E. Allen Arrington and Jose C. Gonsalez

QSS Group, Inc., Cleveland, Ohio

Improvements to the Total Temperature

Calibration of the NASA Glenn

Icing Research Tunnel

NASA/CR—2005-213875

September 2005

AIAA–2005–4276
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E. Allen Arrington and Jose C. Gonsalez

QSS Group, Inc., Cleveland, Ohio

Improvements to the Total Temperature

Calibration of the NASA Glenn

Icing Research Tunnel

NASA/CR—2005-213875

September 2005

National Aeronautics and

Space Administration

Glenn Research Center

Prepared under Contract NAS3–00145

Prepared for the

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cosponsored by the AIAA, ASME, SAE, and ASEE

Tucson, Arizona, July 10–13, 2005

AIAA–2005–4276
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Available electronically at http://gltrs.grc.nasa.gov
NASA/CR—2005-213875 1

Improvements to the Total Temperature Calibration of the NASA 

Glenn Icing Research Tunnel 

E. Allen Arrington and Jose C. Gonsalez 

QSS Group, Inc. 

Cleveland, Ohio 44135 

Abstract 

The ability to accurately set repeatable total temperature conditions is critical for collecting quality icing 

condition data, particularly near freezing conditions. As part of efforts to continually improve data quality in the 

NASA Glenn Icing Research Tunnel (IRT), new facility instrumentation and new calibration hardware for total 

temperature measurement were installed and new operational techniques were developed and implemented. This 

paper focuses on the improvements made in the calibration of total temperature in the IRT. 

Nomenclature 

A0, A1, A2 RTD probe total temperature flow recovery curve fit coefficients 

C0, C1 Test section total temperature calibration curve fit coefficients 

M Mach number 

PT Total pressure, psia 

PS Static pressure, psia 

Pair Spray bar air pressure, psig 

t time, seconds 

TT Total temperature, °C (K, °F) 

TT,jet Total temperature of the free jet calibration facility airflow, °R 

TT,probe Total temperature of the probe (RTD) being calibrated, °R 

TS Static temperature, °C (°F) 

TT,davg Average of the 24 Corner D total temperature measurements, °C (°F) 

U Velocity, knots (ft/sec) 

X Axial coordinate with axis origin at bellmouth/test section weld seam, in. 

Y Spanwise coordinate with axis origin at the test section inner wall, in. 

Z Vertical coordinate with axis origin at the test section floor, in. 

σ Standard deviation 

Subscripts

c Calibrated value 

t time, seconds 

ts Test section conditions

bm Bellmouth conditions 

I. Introduction 

The NASA Glenn Research Center (GRC) Icing Research Tunnel (IRT) is the primary ground test facility for the 

study of aircraft icing phenomena in the United States. As such, the IRT facility staff and GRC icing experts are 

always looking for ways to improve the data quality, data accuracy and test efficiency. In 2004, the IRT team 

responded to icing community suggestions about improving a perceived lack of accuracy in the total temperature 

measurement in the facility. The facility total temperature was monitored using a set of 24 type-T thermocouples 

mounted along the leading edges of the Corner D turning Vanes. It was suggested that the overall measurement 

quality could be improved by replacing the existing thermocouples with resistive temperature device (RTD) 

transducers. The IRT engineering staff completed a detailed review of the available RTD measurement systems and 

replaced the D-Corner thermocouples in early 2004 (during the planned facility downtime for replacement of the 

drive fan inlet guide vanes). This paper provides and overview of the improvements made in the total temperature 

measurement in the IRT, with the focus on the total temperature calibration. 
NASA/CR—2005-213875 2

II. Total Temperature Measurement Issues and Solutions 

In a specialized test facility, like the IRT, it is critical that the test customers have confidence in the data, which 

means confidence in the test facility, test techniques, instrumentation and data systems. The facility staff must 

understand more than just the standard subsonic wind tunnel calibration and flow quality parameters of pressure, 

flow angle, turbulence and Mach number; there are parameters associated with the icing cloud formation, such as 

liquid water content and droplet size that are of paramount importance when setting icing conditions. Depending on 

the specific conditions, such as near freezing, total and static temperature settings are also critical parameters, since 

the type of icing phenomena an aircraft will encounter is dictated in part by the air temperature. Because of the 

criticality of the temperature measurement, the IRT management and staff decided to improve the overall total 

temperature measurement system in the IRT. 

 There were several related issues that were addressed to improve the total temperature measurement system in 

the IRT. While the improvement to the facility instrumentation was the primary change to the total temperature 

measurement system, it was also necessary to improve the total temperature calibration methodology. The following 

is a list of the issues and their solutions that have been implemented in the IRT. The effectiveness of the solutions 

will be addressed throughout the remainder of the paper. 

• Overall total temperature measurement accuracy: The accuracy of the total temperature measurement is very 

important in the IRT, particularly for icing conditions at or near the freezing point. IRT personnel changed the 

facility instrumentation in D Corner to RTDs to improve overall accuracy. 

• Total temperature calibration accuracy: In concert with the facility total temperature instrumentation upgrade, it 

was necessary to replace the temperature calibration instrumentation to improve the overall accuracy of the total 

temperature calibration. RTD probes were selected for use on the test section calibration hardware to provide 

the required accuracy improvement as well as consistency with the facility instrumentation. 

• Spatial and temporal variations: Prior to 2004, all aero-thermal calibration data were collected using a rake that 

spanned the test section horizontally and was positioned at multiple vertical heights to survey a plane in the test 

section. This survey method artificially magnified the apparent total temperature variation over the survey plane 

since it was not possible to account for normal temporal variations in the flow field. A recommendation was 

made following the 2000 calibration that a 2-D array of temperature probes should be used to collect data over 

the entire survey plane simultaneously. 

• Low speed calibration: Spraybar air injection has a significant effect on the test section airspeed at 50 knots. 

The total temperature calibration relationship was tailored to address the affects of spraybar air injection on the 

test section temperature at the low speed condition. 

• Reduction of test time required: The 2-D array described above would have the added benefit of greatly 

reducing the test time and cost needed to complete the total temperature calibration. 

III. Description of Facility 

The NASA Glenn Icing Research Tunnel is a closed-loop atmospheric tunnel with rectangular cross sections. 

