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AJAA

A99-31020

m=-- - -= I*II=

Session: ACT-O 1 Smart Engine Technology

AIM 99-2128 A High-Response High-Gain Actuator for Active Flow Control

Link C. Jaw, Dong N. Wu, Gui A. Zhou, David J. Bryg Scientific Monitoring, Inc. Tempe, Arizona

Marty Walsh U. S. Army Aviation Applied Technology Directorate Ft. Eustis, Virginia

35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit

20-24 June 1999 Los Angeles, California

For permission to copy or to republish, contact the American Institute of Aeronautics and Astronautics, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344.

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AIAA 99-2128

A HIGH-RESPONSE HIGH-GAIN ACTUATOR FOR ACTIVE FLOW CONTROL

Link C. Jaw, Dong N. Wu, Gui A. Zhou, David J. Bryg Scientific Monitoring, Inc., Tempe, Arizona

Link@mi-controlscorn

Marty Walsh Aviation Applied Technology Directorate, Ft. Eustis, Virginia

Abstract Introduction

Advanced turbine engines often’ operate at high pressure loading conditions with an attendant loss of stability margins. To maintain robust operations throughout an engine’s operating envelope and to achieve high performance and operability, active control has been considered an enabling technology.

To address the needs of active controls, Scientific Monitoring, Inc. designed, built, and tested a high- response, high-gain actuator to control the airflow in the engine. The test results of this actuator are presented in this paper. Both steady state and dynamic flow characteristics of the actuator are discussed. The mechanical integrity of the actuator has been demonstrated.

The test results suggest that this technology can potentially be applied to active controls of flow fields. Specifically for turbine engine applications, this technology may be implemented in two different approaches: airflow injection or off-board bleed.

Nomenclature

fps Foot per second KRV High-response valve Hz Cycle per second P1 or P, Valve upstream pressure (psi) P2 or Pd Valve downstream pressure (psi) PPs Pound per second PSD Power spectral density psi Pound per square inch Vamp Translator control potential signal (V) Vcmd Translator position command signal (V) VPzt Translator displacement signal (V)

Copyright 0 1999 The American Institute of Aeronautics and Astronautics, Inc. AU rights reserved.

Air and gas flows in turbine engines are susceptible to instabilities. These flow instabilities are characterized by rapid, unsteady fluctuations in velocity, temperature, and pressure. The unsteady fluctuations associated with surge and stall are often deterministic and repeatable. They disrupt surrounding flow fields, cause severe stresses on engine components, degrade engine efliciency, and even cause flow reversals or flameout.

Rotating stall and surge represent two most notable flow instabilities in a turbine engine compression system [ 1,2, 31. Since engine components are being exposed to increasingly high thermal and aerodynamic loads, and since the components are operating more closely to their physical limits, stall and surge have become important design and operability issues. To address these issues, engineers have tried to avoid, and ultimately to control, stall and surge in turbine engines. Much work has been done on the control of compressor surge and rotating stall in the last 10 years [4]. Most of the work relies on modulating flow properties in the compressor at a high speed (or rate). Fast modulation eliminates stall/surge instabilities while they are still in the beginning stage of development. In the beginning stage, disturbances are small, the control authority required to suppress such disturbances is also small, and the growth of the disturbances can be slow enough to be effectively suppressed.

Two approaches to controlling stall/surge have evolved. One approach involves flow injections at the inlet of a compressor [5, 61, the other approach involves off-board bleed at an inter-stage or the exit of a compressor [7, 81. While inlet injection requires an airllow source, the operating environment of injection actuators is more favorable than the high-temperature and high-pressure environment of bleed actuators. On the other hand inlet injection requires multiple actuators to be sequenced properly to suppress rotating stall cells, exit bleed may only require one or a smaller number of lower-response actuators; however, these

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AIAA 99-2128

actuators will be bigger and will require higher flow control authority than the injection actuators.

Regardless of which approach is taken, actuation technology has consistently been identified as the enabling technology for active stall/surge control. In early 1990’s, the actuation response requirement was characterized as 500 Hz [9, lo]. In recent years, the desire to increase actuation response to beyond 800 Hz was mentioned. Hence, meeting the challenge of high- response actuators was the primary motivation for the work presented in this paper.

