heat exchanger, new turning vanes have been installed in Corners C and 

D, and new outlet guide vanes have been installed around the fan motor housing. The electronic controls in the 

drive control room have also been replaced. 
NASA/TM—2001-210686 18 

0

50

100

150

200

0 50 100 150 200

Distance from North wall, x (in)

Distance from West wall, 

y (in)

C-1

C-2

C-3

C-4

C-5

V IN

V OUT

= 0.59V IN

Corner C

(a) Corner C cascade (16 vanes; expansion ratio = 1.69:1) 

 

0

50

100

150

200

250

300

150 200 250 300 350

Distance from North wall of Stilling Chamber, y (in) 

Distance from West wall, 

x (in)

D-1

D-2

D-3

D-4

D-5

D-6

D-7

D-8

V IN

V OUT

= 1.69 V IN

Velocity vector distribution

as measured at this station

in the 1/10th scale model IRT

(SMIRT)

Corner D

(b) Corner D cascade (16 vanes; contraction ratio = 0.59:1) 

Figure 5. Aerodynamic shapes of replacement turning vanes in Corners C and D of the modified IRT.
NASA/TM—2001-210686 19 

Figure 6. Block diagram representing the various components and functions of the IRT Varichron drive 

system. Only the obsolete microcomputer was upgraded during this program. 

Figure 7. Aerodynamic shape of fan outlet guide vanes installed in the modified IRT. 

 

Brushless

 Exciter

Regulator/Field Exciter

Microcomputer

 Isolation

Transformer

 AC-DC

Converter

DC-AC

Inverter

DC Link

Reactor

 Motor

Disconnect

Synchronous

 Motor

AC AC AC DC DC

Input Signal

-20

-10

0

10

20

30

-40 -20 0 20 40

Chordwise coordinate, x (in)

Lateral coordinate, 

y (in)

45 deg nominal inflow angle

20 deg nominal

inflow angle

Outboard profile

at tunnel wall

Inboard profile

at fan motor housing

Axial flowline
NASA/TM—2001-210686 20 

(a) Layout of a typical middle-tier segment, with integral end flanges for bolting to the lower 

and upper tiers of segments. 

(b) Laminate schedule for walls of the turning vanes, showing glass fiber reinforcement 

Figure 8. Structural configuration of the new turning vanes in Corners C and D. Each vane is composed of three 

segments; each segment is fabricated in two molded halves that are bonded together at leading and trailing edges. 
NASA/TM—2001-210686 21 

(a) Layout of hollow airfoil with two internal spars. Each airfoil is fabricated in two molded halves that are 

bonded together at leading and trailing edges. Flange ends are bolted to the tunnel wall. Inner ends slide in 

sockets bolted to the fan nacelle. 

(b) Laminate schedule for OGV’s, showing glass and carbon fiber reinforcement. 

Figure 9. Structural configuration of the new fan outlet guide vanes (OGV’s).
NASA/TM—2001-210686 22 

(a) The SMIRT in its initial configuration, modeling the original IRT loop. Corner D is in the foreground. 

The fan is in the rear, under the safety shield, and is driven by an air turbine. (C-1996-2408) 

(b) Elevation view of the modified C-D leg. The end wall has been removed to show (l. to r.) the new Corner C 

turning vanes, the outer and inner replacement heat exchanger units, and the new Corner D turning vanes.

Figure 10. The 1/10th scale model of the IRT (SMIRT) showing the two configurations of the C-D leg tested 

during the design verification program. 
NASA/TM—2001-210686 23 

(a) Polar distribution at Vent Tower station, without fan OGV’s. The view is downstream. The close 

agreement shown between the SMIRT and IRT data at this station verifies that the SMIRT accurately models 

the flow quality in the IRT. 

(b) Vertical distribution in the Stilling Chamber. The large distortions in airspeed caused by the old W-shaped 

HX in the IRT are eliminated in the modified SMIRT with its flat HX. 

Figure 11. Comparison of SMIRT and original IRT distributions of axial airspeed across tunnel stations. 

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Normalized axial airspeed, U/U STA

Normalized distance above tunnel floor, z/H

SMIRT modified: y/W = 1/4

SMIRT modified: y/W = 1/2

SMIRT modified: y/W = 3/4

IRT with old HX: y/W = 0.21

IRT with old HX: y/W = 0.43

IRT with old HX: y/W = 0.64

H = tunnel height; W = tunnel width

y/W = normalized lateral distance

from tunnel inner wall

Unmodified IRT

Modified SMIRT

IRT

SMIRT

Lines of constant normalized axial airspeed

Leg fairing locations

0 0.5 1.0 1.5

Airspeed ratio

U SECTOR /U STA

2.0

South Leg North Leg

IRT

SMIRT

Fan

rotation

U SECTOR = axial airspeed averaged over 5 deg sector

U STA = axial airspeed average over the station

View is downstream
NASA/TM—2001-210686 24 

Figure 12. Demolition of Corner D and the original heat exchanger. Corner C is in the background. (C-99-1452) 

