Numerical investigation of the Hypersonic Test Facility Delft (HTFD)

The high speed flows with mach number above 5 are generally categorised as hypersonic flows. In order to generate hypersonic flows in wind tunnel for aerothermodynamic testing, a shock tube type setting is generally known as one of the most commonly used methods. Similarly Hypersonic test facility at TUDelft (HTFD) is a Ludwieg tube type wind tunnel which is made of a storage tube connected to the test section through a converging diverging nozzle which expands the high pressure and temperature gas in storage tube to achieve high speed flows in test section. The tunnel is started by a fast opening piston-valve which creates a strong shock progressing in to the nozzle while an expansion wave progresses in to the storage tube. The appeal of this kind of facility to the hypersonic flow regime lies in the relatively long run times (0.1 to 0.2 seconds), large test section (30 cm) and high Reynolds numbers (order of 5 – 50e+06 m-1).But there are also some technological limitations to such facilities like supply of high temperatures and pressures for times long enough to perform a measurement, fast instrumentation and power requirements to run the tunnel, just to name a few. Through various experiments it has been experienced that during HTFD operations, the total temperature does not remain constant and the drop in total temperature has been experienced during expansion of flow in converging-diverging nozzle. Apparently the external walls and piston valve assembly of HTFD do not have adiabatic walls and there is always finite heat transfer taking place through these walls due to temperature difference between the working gas and the tunnel walls. So, in this thesis the heat transfer through HTFD walls is numerically computed during unsteady starting of tunnel. Secondly the unsteady flow topology through the nozzle with strong discontinuities immediately after the opening of piston-valve and before the exit of shock from the nozzle has been numerically studied in detail. In addition the influence of various boundary conditions on the time needed for the flow to be steady at nozzle exit has been computed and steady state flow properties at the exit, obtained with different boundary conditions have been compared. For this task FineHEXA(Development version 2.5-4) is used for computations and Hexpress /Gambit for modelling and mesh generation. The 2D axissymmetric mesh is used for simulations considering the circular cross section of wind tunnel. Jameson’s second order central scheme is used for spatial discretization and second order backward differencing is used for time integration. The dual time stepping is used for iteratively converging the solution at each time level. The starting of wind tunnel by opening of piston-valve is modelled using deforming mesh generated using ALE(Arbitraty Lgrangian Eulerian) approach and RBF(Radial basis functions). The brief outline of the thesis is can be given as follows. First of all the Riemann’s initial value problem(shock tube problem) is simulated to compare the numerical solutions as obtained by all available numerical schemes, mutually and with analytical solution to analyse the performance characteristics and to choose an appropriate numerical scheme for the purpose. In the next step the flow generated by removal of diaphragm in shock tube problem, is simulated through a converging-diverging nozzle instead of a constant area tube in order to investigate the difference in flow topology. Then the flow is simulated in a computational domain resembling the original HTFD geometry with completely open piston-valve using different boundary conditionsAerospace Engineerin