The airflow is driven by a 25-ft diameter twelve blade fan that is powered by a 5000-horsepower electric motor. The 

tunnel test section is 6-ft high, 9-ft wide, and 20-ft long. There is no divergence along any of the test section 

surfaces. The velocity in an empty test section can be varied between 25 and 340 knots at –17.8 °C (37 to 575 ft/sec 

at 0 °F).*

 A set of ten horizontally oriented spray bars, located in the settling chamber at the bellmouth inlet, inject 

atomized water into the airflow to create icing conditions. The tunnel has been in service since 1944 and has 

undergone several major upgrades and modifications over the years to insure that it remains the lead ground test 

facility for icing research (refs. 1 and 2). In 2004, the inlet guide vanes (IGVs) upstream of the drive fan were 

replaced, primarily for structural reasons, but also to improve aerodynamic performance. The new RTDs were 

installed in D Corner during this downtime. Figure 1 shows the IRT plan view as the tunnel is currently configured. 

More information about the IRT is located in reference 3. 

 

*

In general, English units are used in the aero-thermal calibration of all wind tunnels at NASA Glenn. However, for consistency 

with many of the icing tests conducted in the IRT, velocity is expressed in knots and temperatures in degrees Celsius. Exceptions 

are noted in the text.
NASA/CR—2005-213875 3

 Figure 1. Layout of the NASA Glenn Icing Research Tunnel. 

IV. Hardware Description 

There have been several sets of instrumentation used to calibrate the aero-thermal characteristics of the IRT 

during the course of its history. In general, instrumented rakes of pressure and temperature probes have been used to 

collect both calibration and flow quality data in the IRT test section. In 1997, an instrumented rake, known as the 

9-ft survey rake, was designed specifically for the IRT aero-thermal calibration testing, which allowed the 

simultaneous measurement of total and static pressure, total temperature, flow angle and turbulence. 

In order to improve the accuracy and confidence in the total temperature calibration, it was necessary to upgrade 

the calibration instrumentation from thermocouples to RTDs to match the newly installed instrumentation in 

D-Corner. Recommendations made following the 2000 aero-thermal calibration called for the use of an array or grid 

of temperature probes to collect test section temperature data in order to eliminate any temporal variation in the data 

caused when collecting data using a single rake positioned at multiple heights over the course of several test runs. 

Therefore, rather than refit the 9-ft survey rake with RTDs, a new piece of hardware of developed specifically for 

the IRT total temperature calibration, the 2-D RTD array. 

A. 9-Foot Survey Rake 

The 9-ft survey rake has been the primary tool for carrying out full aero-thermal test section calibrations and flow 

quality measurements since 1997. Figure 2 is a photograph of the 9-ft survey rake installed in the IRT test section at a 

vertical height of Z=36 in. (centerline) and axial position of X=179.3 in. downstream of the tunnel datum line (106.3 in. 

downstream of the test section inlet). Figure 3 shows the plan view of the IRT test section with the survey rake installed. 

The survey rake was supported at both ends by bolting the rake to wall mounted support plates. These support plates are 

6-ft tall and have a bolt pattern that allow the rake to be positioned vertically every 6-in. above or below the test section 

centerline. A vertical strut was also used to support the rake in the center. The main body of the rake is formed by two 

aluminum I-beams and thin aluminum plates riveted together. Thin sheets of aluminum were bent to form the leading 

and tailing edge of the rake body. 

The instrumentation mounted on the 9-ft survey rake includes eleven flow angle pressure probes, eleven total 

temperature thermocouple probes, and three single sensor or dual sensor hot wire probes. The flow angle pressure probes 

are of hemi-spherical head design and have five total pressure ports in the head. The four circumferential total pressure 

ports measure pitch and yaw angle. The center port measures total pressure. Four static pressure ports are located 

downstream of the head. The heads of the probes are 20.75-in. upstream of the rake leading edge; spacing between the 

probes is 9 in. The static pressure taps on each probe are 5.75-in. downstream of the head. The rake is mounted in the test 

section so that the tips of the pressure probes are positioned at the centerline of the test section turntable. The probes 

were calibrated for Mach numbers between 0.1 and 0.6 in the NASA Glenn 3.5-in. diameter free jet calibration facility. 
NASA/CR—2005-213875 4

Figure 2. Photograph of the 9-foot horizontal survey rake installed in the IRT test section.

Datum line 

(weld seam)

Test 

section 

inlet

73.0

179.3

106.3

Figure 3. Plan view of the IRT test section showing the installed location of the 9-foot survey rake.

Aspirated total temperature thermocouple probes with copper/constantan (type T) wires were used. The probes are 

mounted to the bottom surface of the survey rake with the tips of the probes about 0.5-in. upstream of the rake leading 

edge and 2.0-in. below the rake centerline; probe spacing is 9 in. The total temperature probes were calibrated for total 

temperature recovery in the NASA Glenn 3.5-in. diameter free jet calibration facility. 

Three single sensor or dual sensor hot wire probes (0.00015-in. diameter tungsten wires) were used. The probes 

were mounted to the upper surface of the rake body as depicted in figure 2. The probe tips were located 9.75 in. 

upstream of the rake body leading edge and 3.0-in. above centerline. 

B. 2-D RTD Array 

The 2-D RTD Array was designed and built to provide a more accurate total temperature calibration and 

temperature mapping of the test section, while also reducing overall test time and cost. There were several items that 

were considered during the design that are discussed in the following sections. 
NASA/CR—2005-213875 5

1. RTD Array Design 

The first design point was to 

determine the number and 

arrangement of the RTD probes in 

order to provide adequate coverage 

of the test section flow field. 

Reference 5 provided a 

recommendation on the 

arrangement of the probes in the 

test section that was adopted for 

the RTD array. The resulting 

layout is a 7-by-7 grid with the 

probes spaced at 0, ±25, ±50 and 

±75 percent of the test section 

dimension from the horizontal and 

vertical centerlines, as shown in 

figure 4. This arrangement 

provided the test section coverage 

required without incurring an 

unreasonable cost for the RTD 

probes. 

The next step was to design a 

support system for the RTD probes that would allow for the needed test section coverage without excessive 

blockage. Other considerations were weight (for ease of installation), probe installation (to allow for replacement or 

repair of damaged probes) and protection of the instrumentation lines. The final solution was to construct and array 

of seven vertical members, that would each house the seven RTD probes and instrumentation wiring, and four 

horizontal members for structural rigidity. The array would be secured to the test section walls, floor and ceiling, 

however allowances were made to account for thermal expansion of the array. Figure 5 shows the 2-D RTD array 

installed in the IRT test section. 