Figure 13. Construction of the new Corner D and placing of one of the eight heat exchanger modules. (C-99-1997) 
NASA/TM—2001-210686 25 

Figure 14. Interior view of the new Corner C during construction, with three heat exchanger modules in 

place. The end turns in the aluminum coolant tubes indicate the locations of the three streamwise zones in each 

module. The coolant flow in each zone can be controlled independently, to minimize temperature variations in the 

outflow. (C-99-2005) 

Figure 15. View through the roof of the new C-D leg, showing the offset positions of the two heat exchanger 

units. The end turns in the coolant tubes are readily accessible for inspection and repair, without loss of active flow 

area for a corridor between units. (C-99-2178) 
NASA/TM—2001-210686 26 

Figure 16. View of the HX coolant supply (smaller diameter) and return (larger diameter) pipes on the West 

wall of the new C-D leg. Separate pairs of pipes are connected to each of the three streamwise zones in each of the 

four HX modules that are stacked vertically to form the West HX unit. (C-99-2655) 

Figure 17. Installation of the new fiberglass-composite turning vanes in Corner C. The horizontal tie plates 

between the vane segments help carry airloads directed outward along the corner diagonal. Socket connections at 

the ceiling provide for differential thermal expansion and contraction. (C-99-2287) 
NASA/TM—2001-210686 27 

Figure 18. View from the Stilling Chamber, looking upstream at the Corner D turning vanes. The lower 

segment of the seventh vane from the corner is removable, to provide access to the heat exchanger for a maintenance 

lift vehicle. (C-99-2285) 

Figure 19. View in Corner C of the trailing edge of vane C-1, showing the outer end of a tie plate sandwiched 

between bolted flanges. The reinforced end of the tie plate bears against brackets on the outer wall of the tunnel. 

(C-99-2432) 
NASA/TM—2001-210686 28 

(a) Workers installing a device for accurately measuring the variable wall-to-housing distances around each 

airfoil. The inner end of each OGV is contour-trimmed to length and fitted with a reinforcing rib before the 

OGV is hoisted into place. (C-99-2021)

(b) General view of all twelve OGV’s in place. The leg fairings take the place of two additional OGV’s. The 

OGV at the six o’clock position has been eliminated because it would block the primary access path to the fan 

blades. (C-99-2410)

Figure 20. Installation of the fan OGV’s around the motor housing. Views are upstream. Fan blades can be 

seen in the background. 
NASA/TM—2001-210686 29 

Figure 21. Close-up view of the socket connections between the OGV’s and the fan motor housing, to relieve 

radial thermal stresses. The cutout seen in the trailing edge of one OGV permits an access hatch in the side of the 

housing to open. (C-99-2408) 

Figure 22. Comparison of test airspeeds achievable in the IRT before and after tunnel modifications. 

Maximum airspeed was reduced approximately 8 percent. 

0

100

200

300

400

500

0 100 200 300 400 500

Fan shaft speed, N (rpm)

Test airspeed, 

VT (mph)

1994: Old HX

1997: Old HX

1999: New HX

Before modifications

After modifications

7.7 %

reduction
NASA/TM—2001-210686 30 

Figure 23. Comparison of measured and design pressure drops across the replacement heat exchanger. 

Measured pressure drop is approximately 70 percent higher than the final design. 

Figure 24. Improvement in the uniformity of temperature in the outflow of the replacement heat exchanger, 

compared with the original heat exchanger. The standard deviation of the temperatures measured with the array 

of thermocouples in Corner D is used as the measure of uniformity. 

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.000 0.001 0.002 0.003 0.004 0.005

Average duct dynamic pressure at HX inlet, p D,HX (psi)

Static pressure drop across HX, DpS,HX (psi)

New HX test data: No frost (1999)

New HX test data: 0.2- to 1.3-hr frost (2000)

Preliminary Design of new HX (1996)

Final design of new HX (1997)

Curve-fit to new HX data without frost

Final Design points:

4-hr frost, K = 13.2

No frost, K = 11.1

Old HX losses:

4-hr frost

No frost

= Preliminary Design range

Test data: No frost, K = 19.7

Slight increase with frost

K = static pressure drop/duct dynamic pressure

0.0

0.5

1.0

1.5

2.0

2.5

0 100 200 300 400

Test airspeed, V t (mph)

Standard deviation of HX outflow air temperatures, TSTD (F)

New HX: 24 Corner D thermocouples (2000 Activation Tests)

Old HX: 11 Corner D thermocouples (1997 Calibration)

Initial trend with new HX

Empty Test Section; Test Temperatures < 32 F

Initial trend with new HX

With and without icing spray
NASA/TM—2001-210686 31 

Figure 25. Preliminary lowest-temperature data obtained with the pressure regulating valves in place and 

fully open. 

Figure 26. Preliminary comparison of the measured thermal effectiveness of the new HX with that of the 

original HX. 

