[American Institute of Aeronautics and Astronautics 2nd AIAA Flow Control Conference - Portland,...

American Institute of Aeronautics and Astronautics

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Lopera, Ng & Patel AIAA 2004-2695

Experimental Investigations of Reconfigurable Porosity for Aerodynamic Control

Javier Lopera* and T. Terry Ng†

University of Toledo, Toledo, OH, 43606

and

Mehul P. Patel‡ Orbital Research Inc, Cleveland, OH, 44103

Experimental results to demonstrate the application of an innovative, low-power, flow control technique – reconfigurable porosity – for aerodynamic control is presented. The control is based on selective actuation and de-actuation of discrete holes that form unique porous-patterns to enable small amounts of mass transfer in-and-out of the surface. Since the technique relies on flow transpiration caused due to natural pressure loading around the aerodynamic surface, power is required only for the control of hole-patterns, and not for plumbing, as in the case of suction or blowing. Low-power, MEMS-based microvalves can be used to form discrete hole-patterns to further minimize the total power consumption. Transpiration of air at certain optimal locations on the aerodynamic surface is hypothesized to energize the boundary layer, forcing a delay in flow separation. Controlled three-dimensional perturbations caused by patterned-porosity can be rapidly re-configured to adapt to the changing flow conditions so as to continually operate in an optimal configuration for improved effectiveness. To assess the control performance, low-speed experiments are conducted on two aerodynamic models, a multi-wedged supersonic wing model and a complete projectile model (with two four fins arranged in cruciform (+) configuration). Force data as well as flow visualization results are presented to illustrate the patterned-porosity concept. Quantitative results show that control forces of varying magnitude can be generated using different porous patterns for a range of alpha conditions. This control technique has demonstrated the ability to generate adequate levels of control forces for course correction and maneuvering of air vehicles.

I. Introduction riginally developed in the early 1980's as a means of shock-boundary layer interaction control, passive porosity has evolved into an extensively-tested and well-understood flow control technology. Over the years, this

technique has been widely demonstrated for a number of aerodynamic applications, including shock wave–boundary layer control, drag reduction, alleviation of forebody asymmetries, and aerodynamic control.1-7 The use of porosity as a flow control technique is attractive due to its ability to modify the pressure loading around an aerostructure without imposing penalties resulting from parasitic drag, auxiliary power requirements, and complex hardware associated with the control mechanism, as in the case of some other flow control actuators. Passive porosity is, however, a static system where the pores and the pneumatic substructure connecting the pores are incapable of reconfiguring its control parameters to adapt to the dynamical flow conditions. In order to meet the stringent demands of an active flow control system for practical applications, where flow conditions are predominantly dynamic in nature, there exists a need for a flow control system with an ability to reconfigure its control parameters in real-time, so as to provide the most effective control-effect at all times. In addition, the overall cost, power *Graduate Research Assistant, Dept. of Mechanical, Industrial and Manufacturing Engineering, Member AIAA. †Professor, Dept. of Mechanical, Industrial and Manufacturing Engineering, Senior Member AIAA. ‡Director, Aerodynamics Group, Orbital Research Inc., Member AIAA. Copyright ©2004 by Orbital Research Inc, Published by the American Institute of Aeronautics and Astronautics with permission.

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2nd AIAA Flow Control Conference28 June - 1 July 2004, Portland, Oregon

AIAA 2004-2695

Copyright © 2004 by Orbital Research Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.


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Lopera, Ng & Patel AIAA 2004-2695consumption, and the complexity of the flow control system need to be low so that the technology can be transitioned to a large fleet of air vehicles, both in the commercial and military sectors, without necessitating complex and expensive modifications. Strategic advantages of these low-cost, low-power, miniature flow control devices lie in the areas of: (i) unconventional air vehicle designs– where the design is dictated by mission requirements rather than aerodynamic design methodologies– and these control devices can be used to retain the lost aerodynamic efficiency; and (ii) advanced weapons such as the next-generation munitions, projectiles, and missiles– where precision control is required for a short period of flight time, mainly during the end-game maneuvering. This paper presents proof-of-concept of a low-power, adaptive flow control technique, reconfigurable porosity, focusing on aerodynamic control of fixed-wing air vehicles and projectiles. Figure 1 shows an illustration of the application of reconfigurable porosity for projectile control, which is the focus of the present study. The figure of merit for the present application is the ability to generate control forces at low angles of attack (0-20 deg).

