Narrow Results

This paper focuses on turbulence drag reduction of riblet plate in hypersonic turbulent flows. We use direct numerical simulation (DNS) and large eddy simulation (LES) to simulate three-dimensional spatially-developing boundary layer over the flat plate and riblet plate with a free-stream Mach number $Ma=6$. The results reveal the influence of different riblet heights $h_w$ and riblet distances ${\lambda }_w$ on drag reduction effect. The drag reduction effect increases with the increase of riblet height and the decrease of riblet distance within suitable range of parameter values. Through analysis, it can be seen that the riblet plate affects the turbulent contribution of the skin friction by suppressing or destroying the large-scale vortex structure. Combined with the actual engineering design requirements, we can use the riblet plate with appropriate parameters to achieve the purpose of turbulence control.

In this paper, a hybrid lattice Boltzmann flux solver (LBFS) is proposed for simulation of 3D integrated hypersonic fluid-thermal-structural problems. In the solver, the macroscopic 3D Navier–Stokes equations and structural heat transfer equation are discretized by the finite volume method and the numerical fluxes at the cell interface are reconstructed by the local solution of Boltzmann equation. To compute the numerical fluxes, two lattice velocity models are introduced. One is the D1Q4 discrete velocity model for calculating the inviscid flux across the cell interface of N–S equations, and the other one is the D3Q6 model for evaluating the flux of structural energy equation. Furthermore, a new dual-thermal-resistance model is proposed to calculate the thermal properties on the fluid-structure interface. To validate the accuracy and stability of the present solver, applications for hypersonic fluid-thermal-structural analysis are demonstrated on aerodynamically heated blunt cone body at $\mathrm{\text{Ma}}=10.6$. Numerical results showed that the present solver can predict accurately the thermal properties of hypersonic fluid-thermal-structural problems and offer the potential for significant improvements in predicting fluid-structural-thermal problems of long-endurance high speed vehicles.

In order to reveal the effect of aircraft surface concave roughness on the transition, several hypersonic quiet wind tunnel tests were carried out on the flat-plate model with independent concave roughness on the surface. The experimental Mach number was 6.5 and the total temperature was 430 K. Using infrared thermal imaging technology, a general rule of the effect of concave roughness on the boundary layer transition was obtained. The flow visualization results and the PCB pressure measurement results showed that the concave roughness promotes the transition by increasing the growth of the first mode wave rather than the growth of the second mode wave.

A numerical method which is based on unstructured grids to compute high-temperature ionized air radiation is described. The multi-species N-S equations are used and the chemical model includes 11 species (O₂, N₂, O, N, NO, NO⁺, N⁺, O⁺, N⁺₂, O⁺₂, e^-) and 20 reactions. For simulating thermal non-equilibrium effect, the two-temperature model is considered. The finite volume method (FVM) is used for spatial and directional discretization for the RTE on unstructured grids. The code can deal with different kinds of species and radiative bands. Particularly, the Delta, Epsilon, Beta prime and Gamma prime bands of NO are considered in this paper. The numerical results of MESES-C for hypersonic flow with high-temperature ionized radiation are shown, and compared well with the reference data and experimental data.

Two dimensional hypersonic magnetohydrodynamics(MHD) flows with the chemical non-equilibrium effects are numerically simulated using upwind splitting scheme based on unstructured meshes. The governing equations are 2D MHD equations with the chemical components, where 5 species and 17 chemical reactions are considered. The AUSM scheme is implemented in the spatial discretization for the MHD equations, and an explicit 5-stage Runge-Kutta scheme is used for time integration. A loosely coupled approach is used to communicate between the MHD equations and the chemical reaction model. The computational model is a 2D blunt body, around which a dipole magnetic field is located. With hypersonic incoming flows, four different cases are numerically simulated to analyze the effects caused by the magnetic field and/or non-equilibrium chemical reactions. Numerical results are obtained and compared well with available data.

