Michael D. Hathaway

U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio

Self-Recirculating Casing Treatment Concept

for Enhanced Compressor Performance

NASA/TM—2002-211569

July 2002

ARL–TR–2748

GT–2002–30368 U.S. ARMY

RESEARCH LABORATORY
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Michael D. Hathaway

U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio

Self-Recirculating Casing Treatment Concept

for Enhanced Compressor Performance

NASA/TM—2002-211569

July 2002

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

Turbo Expo 2002

cosponsored by the American Society of Mechanical Engineers

and the International Gas Turbine Institute

Amsterdam, The Netherlands, June 3–6, 2002

ARL–TR–2748

GT–2002–30368 U.S. ARMY

RESEARCH LABORATORY
Acknowledgments

My thanks to Ms. Sonia Ensenat for her early efforts in support of this research and to Dr. Anthony J. Strasizar

and Dr. Edward M. Greitzer for their efforts in suggesting and initiating this research effort.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

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Available electronically at http://gltrs.grc.nasa.gov/GLTRS
FOR ENHANCED COMPRESSOR PERFORMANCE

Michael D. Hathaway

Vehicle Technology Directorate

U.S. Army Research Laboratory

ABSTRACT

A state-of-the-art CFD code (APNASA) was employed in a

computationally based investigation of the impact of casing

bleed and injection on the stability and performance of a

moderate speed fan rotor wherein the stalling mass flow is

controlled by tip flow field breakdown. The investigation was

guided by observed trends in endwall flow characteristics (e.g.,

increasing endwall aerodynamic blockage) as stall is

approached, and based on the hypothesis that application of

bleed or injection can mitigate these trends. The “best” bleed

and injection configurations were then combined to yield a selfrecirculating casing treatment concept. The results of this

investigation yielded: 1) identification of the fluid mechanisms

which precipitate stall of tip critical blade rows, and 2) an

approach to recirculated casing treatment which results in

increased compressor stall range with minimal or no loss in

efficiency. Subsequent application of this approach to a high

speed transonic rotor successfully yielded significant

improvements in stall range with no loss in compressor

efficiency.

INTRODUCTION

The current trend toward increased pressure rise per stage

and increased blade aerodynamic loading tends to reduce the

stable operating range of compressors. To provide adequate

stall margin the compressor may operate away from the

optimum efficiency point. Alternatively, methods may be

devised to extend the stable operating range of the compressor.

Over the last 30 years various forms of casing treatment have

been employed for enhancing compressor stall range, generally

though at the expense of compressor efficiency (e.g., Koch, and

Smith, 1968a and 1968b, Prince, et al., 1974, Janssens and

Chedozeau, 1979, Takata and Tsukada 1997, Crook, et al.,

1993).

Some modern casing treatment concepts utilize the

compressor static pressure rise to provide for a recirculation of

high-pressure fluid from the rear to the front of a compressor

rotor through a path contained within the compressor casing

(Koff, et al., 1994, Hobbs, 1995, Nolcheff, 1995). The highpressure fluid is then reinjected at the casing to energize the low

momentum fluid in the compressor endwall that contributes to

compressor stall range limitations. Such recirculated casing

treatment concepts have shown promise for providing the

greatest stall range capability with minimum decrement to

compressor efficiency of any previous casing treatment

concepts, however, for modern well designed compressors they

still result in an efficiency penalty.

The genesis of the research reported herein was based on:

1) Recognition that there is still room for improving the

effectiveness of casing treatments while reducing or eliminating

their detrimental impact to compressor performance, 2) A

validated capability of state-of-the-art computational fluid

dynamic analysis codes to provide reasonably accurate

predictions of compressor rotor endwall flow fields, and 3) A

belief that improved understanding of the compressor endwall

flow phenomena which limit compressor stall range will lead to

improved effectiveness of recirculated casing treatments. As

such, the goal of this research program was to develop an

improved casing treatment concept based on a "first principals"

understanding, as derived from state-of-the-art CFD, of endwall

flow phenomena which limit stall range.