The Actuator Design Problem

In flow controls, actuation response should be considered as the bandwidth of the flow control gsfem, not just the bandwidth of the prime mover. A flow control system consists of several components. These components are needed for flow supply, motion control, valve, and flow delivery (injector). Flow supply and delivery components involve ducting and passages; therefore, they inevitably introduce transport delays. These delays can significantly reduce the response and the effectiveness of an actuation system. Hence, increasing actuation system response is the first challenge for flow control actuator design.

The second challenge for actuator design is the control authority at high frequency. This implies that the actuator must be able to throttle an adequately large amount of flow at high frequency.

Yet another challenge is actuator packaging. Packaging includes the following implementation issues: s Number of actuators and the optimal placement of

these actuators. n Power supply for these high-response actuators. . Supplying, conditioning, and delivery of the

airflow. n Electronic control system and logic.

In this paper, we present the results that address the first two design challenges.

Actuator Design

The Scientific Monitoring, Inc. high-response valve (HEW) used a piezoelectric translator as the prime mover. The cylindricaI translator contained a stack of piezoelectric laminates. The actuator was shaped as a circle to maximize the flow rate through the opening. -The translator pushed at the center of several circular-shaped valve plates causing the outer edge of these valve plates to deflect and form a flow passage. The airflow passing through the valve was

then collected downstream and injected into the engine. This valve concept is illustrated in Figure 1.

Figure 1: SMI actuator concept

The prototype actuator that was tested on AlliedSignal’s T55 compressor rig -is pictured in Figures 2. A 3-D computer-aided -design (CAD) drawing of the valve assembly is shown in Figure 3.

Figure 2: SMI actuator prototype

Figure 3 : A 3 -D CAD drawing of the assembled valve

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Wind Tunnel Testing

Wind tunnel testing of the actuator, as shown in Figure 4, was conducted at the Arizona State University (ASU) from August to September 1996. An actuator prototype was mounted on the top of the test section. The air speed in the test section was in the range of 70 to 80 fps. The purposes of the wind tunnel test were to: n Verify the design integrity of the actuator. . Learn the operational characteristics of the

piezoelectric translator. . Survey the velocity profile of the a.irIlow coming

out of the valve injector. This profile would be used to estimate flow rate and to check the manufacturing tolerances of the valve.

Figure 4: A prototype was tested on wind tunnel

Two types of tests were conducted: static and dynamic flow tests. In the static flow test, the valve flow rate at various translator displacements (or strokes) was measured by using an in-line flow meter. The velocity profile of the airflow downstream of the injector was also measured by using a hot wire anemometer traversed across the width of the injector as shown in Figure 5 (the injector was flushed with the test section upper wall).

Figure 5: Velocity measurement using a hot wire

AIAA 99-2128

In the dynamic test, the velocity of the airflow was measured at the center of the injector; the translator ._. moved. above and below its equilibrium position of 50% stroke following a square-wave command with a duty cycle ranging from 50% to 100%. The frequency range of the dynamic test was between 1 Hz and 50 Hz. The purpose of the dynamic test was mainly to verify the controllability of the valve.

Test results. showed that the maximum flow rate through the actuator at steady state was approximately 0.15 pps and the maximm airflow velocity near the exit of the injector was 270 fps (absolute velocity). The translator stroke ranged from 0 to 0.007 inches. The velocity profile increased with increasing translator stroke.

Rig Testing

An actuator prototype was tested on AlliedSignal’s T55 compressor rig in June 1998. The actuator was mounted on the inlet duct of the rig as shown in Figure 6. The purposes of the rig test were to: . Test the actuator under. realistic engine operating

conditions. = Verify the characteristics of the actuator,

particularly, those under high-frequency operating conditions.

Figure 6: Compressor rig test of the actuator

Again, two types of tests were conducted. In the static test, the airflow supply- pressure was varied between 20 psi(gauge) to 60 psi(gauge). In the dynamic test, the valve was linearly modulated by a sinusoidal command in the frequency range between 10 Hz and 1,000 Hz.

The airflow rate through the actuator at a given valve opening was a function of the translator displacement as well as the supply pressure of the air. The translator displacement was proportional to the electrical potential applied to it. The applied potential

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AIAA 99-2128 _.

for the translator was between 0 and 100 V (corresponding to the maximum stroke of 0.0035 inches). In the test, the applied potential was generated by a pair of bipolar power amplifiers, which were configured to receive the displacement command signal between 0 and 10 V from the control computer.