II. Reconfigurable Porosity In reconfigurable porosity, control is implemented through discrete holes in the form of a patterned, spanwise,

periodic perturbation across the boundary layer. This form of perturbation is based on a previously demonstrated flow control technique, discrete suction.8 Discrete suction control is an active suction system consisting of a series of small, individually-controlled discrete suction holes along the aerodynamic surface. Control is implemented by arranging these discrete holes in the form of a spanwise, periodic perturbation across the boundary layer prior to separation. During separation, this (controlled) perturbation produces a three-dimensional, spanwise variation at the separation line. A series of counter-rotating vortex motion forms through a natural flow instability. This leads to a strong entrainment of high momentum fluid onto the surface, thereby delaying separation. Unique features of the concept is that the controls are based on triggering a natural instability in the separated flow itself; thereby requiring only a small input, since most, if not all, vorticity associated with the control originates from the base flow and not the control input. Discrete suction control has been demonstrated for aerodynamic applications such as– control of shear flow unsteadiness and leading edge flow separation.8,9

In reconfigurable porosity, the (controlled) perturbation is provided naturally due to the high– and low pressure regions in the near-wall flowfield rather than using a separate source for suction and blowing. The natural pressure differences enable flow transpiration through the windward and leeward surfaces of the aerodynamic surface. The pressure difference on these surfaces is higher at certain angles of attack, which makes the control system more effective than other angles of attack. The effects of reconfigurable porosity are currently being viewed

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Figure 1: An illustration demonstrating the application of reconfigurable porosity for projectile control


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Lopera, Ng & Patel AIAA 2004-2695as a synthesized effect of discrete suction and jet blowing. While the effect of suction is apparent, the effect of blowing is still being examined. It is hypothesized that at appropriate levels, blowing functions as a vortex generating jet that forces a delay in flow separation, similar to the effect caused by suction. The interaction of fluid from the 3-D porous holes with the incoming fluid enhances momentum mixing and causes a delay in flow separation. It is anticipated that an investigative study of flow visualization and force data will shed some light on the fundamental flow physics that lead to such favorable flow effects. These findings will also aid in improvement and optimization of hole-patterns, leading to a repeatable force modulation system that can be used for control of air vehicles. Computation Fluid Dynamics (CFD) studies are also being conducted in parallel to aid in the understanding of flow behavior and the effects of patterned-porosity. The main challenge in the CFD study is the accurate modeling and representation of the internal chamber that connects the high– and low pressure regions on the aerodynamic surface. Currently, a new boundary condition based on the existing screen boundary condition is being developed to model the patterned-porosity system. Preliminary results from the CFD study on a porous wing model are in good agreement with experimental results, and validation efforts – to be reported at a later stage – are in progress.

Another key component of the reconfigurable porosity system is the internal packaging module that enables different porous-patterns to selectively activate and de-activate the holes. This can be conceivably achieved by using MEMS-based microvalves, which can be tightly packed in a low-volume, light-weight, Control Actuation System (CAS). Figure 2 shows a schematic (in a cross-section view) of an integrated MEMS-microvalve based CAS for reconfigurable porosity. Details on the design, development, and testing of MEMS-microvalves to be used for an aerodynamic CAS has been previously reported.10 Since the focus of this paper is on the assessment of reconfigurable porosity for aerodynamic control, and not CAS hardware development, the discussion in this paper is limited to the experimental validation of the control concept. It is important, however, to note that a prototype CAS using MEMS-microvalves has been successfully tested in low-speed wind tunnel conditions.