To achieve this goal a state-of-the-art CFD code

(APNASA, Adamczyk 1995) was employed in a

computationally based investigation of the impact of

NASA/TM—2002-211569 1

SELF-RECIRCULATING CASING TREATMENT CONCEPT

Cleveland, Ohio 44135
independent casing bleed and injection on the stability and

performance of a moderate speed fan rotor wherein the stalling

mass flow was controlled by tip flow field breakdown. This

investigation was guided by observed trends in endwall flow

blockage as stall is approached (Smith, L. H., 1970, Koch,

1981, Kahlid, 1994, Suder, 1997, Kahlid, et al., 1998, Cho, D.

L., 1995), and based on the hypothesis that application of

endwall bleed or injection can mitigate these trends (Koch and

Smith, 1968a & 1968b, Smith & Cumpsty, 1982, Crook, et al.,

1993). The best bleed and injection configurations were then

combined to yield a self recirculated casing treatment concept

that provided a significant increase in stall range and

compressor efficiency by reducing the casing endwall blockage.

Subsequent application of this approach to a high speed

transonic rotor successfully yielded similar improvements in

stall range with no loss in compressor efficiency.

NOMENCLATURE

P Static pressure, Pa

Pt Total pressure, Pa

Tt Total temperature, ο

K

Utip Rotor tip speed, m/sec

V Velocity, m/sec

a Area, m2

m Mass flow rate, kg/sec

mchoke Choke mass flow rate at design speed, kg/sec

r Radius, m

α Pitch angle, Deg.

β Absolute flow angle, Deg.

γ Ratio of specific heats

ρ Density, kg/m3

ω Fractional loss in dynamic pressure

Subscripts

1 Bleed port

2 Injection port

abs Absolute frame of reference

c Flow path casing

n Normal component

t Rotor blade tip

x Axial component

COMPUTATIONALLY BASED STUDY

A computationally based study of various casing bleed and

injection configurations was performed using the Average

Passage code (APNASA) developed by Adamczyk, 1985.

APNASA is a 3D time-averaged Navier-Stokes code developed

for multistage compressor analysis. For these simulations the

CMOTT k-e turbulence model was used (Shih, et al., 1995 &

1996). The simulations were of an isolated blade row using an

axisymmetric mass flow boundary condition (Shabbir. A., et al.,

1997) to simulate casing bleed and injection. The upstream

boundary condition was prescribed at standard day inlet

conditions with 5% boundary layer thickness, based on span, on

both endwalls. The downstream hub static pressure was set and

adjusted in steps to develop a prediction of the rotor speed line

for various casing bleed/injection configurations. Convergence

was deemed to be achieved when the mass flow rate, pressure

ratio, efficiency, and number of separated points remained

essentially constant with increasing iteration count.

As stall is approached the number of separated points in the

flow field and other flow field parameters may vary as a

function of iteration count. However, the simulation approaches

a limit cycle in which the peak-to-peak amplitude of the flow

field differences does not grow with increasing iteration count.

Away from stall the convergence is well behaved with little or

no variation with increasing iterations. The predicted stall point

was judged to be the last stable condition prior to incurring, for

a fixed hub static pressure, a continual drop in mass flow rate

and pressure ratio with increasing iteration count.

The ability of the APNASA code to predict the stalling

mass flow rate for an isolated transonic rotor (R35) has been

demonstrated by Van Zante, et al. (1999), see Figure 1. Van

Zante, et al. concluded that accurate prediction of the stable

operating range requires careful attention to grid resolution near

the casing. Also shown in Figure 1 is a comparison of the

measured and predicted stalling mass flow rates for the

transonic rotor studied herein (R67). Though the question still

remains as to whether the code can adequately predict stall for

any rotor, it was deemed reasonable to expect that if the code

predicts an improvement in stall range that such would be

realized experimentally, though perhaps to a different degree.

