Transcript Control of Flow Separation for Automobiles and Low

Control of Flow Separation for Automobiles and Low-Pressure Turbine (LPT) Blades
Michael Cline
Mechanical Engineering – ACCEND
Class of 2014
Dr. Kirti Ghia,
Project Mentor
School of Aerospace Systems
Brandon Mullen
Aerospace Engineering
Class of 2016
NSF Type 1 STEP Grant, Grant ID No.: DUE-0756921
2. What is “flow control?”
1. What is “flow separation?”
• Our first goal was to learn about and understand flow separation.
• Flow control is used to add momentum to the boundary layer and reduce the flow separation.
• As fluid moves over a surface, a “boundary layer” of slow-moving fluid
builds up.
• This study investigated two flow control techniques: surface motion and plasma actuation.
• If flow pressure decreases, the boundary layer “separates” from the
surface, generating a “wake,” or large area of low-momentum,
recirculating flow. The wake is best visualized using streamlines.
• Computational Fluid Dynamics (CFD) was used to simulate the techniques for two different applications.
3. Method
Streamlines of “Attached” Flow
• The wake increases drag.
• An NACA0012 airfoil was chosen for the LPT blade application.
• The size of the wake is related to the magnitude of the pressure drop
and body shape.
• A Toyota Camry was chosen for the automobile application.
• Our second goal was to reduce the size of the wake. The smaller the
wake, the smaller the drag, and the greater the efficiency.
• Given the preliminary nature of this study, the simulations were performed in two dimensions.
• The models were simulated numerically using the CFD software, Fluent and Gambit.
Streamlines of “Separated” Flow with Wake
• First the two models were simulated to determine a baseline situation.
4a. Automobile Application: MSBCs
4b. NACA0012 Application: SDBDP Actuators
(Moving Surface Boundary-Layer Control)
(Single Dielectric Barrier Discharge Plasma Actuators)
How it works
• Two electrodes on the airfoil surface generate an electric field using a
high voltage and high-frequency A/C current (right).
• Revolving cylinder is placed at beginning of flow separation wake
• Detached flow is accelerated by cylinder’s surface and reattaches to
free stream flow
• The electric field ionizes the air, and plasma forms. The plasma
produces a body force on the boundary layer, imparting momentum to
it and driving it downstream.
• The governing equations for the electric field and body force values
were derived from a prior study by Shyy et al.
Model Development
• Image of 2013 Toyota Corolla used for
Modeling
• Edge line surrounds model
• Vertices from pixels of edge line set in
X-Y coordinate plane
Results
(a) Streamlines with no control
Results
Span-wise magnified view of electrode
configuration on airfoil.
• A computational mesh was generated using Gambit.
(b) Streamlines with nominal Shyy values
• Application of plasma actuation with Shyy nominal values (b) eliminated flow separation present in (a).
• The effect of electrode voltage and A/C frequency reduction was also investigated.
No Cylinders
Cylinder with no rotation
Rotation (λ=6)
Significant reduction in wake implies reduction in form drag
(c) Streamlines with voltage at 60% of nominal
(d) Streamlines with frequency at 25% nominal
• No significant wake appeared until voltage shrunk 40% and frequency dropped 75%.
• The minimum effective voltage and frequency are vital when considering transition from theory to realworld implementation.
Conclusion: Qualitatively, it is concluded MSBCs and SDBDP Actuators are very effective at reducing or eliminating the local wake.
The effectiveness of both strategies is predictably changed through manipulation of their
governing traits, including angular velocity for MSBCs and voltage and A/C frequency in SDBDP Actuators. This variability is ideal for real-world application and the cost/reward compromise associated with it.
Future Work: 1) Perform a quantitative wake reduction analysis. 2) Perform a grid independent study. 3) Perform verification and validation on this study to assure it is a genuine addition to the current body of information available.
References:
Shyy, W., Jayaraman, B., and Andersson, A., “Modeling of glow discharge-induced fluid dynamics,” Journal of Applied Physics, 2002, pp. 6434.
Thomas, F. O., Kozlov, A., and Corke, T. C., “Plasma Actuators for Cylinder Flow Control and Noise Reduction,” AIAA Journal, Vol. 46, No. 8, 2008, pp. 1921-1931.
Modi, V.J. “Moving Surface Boundary Layer Control: A Review,” Deprt. Of Mechanical Engineering, Univ. of B.C.,B.C., Canada, 1997.
Acknowledgements: Special thanks to Dr. Urmila Ghia, Kristen Strominger, Dr. Anant Kukreti, Santosh Roopak Dungi,
Rahul Singh, Alain Kuchta, the National Science Foundation and the University of Cincinnati.