Previous studies conducted at a low-subsonic speed of Mach 0.1 on the wing model presented preliminary estimates of the control forces and the effects of various pattern configurations on the wing aerodynamics.11 Comparison between symmetric and asymmetric patterns on the top and bottom surfaces showed distinct effects caused due to porous patterns. Different porosity pattern configurations were shown to be able to generate forces which demonstrated a near-linear relationship between the forces generated (about the body fixed axis) and the porous patterns. Actuator configurations can thus be created that correspond to known pitch-roll-yaw rates about the body fixed axes. In continuation, this paper presents flow visualization results from additional low-speed wind tunnel experiments conducted on the supersonic wing model. Additional porosity experiments are conducted on the complete projectile model to access the effectiveness of fin- and boattail-based (porosity) control for pitch-yaw-roll maneuvering. The focus of this paper is thus on both the quantitative (force) estimates as well as qualitative investigations (from flow visualization) of the patterned-porosity actuators. Presented below are the details of the aerodynamic models, experimental set-up, and results from wind tunnel experiments.

III. Aerodynamic Models and Experimental Set-Up

A. Supersonic (Multi-Wedged) Wing Model

A symmetric supersonic wing model with a chord length, c, of 329 mm, is designed and fabricated. Figure 3 shows a schematic and a picture of the wing model. The wing-root chord is 329 mm and the wing-tip chord is 80 mm. The wing has a leading-edge sweep angle of 61.5 deg. The wing is symmetric in design and consists of three double–wedges, one at x/c = 0.2, second at x/c = 0.55, and the third at x/c = 0.84. The third double-wedge (at x/c = 0.84) forces a 16 deg expansion

MEMS-microvalve packaging to enable active control of porous holes

Porous holes on the windward and leeward surfaces of a wing

MEMS-microvalve packaging to enable active control of porous holes

Porous holes on the windward and leeward surfaces of a wing

Figure 2: Conceptual design of a Control Actuation System (CAS) using MEMS-microvalves for an “active” reconfigurable porosity control system (cross-sectional view)


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Lopera, Ng & Patel AIAA 2004-2695facet near the trailing-edge. This design modification causes the flow to separate near the trailing edge at relatively low angles of attack, thereby mimicking the flow phenomena over an unconventional air vehicle design– where the design is dictated by mission requirements rather than aerodynamic design principles. This design modification also augments the effectiveness of flow control actuators by forcing a region of pressure difference (along the entire wing span). The wing is integrated with four spanwise arrays of miniature holes before and after the trailing-edge (at x/c = 0.84) wedge (reflex line) on both windward and leeward surfaces of the wing. A common plenum inside the wing model enables flow communication between these surfaces as well as between the facets near the trailing-edge wedge.

B. Projectile Model

To assess the performance of the reconfigurable porosity flow control technique for projectile control, experiments are conducted on a 70% scale model of a next-generation multi-role projectile. Figure 4 shows the projectile model used for this study. The model is 56 cm in length with a maximum diameter of 7.35 cm, yielding a fineness ratio of 7.62. The projectile was equipped with an internal sting mount (force balance) to measure pitching and yawing forces. The original fins of the multi-role projectile were planar in design with a rectangular cross-section. This (fin) design was modified to include a sweep and a cross-section as shown in Fig. 5, with a trailing-edge wedge expansion angle of 16 deg, similar to the wing model. The new fin includes integrated flow control actuators and is referred to as the Aero Control Fin (ACF). The boattail design is also modified by increasing the boattail expansion slope from 7.47 deg to 20 deg for improved control effectiveness. Both the boattail and the Aero Control Fins (ACF) include miniature holes (for reconfigurable porosity) near the trailing edge wedged reflex line, as shown in Fig. 5.

C. Experimental Set-up and Wind Tunnel Testing

Wind tunnel experiments were performed at The University of Toledo’s 0.9 m × 0.9 m (3 ft. × 3 ft.) closed-circuit wind tunnel. The set-up included a C-strut model support and a turntable to allow for different model orientations. A motor incorporated in the turntable was used for remote model positioning. The flow was driven by a 14-blade, variable-pitch fan coupled to a 150-hp electric motor, that allowed for speeds over 200 mph (300 ft/s). Two tempered-glass sidewalls and a large Plexiglas window on the ceiling provided convenient access for flow visualization. The flow in the test section was uniform with a turbulence level of 0.2% outside of the wall boundary layers.

