Design and Parametric Analysis of a Mach 4 Wind Tunnel for SSLCs Studies

The use of shear sensitive liquid crystals (SSLCs) provides a nonintrusive technique for accurate visualization and quantification of shear stress on surfaces under investigation. However, investigations using liquid crystal involving supersonic and hypersonic flows poses specific requirements for the design of wind tunnel. These constraints are pertaining to time response, erosion, and repeated application of the layer of SSLCs on the model surface as well as its sensitivity to wall temperature under the influence of high-speed flows. In this research, the Mach 4 wind tunnel facility is designed using existing empirical, semi-empirical methods and detailed literature survey and is analyzed numerically in ansysfluent 19.0 environment using transient k–ω shear stress transport Reynolds-averaged Navier–Stokes turbulence model. The influence of geometric contouring of converging section of the supersonic nozzle on the reservoir pressure requirement to establish a M = 4 flow condition in test section is also analyzed. The iterative design method is adopted for the supersonic diffuser section of the wind tunnel where different geometric parameters are varied to achieve higher diffuser efficiency as well as minimum startup time requirement. The parametric study is carried out to ascertain the factors influencing test section wall shear stress during wind tunnel startup process and a novel approach is explored in which the Coanda effect is generated to keep the jet emanating from the supersonic nozzle away from the applied SSLC layer, thereby reducing its erosion effect. Furthermore, the influence of the location of a diaphragm for the partially ruptured case on the wind tunnel startup is also critically analyzed.