A moderate speed fan rotor was selected for the

computationally based investigation of the impact of casing

endwall bleed and injection on rotor performance. The fan rotor

had 18 blades, an inlet tip radius of 28.13 cm, a hub-tip radius

ratio of 0.426, an aspect ratio of 2.75, a tip solidity of 0.6, and

an axial chord of 5.87 cm at the tip and 5.82 cm at the hub. The

rotor tip clearance gap was modeled (by enforcement of

periodicity across the tip gap) at 6.8% of tip axial chord (3

times the design clearance) to assure that the tip flow field

would control the stall point. Based on simulation results at

kg/sec based on simulations, the blade tip speed is 258 m/sec

(846 ft/s), the total-to-total pressure ratio is 1.22, and the

adiabatic efficiency is 87.3 %. The mesh size used for the

simulations of the moderate speed fan is 162 axial x 51 radial x

55 tangential nodes with 10 cells in the rotor tip clearance gap.

Though this fan performance is not commensurate with that

of modern fans, as a representative tip critical flow field

generator, this fan case was considered suitable for investigating

the benefits of casing endwall bleed and injection. To assess the

general applicability of the “lessons learned” from the moderate

speed fan simulations, subsequent simulations of the “best”

candidate casing treatment would be evaluated on a high-speed

fan rotor with good performance (R67).

NASA/TM—2002-211569 2

8750 RPM, the choking mass flow rate at that speed is 38.995
Figure 1 Comparison of predicted and measured stalling

massflow rates for two transonic rotors.

The investigation was guided by reported observations

(Smith, L. H., 1970, Koch, 1981, Kahlid, 1994, Suder, 1997,

Kahlid, et al., 1998, Cho, D. L., 1995) that endwall

aerodynamic blockage accumulates rapidly as a fan/compressor

approaches stall. The accumulation of low momentum endwall

fluid is exacerbated by the incoming low momentum "boundary

layer" fluid adjacent to the endwall, blade/endwall flow field

interactions, shock/vortex interactions, shock/tip- leakage-jet

interactions, radial migration of low momentum fluid to the

endwall, etc. It was hypothesized that directly controlling the

low momentum producing mechanisms would reduce the rate of

accumulation of endwall blockage thereby improving rotor

endwall performance and as a result increasing fan/compressor

stall range.

An investigation of the impact on compressor performance

of various bleed and injection locations was thus conducted

using computational simulations including a model for

simulating casing endwall bleed and injection. The uncoupled

bleed and injection cases were simulated with the bleed and

injection port mass flow rates fixed at nominally 1% of the

compressor mass flow rate, and the axial extent of the ports

fixed at 10% of rotor tip chord. This investigation attempted to

simulate the benefits of using endwall bleed to remove low

momentum fluid near the endwall, thereby reducing endwall

blockage. The benefits of injection were also simulated based

on using high relative-total-pressure fluid to "energize" low

momentum endwall fluid, thus reducing endwall blockage

accumulation. The best candidate bleed and injection

configurations were then simulated in a "coupled" fashion

whereby the low momentum fluid bled off the casing endwall

was recirculated upstream to supply fluid for the optimum

injection configuration. It was envisioned that relying on the

positive static pressure gradient across the rotor to self

recirculate the low momentum fluid bled from the casing

endwall to supply high relative total pressure fluid to the

injection point would provide performance benefits from both

bleed and injection. This is not a new concept as there is are

existing patents (Koff, et al., 1994, Hobbs, 1995, Nolcheff,

1996) for such a casing treatment concept. The selfrecirculating casing treatment concept reported herein

additionally provides:

1) A description of the methodology for identification

and direct control of the most significant endwall

blockage producing mechanisms limiting blade

endwall performance (efficiency and stall range), and

2) Implementation of discrete single-pass recirculation to

 prevent continuous recirculation of high entropy fluid.

The rationale for determining the axial extent of the bleed and

injection ports as well as the recirculated mass flow rate will be

described later in the Results and Discussion.

As will be shown herein, directly controlling the fluid

mechanisms producing endwall blockage results in a decrease

in endwall blockage production and a consequent predicted

improvement in both stall range and efficiency. These predicted

performance improvements are a result of a CFD based

fundamental understanding of the endwall fluid mechanisms

most important to control, and how best to configure the bleed

and injection ports to achieve efficiency and stall range

improvement. Table 1 lists the bleed, injection, and coupled

configurations established for simulation to predict their

potential performance benefits. Also included in table 1 are the

figure symbols commensurate with each case plotted in the

succeeding figures, as well as the predicted range increase for

each case.