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Figure 3. Illustrations of the supersonic wing model used for flow visualization studies using reconfigurable porosity


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For the projectile model, experiments were conducted at Mach 0.1 for angles of attack ranging 0 deg to 18 deg. Tests were conducted at a Reynolds number, Re of 0.14 × 106 based on a freestream velocity of 28 m/s and a model diameter of 7.35 cm. Key objectives of the experiments were to: (1) quantify as well as demonstrate the ability of reconfigurable porosity for aerodynamic control of air vehicles; (2) create an extensive matrix of different porous patterns and distinguish those with the most beneficial aerodynamic control effects at low-alpha, low-speed flow conditions, and (3) attempt to understand the fundamental flow physics behind the reconfigurable (patterned) porosity control technique.

Different porous patterns (also referred to as configurations) tested on the projectile ACF (near the 16 deg trailing-edge wedge) are presented in Fig. 6 and the porous patterns tested on the modified boat-tail of the projectile model with no ACF, are shown in Fig. 7.

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Figure 4. Illustrations of the scaled projectile model used for wind tunnel experiments

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Projectile boattail with ACF Projectile boattail with porosity

Aero Control Fin (ACF) – Fin with porosity

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Figure 5. Pictures of the projectile boattail and Aero Control Fins (with porosity)


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IV. Flow Visualization Experiments and Results Flow visualization was conducted on the wing model, shown in Fig. 3, in both wind– and water tunnel

experiments. Figure 8 shows the porous patterns tested on the wing model for flow visualization studies. Wind tunnel flow visualization were conducted at a Re of 1.14 × 105 based on the chord length of 329 mm, and three flow visualization techniques were used to capture the flow patterns: surface tufts, smoke with a laser sheet, and surface fluorescent oil. Water tunnel flow visualization was conducted in a 7” × 9.5” × 18” (length), closed-circuit low-speed water tunnel at a Re of 21. Two visualization techniques were implemented in this study: dye and hydrogen-bubble with a laser sheet.

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Figure 6. Porosity patterns tested on the ACFs of the projectile model, ACFs in + (cruciform) configuration


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The most interesting results from the surface flow visualization experiments conducted on the wing model were obtained using tufts and fluorescent oil. The goal of these experiments was to gain a better understanding of the physics behind the natural– blowing and suction that occur during the transpiration process of reconfigurable

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Figure 7. Porosity patterns tested on the boattail of the finless projectile model


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porosity. Figures 9-a and 9-b show images of visualization studies on the baseline case, where no holes are actuated at 0 deg and 6 deg alpha using tufts. Results show that the flow is separated on the region past the trailing edge. Figures 9-c and 9-d show a snapshot of tufts from flow visualization experiments using pattern 15. These images show that at 0 deg alpha the flow is partially reattached, and at 6 deg alpha the flow is mostly re-attached compared to the baseline case.

Surface flow visualization studies were also conducted using fluorescent oil, composed of a mixture of ZL-37 (Zyglo) and paint thinner, in conjunction with a black-light lamp. Tests were conducted for porous patterns shown in Fig. 8 at 8 deg alpha. Figure 9-e shows that the oil glides past the “closed” porosity holes, and the flow has a region of flow reversal near the trailing edge of the wing. Results for pattern 15 tests are presented in Figs. 9-f and 9-g. Figure 9-f shows that for some cases the “saw-tooth” patterns forces the oil towards the outer edge of the wing in the spanwise direction. Figure 9-g shows that there is a small accumulation of oil in between the “saw-tooth” patterns. This accumulation signifies the presence of spanwise periodical recirculation regions, which in turn indicates a likewise separation pattern. The presence of such a separation pattern can lead to the formation of counter-rotating vortex motion near the surface and delay separation. The present study however, is not able to provide a detailed view of the flow pattern.

Figure 9-h shows flow visualization from pattern 3 where all holes are opened. It is interesting to note that when the holes stay open, the oil flows around the edges of the hole. The pattern also shows how the oil is redirected at the front of the hole-patterns to the outside of the wing without crossing the holes; this event is likely to be caused by blowing during the transpiration process between the top and bottom facets of the wing.

V. Patterned-Porosity Control Effectiveness Results Force and moment data were gathered on the projectile model from low-speed tests using two reconfigurable

porosity configurations: (1) porosity actuated on two aero control fins, and (2) porosity actuated on the modified boat-tail with no ACFs. Only the normal force and pitching moment coefficients are discussed in this paper. Measurements are taken with a reference point located 32.4 cm from the nose tip. Results show aerodynamic moments and forces versus alpha for different porous patterns.

