1. Synthetic Jet Actuators for Aerodynamic Control
Research Internships in Science and Engineering
University of Maryland, College Park, MD
Hello and Welcome. We are the team working under Dr. Allison Flatau and Sandra Ugrina on the project titled Synthetic Jets for Aerodynamic Control. [Introduce names in listed order]. Mention that this is Sandra’s PHD work.
Jeffrey D. Bennett
Trinity University
Allison K. Jones
Rose-Hulman Institute of Technology
Anita W. Leung
University of Michigan
Colleen E. Rainbolt
Purdue University

2. Objectives Background Methods Results Analysis Conclusion
Actuator design
Pressure analysis
Control algorithm
Wind tunnel testing
Results
Analysis
Conclusion
Our first objective in today’s presentation is to introduce the history of using synthetic jet actuators for flow control. We divided our experiment into four parts. After Jeff designed and manufactured our actuators, and we needed to understand the pressure over our wings, which I completed. Colleen developed a control algorithm to control the actuators and Allison worked on the actual wind tunnel testing. Today, we will discuss these four aspects, as well as cover our results and the analysis of testing. We will conclude with a summary and discuss the need for further research.

3. Background What is a synthetic jet? Previous Research
Smith, B. L. and Glezer, A., 1997
Lachowizc, J. T. Yao. C-S, and Wlezien, R. W., 1998
Rathnasingham, R. and Breuer, K. S., 1996
Hassan, A. A. and JanakiRam, R. D., 1998
Let’s start with some background information. The study of synthetic jets has emerged as an intriuging new field in the past few years. In prior research, they have been shown to increase lift up to 7% but only at low Reynolds numbers, which means lower speeds. A synthetic jet actuator adds momentum to airflow without adding mass. This (point) is a diagram of a synthetic jet . A conventional jet sucks in air, accelerates this air, and exhausts the air out of a different opening, maintaining an airflow. In contrast, a synthetic jet alternates sucking in and blowing out air through the same opening at high frequencies. One method for creating this jet is to use a piezoelectric diaphragm to act as the oscillating membrane. When this membrane oscillates, it sends puffs of air through the cavity and out of a small surface hole.

4. Background What is a Micro Air Vehicle (MAV)?
Our goal is to embed these synthetic jets in the wings of a micro air vehicle, or MAV. A micro air vehicle is a small, unmanned aircraft. They are developed for uses such as entering forest fires to determine where water should be dropped. Another application is in reconnaissance, or search and rescue missions. You can also find a form of a MAV commercially, such as the remote-controlled toy airplane on the left. However, toy airplanes can typically fly for about 15 minutes before needing to recharge. These three pictures on the right are prototypes of current micro air vehicle developments, which fly longer and with less power than toy airplanes. Because they are so small and travel at low speeds, they are generally difficult to power and control. We are hoping that by putting our jet actuators in the wings of these MAVs, we will increase lift, which increases stability and flight lifespan.

5. Project Goals Explore the applications of synthetic jet actuators
to the control of the flow about Micro Air Vehicles
with the final goal of providing improved
aerodynamic performance and flight control
Study the use of synthetic jets for aerodynamic
control in a range of fluid dynamic regimes
Perform flow visualization techniques to aid in
understanding the interaction effects in arrays
of synthetic jets.
This is a (point) picture of flow over a wing surface (point) when the aircraft is moving at low speeds. One of the problems with MAVs is that a bubble of flow can form on the wing. This bubble is an unattached, turbulent flow that increases drag and decreases lift, which is undesirable. One of the project goals was to keep this bubble of flow attached at higher angles of attack, which is an improvement of aerodynamic performance and flight control. Angle of attack is the degree of the nose of the plane to horizontal. As the angle of attack increases, the bubble gets bigger, and will cause the wing to stall, causing an airplane crash. Another project goal was to use flow visualization techniques to help us see and understand the effects of the synthetic jets on the bubble.