2. Selection of RTD Probes 

The RTD total temperature probe selection process first began with a review of the desired total temperature 

accuracy. The thermocouple total temperature probes used for previous test section aero-thermal calibrations had an 

absolute measurement uncertainty of ±1.1 °C (±2 °F) (ref. 4). The goal was to improve the absolute measurement 

uncertainty. The resulting 4-wire RTD total temperature probe system has an absolute measurement uncertainty of 

±0.10 °C (±0.18 °F) for a probe that was individually calibrated for total temperature flow recovery. The details of 

this uncertainty analysis are left to the uncertainty section of this paper. 

Figure 5. Installation of the 2-D RTD Array in the IRT test section. (a) view looking downstream. 

(b) view looking upstream.

(a) (b)

-36

-27

-18

-9

0

9

18

27

36

-54 -40.5 -27 -13.5 0 13.5 27 40.5 54

Distance from centerline, in.

Distance from centerline, in

Figure 4. 7x7 grid arrangement of the RTD probes in the IRT test section. The 

intersections of the dotted lines indicate the probe positions.
NASA/CR—2005-213875 6

RTD ceramic 

capsule

Prototype “A”

Prototype “B”, types 1 and 2

Prototype “C”

φ0.28 φ0.38

0.06 0.59

45o internal 

chamfer (typical)

φ0.19 φ0.19 φ0.25

4 holes, φ0.065 0.27

0.69

φ0.19

4 holes, φ0.065 

and φ0.110

0.25

0.75

4 holes, φ0.065

φ0.19 φ0.19 φ0.25

0.51

0.69 1.00

Figure 6. Three prototype RTD probes evaluated for use on the 2-D RTD array (dimensions 

in inches).

Selection of the actual RTD total 

temperature probe began by testing the 3 

prototype probes shown in figure 6. The 

evaluation testing was conducted in the 

NASA Glenn 3.5-in. diameter free jet 

facility (reference 6 provides a 

description of the test facility and typical 

test procedures). Figure 7 shows the 

results from the prototype evaluation 

tests in the form of the actual free jet 

stagnation temperature normalized by the 

total temperature as measured by the 

prototype RTD probe immersed in the 

free jet. Note that the data were collected 

at a nominal free jet stagnation 

temperature of 520 oR and that the 

temperature recovery factors in figures 7, 

8 and 9 use the data as collected 

(therefore the units are oR/oR). 

The results of the evaluation testing 

are summarized as follow: 

• Prototype “A” had the best temperature recovery (smallest deviation from 1.0 with increasing Mach number); 

however, it was not durable. The RTD capsule was solely supported by the small RTD lead wires which could 

not handle the dynamics associated with high speed flow. Movement of the capsule within the aspirator would 

eventually cause the support/RTD lead wires to break. 

• Prototype “B” was designed and built to solve the durability problem. It had a ceramic RTD capsule protected 

within a stainless steel sheath. This was the most durable design; however, it had the disadvantage of having 

the worst temperature recovery of the three prototype designs. For this prototype design, two aspirator hole 

sizes were tried. The larger holes resulted in poorer recovery. 

0.999

1.000

1.001

1.002

1.003

1.004

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Mach Number

Temperature Recovery, TTjet / TTprobe

Prototype 'A'

Prototype 'B', 0.065" Diameter Aspirator Holes

Prototype 'B', 0.110" Diameter Aspirator Holes

Prototype 'C'

Figure 7. Total temperature recovery results for RTD prototype probes.

0.0 0.1 0.2 0.3 0.4 0.5

Mach number

Temperature recovery, TT,jet/TT,probe, oR/oR

1.000

1.003

1.001

0.999

1.002

1.004

Prototype “A”

Prototype “B” (0.065 in. dia. aspirator holes)

Prototype “B” (0.110 in. dia. aspirator holes)

Prototype “C”

Data collected at TT,jet = 520 oR (nominal)
NASA/CR—2005-213875 7

0.9998

1.0000

1.0002

1.0004

1.0006

1.0008

1.0010

1.0012

1.0014

1.0016

1.0018

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Mach Number, M

Total Temperature Recovery, TTjet / TTprobe

TTjet / TTprobe = 6.099340E-03*M**2 + 6.670401E-04*M + 1.0

0.9995

1.0000

1.0005

1.0010

1.0015

1.0020

0.00 0.10 0.20 0.30 0.40 0.50

Mach Number, M

Total Temperature Recovery, TTjet / TTprobe

TTjet / TTprobe = 6.881316E-03*M**2 + 1.490507E-04*M + 1.0

Figure 8. Typical total temperature flow 

recovery curve for the 2-D RTD array probes.

Figure 9. Total temperature flow recovery data for 

RTD probes 1 through 23 with average curve fit.

Mach number, M

0.0 0.1 0.2 0.4 0.3 0.5

Total temperature recovery, TT,jet/TT,probe, oR/oR

0.9998

1.0000

1.0002

1.0004

1.0006

1.0008

1.0010

1.0012

1.0016

1.0018

1.0014

TT,jet/TT,probe = 1.0 + 6.670401x10-4·M

+ 6.09934x10-3·M2

Probe number 15

0.0 0.1 0.2 0.3 0.4 0.5

Mach number, M

0.9995

1.0000

1.0005

1.0010

1.0015

1.0020

TT,jet/TT,probe = 1.0 + 1.490507x10-4·M

+ 6.881316x10-3·M2

Data collected at TT,jet = 520 oR 

(nominal)

Total temperature recovery, TT,jet/TT,probe, oR/oR

• Prototype “C” seemed to be the best compromise between recovery and durability. It featured an exposed 

ceramic RTD capsule that was partially pulled back and potted into the supporting probe shaft (the RTD length 

was half that of prototype “A”). This gave it good durability and recovery better than having the RTD capsule 

encased in a stainless steel sheath. The recovery characteristics of this prototype in comparison to prototypes A 

and B are shown in figure 7. 