The first configuration tested was the projectile model with four aero control fins with a 16 deg expansion at the trailing-edge and a 20 degree modified boat-tail. Over 50 different porous patterns were tested. Experiments were conducted with two opposing aero control fins with reconfigurable porosity actuators, while the other set of aero control fins had no control. Results for 15 of the porous patterns tested are presented in Figs. 10 thru 12. Details of the patterns used for these tests are shown in Fig. 6.

Low-speed experiments were also conducted on the projectile model with no ACFs configuration, but with porosity on the modified boattail instead, as shown in Fig. 5. A total of 48 porous patterns were tested using the modified boattail, and results for 15 porous patterns are presented in Figs. 13 thru 15. Details of the porous patterns tested are shown in Fig. 7.

Figures 10-a thru 10-e show the pitch moment coefficient of different porous patterns compared to the baseline case. Baseline case shows a significant nose-down pitching moment that extends through most of the alpha range. The porous patterns, in general, reduce the nose-down pitching moment. When asymmetric patterns are used between the leeward and windward facets of the fin, a larger control force is achieved, compared to symmetric patterns. Patterns that use a “saw-tooth” arrangement are some of the most effective patterns as shown in Figs. 10-d and 10-e. Figures 11-a thru 11-c show pitching moment coefficient increments compared to the baseline case for the porous patterns (shown in Fig. 6). Some porous patterns create a comparable pitching moment of a fin deflection ranging from 2 to 5 degrees over a wide range of alpha based on baseline fin deflection studies.

Baseline Pattern 3 Pattern 15Baseline Pattern 3 Pattern 15

Figure 8. Porosity patterns tested on the wing model during flow visualization experiments


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Results also show that porous patterns with smaller and repeated “saw-tooth” geometries, as represented by pattern S-20, is more effective over a broad alpha range than larger “saw-tooth” patterns such as pattern S-15 and S-23. A wide range of control forces are achieved and control “maps” can be created using reconfigurable porosity. Intermediate control forces can be generated by modulating different porous patterns. Figure 12 shows the normal force coefficient for the baseline case and patterns S-15, S-20-, and 24-b. In general, the normal force is reduced using these porous patterns, with the effect persistent over the tested alpha range (0 – 18 deg).

The reconfigurable porosity concept was tested on the modified boattail using different porous patterns. Tests were conducted with no ACFs, or, otherwise known as a “fin-less projectile”. Figures 13-a thru 13-e show the pitching moment coefficient for various porous patterns, as shown in Figure 7. The baseline case shows that the projectile model has a “naturally” occurring nose-up pitching moment with increasing alpha when no ACFs are installed. This indicates that the nose-down pitching moment in Fig. 10 is due to the fins. Some of the porous patterns tested increase the nose-down pitch, while others create a nose-up pitch compared to the baseline case. Patterns 7-e, 8-f, and 9-d create a considerable nose-down pitch control that extends through a wide alpha range. On the other hand, patterns 3 and 5 have the opposite effect of producing a slight nose-up pitch control. Figures 14-a thru 14-c show the pitching moment increments with respect to the baseline case. Patterns that use “saw-tooth” geometries, such as patterns 8-f, 8-g, and 9-d, produce some of the largest control forces. Figure 15 displays the normal force coefficient for the baseline case and three of the patterns tested. Pattern 5 increases the normal force throughout the alpha range tested, while patterns 7-e and 8-f reduces the normal force. A control map can be produced by using results of the control moments associated with actuating different porous patterns. The added control from the boat-tail can potentially allow the use of smaller tails fins, thereby reducing the drag during cruise flight.

