The Recent Research Activities in High-speed Thermo-fluid and MAV/UAV Laboratory (HTML),HKPolyU
Prof. Wen Chih-Yung
The Hong Kong Polytechnic University
The report includes two parts: The first part will give an update on the numerical investigation of the coupled vibration-chemistry-vibration effect on the detonation cell size. A preliminary sensitivity analysis is conducted on the the ignition delay time for the H2-O2 mixtures using CHEMKIN software to identify the most sensitive reactions to the vibrational nonequilibrium effects in different temperature regimes. The one-dimensional Zel'dovich–von Neumann–Döring (ZND) model is modified to include vibrational nonequilibrium effects. Park’s two-temperature is used to account for the coupling effect between vibrational nonequilibrium and chemical reaction rates. The impact of vibrational nonequilibrium on the length scale of the induction and reaction zones in the ZND model will be first reported. The second part will introduce the application of the characteristic space-time conservation element and solution element (CE/SE) method on the Richtmyer-Meshkov (RM) instability developed during the interaction of a spherical converging shock wave with a spherical disturbed interface.
A series of 2D simulation, which have almost the same configuration with the experiment, are detailedly analyzed with different combinations of wave number (k0) and initial amplitude (a0). For a certain invariable wave number, small initial amplitude will lead to beforehand phase inversion but big initial amplitude will not. A balanced state is found between them, accompanied with the appearance of wavenumber-doubling feature. An analysis of frequency spectrum and periodical Rayleigh-Taylor phase diagram is adopted to help explaining the mechanism. A balanced line is obtained in the variable space of (k0, a0), standing for the initial amplitude which will lead to balanced state in each wavenumber. A frequency-truncation phenomenon is also found: if the wave number is smaller than a certain value, the beforehand phase inversion can’t happen on any initial amplitude. Bell’s theoretical models are adopted to predict the development of disturbance and they show fairly good performance in early stage but obvious divergence at later stage. several physical parameters are separately tested to study their influence. It is found that the starting point of balanced line is negatively correlated to the Atwood number and initial shock Mach number to a significant degree, but insensitive to the radius of initial interface. A bigger Atwood number or a lower Mach number will lead to a higher peak of the balanced line. The value of the balanced line is approximately proportional to the initial radius of initial interface A bigger initial radius will lead to higher value of the balanced line, explaining why the beforehand phase inversion has not been pointed out in previous research.
Wen Chih-Yung (Prof)
Professor/Associate Head, Research
BEng (National Taiwan University); MSc (Caltech, U.S.A.); PhD (Caltech, U.S.A.);
Associate Fellow of AIAA, HKIE Fellow
(852) 2766 6644
Area of Specialization
Aerodynamics of hypersonic vehicles; Supersonic combustion; Active flow control; MAV/UAV technologies; Shock/two phase fluids interaction; Detonation
Professor Wen received his Bachelor of Science degree from the Department of Mechanical Engineering at the National Taiwan University in 1986 and Master of Science and PhD from the Department of Aeronautics at the California Institute of Technology (Caltech), U.S.A. in 1989 and 1994 respectively. He worked at Caltech as a Research Fellow from February 1994 to July 1994 and then continued his teaching and research works at the Department of Mechanical Engineering at the Da-Yeh University, Taiwan. He was promoted to full professorship in February 2002. He had been the Chairman of the Department of Mechanical and Vehicle Engineering from August 1997 to July 2000, and the Provost from August 2004 to July 2006 in the Da-Yeh University, Taiwan. In August 2006, Professor Wen joined the Department of Aeronautics and Astronautics of the National Cheng Kung University (NCKU), Taiwan, before joining the Department of Mechanical Engineering, The Hong Kong Polytechnic University in 2012 as professor. Professor Wen has authored and co-authored many scientific papers, conference papers and book chapters. He was also awarded 13 patents. His current research interests are in the areas of (1) Flow Control by plasma actuators on a delta wing; (2) Technology development of UAVs and MAVs; (3) Hypersonic aerodynamics and scramjet engine design; (4) Shock/Droplet and Shock/Droplet Interactions; (5) Detonation; and (6) Ice Accretion. Professor Wen, currently an AIAA Associate Fellow and editor of the prestigious international journal—AIAA Journal and Shock Waves, serves as the Vice-Chair of Fluid Mechanics Technical Committee of the Fluid Engineering Division, ASME, and a member of, various key professional boards and bodies related to the Aerospace Engineering.