Through this series of evaluation tests, prototype “C” was selected as the actual probe design to be used on the 

IRT test section RTD array. A total of 52 RTD probes were built for use in the IRT aero-thermal calibration based 

on the prototype “C” design. Three of the probes were mounted on the subsonic quick-check rake (serial numbers 1 

through 3) and the remaining probes were assigned to the 2-D RTD array (serial numbers 4 through 52). 

3. Flow Recovery Testing 

A portion of the RTD probes (serial numbers 1 through 23) were calibrated for temperature flow recovery in the 

3.5-in. Diameter Free Jet Facility. The recovery testing was conducted to determine how well the probes sense the 

total pressure over a range of airflow conditions. During the testing, the free jet air temperature was set to a nominal 

condition (about 520 °R) and held constant while the free jet Mach number was varied from 0 to 0.5. Figure 8 shows 

the total temperature recovery results for a typical probe (serial number 15) with its individual flow recovery curve. 

The recovery curves were subsequently used to correct data collected in the IRT. The 20 RTD probes that were 

individually calibrated for flow recovery were mounted in the center of the 2-D RTD array. The probes that did not 

have their recovery characteristics directed measured were mounted around the periphery of the array and used the 

average recovery from all the calibrated probes (fig. 9). 

C. Facility Instrumentation 

The following standard facility instrumentation was used during this test program: 

1) Bellmouth/test section pitot-static probes: Two probes are mounted near the exit of the bellmouth, one on the 

inner wall and one on the outer wall. These probes are used to measure the test section total and static pressure. 

Measurements from both probes are averaged to arrive at PT,hm and PS,,bm. These probes are shown in figure 3. 

2) Total temperature probes in corner D: Twenty-four RTD probes are arrayed on the leading edges of the turning 

vanes in Corner D to measure the temperature profile exiting the facility cooler. The distribution of the 

measured temperatures and the average of these twenty-four probes, TT,davg, is used to monitor the operation of 

the heat exchanger. The locations of these probes are shown in figure 10. 
NASA/CR—2005-213875 8

8.7 5.8 5.8 8.7 8.7

49.2

2.9

Outer wall

Dxx : RTD probe

22.9

16.4

3.3

9.8

Figure 10. Layout of the RTD probes mounted on the Corner D turning vanes. View looking upstream. 

Dimensions in feet (not to scale).

D11 D12

D31 D32

D51 D52

D71 D72

#1

#3

#5

#7

D23 D22 D21

D33 D43 D42 D41

D53 D63 D62 D61

D73 D83 D82 D81

#2

#4

#6

#8

D13

Heat exchanger 

module number

Inner wall

D. Steady-State Data Acquisition System 

Real-time steady-state data acquisition and data display was provided by a NASA Glenn Escort Alpha system. This 

system is the standard data acquisition and data display system used in the large test facilities at NASA Glenn. The 

system accommodates inputs from the Electronically Scanned Pressure System (ESP), inputs from the facility distributed 

process control system, and inputs from any analog devices such as thermocouples, RTDs and pressure transducers. This 

system recorded all steady-state pressures and temperatures from the 9-ft survey rake, 2-D RTD array, the tunnel 

bellmouth pitot-static probes, and the total temperature probes in Corner D. It also recorded important facility parameters 

such as fan rotational speed and spray bar air pressure. 

The Electronically Scanned Pressure system used during this test program utilized plug-in modules that each 

contained 32 individual transducers with individual ports. Each transducer/port can be addressed separately and scanned 

at a rate of 10,000 ports per second. Calibration of all ESP transducers was performed automatically by the system at 

least every 30 minutes. For this test program, ±5 psid modules were used. 

V. Test Procedures 

In addition to the improvements in test hardware and instrumentation, there were also improvements in the test 

procedures and modifications to the total temperature calibration test matrix, since the 2000 test section calibration. 

Detailed descriptions of the test procedures for the 2000 calibration are found in reference 7; the detailed report on 

the 2004 and 2005 calibrations will be published later in 2005. The procedures used in the 2000, 2004 and 2005 

calibrations are summarized below. 

A. 2000 Calibration 

The 2000 aero-thermal calibration (ref. 7) was the second full test section calibration using the 9-ft survey rake 

as the primary aero-thermal calibration measurement platform (this initial use of the 9-ft survey rake was in 1997). 

The thought was to use a single piece of hardware to collect all of the required test data in a given location at one 

time, but to use a single element rake to minimize the size and blockage of the test hardware to reduce influence on 

the pressure measurements. The trade-off was the added test time required to completely survey a cross-sectional 

plane in the test section by moving the rake through 11 vertical positions. The test time was further increased due to 

the need to run the “aero” portion of the test matrix separately from the temperature surveys, since the pressure 

probes ice-up at lower temperatures. The test matrix for the 2000 aero-thermal calibration is shown in table 1. A 

total of 8 test days were required to complete the aero-thermal calibration testing using the 9-ft survey rake. 

Two recommendations were made following the 2000 aero-thermal calibration, as listed in reference 7. First, all 

pressure data should be collected at ambient temperature settings in order to reduce the risk of water condensation in 

the tunnel which would cause the probes to ice-up or results in water in the instrumentation lines. The second 

recommendation was to fabricate a 2-D grid of temperature probes in order to reduce the time required to collect 

temperature data and to separate spatial and time variations in the temperature data. 
NASA/CR—2005-213875 9

TABLE 1.—TEST MATRIX FOR THE 2000 AERO-THERMAL 

CALIBRATION OF THE IRT TEST SECTION 

Rake vertical position 

from floor, Z, 

in. 

Total temperature, 

TT,davg, 

°C 

Spraybar air 

pressure, 

Pair , 

psig 

Test section velocity, 

Uts , 

knots 

36 4.4 0, 80 0, 22, 43, 65, 87, 108, 130, 152, 173, 

195, 217, 239, 260, 282, 304 

36 21.1, –17.8, –28.9 0 0, 22, 43, 65, 87, 108, 130, 152, 173, 

195, 217, 239, 260, 282, 304 

36 –1.1, –6.7, –9.4, 

–12.2, –15, –23.3 

0 0, 43, 87, 130, 173, 217, 260, 304 

6, 12, 18, 24, 30, 42, 48, 

54, 60, 66 

21.1, 4.4 0 0, 43, 87, 130, 173, 217, 260, 304 

6, 12, 18, 24, 30, 42, 48, 

54, 60, 66 

–1.1, –17.8, –28.9 0 0, 43, 130, 217, 304 

B. 2004 Calibration 

The recommendations made following the 2000 aero-thermal calibration were implemented for the next full 

calibration which occurred in 2004. The “aero” and “thermal” data collection were separated; the 9-ft survey rake 

was used to collect the “aero” data at ambient temperature conditions and the 2-D RTD array was used to collect all 

temperature calibration data. The “aero” test matrix (table 2) was completed in 3 test days, while only 1 day was 

required to complete the RTD array test matrix (table 3). 