6. Wing Design Airfoil: NACA 0012 Wing Dimensions: 3” x 6”
Shell Fabrication Method:
Sand wings
Bake in mold
Cover with fiberglass
Remove core
This is our wing design (point). The airfoil was a NACA 0012 chosen because it is a symmetric design that has been studied in great depth. Our wing dimensions were 3” from leading edge to trailing edge, with a 6” wingspan. To make our test wings, we first took a white foam block and sanded it into the approximate final shape. Then, we baked this foam in a mold for several hours to compress the foam into the desired shape. Then, we covered the wing with 2 or 3 layers of fiberglass sheeting and baked it in the mold again, for the fiberglass to cure. Finally, we removed the foam core, leaving us a fiberglass shell to work with. (Pass wing around)

7. Pressure Tap Design
In order to analyze how the flow traveled over the wing and locate the bubble, we needed to know the distribution of pressure. To do so, we used pressure taps, which consisted of a hole on the wing surface then directing the pressure out the side of the wing. This air pressure was then hooked up to a digital pressure sensor that read off usable pressure values. In the first pressure tap design (point), we dug grooves of variable lengths on the wing surface, then placed a fiberglass shell over these grooves. Small metal tubes to lead the flow to the digital pressure sensor can be seen here. This was not an accurate design, so we next used a plastic material, called Delrin, and used a precise milling machine to drill the hollow tubes (point).
Metal tube pictures, specs on the size of tubing, how tubing hooks up to pressure meter, picture of pressure meter, drill holes down to meet the pressure taps in the wing
Pressure tap design #1
Pressure tap design #2
Designed taps to transfer pressure from airflow over the wing to a pressure reading device

8. Actuator Design Diaphragm attached to individual airfoil sections
The actuators were required to be small enough to fit inside of the wings yet still needed to be powerful enough produce enough displacement. Previous designs involved using pistons or piezoelectric diaphragms to create the synthetic jet. Due to the small size of the wing and the large number of actuators that we tried to fit in the wing, we decided on using the piezoelectric diaphragms. The diaphragms were created using round PZT disks and brass foil. Originally we made them with an aluminum cavity with replaceable exit nozzles as shown. However, due to manufacturing difficulties, we switched to a plastic segment design shown on the top left. This design allowed for wing support, and was easily and precisely manufactured.
Diaphragm attached to individual airfoil sections
Actuators designed to:
Be small
Produce ample displacement
Actuator Design #1
Various exit nozzles

9. What is a PZT? Lead Zirconium Titanate Ceramic Material
Expands and contracts with applied AC voltage
Prior work demonstrated PZT as useful driver for synthetic jets
The actuators were required to be small enough to fit inside of the wings yet still needed to be powerful enough produce enough displacement. Previous designs involved using pistons or piezoelectric diaphragms to create the synthetic jet. Due to the small size of the wing and the large number of actuators that we tried to fit in the wing, we decided on using the piezoelectric diaphragms. The diaphragms were created using round PZT disks and brass foil. Originally we made them with an aluminum cavity with replaceable exit nozzles as shown. However, due to manufacturing difficulties, we switched to a plastic segment design shown on the top left. This design allowed for wing support, and was easily and precisely manufactured.

10. Wing Fabrication Wing sections connected with threaded rod
Actuators share common ground
Covered in fiberglass shell (not shown)
As you can see, here are the wing sections with the diaphragms attached to the wings and wired. Once these sections were connected together with a threaded rod, the actuators were wired, sharing a common ground. Finally, the wing was covered with a fiberglass shell. Pressure taps were then inserted along with a mounting rod to attach the wing to a testing apparatus.

11. Control System Design Allow for precise data acquisition User varies:
On/Off states
Amplitude
Frequency
Simulink algorithm
Automated control systems for lab experiments allow data to be collected in a more precise fashion and keep user generated errors to a minimum. For these reasons, several control systems were created for use in this experiment.
The main system was created to control the actuators in the wings by switching them between on and off states and to change the frequency and amplitude of the sine wave sent to the piezo electric. This was accomplished by use of a Simulink control system that interfaced with a dSPACE setup. The Simulink system fed a square wave through a switch and relay combination that output a value of zero when the actuator was off and a value of one to simulate the actuator being on. When the output value was one, it was multiplied by a sine wave and that wave was sent to the piezo electric. dSPACE then allowed the user to be able to switch the actuators between their on and off states by simply clicking on a button, as well as control the frequency and amplitude of the output sine wave by turning a dial.
Although the Simulink/dSPACE control system was both efficient and user friendly, it created problems with the sine wave output. The dSPACE control board could only output values to an accuracy of one sample per seconds, which made the output sine wave _____ at high frequencies. In order to control the piezo, a smooth sine wave was needed. Because of this problem, the Simulink/dSPACE control system was set aside and different methods of creating sine wave outputs with changeable frequency values were investigated.
It is possible that the synthetic jet actuators can also be used to control the roll of an aircraft. For this reason, a second control system was created. The control system allowed the user to input a desired roll angle and powered on various actuators for previously determined time periods until the aircraft reached the desired roll angle. This control system was never implemented into the project, but could be considered in future experiments.
dSPACE controls

12. Control System Benefits
Actuators
Flow
Wing
Surface
Flow
Roll Control
Varied Jet Control
Wing
Surface
Actuators
Actuators

13. Locating Resonance Frequencies
Each synthetic jet actuator has two resonance frequencies--one of the piezo electric and the other for the cavity beneath. Locating these resonance frequencies became important in the experiment because if the piezo is actuated at resonance, _______.
Finding resonance frequency began with a microphone setup. The microphone was suspended ___ inches above the piezo electric in a test section of the wing. SigLab was used to send a sine wave to the piezo and constantly step up the frequency values of that sine wave. Data was collected for each actuator in the wing and a resonance frequency was determined by the peaks in the plots.