RESULTS AND DISCUSSION

Figure 2 shows a comparison of the computational

results of a study of casing bleed. Each of the bleed cases were

selected to bleed off endwall fluid identified from CFD

simulations as potential contributors to endwall blockage

production. Both mass averaged total pressure ratio and

adiabatic efficiency are presented in Figure 2. As evident from

Figure 2, casing endwall bleed is in most cases beneficial, but in

some instances can be detrimental to overall performance. The

performance parameters in Figure 2 are based on a control

volume analysis of the rotor, and therefore take into account the

energy of the fluid entering and leaving the control volume,

including that which crosses the casing boundary. As such, no

credit to performance is obtained from bleeding off low

momentum fluid unless the gains are accrued from increased

aerodynamic performance. The “% range extension” indicated

in this and subsequent figures is the increase in mass flow range

relative to the smooth wall mass flow range (mass flow range =

choke flow rate – stalling flow rate). Thus, no credit to stall

range increase is given for increased pressure rise capability.

Figure 3 shows a comparison of the computational

results of a study of endwall injection. Each of the injection

cases were selected to affect control over a specific endwall

fluid mechanism (e.g., leakage vortex, endwall boundary layer,

etc., see Table 1) identified from CFD simulations to be a

NASA/TM—2002-211569 3
Table 1 Moderate Speed Fan Bleed, Injection, and Coupled Cases Investigated

-1.3 26

-0.1 45

-1.3 12

-2.3 -34

-1.3 21

-2.6 42

-3.5 55

-2.6 60

α β

1.3 -30 0

1.3 -30 0 38

1.3 -90 0 6

1.2 -30 0 43

1.9 -60 0 64

1.9 -30 0 60

Coupled Bleed and Injection 

B - Bleed low monentum exit fluid 

I - Energize tip gap leakage fluid

Energize casing inlet fluid

Energize tip gap leakage fluid

"

"

"

Bleed casing exit blockage

Bleed tip gap leakage jet blockage

"

"

Bleed blockage aft of leakage jet

100110120

Bleed inlet "boundary layer" fluid

Extent of rotor tip chord Bleed/Injection Port Beginning of Tip Gap Leakage Jet

% Range 

Increase

Bleed, B Inject, I Coupled

-20-10

0

102030

Low momentum fluid targeted in this 

investigation

Figure 

Symbol

% Rotor Chord

% mchoke

405060708090

potential contributor to endwall blockage production. For all

moderate speed fan cases studied the absolute flow angle of

the injected fluid was set at zero degrees, which based on CFD

simulations at the design conditions produced a relative flow

angle approximately aligned to the local blade tip mean

camber angle. It’s evident from Figure 3 that casing mass

injection can hurt or help overall performance, and in one case

has the potential for increasing adiabatic efficiency. The

injection case that produced an increase in adiabatic efficiency,

and stall range, is the case that impacted the most significant

blockage producing mechanism identified from the CFD

simulations, in this case the tip leakage vortex. As will be

shown for the best coupled bleed and injection configuration a

significant reduction in endwall blockage results, which

improves rotor efficiency and increases stall range.

Based on the results of these independent computationally

based studies of casing bleed and injection additional

simulations were performed which coupled the best bleed and

injection cases to model a self-recirculating casing treatment.

The coupled self-recirculating casing treatment model

employed in the simulations is illustrated in Figure 4. The

model requires the injected and bleed mass flow rates (m2 and

m1) to be the same, and the total temperature of the injected

fluid (Tt,2) to be that of the mass averaged total temperature of

the fluid bled from the rotor flow field (Tt,1). The total pressure

of the injected fluid (Pt,2) is derived from the average static

pressure of the bled fluid (P1) plus the mass averaged dynamic

pressure of the bled fluid (1/2γP1Mabs,12

) with an assumed loss

(ω=0.20) in dynamic pressure due to bleed cavity entrance

losses and loss incurred within the re-circulated casing

treatment flow path.