Table 3 also shows a change in how the temperature calibration test matrix was constructed. In previous tests, 

the total temperature calibration test matrix was set up to cover the operating range of the IRT by selecting test 

points at minimum and maximum conditions and at regular intervals in between based on the D-Corner total 

temperature. Starting in 2004, the temperature calibration test matrix was based on the test section static temperature 

as outlined in the guidelines provided in reference 5. The actual test points are still the test section airspeed and DCorner total temperature, but the total temperature setting is determined from the airspeed and desired test section 

static temperature. The order of test points was arranged from highest to lowest in order to reduce the test time 

needed. 

TABLE 2.—TEST MATRIX FOR THE IRT AERO-THERMAL CALIBRATION 

USING THE 9-FT SURVEY RAKE (2004 TEST) 

Rake height, 

Y, 

in. 

Total temperature, 

TT,davg, 

oC 

Test section 

airspeed, 

Uts, 

knots 

Spraybar air 

pressure, 

Pair, 

psig 

36 Ambient 

(nominally 20) 

0, 43, 65, 87, 100, 

130, 152, 173, 200, 

217, 240, 260, 282, 

304, 339 

0, 70 

6, 12, 18, 24, 30, 

42, 48, 54, 60, 66 

ambient 0, 43, 87, 100, 130, 

173, 200, 217, 260, 

304 

0 
NASA/CR—2005-213875 10

C. 2005 Calibration 

The 2005 aero-thermal calibration test matrices was identical to those used in 2004, except for the addition of 40 

psig spraybar air setting. This condition was added to check the sensitivity of the airspeed and temperature 

calibrations with respect to spraybar air pressure, especially at the very low speed settings. 

Also during 2005, the RTD array was used to study the spatial and temporal stability of the D-Corner and test 

section total temperature measurements. The goal of this study†

 was to develop a graphical tool for monitoring the 

stability of the D-Corner total temperature in order to determine the best conditions to collect research test data. The 

graphical tool monitored the change in the standard deviation of the average D-Corner or test section temperatures 

over time. While still in development, this tool was used during the collection of the temperature calibration data. 

Figure 11 provides an example of the data used to determine the stability of the D-Corner and test section total 

temperatures. For the D-Corner temperature, the instantaneous average temperature was computed each time the 

Escort data system scanned the data channels (once per second). The standard deviation of the average D-Corner 

total temperature was completed using the previous 10 scans (10 seconds) of data and was updated every second. 

For example, at time = 10 seconds, the standard deviation data point was calculated from scans 1 through 10; at 

time = 11 seconds, the calculation used scans 2 through 11, and so on. The standard deviation for the D-Corner 

average total temperature for time = t is 

1

( )

( 1)

2 , , ,

−

−

σ =

∑

= − − = n

T T

t

i t n

T davg i T davg

t t

Similar equation was used to calculate the test section total temperature stability parameter. 

 

†

The details of the D-Corner temperature stability study are outside the scope of this paper. This study was conducted by Ide and 

Del Roso and a paper describing the study is planned.

TABLE 3.—TEMPERATURE CALIBRATION TEST MATRIX USING THE 2-D RTD ARRAY (2004 TEST) 

Test section 

static 

temperature, 

TS,ts, 

oC 

Test section 

airspeed, 

Uts, 

knots 

D-Corner total 

temperature, 

TT,davg, 

oC 

Spraybar 

air 

pressure, 

Pair, 

psig 

Test section 

static 

temperature, 

TS,ts, 

oC 

Test 

section 

airspeed, 

Uts, 

knots 

D-Corner 

total 

temperature, 

TT,davg, 

oC 

Spraybar 

air 

pressure, 

Pair, 

psig 

–30 43 –29.8 0, 70 –5.6 43 –5.3 0, 70 

–30 100 –28.7 0, 70 –5.6 109 –4.2 0, 70 

–30 130 –27.8 0, 70 –5.6 130 –3.3 0, 70 

–30 200 –24.5 0, 70 –5.6 200 –0.3 0, 70 

–30 217 –23.8 0, 70 –5.6 217 0.7 0, 70 

–30 304 –17.8 0, 70 0 43 0.2 0, 70 

–17.8 43 –17.6 0, 70 0 100 1.3 0, 70 

–17.8 100 –16.4 0, 70 0 130 2.2 0, 70 

–17.8 130 –15.6 0, 70 –0.6 200 4.7 0, 70 

–17.8 200 –12.5 0, 70 –1.7 217 4.6 0, 70 

–17.8 217 –11.6 0, 70 –7.2 304 4.9 0, 70 

–17.8 304 –5.6 0, 70 4.4 43 4.7 0, 70 

 3.3 100 4.7 0, 70 
NASA/CR—2005-213875 11

00

01

02

03

04

05

06

07

08

0 50 100 150 200 250 300 350 400

Elapsed time, seconds

0

10

20

30

40

50

60

70

80

Spray bar air pressure, Pair , psig

D-Corner temperature parameter

Test section temperature

parameter

spray bar air pressure

0

0 200 300 400 100

80

60

40

20

0

Spray bar air pressure, Pair, psig

2

4

6

8

D-Corner temperature parameter

Test section temperature parameter

Spray bar air pressure

(b)

Elapsed time, t, seconds

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 50 100 150 200 250 300 350 400

Elapsed time, seconds

Total temperature standard deviation parameter

0

1

2

3

4

5

6

7

8

Total temperature stability parameter, σt, oC

0.02

0.04

0.06

0.08

0 200 300 400 100

Elapsed time, t, seconds

0.00

8

6

4

2

0

(a)

Figure 11. Typical results of the total temperature stability studies. (a) Uts= 200 knots, TT,davg=0 oC. (b) Uts=290 knots, 

TT,davg=0 oC.

