Toward a Low Noise Shock Tunnel Facility via Multiobjective Optimization of Hypersonic Nozzle

In this paper, a systematic approach is considered for the development of a low noise shock tunnel facility. For this purpose, an optimal hypersonic nozzle and test section configuration is presented along with a previously developed low noise shock tube design. In hypersonic experimental studies, one of the most important requirements is a low noise test section with a high-quality uniform flow. The main sources of perturbations are acoustic fluctuations that occur through the turbulent boundary layer and Mach line fluctuations with the passage of turbulent flow through the hypersonic nozzle. The fluctuations are correlated to wall boundary layer thickness, radiated disturbances, and their concentration on the nozzle axis. These parameters can be indirectly controlled via definition of three weighted objective functions—minimum total pressure loss, uniform Mach number distribution, and minimum axial flow deviation—combined to attain the final scalar objective function. Then, a modern optimization strategy is implemented based on a genetic algorithm, parallel CFD solver, and the requirements and constraints from conceptual and preliminary design. In this way, parameterization of the overall nozzle contour is performed with a few control points and Bezier curve that showed good flexibility for generating appropriate nozzle curves. Design objectives are evaluated using a Navier–Stokes solver with a k-ω turbulence model. Various geometrical and physical constraints such as nozzle length, throat area, inlet and outlet diameters, and inlet boundary conditions are considered. It is concluded that the proposed strategy for tuning the nozzle convergent-divergent contour minimizes the boundary layer effects and shows a significant improvement in the quality of test section flow and consequently a reduction in the noise level of shock tunnel test facility.