Accurate description of the aerodynamic and aerothermal environment is crucial to the integrated design and optimization for high performance hypersonic vehicles. In the simulation of aerothermal environment, the effect of viscosity is crucial. The turbulence modeling remains a major source of uncertainty in the computational prediction of aerodynamic forces and heating. In this paper, three turbulent models were studied: the one-equation eddy viscosity transport model of Spalart-Allmaras, the Wilcox k-ω model and the Menter SST model. For the k-ω model and SST model, the compressibility correction, press dilatation and low Reynolds number correction were considered. The influence of these corrections for flow properties were discussed by comparing with the results without corrections. In this paper the emphasis is on the assessment and evaluation of the turbulence models in prediction of heat transfer as applied to a range of hypersonic flows with comparison to experimental data. This will enable establishing factor of safety for the design of thermal protection systems of hypersonic vehicle.

In this paper, a numerical study of the interaction between transverse cold jets on slender body in front of or between X-shape rudders with rudders in the oncoming free stream is presented. Firstly, the flow field at different jet conditions is simulated and analyzed. Then, the total force and moment amplification factors of the corresponding slender body with jet at different locations are analyzed and compared with those results of non-jet flow. Numerical results show that interactions take a great effect to the configuration of the flow field around rudders and the pressure distribution on slender surface. Moreover, the force and moment amplification changes regularly along with the location of jet nozzle.

The interaction effect between jet and control surface in supersonic and hypersonic flow is one of the key problems for advanced flight control system. The flow properties of exhaust jet secondary combustion in a hypersonic compression ramp flow field were studied numerically by solving the Navier–Stokes equations with multi-species and combustion reaction effects. The analysis was focused on the flow field structure and the force amplification factor under different jet conditions. Numerical results show that a series of different secondary combustion makes the flow field structure change regularly, and the temperature increases rapidly near the jet exit.

The air chemical non-equilibrium effect (ACNEE) on hydrogen-air combustion flow fields at Mach number of 10 is numerically analyzed for a semi-sphere with a sonic opposing-hydrogen jet. The 2D axisymmetric multi-components N-S equations are solved by using the central scheme with artificial dissipation and the S-A turbulence model. Numerical results show that as compared to the result without ACNEE, the ACNEE has little influence on the structure of flow field, but has a considerable impact on fluid characteristics which reduces the maximum value of mass fraction of water in the flow field and increases the maximum value of mass fraction of water on solid surface, as well as the maximum surface temperature.

Roughness element induced hypersonic boundary layer transition on a flat plate is investigated using infrared thermography at Ma = 5 and 6 flow condition. Surface Stanton number is acquired to analyze the effect of roughness element shape and height on the transition process. The correlation between the vortex structure induced by roughness element and the wall heat streaks is established. The results indicate that higher roughness element would induce stronger streamwise heat flux streaks, lead to transition advance in streamwise centerline and increase the width of spanwise wake. Moreover, for low roughness element, the effect of the shape is not obvious, and the height plays a leading role in the transition; for tall roughness element, the effect on accelerating transition for the diamond roughness element is the best, the square is the worst, and the shape plays a leading role in the transition.

The expressions of unsteady gust loads are derived based on the piston theory in this paper. The aerothermoelastic response of hypersonic two degree-of-freedom airfoil is analyzed. The calculation of the unsteady aerodynamic lift and moment are given based on third-order piston theory. Also considered is the loss of torsional stiffness that may be incurred by lifting surface subject to axial stresses induced by aerodynamic heating. The aerodynamic heating effects are estimated based on the adiabatic wall temperature due to high speed airstreams. The effect of horizontal gust loads on aeroelastic response system is compared with vertical gust loads. Then the relationship between the pitching displacement amplitude and the gust velocity is analyzed. Numerical results show that horizontal gust has little effect on the stabilization system, while the vertical gust has a significant effect on the aeroelastic system. The acceleration of airfoil which is generated due to the vertical gust can cause the system to become vibrating for a long time. The results also show that pitching displacement amplitude of the aeroelastic response is in the direct proportion to the gust velocity, the proportion is about 3.8 × 10^-4.