Nov 2011 Featured Scientist – GeCheng Zha, PhD

November 2011

Dr. GeCheng Zha is the Director of the Aerodynamics and Computational Fluid Dynamics (CFD) Lab at the University of Miami and holds the rank of Associated Professor in the College of Engineering,  Department of Mechanical and Aerospace Engineering.

Originally trained in aerospace engineering, Dr. Zha’s recent work involves CFD, fluid-structural interaction, flow control, and aircraft design.  In CFD, Dr. Zha and his colleagues have developed high order discontinuities capturing schemes using compact differencing and weighted essentially non-oscillatory (WENO) schemes with low diffusion Riemann solvers. In aerodynamics, a shock wave is mathematically treated as a discontinuity and poses a great challenge when solving the Navier-Stokes flow governing equations. Similar discontinuities also exist in other flow phenomena such as air-water interface, where the density jumps about 1000 times from air to water. The high order schemes developed in Dr. Zha’s CFD Lab are crucial to simulate flow turbulence, aero-acoustics and fluid-structural interaction, in particular  high speed aerodynamic flows with shock wave/turbulent boundary interaction of aircraft.  The CFD code developed in the CFD lab also has high parallel computing scalability.

Figure 1 demonstrates the simulated density contours of shock  interaction  with a shear layer using a finite compact differencing.  The shock wave is crisply captured and the vortices of the shear layer is very well resolved.  Figure 2 represents the vorticity contours of a turbulent flow passing a cylinder obtained by  Large Eddy Simulation with the high order schemes. It shows that there are many small turbulent structures resolved.

Fig. 1Simulated density contours of shock interaction with a shear layer using a finite compact differencing.

Fig. 2 LES vorticity contours of turbulence flow passing a cylinder

Dr. Zha has also been working on applying high order schemes to fluid-structural interaction, such as simulation of aircraft wing flutter and aircraft engine turbomachinery blades vibration induced by fluid. Figure 3 demonstrates the pressure contours of an aircraft engine compressor rotor with tip tornado type vortices obtained by Detached Eddy Simulation of a transonic full annulus rotor.  The tip vortices induce blade non-synchronous vibration.

Fig. 3 Pressure contours of aircraft engine compressor rotor with tip tornado type vortices obtained by DES of a transonic full annulus rotor.

Dr. Zha’s research interests also include high performance airfoil flow control and new concept aircraft design. Figure 4 illustrates the vorticity contours obtained by LES for a co-flow jet (CFJ) airfoil at a 30 degree angle of attack. The CFJ airfoil is proved by wind tunnel experiments and CFD simulations to drastically increase lift, stall margin, and reduce drag at a low energy expenditure.

Fig. 4 Vorticity contours of a co-flow jet flow control airfoil at angle of attack 30deg obtained by LES.

Figure 5 represents a new concept supersonic bi-directional (Sbi-Dir) flying wing airplane, which is to cancel sonic boom, achieve low supersonic wave drag and high subsonic performance. The SBiDir-FW platform is symmetric about both longitudinal and span axes. For supersonic flight, the planform will have a low aspect ratio and a high sweep angle to minimize wave drag. For subsonic mode, the airplane will rotate 90deg, the sweep angle will be reduced, and the aspect ratio will be increased. To minimize sonic boom, the pressure surface of the flying wing employs an isentropic compression surface.   The CFD simulation shows that a supersonic business jet flying at Mach 2  obtains a low ground sonic boom overpressure of 0.3psf with L/Dp = 16. Furthermore, the ground pressure signature is not the N shape wave with two strong shock wave pulses, but is in a smooth sine wave shape.

Fig. 5 Supersonic Bi-Directional Flying Wing airplane

Dr. Zha’s research has been funded by NASA, Air Force Office of Scientific Research (AFOSR), Air Force Research Lab, GUIde (Government, Universities, Industry Consortium), Florida Center for Advanced Aerodynamics and Propulsion (FCAAP) and other agencies.  The CFD simulation is conducted at the Center for Computational Science at the University of Miami and Air Force Research Lab DoD Supercomputing Centers.