The injected fluid should be directed to lie along the

casing endwall to energize the low momentum fluid in the

vicinity of the casing endwall. The injection port should be

located just upstream of the region of low momentum fluid

(identified by the region of low relative total pressure) to be

energized, see Fig. 5. The absolute flow angle of the injected

fluid should be set such that, in the frame of reference relative

to the rotor, the fluid is aligned with the local rotor blade tip

mean camber angle. The mass flow recirculated through the

casing treatment should initially be sized commensurate with

the local mass flow deficit in the rotor blade tip-clearance gap,

Eq. 1 (i.e., typically that mass flow associated with the over tip

leakage vortex which contributes most to the endwall blockage

accumulation). The velocity of the injected fluid in the frame

of reference of the casing, V2, will be that dictated by the

pressure ratio between the bleed and injection ports and the

pressure losses associated with the casing treatment, Fig. 4 and

Eq. 2. To the extent possible by the available pressure rise

across the rotor and the absolute angle of injection, it is

desirable to attempt to achieve a relative velocity for the

injected fluid commensurate with the free stream velocity

away from the influence of the tip clearance flow. With the

initially established mass-flow rate through the casing

treatment, the prescribed injection angles, and the pressure

ratio set by the location of the bleed and injection ports the

NASA/TM—2002-211569 4

-28
Figure 2 Casing Bleed Cases Applied to Moderate Speed Fan

Rotor.

area of the injection port is established, Eq. 4. The bleed port

area is sized to accommodate the injection mass flow rate and

to insure that the flow will not choke at the bleed port.

Eq. 1 rV2)rr(Vm dr

c

t

r

r

2 x,2

2

t

2

t2 x, ct ∫ ρ π −−= π ρ

Eq. 2 ( )( ) [ ] γ γ

γ

γ /1

t,2 2 t,2

c

2 P1T /P

1-

2 Rg V − −=

Eq. 3 n,2 22 = VV sinα

Eq. 4 ( ) = ρ 222 V/ma n,2

At the completion of each flip of the APNASA

simulations the bleed and injection boundary conditions are

updated. This is accomplished with an external FORTRAN

program which mass averages the flow conditions over the

bleed and injection ports and then imposes the casing

Figure 3 Casing Injection Cases Applied to Moderate Speed

Fan Rotor.

Figure 4 Self-Recirculating Casing Treatment Model.

treatment model and the prescribed injection and bleed port

conditions as described above. The simulation is converged

when both the APNASA convergence criteria are met and the

bleed and injection boundary condition parameters do not

change from flip to flip.

NASA/TM—2002-211569 5
Figure 5 Relative Total Pressure Contours at Tip Section of

Moderate Speed Fan Rotor Identifies Blockage Producing

Mechanism to Control.

As evidenced by the results of the coupled bleed and

injection casing treatment model shown in Figure 6, not only

does the self-recirculating casing treatment concept provide

increased range it also has potential for increasing total

pressure rise capability of the rotor and adiabatic efficiency.

This occurs due to the effectiveness of the casing treatment in

reducing the endwall blockage, thus enabling the blade tip

elements to impart more work to the fluid, and in a more

efficient manner. As indicated by the differences in the selfrecirculated casing treatment results presented in Figure 6,

implementation is important for maximum benefit. However,

all cases presented provided range increase with no decrement

in efficiency from the smooth untreated case

Evidence supporting the predicted performance

improvements are provided in Figure 7 which shows a

comparison of relative total pressure contours between the

self-recirculated casing treatment case and the smooth

untreated case. As shown in Figure 7 the extent of low relative

total pressure accumulated near the casing endwall is

significantly less for the case employing the self-recirculating

casing treatment model relative to the smooth untreated case.

 The impact of the endwall blockage reduction on the

fan rotor blade-element performance is indicated in figure 8.

As is evident from figure 8, for each case plotted the fan rotor

efficiency is essentially unchanged across the rotor blade span

until just out board of about 75 % span. Beyond 75 % span

there is a marked improvement in the blade element

performance even for the lower flow rates obtained as a result

Figure 6 Coupled Bleed / Injection Cases Applied to Moderate

Speed Fan

Figure 7 Comparison of Relative Total Pressure Contours for

Smooth and Treated Casing Endwalls of Moderate Speed Fan

Rotor.

