Computational fluid mechanics researchers in the Departmental of Mechanical Engineering were recently awarded a Collaborative Center of Excellence in Aeronautical Sciences by the Air Force Research Laboratory (AFRL). The objective of the Center, which will operate as a collaboration with researchers at the University of Michigan's Dept. of Aerospace Engineering, is to provide the Air Force Research Laboratory with expertise to support of their mission to develop the aerodynamic aspects of next-generation flight vehicles, over the next five years. The MSU research effort will be headed by Dr. Mei Zhuang, together with Drs. Giles Brereton and Farhad Jaberi, and will draw on their expertise in computational fluid dynamics, computational acoustics, mathematical modeling of turbulent fluid flows, and large-eddy simulations of turbulence. The focus of the center is on developing and integrating all of the computational tools required to perform reliable, high-fidelity, multi-disciplinary analysis of airbreathing vehicle concepts. A unique feature of the center is that its efforts will be directed at `problem areas', which will be defined by the Air Force as they arise, in the quest to make accurate and reliable predictions of the flow fields around high-speed and low-speed aerodynamic structures with non-traditional geometries. Two of the research areas identified to be of prime importance to the Air Force are particularly of the interest and expertise at MSU: low Reynolds-number (Re) aerodynamic flows over flexible/flapping-wing vehicles, and shock boundary-layer interactions (SBLIs) in supersonic and hypersonic air vehicles.
The low Re flows project is motivated by the design of micro air vehicles (MAVs). The concept of MAVs is a small, inexpensive, and expendable platform that can be used for missions of surveillance and measurements in situations where larger vehicles are not practical. Because of the recent availability of very small sensors, video cameras, and control hardware; practical applications of MAVs are becoming reality rather than science fiction. The size of a typical MAV is less than 15 cm (about 6 inches) in length, width or height. This physical size puts this class of vehicle at least an order of magnitude smaller than any missionized unmanned aerial vehicle (UAV) developed to date. The coupling of small length scale with low flight velocities results in a flight regime with low-wing chord Re well below that of conventional aircraft (see Figure 1). These vehicles, therefore, require efficient low Re flexible/flapping airfoils/membranes that are not overly sensitive to wind shear, gusts and the roughness produced by precipitation. Our main objectives of the project are to develop numerical design tools that can effectively simulate complex fluid flow around flexible/flapping structures, and to understand the fundamental physics of laminar to turbulence transition and the global instabilities of separated flows in aerodynamics applications.
Interactions between shock waves and boundary layers can profoundly influence the flow over supersonic/hypersonic vehicles. At supersonic/hypersonic speeds, vehicles excite the air surrounding them to very high temperatures due to the SBLIs. As a result, various chemical reactions associated with the elevated temperatures are initiated. Hence, supersonic and hypersonic flows involve complex and strongly coupled physical and chemical processes such as turbulence, shock waves and chemical reaction. Accurate and efficient numerical tools are therefore needed to predict these complex processes and to predict the aerodynamic and thermal loads experienced by supersonic/hypersonic vehicles. We have proposed using large-eddy simulation to calculate the large scales of the compressible flow over high-speed surfaces while developing new and more faithful models for the residual stresses.
As explicitly stated by Air Force representatives, AFRL is interested to expand its support level for the center through office of scientific research at Air Force (AFOSR) and other Air Force labs, provided that significant progress and potential for growth be demonstrated by the center in its first few years of operation. In addition, the center has created a great opportunity for ME and CoE to seriously engage in other relevant DoD and NASA programs.