Figure 9-a: baseline, α = 0 deg Figure 9-b: baseline, α = 6 deg Figure 9-c: pattern 15, α = 0 deg

Figure 9-d: pattern 15, α = 6 deg Figure 9-e: baseline, α = 8 deg Figure 9-f: pattern 15, α = 8 deg

Accumulation

Figure 9-g: pattern 15, α = 8 deg Figure 9-h: pattern 3, (all open), α = 8 deg

Figure 9-a: baseline, α = 0 deg Figure 9-b: baseline, α = 6 deg Figure 9-c: pattern 15, α = 0 deg

Figure 9-d: pattern 15, α = 6 deg Figure 9-e: baseline, α = 8 deg Figure 9-f: pattern 15, α = 8 deg

AccumulationAccumulation

Figure 9-g: pattern 15, α = 8 deg Figure 9-h: pattern 3, (all open), α = 8 deg Figure 9. Snapshots from flow visualization experiments on the wing model using reconfigurable porosity


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Figure 10. Coefficient of pitching moment versus angle of attack (alpha) for projectile model, reconfigurable

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41

S-1

5-b 2

4-a

-0.005

0.000

0.005

0.010

0.015

0.020

0.025∆

Cm

α = 0 deg

43

S-5

b

S-6

24-a

S-2

3

S-1

5-b

S-2

0

141

S-1

5

24-b

S-1

4-b S

-7 19

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

∆C

m

α = 4 deg

S-7 24-a 43

S-5

b1 S-6 1

9S

-15-b

S-1

4-b

24-b S

-15 41 S

-23

S-2

0

0.030

0.040

0.050

0.060

0.070

0.080

0.090

∆C

m

α = 10 deg

11-a 11-b

11-c

Porosity patterns Porosity patterns

Porosity patterns Figure 11. Increments in the coefficient of pitching moment (compared to the baseline case) for the porous patterns

for the projectile model, reconfigurable porosity on horizontal set of ACFs

-0.30

0.00

0.30

0.60

0.90

1.20

1.50

1.80

0 4 8 12 16 20

AOA

CN

BaselinePattern 24-bPattern S-15Pattern S-20

Figure 12. Coefficient of normal force for the baseline case

and patterns S-15, S-20-, and 24-b


12


-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 7

Pattern 7-e

Pattern 7-f

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

BaselinePattern 8-f

Pattern 8-gPattern 8-i

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

BaselinePattern 9Pattern 9-dPattern 9-i

13-a 13-b

13-c

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 8-h

Pattern 3

Pattern 5

13-d

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 10-f

Pattern 10-i

13-e

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 7

Pattern 7-e

Pattern 7-f

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

BaselinePattern 8-f

Pattern 8-gPattern 8-i

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

BaselinePattern 9Pattern 9-dPattern 9-i

13-a 13-b

13-c

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 8-h

Pattern 3

Pattern 5

13-d

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 10-f

Pattern 10-i

13-e

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 4 8 12 16 20

AOA

Cm

Baseline

Pattern 10-f

Pattern 10-i

13-e

Figure 13. Coefficient of pitching moment versus alpha for porous patterns on the finless projectile model


13


8-f

8-i 7

9-d

37-f

8-h

9-i 9

10-i

5 10-f

8-g

7-e

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010∆

Cm

α = 0 deg

14-a

8-f 7-e

8-g

8-i 7 9

-d 7-f

8-h

9

9-i

310-i

10-f 5

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0.010

∆C

m

α = 4 deg

14-b

8-g 8

-f 7-e

7-f 8

-i 8-h 7

9

9-i 1

0-f 10-i 3

5

9-d

-0.055

-0.045

-0.035

-0.025

-0.015

-0.005

0.005

∆C

m

α = 10 deg

14-c

8-f

8-i 7

9-d

37-f

8-h

9-i 9

10-i

5 10-f

8-g

7-e

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010∆

Cm

α = 0 deg

14-a

8-f

8-i 7

9-d

37-f

8-h

9-i 9

10-i

5 10-f

8-g

7-e

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010∆

Cm

α = 0 deg

14-a

8-f 7-e

8-g

8-i 7 9

-d 7-f

8-h

9

9-i

310-i

10-f 5

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0.010

∆C

m

α = 4 deg

14-b

8-f 7-e

8-g

8-i 7 9

-d 7-f

8-h

9

9-i

310-i

10-f 5

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0.010

∆C

m

α = 4 deg

14-b

8-g 8

-f 7-e

7-f 8

-i 8-h 7

9

9-i 1

0-f 10-i 3

5

9-d

-0.055

-0.045

-0.035

-0.025

-0.015

-0.005

0.005

∆C

m

α = 10 deg

14-c8-g 8

-f 7-e

7-f 8

-i 8-h 7

9

9-i 1

0-f 10-i 3

5

9-d

-0.055

-0.045

-0.035

-0.025

-0.015

-0.005

0.005

∆C

m

α = 10 deg

14-c

Figure 14. Increments in the coefficient of pitching moment (compared to the baseline case); patterns with “saw-tooth”

configurations, such as patterns 8-f, 8-g, and 9-d, produce some of the largest control forces