NASA/TM—2002-211569 6
Figure 8 Spanwise distributions of adiabatic efficiency for the

moderate speed fan with and without recirculated casing

treatment.

of the recirculated casing treatment relative to the untreated

(smooth case) stalling mass flow rate.

The moderate tip speed fan study provided a fundamental

understanding of the fluid mechanisms important to control to

obtain improvement in stall range without a decrement in

efficiency. A concept for implementing a self-recirculating

casing treatment was formulated and demonstrated by the

results of the simulations with the coupled bleed and injection

model as applied to this moderate speed tip-critical fan.

To assess how generic this self-recirculated casing

treatment concept is it was applied to an efficient transonic fan

rotor, NASA Rotor 67, Strazisar, et al. (1989). Rotor 67

measured peak adiabatic efficiency is reported at 93 %, at

34.573 kg/sec (76.06 lbm/sec) achieving 1.642 total-to-total

pressure ratio, at design speed, Utip = 429 m/sec (1409 ft/sec).

The measured efficiency spiked to 93 % at essentially a single

mass flow rate and dropped to 91 % for a less than 1% change

in mass flow rate.

The results of APNASA simulations of Rotor 67

without casing treatment were used to guide the configuration

of the self-recirculating casing treatment concept to be

employed for Rotor 67. The fluid mechanism identified from

the simulations to be most responsible for producing endwall

blockage for Rotor 67, see Fig. 9, was similar though

somewhat different from that identified for the moderate speed

fan rotor, see Fig. 5. The presence of a passage shock

terminating on the suction surface in the region of low relativetotal-pressure fluid caused concern for locating an injection

port there. Furthermore, unlike the moderate tip speed fan case

the leakage vortex, which was identified as most responsible

for casing endwall blockage production, moved upstream as

the rotor was throttled towards stall. Therefore the injection

port was located near the blade leading edge to affect control

over the leading edge vortex and tip section loading with the

Figure 9 Relative Total Pressure Contours at Tip Section of

Transonic Fan Rotor 67 Identifies Blockage Producing

Mechanism to Control.

expectation that it would beneficially impact the extent of low

relative total pressure leaking across the blade tip gap. The

results shown in Figure 10 show the self-recirculated casing

treatment concept employed (where ω=0.20) does provide

benefits to Rotor 67 performance. Significant stall range

increase was predicted with no decrement in rotor efficiency.

Since Rotor 67 already has good stall range capability,

and as a test of the applicability of the concept to effectively

extend stall range for a distorted inlet condition, simulations of

Rotor 67 with and without inlet distortion were conducted. The

distorted and undistorted inlet profiles are shown in Figure 11.

The distortion was only applied to the casing endwall to

reduce stall range relative to the undistorted case. As shown in

Figure 12 the self-recirculated casing treatment concept also

provides considerable benefit in extending the stall range when

there is an inlet distortion. Although neither the distorted or

undistorted cases showed improved efficiency as a result of the

self-recirculated casing treatment they both show significant

range increase without the usual decrement in efficiency

relative to the baseline untreated case.

Previous investigations of discrete upstream casing tip

injection for stability enhancement (Hathaway and Strazisar,

1998, Suder, et al., 2000) demonstrated that discrete tip

injection with as few as three injectors provided essentially the

same range extension as twelve injectors. The main

requirement for range extension was shown to be the

injected/free-stream velocity ratio. The potential for stall range

improvement with lower loss using part-circumference casing

treatment has been shown by Cumpsty, 1989. Based on these

reported results it is proposed that further improvement in

NASA/TM—2002-211569 7
Figure 10 Re-Circulated Casing Treatment Model Applied to

Transonic Fan Rotor 67 without Inlet Distortion.

Figure 11 Rotor 67 Distorted and Non-Distorted Inlet Total

Pressure Profile Applied to Transonic Fan Rotor 67.

existing re-circulating casing treatments could be realized by

implementing a discrete self-recirculating casing treatment

concept. Figure 13 shows a representation of such a concept.

