The design of a square section nozzles for the small hypersonic shock tunnel facility is currently underway in the Department of Mechanical engineering. A square section nozzle produces a cleaner test flow in comparison to conventional axisymmetric nozzles. Axisymmetric nozzles focus disturbances at the center and these disturbances propagate to the test core. Square section nozzles do not focus disturbances to a point but rather to the two symmetry lines which is more dissipative.
The design of a square section nozzle is a highly three- dimensional problem which cannot be handled with traditional design techniques. The approach being taken for this study is computational. A three-dimensional fluid dynamic flow solver has been written (which was developed on the SGI) that can simulate the flow through arbitrary ducts with high fidelity. The solver is being used to simulate the flow through a base line nozzle design of a square section nozzle and then an optimisation routine iteratively makes slight modifications to the design to achieve the desired flow conditions at the exit. Each nozzle simulation takes approximately 24hrs (based on current SGI load) to complete and the optimiser takes anywhere from 20 to 100 iterations to reach a converged solution.
Currently, the SGI is being used to find an efficient base line design. It is crucial to start with a promising design before the optimisation routine is started since many hours of CPU time could be wasted. Clearly, looking at the solution time scale, a fast machine is required to solve this design problem.