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 4 8 12 16 20

AOA

CN

BaselinePattern 5Pattern 7-ePattern 8-f

Figure 15. Coefficient of normal force for baseline case and three of the patterns tested on the finless projectile model


14


VI. Conclusions Wind tunnel experiments were conducted at low-speeds on a supersonic wing model and a complete projectile

model with 4 fins arranged in a cruciform (+) configuration to assess the performance of reconfigurable porosity for aerodynamic control. It is found that certain hole patterns are more effective than others in creating a favorable aerodynamic flow effect, however, all patterns, if used in certain combinations, are able to generate a near-linear relationship between the control force generated about the body fixed axis and the actuator configurations. A correlation between the actuator configurations and traditional fin deflections for the desired turning moment (pitch-roll-yaw) can be created. Results show that the forces generated using reconfigurable porosity can be effectively used to steer and maneuver air vehicles. From a diverse array of porous patterns that are examined, patterns with a “saw-tooth” configuration seems to be the most effective in generating control forces over a wide alpha range. Flow visualizations on the wing model show that certain porous patterns are capable of reattaching the flow to a great extent at different alpha conditions. The ability to control flow separation using a low-power, light-weight, flow control actuator is highly significant, within and beyond air vehicle control.

Acknowledgment This work is supported by a SBIR Phase II Contract from the U.S. Army, TACOM-ARDEC, under Contract No.

DAAE30-03-C-1058. The Program Manager is Robert C. Testa. The U.S. Government is authorized to reproduce and distribute reprints for government purposes not withstanding any copyright notation therein.

References 1Bahi, L., and Ross, J.M. “Passive Shock Wave/Boundary Layer Control For Transonic Airfoil Drag Reduction,”

AIAA Paper 1983-0137, January 1983. 2Raghunathan, S. “Passive Shockwave Boundary Layer Control Experiments on a Circular Arc Model,” AIAA

Paper 1986-0285, January 1986. 3Nagamatsu, H. T., Trilling, T.W., and Bossard, J.A., “Passive Drag Reduction on a Complete NACA 0012 Airfoil

at Transonic Mach Numbers,” AIAA Paper 1987-1263, June 1987. 4Chen, C.-L., Chow, C.-Y., Van Dalsem, W., and Holst, T., “Computation of Viscous Transonic Flow over Porous

Airfoils,” AIAA Paper 1987-0359, January 1987. 5Wood, R. M., Banks, D.W., and Bauer, S. X. S., “Assessment of Passive Porosity with Free and Fixed Separation

on a Tangent Ogive Forebody,” AIAA Paper 1992-4494, 1992. 6Bauer, S. X. S. and Hemsch, M. J., “Alleviation of Side Force on Tangent-Ogive Forebodies Using Passive

Porosity,” Journal of Aircraft, Vol. 31, No. 2, pp. 354-361, 1994. 7Hunter, C. A., Viken, S. A., Wood, R. M., and Bauer, S. X. S., “Advanced Aerodynamic Design of Passive

Porosity Effectors,” AIAA Paper 2001-0249, January 2001. 8Ng, T.T., Lang, Yue, “Shear Layer Instability Induced Separation Control,” AIAA Journal, Vol. 37, No.3, pp. 386-

388, 1999. 9Ng, T.T., “Control of Shear Flow Unsteadiness Using a Streamwise Instability,” AIAA Paper 1999- 0131, January

1999. 10Patel, Mehul P., Skebe Gerard, Ng, Terry T., and Lisy, Frederick J., “Development of a MEMS Based Microvalve

for Flow Control Using Active Dimples, AIAA 2002-0272, 40th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 2002.

11Patel, Mehul P., DiCocco, Jack M., Prince, Troy S., and Ng, Terry, T., “Flow Control Using Reconfigurable Porosity,” AIAA Paper 2003- 3665, 21st AIAA Applied Aerodynamics Conference, FL, 2003.

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