The flow rate was measured in the test cell. The actuator demonstrated a flow capacity of more than 0.2 pps at the maximum stroke. The valve flow rate versus the translator position command (or the stroke) under the supply pressure condition of 20 psig is shown in Figure 7. Note that a slight leakage (about 0.035 pps) was observed during the test.

Steady State Flow Rate of SMI High Response Vake Steady State Flow Rate of SMI High Response Vake

0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8-9 8-9 IO IO Position Command (V) Position Command (V)

Figure 7: Static flow rate through the actuator (supply air pressure = 20 psig)

In the dynamic test, five measurements were are shown in Figures 10 and 11 for the two test made, of which three were related to the translator and frequencies, respectively. Note that two flow rates were were recorded at the rate of 5,000 samples per second calculated based on the static pressure measurements. by the data acquisition module within the control In the first calculation, the pair of static pressure. values system., These three signals were: the translator were substituted into a flow model assuming that the command from the computer (V,, , drawn in blue pressures were uniformly distributed over the entire color in the following two figures), the translator circumference of the valve and that the measurements electrical potential from power amplifiers (2O*V,, , in were taken immediately upstream and downstream of green), and the translator displacement (VP, , in red). the valve. Unfortunately, both assumptions were not The remaining two measurements were related to the true resulting in less calculated flow., In the second static pressures on the valve and were recorded at the calculation, the downstream pressure was adjusted rate of. 12,500 samples Irer second by AlliedSignal’s such that the time-averaged mean flow rate was high-speed digital data recorder. These two signals equivalent to what was measured in the steady state were: the static pressure on the supply side (upstream) actuator test, i.e., we matched the RMS value of the of the valve (PJ and the static pressure on the exit side dynamic flow rate to the steady state flow rate by (downstream) of the valve (Pd. Only one high- biasing the downstream pressure, then we used this response pressure sensor was installed on each side of biased pressure to estimate the dynamic flow rate and the valve. called it the calibrated flow.

The translator control signals in the 10 Hz and the 1,000 Hz tests are shown in Figures 8 and 9, respectively. The two pressure signals, together with the calculated flow rates through the valve and the estimated power spectral density (PSD) of the flow rate

The calculated flow rates, even v&h large variations, clearly exhibited the same frequency characteristics as the valve excitation signal (command). The frequency response of the actuator was computed and shown in Figure 12.

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AlAA 99-2128

10 -

1 I I I I I I 1 I I

0 100 200300400500 600 700 800 900 Iwo Time (ms)

Figure 8: Control signals in the 10 Hz test

1

-11 I I I I I 8 I I I 0 1 2 3 4 5 6 7 8.9 IO

Time (ms)

Figure 9: Control signals in the 1,000 Hz test

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PI and P2

(jO[c..,,...,.....,..ll

I 14 14.5 15

lime set) Uncalibrate d mass flow

AIAA 99-2128

Power spectral density of mass flow

o.51 0.4

5:

a 0.2

0.3 l-L---l

0.1

0 0 500 IWO

Frequency (Hz Calibrated mass 4 ow

14.5 15 “l4 14.5 15 ‘Time (set) Time (set)

Figure 10: Pressure signals and estimated flow rates in the 10 Hz test

PI and P2 Power spectkal density of mass flow

0.4

5: 0.3

a 0.2

0.1

0 : 100 100.5 101

Time set) Uncalibrate d mass flow

O.’ I - 0.08 i!i $ 0.06 t

100.5 lime (set)

0 500 IWO 1;oo Frequency (Hz

Calibrated mass d ow

- I:

0.08

f 0.06

9 ii 0.04

2 0.02

o- 100 100.5 101

lime (set)

Figure 11: Pressure signals and estimated flow rates in the 1,000 Hz test

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AIAA99-2128

Gain ratio

IO' Fw 0-W

Figure 12: Frequency response of the actuator

Conclusions

A high-response flow control actuator was designed and built. The actuator used a piezoelectric material as the prime mover to achieve high bandwidth. The actuator incorporated a novel valve design to throttle the airflow through the actuator. A close-coupled injector was fitted at the downstream side of the valve to reduce the transport delay.

The design was first tested on a low-speed wind tmmel and then on a compressor rig. Test results confirmed the actuation concept and demonstrated its capabilities to control the airtlow at 1,000 Hz. The actuator also demonstrated a steady state flow control capability of 0.2 pps.

