Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

Comparisons between Measurements in Regions of Laminar Shock Wave Boundary Layer Interaction in Hypersonic Flows with Navier-Stokes and DSMC Solutions

Abstract: : Experimental studies were conducted in conjunction with computations in a code validation exercise to examine the ability of DSMC and Navier-Stokes techniques to predict the complex characteristics of regions of shock/shock and shock/ boundary layer interactions in hypervelocity flows In the experimental program, detailed heat transfer and pressure measurements in laminar regions of shock wave/boundary layer interaction, and shock/shock interaction, over hollow cylinder/flare and double cone configurations in hypersonic flow The experimental studies were conducted for a Mach number range from 10 to 12 with Reynolds numbers from 1 x 104 to 5 x 105 and stagnation temperatures from 2,000 R to 5,000 R Miniature high-frequency thin-film and piezoelectric instrumentation were employed to obtain the high spatial resolution required to accurately define the distribution of heat transfer and pressure in the strong gradients which occur in regions of shear layer reattachment and shock/shock interaction The program reported here was conducted in two phases In the first phase of the code validation study, measurements and blind computations were made over complete hollow cylinder/flare and double cone configurations in high temperature flows at Mach 10 and 12 for a range of freestream Reynolds numbers In the second phase of the program, detailed heat transfer and pressure measurements were made over an extensive range of Reynolds number and total enthalpy conditions using only the hollow cylinder and the 25 conical segment of the models tested earlier in phase I The selection of the freestream conditions employed in this second phase of the program was performed in conjunction with computations of the contoured nozzle flows and the flows over the two simple model configurations Based on the results of the latter studies, we validated the computational schemes used to predict the properties of the freestream developed in the test section of the tunnel

Nonsteady supersonic flow over spiked bodies

Abstract: In longitudinal supersonic flow over spiked cylinders nonsteady regimes can occur in which a separation zone is periodically generated at the spike, grows vigorously in size, and then vanishes. Several authors [1–6] have investigated the physical pattern of flow with separation zone fluctuations (using shadowgraphs) and have determined the boundaries of existence of the nonsteady regime as a function of the ratio between the spike length and diameter of the cylinder. The authors, however, did not systematically study the dependence of the pulsation frequency on the freestream Mach and Reynolds numbers or on the relative diameter and tip angle of the spike. We have undertaken such an investigation. We are concerned primarily with the influence of the dimensionless parameters on the Strouhal number Sh of the separation zone pulsations at a spike attached to the front of a flat-ended cylinder. Earlier investigations [4–6] have been carried out using motion pictures with film speeds up to 32·103 frames/sec. In the present study we used high-speed motion pictures with a speed of 6.25· 105 frames/sec. This speed allowed us to determine the precise sequence of phases of the pulsations and their relative durations, as well as the speed at which the boundaries of the separation zone move.

Direct Numerical Simulation of a eflected-Shock- Wave/Turbulent-Boundary-Layer Interaction

Abstract: A direct numerical simulation of a reflected-shock-wave/turbulent-boundary-layer interaction at Mach 2.9 and Re θ = 2300 with a flow deflection through the incident shock of 12 deg is presented. A modified weighted essentially nonoscillatory method is used for the spatial discretization of the inviscid fluxes. The numerical scheme has previously been validated in the direct numerical simulation of a compression-ramp interaction against experiments at matching conditions. The flowfield for the present simulation is visualized using a numerical schlieren technique, and a movie of the flow reveals the unsteady shock motion. From the wall-pressure signal in the interaction region and pressure measurements in the freestream, the characteristic low frequency of the shock motion is inferred and found to agree with a scaling previously proposed. The evolution of the mean and fluctuating flow quantities through the interaction is studied. It is observed that the turbulence levels are greatly amplified in the downstream flow and that significant departures from the strong Reynolds analogy occur.