-50

-40

-30

-20

-10

0

0 100 200 300 400 500

T est airsp eed, V T (mph)

Min imum static test tem perature, 

Ts,m in (F)

FAA requirement

HX design requirement (1995)

HX design goal (1995)

P reliminary test of new HX: Dry condition (2000)

P reliminary test of new HX: With icing spray (2000)

Design requirement:

O ption E

Design goal:

 Option F

FA A requirement

Dry

With spray

Empty Test Section;

Pressure Regulating Valves installed

eta = (TC - TD)/(TC - TF)

T C, T D = Corner C, Corner D average air temperatures

T F = average Freon temperature in HX

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 100 200 300 400 500

Test airspeed, Vt (mph)

HX thermal effectiveness, eta

Old HX: Envelope of thermal effectiveness with and

without icing spray (1996)

New HX without spray (preliminary): Pressure

regulating valves (PRVs) installed

New HX with spray (preliminary): 5 - 10 min spray;

PRVs installed

Old HX

with and without icing spray
NASA/TM—2001-210686 32 

0

20

40

60

80

100

0 20 40 60 80 100 120

Lateral distance from inner wall of Test Section, y (in.)

Vertical distance above floor of Test Section, z (in.)

Test Section perimeter: 6-ft x 9-ft

Uniformity grid: 6-ft square; 6" x 6" mesh size

Typical location for measuring ice thickness

1

2

3

4

5

6

7

8

9

1/8" x 2"

stainless

steel bars

10

11

12

A B C DE FG H I J K LM

Typical ice

thickness

coordinates:

J7

Figure 27. Layout of the grid of steel bars used to measure the uniformity of ice accretion in the IRT Test 

Section. 

Figure 28. Typical contour plot of the variability of ice accretion across a 6-ft by 6-ft (1.8-m by 1.8-m) zone in 

the middle of the Test Section 

-36 -30 -24 -18 -12 -6 0 6 12 18 24 30 36

69

63

57

51

45

39

33

27

21

15

9

3

Dista nce from Ce nte rline (in.)

Dista nce a bove Floor 

LW C Uniform ity: Noz zle = M od1, V = 150 kts, M V D = 21um

0.50-0.60 0.60-0.70 0.70-0.80 0.80-0.90 0.90-1.00 1.00-1.10 1.10-1.20 1.20-1.30 1.30-1.40
NASA/TM—2001-210686 33 

Figure 29. Standard deviation of axial airspeed in the middle of the Test Section, as a function of the test 

airspeed. Airspeed deviations in the modified IRT are compared with measurements made in 1997. 

0.0

0.4

0.8

1.2

1.6

2.0

0 100 200 300 400

Axial airspeed in Test Section, U T (mph)

Standard deviation of total test temperature, 

TSTD (F)

1997: T = + 40 F

2000: T = + 28 F to + 32 F

2000: T = - 2 F to + 5 F

2000: T = - 23 F to - 10 F

4-ft x 5-ft area of Test Section

Figure 30. Standard deviation of total test temperature in the middle of the Test Section, as a function of the 

test airspeed and temperature. Temperature deviations in the modified IRT are compared with measurements 

made in 1997.

0.0

0.4

0.8

1.2

1.6

2.0

0 100 200 300 400

Axial airspeed in Test Section, UT (mph)

Standard deviation of axial airspeed, USTD (mph)

1997: 6-ft x 9-ft area

2000: 6-ft x 9-ft area

1997: 4-ft x 5-ft area

2000: 4-ft x 5-ft area
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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NASA TM—2001-210686

AIAA–2001–0229

E–12613

WU–708–90–1A–00

39

A03

Overview of the Icing and Flow Quality Improvements Program

for the NASA Glenn Icing Research Tunnel

Thomas B. Irvine, Susan L. Kevdzija, David W. Sheldon, and David A. Spera

Wind tunnel; Subsonic; Modifications; Icing; Flow quality

Unclassified -Unlimited

Subject Category: 09 Distribution: Nonstandard

Prepared for the 39th Aerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and

Astronautics, Reno, Nevada, January 8–11, 2001. Thomas B. Irvine, Susan L. Kevdzija, and David W. Sheldon, NASA

Glenn Research Center; and David A. Spera, Dynacs Engineering Company, Inc., 2001 Aerospace Parkway, Brook Park,

Ohio 44142. Responsible person, Thomas B. Irvine, organization code 7502, 216–433–5369.

Major upgrades were made in 1999 to the 6- by 9-Foot (1.8- by 2.7-m) Icing Research Tunnel (IRT) at the NASA Glenn

Research Center. These included replacement of the electronic controls for the variable-speed drive motor, replacement

of the heat exchanger, complete replacement and enlargement of the leg of the tunnel containing the new heat-exchanger,

the addition of flow-expanding and flow-contracting turning vanes upstream and downstream of the heat exchanger,

respectively, and the addition of fan outlet guide vanes (OGV’s). This paper describes the rationale behind this latest

program of IRT upgrades and the program’s requirements and goals. An overview is given of the scope of work undertaken by the design and construction contractors, the scale-model IRT (SMIRT) design verification program, the comprehensive reactivation test program initiated upon completion of construction, and the overall management approach

followed.