VI. Data Analysis 

Detailed discussion on the data analysis used for all aspects of the aero-thermal calibration are found in the 

specific reports for each test (reference 7 for the 2000 calibration and a NASA CR for the 2004 and 2005 tests that 

will be published later in 2005). The following sections pertain only to the improvements in the total temperature 

measurements and address the measurement uncertainty, flow quality and calibration curves. 

A. RTD Temperature Uncertainty 

The individual component uncertainties were reviewed for the RTD total temperature probe system. The 

component uncertainties are given in table 4. The component uncertainties were combined using a root-sum-squared 

(RSS) technique to yield a system uncertainty of ±0.10 oC for a probe that had been individually calibrated for flow 

recovery and ±0.16 oC for a probe that had not been individually calibrated for flow recovery. The uncertainties 

associated with the RTD probes are over and order of magnitude improvement over the uncertainty estimate for the 

thermocouples on the 9-ft survey rake (±1.1 oC or ±2 oF) (refs. 4 and 6). The RSS computations are show below: 

For probes that were tested for total temperature flow recovery: 

RSS = (0.0302 + 0.0802 + 0.0062 + 0.0262 + 0.0402 + 0.0302 ) = ±0.10 oC

For probes using average flow recovery coefficients: 

RSS = (0.0302 + 0.0802 + 0.0062 + 0.0262 + 0.0402 + 0.1232 ) = ±0.16 oC

TABLE 4.—RTD TOTAL TEMPERATURE PROBE SYSTEM COMPONENT UNCERTAINTIES 

Component 

Uncertainty, 

oC 

Component Description 

±0.030 RTD capsule, 0.01% DIN curve 

±0.080 RTD temperature transmitter 

±0.006 Resistor to convert transmitter 4 to 20mA output to DC volts (USF 240 250Ω 0.01% 2ppm/oC) 

±0.026 Escort data system analog to digital conversion error 

±0.040 Flow recovery reference temperature measurement error (jet plenum reference) 

±0.030 Flow recovery curve uncertainty (individual probe cal) 

±0.123 Flow recovery curve uncertainty (probe not calibrated for flow recovery, average coefficients) 
NASA/CR—2005-213875 12

B. Total Temperature Uniformity 

The spatial uniformity of a given 

flow field parameter in a wind tunnel 

test section is important to know to aid 

in the evaluation and possible 

correction of test data. In an icing 

wind tunnel, the temperature 

distribution in the test section flow 

field is critical as it will affect the 

icing cloud characteristics. Testing 

conducted in 2000 and earlier used the 

9-ft. survey rake which required 

several tunnel runs to completely 

survey the test section flow field by 

moving the rake through 11 vertical 

positions. It was discovered during the 

2000 testing that this survey method 

artificially increased the apparent total 

temperature distribution in the test 

section. This was due in part to 

temporal differences between the DCorner total temperature and the test 

section measurements (as illustrated in 

fig. 11) and the accuracy of the 

thermocouples used for both the DCorner and test section measurements. 

The driver of the temporal differences 

is that control setting changes to the 

facility heat exchanger have a much 

larger and more immediate affect on 

the test section flow than in D-Corner, 

most likely due to the difference in 

volume and airspeed. As mentioned, 

following the 2000 test a 

recommendation was made to use a 

2-D array of temperature probes to 

survey the test section in order to 

eliminate the spatial and temporal 

issues and this recommendation was 

implemented in 2004. 

Figure 12 shows typical test 

section total temperature distribution 

data collected in 2000 and 2005. Note 

that only 8 of the 11 vertical rake 

positions are shown for the 2000 data; 

this was done to provide a more direct 

comparison with the corresponding 

probe positions in the 2005 data. The 

overall spread in the 2000 data is 

about 1.6 oC (excluding the “hot 

spots” recorded near the test section 

floor and walls), while the spread in 

the 2005 data at similar airspeed and 

temperature settings is only 0.5 oC. 

Between 2000 and 2005, there were 

no changes made to the IRT tunnel 

0.993

0.994

0.995

0.996

0.997

0.998

0.999

1.000

1.001

1.002

1.003

1.004

1.005

1.006

1.007

1.008

0 12 24 36 48 60 72 84 96 108

Distance from inside wall, inches

TT,ts(K)/TT,dc(K)

253.4

253.6

253.8

254.0

254.2

254.4

254.6

254.8

255.0

255.2

255.4

255.6

255.8

256.0

256.2

256.4

256.6

256.8

257.0

257.2

Approximate absolute temperature, K

 Z = 58 inches

 52

 46

 40

 34

 28

 22

 10

Figure 12. Comparison of test section total temperature flow field

distributions collected in 2000 using the 9-ft survey rake and in 2005 using

the 2-D RTD array. (a) 2000 data: Uts = 133 knots, TT,davg = -18.0 oC. (b)

2005 data: Uts = 132 knots, TT,davg = -15.4 oC.

Approximate absolute temperature, K

Temperature ratio, TT,ts/TT,davg, K/K

-16.6

-16.4

-16.2

-16.0

-15.8

-15.6

-15.4

-15.2

-15.0

-14.8

-14.6

0 12 24 36 48 60 72 84 96 108

Distance from Inner wall, inches

Test section total temperature, TT,ts, C

 Z = 63 inches 54

 45 36

 27 18

 9 TT,dc

Distance from inside wall, inches

Total temperature, TT,ts, oC

0 12 24 36 48 60 72 84 96 108

-15.0

-16.4

-16.2

-16.0

-15.8

-15.6

-15.4

-15.2

-16.6

-14.8

-14.6

(a)

(b)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

25 50 75 100 125 150 175 200 225 250 275 300 325

2000; TT,dc>4 C 2005; TTdc>1 C

2000; -2<TT,dc<0 C 2005; -6<TT,dc<1

2000; -19<TT,dc<-17 C 2005; -17<TT,dc<-11

2000; TT,dc<-28 C 2005; TT,dc<-24

Test section airspeed, Uts, knots

Standard deviation of test section total temperature, oC

Figure 13. Comparison of standard deviation in test section total 

temperature distribution data between the 2000 (9-ft rake data) and 2005 

(2-D RTD array data) tests.

