Hypersonic Separated Flows Research Articles

High order discontinuous Galerkin simulation of hypersonic shock-boundary layer interaction using subcell limiting approach

Numerical simulation of shock-boundary layer interactions in the hypersonic regime has for long been a challenge, plagued by high sensitivity of the surface predictions to grid and numerical details. In the course of developing adaptive high order methods to mitigate this issue, discontinuous Galerkin method has emerged as a promising alternative to the conventionally used finite volume method. However, till date, among the reported finite element method-based simulations of these flows, only a few have presented high order simulations using a higher than linear basis. In this work, a subcell limiting technique devised for the compressible Navier-Stokes equations is extended for use in the hypersonic regime. The proposed extension is tested by performing simulations of several shock-boundary layer interaction cases in the freestream Mach number range 6 to 14 using a quadratic basis. For a set of cases at Mach 6, grid converged simulations are presented that agree reasonably well with experimental data and other numerical solutions. More importantly, simulations of a Mach 11 case that are performed using two different flux schemes are shown to yield nearly identical predictions of the surface pressure and heat transfer, suggesting that high order solutions can reduce the sensitivity of numerical predictions to the computational details. Grid convergence studies of two cases at Mach numbers 11 and 14 led to observing large scale oscillations in the separation bubble in finer grid simulations, suggesting that explicit time integration may not always be suitable for high order computation of hypersonic separated flows at very high Mach numbers.

Theory-based prediction of separation angle and peak pressure for laminar separated hypersonic compression corner flows

Interactions between shock waves and the boundary layer will cause high pressure loads and severe heating locally on the material surface in hypersonic separation–reattachment flows. In this paper, theoretical modeling is employed to study the separation angle and peak pressure of hypersonic compression corner flows with separated regions at low-to-medium Reynolds number. According to the characteristics of wall pressure distribution and flow field structures, an equivalent double shocks inviscid flow model for peak pressure is introduced. Based on this model, combining the “free-interaction theory,” formulas for the separation angle and peak pressure with freestream parameters (Mach number and Reynolds number) and the geometry corner angle are derived, and the reasonability and effectiveness are also shown by the numerical data provided by the direct simulation Monte Carlo method. It is revealed that the separation angle is almost independent of the freestream Mach number, and the ratio of peak pressure to freestream pressure is approximately proportional to the square of the freestream Mach number under strong viscous interaction conditions. Moreover, it is indicated that present theoretical results can be extended to axisymmetric flows through the discussion of hypersonic separated flows generated by a hollow cylinder-flare geometry.

Kinetic modeling of unsteady hypersonic flows over a tick geometry

Hypersonic separated flows over the so-called “tick” geometry have been studied using the time-accurate direct simulation Monte Carlo (DSMC) method and global linear theory. The free stream condition for two experimental cases studied in the free-piston shock tunnel (named T-ADFA) was modeled. These two cases span a Knudsen number from transitional to continuum, a Mach number of about 10, a free stream enthalpy from 10 to 3 MJ/kg, a Reynolds number varying by a factor of four, and a leading edge geometry varied from sharp to one with a bevel of 0.2 mm. For the first time, the time dependence of flow macroparameters on the leading edge nose radius and the Reynolds number are studied using global linear theory. High-fidelity DSMC simulations showed that the temporal behavior of the separation region, which has significant effects on the surface parameters, depends closely on the leading edge bluntness and wall temperature. The formation of a secondary vortex was seen in about 2 ms for the sharp leading edge, whereas in the rounded leading edge geometry, it formed at earlier 0.7 ms. At a steady state, the size and structure of the separation zone, vortex structures, and surface parameters predicted by DSMC were found to be in good agreement with computational fluid dynamics for the higher density case. Finally, linear stability theory showed that for some leading edge shapes and flow densities, the time to reach the steady state was longer than the facility measurement time.

Modal analysis with proper orthogonal decomposition of hypersonic separated flows over a double wedge

A study combining direct simulation Monte Carlo simulations with window proper orthogonal decomposition investigates the temporal characteristics of unsteady, laminar shock boundary-layer interactions for different gas mixtures for an Edney type-IV flow.

Experimental and Numerical Investigation of the Oblique Shock Wave/Turbulent Boundary Layer Interaction at M=5

AbstractThe results of the joint experimental investigations and numerical simulations of hypersonic separated flows are presented. The computed and experimental results are compared with respect to surface pressure, skin friction and Stanton numbers distributions as well as the integral boundary layer parameters and the mean gas‐dynamic profiles.

Properties of hypersonic separated flows at moderate reynolds numbers

The hypersonic rarefied flow past a flat plate with a transverse barrier and past a plate with a bend in the generator (a compression angle) is studied at Reynolds numbers Re≤104. Direct statistical modeling (Monte Carlo method) is used to investigate the characteristics of the separated flow formed on the plate as a function of the Reynolds number, the surface temperature, the barrier dimensions, and the internal degrees of freedom of the molecules. The results obtained are compared with those for analogous high-Re flows. The possibility of using the similarity criteria derived for the continuum flow regime is considered.

A mixed explicit-implicit antidiffusive method of navier-stokes equations for supersonic and hypersonic separated flows

The supersonic and hypersonic, laminar and turbulent viscous separated flows over two and three-dimensional compression corners are solved by the antidissipative explicit-implicit difference scheme presented in this paper. The results obtained show that a high accuracy has been achieved by this method and the time needed for computation is greatly reduced.

Use of transient ''thin-wall'' technique in measuring heat transfer rates in hypersonic separated flows

Use of transient ''thin-wall'' technique in measuring heat transfer rates in hypersonic separated flows