We believe that the maximmn steady state flow rate through the valve could be increased if the actuator were modified to improve manufacturing tolerances and calibration.

Although the actuator was tested at very high frequencies (beyond 500 Hz) for only a short period (approximately 15 seconds) at each test frequency, the heat dissipation of the piezoelectric translator was not as high as anticipated.

Based on the rig test results, we estimated that the actuator system bandwidth was between 1,200 to 1,500 Hz. Although the concept was conceived almost five

years ago, and the piezoelectric translator represented the best commercially available technology at that time, this high-response actuator has proven to be a promising technology even to date for controlling a large amomt of flow beyond 500 Hz.

The results suggested that this type of actuator be implemented in two different approaches: air flow injection and off-board bleed. In the injection approach, it can be used to compensate for flow momentum deficit. In the bleed approach, it can be used to relieve excess energy. The actuator may also be applied to an indirect control of flow fields by throttling a secondary (or synthetic) jet.

References

1) Emmons, H. W., Pearson, C. E., and Grant, H. P.; “Compressor Surge and Stall Propagation,” Transactions of the ASA4E, May 1955, pp. 455-469.

2) Greitzer, E. M.; “Surge and Rotating Stall in Axial Flow Compressors, Part I: Theoretical Compression System Model; and Part II: Experimental Results and Comparison with Theory,” ASME J. of Engrg. for Power, April 1976, Vol. 98, No. 2, pp. 190-216.

3) Moore, F. K.; “A Theory of Rotating Stall of Multistage Compressors, Part I, II, III,” ASME J. of

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Engrg. for Power, April 1984, Vol. 106, No. 2, pp. 313-336.

4) Paduano, J. D.; “‘Recent Developments in Compressor Stability and Control,” keynote paper presented at the International Symposium on Rotating Machinery, Honolulu, February 1998.

5) Day, I.J., “Active Suppression of Rotating Stall and Surge in Axial Compressors,” ASME paper no. 91- GT-87.

6) Epstein A.H., Ffowcs Williams, J.E., and Greitzer, E.M.; “Active’ Suppression of Aerodynamic Instabilities in Turbomachines,” AIAA paper no. 86-1994. Also J. of Propulsion, 1989, Vol. 5, No. 2, pp. 204-211.

7) Adomaitis, R. A. and Abed, E. H.; ‘Zocal Nonlinear Control of Stall Inception in Axial Flow Compressors,” AIAA paper no. 93-2230, 1993.

8) Badmus, 0. O., Chowdhury, S., Eveker, K. M., and Nett, C. N.; “Control-Oriented High-Frequency Turbomachinery Modeling: Single-Stage Compression System 1D Model,” paper presented at the Int’l Gas Turbine and Aeroengine Congress and Exposition, Cincinnati, Ohio, May 1993, ASME paper no. 93-GT-18.

9) Berndt, R G., et al.; “Experimental Techniques for Actuation, Sensing and Measurement of Rotating Stall Dynamics in High Speed Compressors,” SPIE Proceedings for Sensing, Actuation, and Control in Aeropropulsion, J. D. Paduano Editor, April 1995, pp. 166-185.

lO)Mattem, D and Owen, A. K.; “A Voice Coil Actuated Air Valve for Use in Compressor Forced Response Testing,” SPIE Proceedings for Sensing, Actuation, and Control in Aeropropulsion, J. D. Paduano Editor, April 1995, pp. 215-223.

Acknowledgment

Scientific Monitoring, Inc. is grateful for the U. S. Army Aviation Applied Technology Directorate (AATD) for providing financial support and encouragement during the course of this project.

SMI should like to thank AlliedSignal Engines for many valuable discussions and for its support of the T55 compressor rig testing. Particularly, we would like to acknowledge the support from Dr. Arun Sehra (now with NASA Glenn Research Center), Mr. John Dodge, Mr. Jim Sublet& Dr. William Cousins, Mr. Mike Holbrook, and Mr. John White.

SMI should like to thank Phoenix Analysis and Design Technologies (PADT) for its support of mechanical design and manufacturing of prototype actuators.

ALL4 99-2128

SMI should also like to thank Dr. William Saric of the Arizona State University for his support of the wind tunnel testing.

Lastly, we thank Dr. Frank Q. Liu for his contributions in actuator design, flow modeling, and wind tunnel test support.

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