As shown in Figure 13 low momentum fluid is bled through

discrete bleed ports along the compressor casing near the blade

trailing edge (or where an available source of sufficient highFigure 12 Re-Circulated Casing Treatment Model Applied to

Transonic Fan Rotor 67 with Inlet Distortion.

pressure fluid can be obtained). The low momentum fluid bled

off via the bleed ports is then de-swirled as necessary and

accelerated through a convergent channel where it is reinjected into the blade passage via discrete injection ports

located near the blade leading edge (or where deemed most

beneficial to overall performance). Due to the increased static

pressure of the bleed fluid relative to the injection fluid in the

rotor frame of reference the casing treatment increases the

relative total pressure of the fluid in the casing treatment flow

path. The injection ports are circumferentially displaced

relative to the bleed ports to preclude the potential for reingestion of the injected fluid into the bleed ports. This

alleviates the tendency for typical self-recirculating casing

treatments to produce excessively high temperatures along the

case and in the casing treatment flow path due to re-working

continually re-circulated fluid which can result in melting of

the casing treatment components (Kerney, P., 1994).

CONCLUSIONS

A self-recirculating casing treatment concept has been

demonstrated via CFD simulations to provide a considerable

benefit in stall range extension with no predicted loss in

efficiency or total pressure rise capability. The concept is

shown to benefit performance by decreasing the extent of low

NASA/TM—2002-211569 8
relative total pressure fluid typically accumulating in the

casing endwall region as stall is approached (i.e., endwall

blockage). The key aspects for consideration in assuring

maximum stall range increase without the usual decrement to

efficiency are:

1) Target the major contributor to endwall blockage

accumulation, typically the leading-edge or tipclearance vortex, and locate the injection port

commensurate with such.

2) Assure that the injected fluid is aligned in the relative

 frame with the blade mean camber angle.

3) Inject at high relative velocity to energize the low

 momentum fluid compromising blade row

 performance (i.e., attempt to match the injected

 velocity to be commensurate with the design intent).

4) Inject sufficient fluid to fill the mass deficit

 associated with the leakage vortex, but limit the

 amount of injected fluid so as not to adversely impact

 the spanwise loading distribution outside of the

 vicinity of the blade tip clearance gap.

5) Locate and size the bleed port to provide sufficient

 pressure rise for 3) and 4) while not allowing the

 bleed port to be the choking element.

6) Implementation of discrete bleed and injection ports

which are circumferentially displaced to prevent reingestion of injected fluid into the bleed ports.

Though the CFD predictions presented herein have shown

the potential for this casing treatment concept to provide

significant range extension with out the usual attendant loss of

efficiency they have only considered range extension at design

speed conditions. Any general assessment of its effectiveness

must include consideration of the potential for range extension

at off-design conditions. The extent to which the fluid

mechanism identified as most responsible for blockage

production at design speed conditions contributes to blockage

production at off-design conditions must be considered for

assessing the general applicability of the casing treatment

concept. The results of Suder et al, 2000 showing increased

effectiveness of upstream casing injection (similar to the

concept reported herein except for the location of the injection

point) at off-design conditions suggests the possibility for

general applicability of the casing treatment concept presented

herein.

Figure 13 Discrete Recirculating Casing Treatment Concept

NASA/TM—2002-211569 9
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Clearance Flow Blockage in Turbomachines, “ Masters Thesis,

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Crook, A. J., Greitzer, E. M., Tan, C. S., Adamczyk, J. J.,

"Numerical Simulation of Compressor Endwall and Casing

Treatment Flow Phenomena," ASME Journal of

Turbomachinery, Vol. 115, pp. 501-512, July 1993.

Cumpsty. N. A., “ Part-Circumference Casing Treatment and

the Effect on Compressor Stall, “ ASME paper No. 89-GT312, 1989.

Hathaway, M. D., Strazisar, A. J., “ Impact of Discrete Tip

Injection on Stabilization of a Transonic Compressor Rotor,”

21st Army Science Conference, Norfolk, VA, June 15-17,

1998.

Hobbs, D. E., “ Active Vaned Passage Casing Treatment, “

U.S. Patent (5,431.533), July 11, 1995.

Janssens, G., Chedozeau, M., “ Controle du Decollement

Parietal dans les Compresseurs Axiaux par Aspiration ou

Soufflage de la Couche Limite, “ Communication presentee au

XVI Colloque d’Aerodynamique Appliquee (AAAF), Lille,

13-15 November, 1979.