2000; TT,davg > 4 oC

2000; -2 < TT,davg < 0 oC

2000; -19 < TT,davg < -17 oC

2000; TT,davg < -28 oC

2005; TT,davg > 1 oC

2005; -6 < TT,davg < 1 oC

2005; -17 < TT,davg < -11 oC

2005; TT,davg < -24 oC
NASA/CR—2005-213875 13

loop that would account for 

improvements of this magnitude in 

the total temperature distribution, 

therefore the spread in the 2000 

data is attributed to the 

measurement technique (the 

replacement of the drive fan inlet 

guide vanes would not have this 

kind of effect on the test section 

total temperature distribution. 

 The results shown in figure 12 

are typical across the operating 

range of the IRT. Figure 13 

compares the standard deviation of 

the test section total temperature 

distribution data for the 2000 and 

2005 tests across the airspeed and 

temperature range of the tunnel 

with the spraybar air turned off 

(Pair = 0 psig). The data in figure 

13 are binned by total temperature range and while the bins do not match exactly between the 2000 and 2005 data 

due to differences in the test matrices, they do provide a sufficient basis for comparison. 

 For all the data represented, the standard deviation in the 2005 data is considerably smaller than the 2000 data, 

except for the very low speed and very low temperature setting, where there 2000 and 2005 data were about equal. 

The largest effect was seen in the high temperature range (above freezing) where the 2000 data showed standard 

deviations of greater than 1 oC but the 2005 data showed that the actual standard deviation was less than 0.5 oC. In 

the airspeed range of 100 to 250 knots, where much of the research testing is conducted, all of the conditions 

surveyed in 2005 showed standard deviations of less than 0.5 oC; the total temperature standard deviation in this 

airspeed range was less then 0.2 oC for temperature settings above -24 oC. 

 The true test section total temperature flow quality is represented by the 2005 test data in figures 12 and 13. The 

2004 and 2005 data sets can be used to address any questions concerning the test section flow quality following 

2000 facility modifications that included the installation of flat heat exchangers and new D- and C- corner turning 

vanes (ref. 7). The facility modifications had a significant positive impact on the overall test section flow quality, but 

the full extent of the improvements were not recognized due to limitations of using the 9-ft survey rake to document 

the total temperature distributions in the test section. The data collected with the 2-D RTD array in 2004 and 2005 

shows complete impact of the facility modifications. Additional examples form the 2005 are provided in appendix 

A. Full documentation of the flow quality data will be presented in a NASA Contractor Report. 

C. Total Temperature Calibration 

The total temperature calibration relationship is one of a set of three calibrations used to fully define the aerothermal operating conditions in the IRT test section (the other two calibration relationships are static pressure and 

Mach number). The total temperature calibration simple relates the test section total temperature measured by the 2-

D RTD (average of 49 measurements) array to the total temperature measured in D-Corner (average of 24 

measurements). Previous to 2005, a single curve-fit was used to represent the total temperature calibration across the 

operating range of the IRT. This single curve-fit did not include data collected at low speed with the spray bar air 

turned on due to the amount of scatter in these data relative to the data collected at higher airspeeds. 

The current total temperature calibration relationship was created using the 2005 data. Due to the improved 

measurement accuracy and because of increased interest in low speed test conditions, some analysis was done to 

determine if a family of calibration curves was needed for the total temperature to account for airspeed and spraybar 

air pressure effects. The final conclusion was that there is a break-point between 50 and 100 knots where at above 

this point, spraybar air pressure no longer has a significant effect on the total temperature calibration. The result was 

to create a set of four calibration curves, one for airspeeds greater than 50 knots and three for airspeed less than 50 

knots based on the spraybar air pressure setting (0, 40 or 70 psig). The resulting total temperature calibration curves 

are shown in figure 14. Table 5 provides the details for the calculation of the calibrated test section total temperature 

from the measured D-Corner total temperature. In order to provide some degree of vernier on the spraybar air 

pressure at the low speed conditions, the slope and intercept from each of the low speed calibration curve-fits were 

-30

-25

-20

-15

-10

-5

0

5

-30 -25 -20 -15 -10 -5 0 5

V>50 knots; all P settings

V<50 knots; P=0 psig

V<50 knots; P=40 psig

V<50 knots; P=70 psig

Linear (V>50 knots; all P settings)

Linear (V<50 knots; P=0 psig)

Linear (V<50 knots; P=70 psig)

Linear (V<50 knots; P=40 psig)

D-Corner total temperature, TT,davg, oC

Test section total temperature, 

TT,ts, oC

Figure 14. Total temperature calibration curves for the IRT.

Uts > 50 knots; all Pair settings

Uts < 50 knots; Pair = 0 psig 

Uts < 50 knots; Pair = 40 psig 

Uts < 50 knots; Pair = 70 psig

(Uts > 50 knots; all Pair settings)

(Uts < 50 knots; Pair = 0 psig) 

(Uts < 50 knots; Pair = 40 psig) 

(Uts < 50 knots; Pair = 70 psig)
NASA/CR—2005-213875 14

plotted against the spraybar air pressure so that calibration curve coefficients could be estimated for other spraybar 

air settings. The resulting curve-fit equations for estimating C0 and C1 for Uts < 50 knots are listed below: 

For 0 < Pair < 40 psig: 

C Pair = 0.98917044 − 0.00001881⋅ 0

For 40 < Pair < 70 psig: 

C Pair = 0.99428850 − 0.00014676 ⋅ 0

For all Pair settings not specifically listed in table 5: 

2 C1 0.06550710 0.01720280 Pair 0.00004323 Pair = + ⋅ + ⋅

These calculated values for C0 and C1 are then used in the calibration equation (table 5) to determine TT,ts at the low 

speed conditions. 

TABLE 5.—GENERAL EQUATION AND CURVE FIT COEFFICIENTS USED IN 

THE CALCULATION OF THE CALIBRATED TEST SECTION TOTAL 

TEMPERATURE 

TT,ts,c = C0 + C1 ⋅TT,davg

Test section 

airspeed, 

Uts, 

knots 

Spraybar air 

pressure, 

Pair, 

psig 

Curve fit intercept 

term, 

C0, 

oC 

Curve fit slope 

term, C1, 

oC/oC 

> 50 ≥ 0 –0.19470324 0.99014859 

< 50 0 0.06550710 0.98917044 

< 50 40 0.82278309 0.98841811 

<50 70 1.48151795 0.98401532 

VII. Summary of Results 

 There were several improvements made to the measurement and calibration of the total temperature in the 

NASA Glenn Icing Research Tunnel starting in 2004. The need for these improvements were driven by customer 

requirements and by the philosophy of continually striving to improve test facilities and techniques at the Glenn test 

facilities. The primary results from the 2004 and 2005 aero-thermal calibration that pertain to the total temperature 

calibration are summarized below: 

 

• The measurement uncertainty for both the facility and test section calibration total temperature 

measurements were decreased by an order of magnitude by using RTD probes instead of thermocouples. 