14. Flow Visualization Using flow visualization, the bubble was
observed at 14º angle of attack
In theory, using synthetic jet actuators will
keep flow attached at higher angles of attack

15. Measurements Applied force causes strain gages produce a voltage drop
In order to determine the effects of the synthetic jet actuators, we needed a way to measure the forces of lift and drag exerted on the airfoil.
For this purpose we used a force balance.
This balance converts force parallel to airflow, drag, and force perpendicular to airflow, lift, into voltage drops using strain gages pictured here, which change their resistance when bent tiny amounts.
Once the balance has been calibrated the wing can be mounted vertically to the balance and voltages can be read off a simple digital multimeter while the wind tunnel is running
These voltages can be easily converted to forces of lift and drag for analysis.
Applied force causes strain gages produce a voltage drop
Allows measurement of lift and drag

16. Wind Tunnel Setup Electronics Setup Setup #1 Digital pressure sensor
Variable gain amplifiers
Digital multimeters
Function generator
Setup #1
Open wind tunnel
Wing mounted vertically
We used two experimental setups to test our airfoil models and the embedded synthetic jets.
The first was an open wind tunnel where we mounted our wing vertically in front of the opening of the wind tunnel.
The second had a enclosed test section where we mounted our wing horizontally, as it would be oriented during flight.
To run our piezos and measure their effects we needed to make use of such diverse equipment as a digital pressure sensor, variable gain amplifiers, digital mulitmeters, a signal conditioner and a function generator, some of which are pictured here in the wind tunnel.
Setup #2
Closed test section
Wing mounted horizontally

17. Results Constructed testable airfoil
Collected data in wind tunnels, varying:
frequencies
angles of attack
exit nozzle diameter
As a result of our summer of research we designed and constructed an airfoil embedded with synthetic jets that we tested in a wind tunnel.
In an attempt to pinpoint the parameters that will make the jets most useful we varied angles of attack, exit nozzle diameter, and frequency to account for the different resonances.
A few of our analysis graphs are shown here.
As you can see from the top graph, we observed lift forces very close to what we theoretically predicted.
Although most of our observed data varies very little whether the jets were on or off, this bottom graph shows that at 175 hz and lower angles of attack we were having some impact on the pressure level on the surface of the wind towards the trailing edge.
The bottom graph shows the relative pressure distribution of air flowing over the wing at 175 Hz.
The top two lines, blue and purple depict the wing at stall, and show that the actuator made no difference at those angles. However, more interestingly, at lower angles, pressures near the trailing edge differed substantially when the piezos were turned on. This trend shows that our actuators are making some measurable difference at 175hz. This trend was not observable at other frequencies, and more study is needed to explain this phenomena and its implications.

18. Analysis
Some collected data disagreed significantly with theoretical values
Actuator effects were often indiscernible from signal noise
Further analysis of our data, however, is mostly inconclusive.
As you can see from this graph, where the light blue line along the bottom is theoretical values for drag and the pink lines are our experimental results, we did not observe what we would have expected.
As the NACA0012 is a well studied airfoil, this brings our construction or data collection methods into question..
Also, background variations in our readings were often substantial enough that they might have overshadowed the impact of turning on and off our synthetic jet actuators.

19. Conclusions
More testing needed to determine the effect of synthetic jet actuators
More sensitive equipment needed to test on small scale
Gained experience in such areas as:
Wind tunnel testing
Prototype design and construction
Modern research methods and techniques

20. Future Work Different actuator design Multiple rows of actuators
Vary exit nozzles
Shape
Size
Angle
Different pressure sensing apparatus
Implement fuzzy logic and/or neural networks into the controls

21. Contact Information
Jeffrey D. Bennett --
Trinity University
Engineering Sciences
Allison K. Jones --
Rose-Hulman Institute of Technology
Physics and Applied Continuous Mathematics
Anita W. Leung --
University of Michigan
Aerospace Engineering
Colleen E. Rainbolt --
Purdue University