Kerney, P. “ Recirculating Cavity Casing Treatment Failure, “

Wright Laboratories Report WL-TR-94-2092, 1994.

Khalid, S., “ The Effects of Tip Clearance on Axial

Compressor Pressure Rise, “ Ph.D. Dissertation,

Massachusetts Institute of Technology, 1994.

Khalid, S. A., Khalsa, A. S., Waitz, I. A., Greitzer, E. M., Tan,

C. S., Cumptsy, N. A. Adamczyk, J. J., Marble, F. E., “ Endwall

Blockage in Axial Compressors, “ ASME Paper 98-GT-188,

1998.

Koch, C. C., Smith, L. H. Jr., "Experimental Evaluation of

Outer Casing Blowing or Bleeding of Single Stage Axial Flow

Compressor, Part IV - Performance of Blowing Insert

Configuration No. 1," NASA CR-54589, 1968a.

Koch, C. C., Smith, L. H. Jr., "Experimental Evaluation of

Outer Casing Blowing or Bleeding of Single Stage Axial Flow

Compressor, Part IV - Performance of Bleed Insert

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Koch, C. C., “ Stalling Pressure Rise Capability of Axial Flow

Compressor Stages, ” Transaction of the ASME, Journal of

Engineering for Power, Vol. 103, pp. 645-656, October, 1981.

Koff, S. G., Mazzawy, R. S., Nikkanen, J. P., Nolcheff, N. A.,

“ Case Treatment for Compressor Blades. “ U.S. Patent

(5,282,718), February 1, 1994.

Nolcheff, N. A., “ Flow Aligned Plenum Endwall Treatment for

Compressor Blades, “ U.S. Patent (5,586,859), December 24,

1996.

Prince, D. C. Jr., Wisler, D. D., Hivers, D. E., "Study of

Casing Treatment Stall Margin Improvement," NASA CR134552, 1974.

Shabbir. A., Celetina, M. L., Adamczyk, J. J., and Strazisar, A.

J., “ The Effect of Hub Leakage Flow on Two High Speed

Axial Flow Compressor Rotors,” ASME Paper No. 97-GT346, 1997

Shih, T. H., Liou, W. W., Shabbir, A., Zhu, J. and Yang, Z., “ A

New k-e Eddy Viscosity Model for High Reynolds Number

Turbulent Flows, “ Computers Fluids, 24, 3, 227-328, 1995.

Shih, T. H., Zhu, J. Celestina, M. L., “ Assessment of Three

Turbulence Models in a Compressor Rotor, “ ASME Paper

No. 96-GT-198, 1996.

Smith, G. D. J., Cumpsty, N. A., “ Flow Phenomena in

Compressor Casing Treatment, “ ASME Journal of

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NASA/TM—2002-211569 10
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1L161102AH45

16

Self-Recirculating Casing Treatment Concept for Enhanced Compressor

Performance

Michael D. Hathaway

Machines for compressing air or other fluids

Unclassified -Unlimited

Subject Category: 07 Distribution: Nonstandard

Prepared for the Turbo Expo 2002 cosponsored by the American Society of Mechanical Engineers and the International

Gas Turbine Institute, Amsterdam, The Netherlands, June 3–6, 2002. Responsible person, Michael D. Hathaway,

organization code 5810, 216–433–6250.

A state-of-the-art CFD code (APNASA) was employed in a computationally based investigation of the impact of casing

bleed and injection on the stability and performance of a moderate speed fan rotor wherein the stalling mass flow is

controlled by tip flow field breakdown. The investigation was guided by observed trends in endwall flow characteristics

(e.g., increasing endwall aerodynamic blockage) as stall is approached and based on the hypothesis that application of

bleed or injection can mitigate these trends. The “best” bleed and injection configurations were then combined to yield a

self-recirculating casing treatment concept. The results of this investigation yielded: 1) identification of the fluid mechanisms which precipitate stall of tip critical blade rows, and 2) an approach to recirculated casing treatment which results in

increased compressor stall range with minimal or no loss in efficiency. Subsequent application of this approach to a high

speed transonic rotor successfully yielded significant improvements in stall range with no loss in compressor efficiency.