The uncertainty in the total temperature measurement made in the test section calibration was reduced from 

±1.1 °C using the thermocouples probes in the 9-ft survey rake to ±0.10 °C using the RTD probes on the 2-

D RTD array. 

• Using the 2-D RTD array provides a more accurate representation of the test section total temperature 

distribution since the entire flow field is surveyed simultaneously, thus eliminating the temporal variations 

seen in the data collected using the 9-ft survey rake. Over most of the IRT operating range, the overall total 

temperature variation in the test section is on the order of ±0.5 °C. 

• The total temperature calibration was refined to include spraybar air pressure effects on the test section total 

temperature at low airspeed settings (less than 50 knots). Spraybar air pressure was not a significant effect 

for airspeed setting of 100 knots and higher. 

• In addition to the data and flow quality issues listed above, the introduction of the 2-D RTD array also 

reduced the amount of test time needed for a full aero-thermal calibration of the IRT test section. During the 

2000 test, the 9-ft survey rake was used to collect all of the flow quality and calibration data and required 
NASA/CR—2005-213875 15

67.5 hours of test time over 8 days. In 2004, the 9-ft survey rake was used to collect only pressure data 

and the 2-D RTD array was used to collect all temperature data; the combined test time was 25.25 hours 

over 4 days. 

VIII. Recommendations 

The following recommendations are presented as means to provide additional improvements to the temperature 

calibration of the NASA Glenn Icing Research Tunnel: 

• One of the drivers for the improvements listed in this paper was input from the IRT customers as to changes 

to their test requirement needs. It is vital that input from the IRT test customers is solicited and integrated 

into the test section calibration requirements. Insuring that test customer requirements are achieved is a 

critical issue in developing a successful wind tunnel calibration program (ref. 8). 

• The data collected in 2004 and 2005 showed that spraybar air injected into the airstream has a very 

noticeable effect on the test section operating conditions as the very low speed settings (less than 50 knots). 

Additional testing is needed to determine (1) the test section airspeed at which spraybar air pressure no 

longer has a significant effect and (2) the minimum spraybar air pressure that causes a noticeable effect at 

the low speed settings. 

References 

1. Leary, William M., “We Freeze to Please: A History of NASA’s Icing Research Tunnel and the Quest for Flight 

Safety,” NASA/SP—2002–4226, 2002. 

2. Irvine, T.B., Kevdzija, S.L., Sheldon, D.W. and Spera, D.A., “Overview of the Icing and Flow Quality 

Improvements Program for the NASA Glenn Icing Research Tunnel,” AIAA–2001–0229, 2001. 

3. Soeder, R.H., Sheldon, D.W., Ide, R.F., Spera, D.A. and Andracchio, C.R., “NASA Glenn Icing Research 

Tunnel User Manual,” NASA/TM—2003-212004, 2003. 

4. Gonsalez, J.C., and Arrington, E.A., “Aerodynamic Calibration of the NASA Lewis Icing research Tunnel 

(1997 Tests),” NASA/CR—2001-210809, AIAA–98–0633, 2001. 

5. “Calibration and Acceptance of Icing Wind Tunnels,” SAE Standards ARP5902, 2003. 

6. Gonsalez, J.C., Arrington, E. A., “Five-Hole Flow Angle Probe Calibration for the NASA Glenn Icing Research 

Tunnel,” NASA/CR—1999-202330, AIAA–96–2201, 1999. 

7. Gonsalez, J.C., Arrington, E.A., and Curry III, M.R., “Aero-Thermal Calibration of the NASA Glenn Icing 

Research Tunnel (2000 Tests),” NASA/CR—2001-210685, AIAA–2001–0233, 2001. 

8. “Calibration of Subsonic and Transonic Wind Tunnels,” AIAA Recommended Practice R-093-2003, 2003. 

NASA/CR—2005-213875 17

Appendix A. Typical Total Temperature Flow Quality Data 

-18.0

-17.0

-16.0

-15.0

0 12 24 36 48 60 72 84 96 108

-1.0

0.0

1.0

2.0

0 12 24 36 48 60 72 84 96 108

 Z = 63 inches 54

 45 36

 27 18

 9 TT,dc

-19.0

-18.0

-17.0

-16.0

0 12 24 36 48 60 72 84 96 108

0.0

1.0

2.0

-1.0

Distance from inside wall, inches

Test section total temperature, 

TT,ts, oC

(a)

(b)

(c)

Figure A1. Typical total temperature distribution data collected in the IRT test 

section during the 2005 aero-thermal calibration using the 2-D RTD Array (Pair = 

0 psig). (a) Uts = 100 knots. (b) Uts = 220 knots. (c) Uts = 290 knots.
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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NASA CR—2005-213875

AIAA–2005–4276

E–15246

WBS–22–077–41–14

NAS3–00145

23

Improvements to the Total Temperature Calibration of the NASA Glenn

Icing Research Tunnel

E. Allen Arrington and Jose C. Gonsalez

Wind tunnel; Calibration; Temperature; Icing; Flow quality; Subsonic

Unclassified -Unlimited

Subject Category: 09

QSS Group, Inc.

21000 Brookpark Road

Cleveland, Ohio 44135

Prepared for the 41st Joint Propulsion Conference and Exhibit cosponsored by the AIAA, ASME, SAE, and ASEE,

Tucson, Arizona, July 10–13, 2005. Project Manager, Robert Freedman, Research Testing Division, NASA Glenn

Research Center, organization code DRA, 216–433–2038.

The ability to accurately set repeatable total temperature conditions is critical for collecting quality icing condition data,

particularly near freezing conditions. As part of efforts to continually improve data quality in the NASA Glenn Icing

Research Tunnel (IRT), new facility instrumentation and new calibration hardware for total temperature measurement

were installed and new operational techniques were developed and implemented. This paper focuses on the

improvements made in the calibration of total temperature in the IRT.