Ballistic Range Testing Data Analysis of Tianwen-1 Mars Entry Capsule

A typical blunt body such as Tianwen-1 Mars entry capsule suffers dynamic instability in supersonic regime. To investigate the unstable Mach range of flight and to confirm the design of aerodynamic shape and mass properties, a ballistic range test was carried out aiming at capturing supersonic dynamic characteristics of Tianwen-1. Aerodynamic coefficients of free-flight scaled models were derived by modified linear regression method based on position and attitude data, while the dynamic coefficients were established under the assumption of small angle linearization. The static moment coefficients and dynamic derivatives were identified thereafter. Results show that models in untrimmed configuration are dynamically unstable at certain Mach numbers, whereas models in trimmed configuration are dynamically stable at other Mach numbers tested. Both trimmed and untrimmed configurations are statically stable in all testing cases.

Shock Structures Using the OBurnett Equations in Combination with the Holian Conjecture

In the present work, we study the normal shock wave flow problem using a combination of the OBurnett equations and the Holian conjecture. The numerical results of the OBurnett equations for normal shocks established several fundamental aspects of the equations such as the thermodynamic consistency of the equations, and the existence of the heteroclinic trajectory and smooth shock structures at all Mach numbers. The shock profiles for the hydrodynamic field variables were found to be in quantitative agreement with the direct simulation Monte Carlo (DSMC) results in the upstream region, whereas further improvement was desirable in the downstream region of the shock. For the discrepancy in the downstream region, we conjecture that the viscosity–temperature relation (μ∝Tφ) needs to be modified in order to achieve increased dissipation and thereby achieve better agreement with the benchmark results in the downstream region. In this respect, we examine the Holian conjecture (HC), wherein transport coefficients (absolute viscosity and thermal conductivity) are evaluated using the temperature in the direction of shock propagation rather than the average temperature. The results of the modified theory (OBurnett + HC) are compared against the benchmark results and we find that the modified theory improves upon the OBurnett results, especially in the case of the heat flux shock profile. We find that the accuracy gain is marginal at lower Mach numbers, while the shock profiles are described better using the modified theory for the case of strong shocks.

Physical and Mathematical Modeling of the Interaction of Water Droplets and High-Speed Gas Flow

Present work is devoted to physical and mathematical modeling of the secondary disintegration of a liquid jet and gas-dynamic breakup of droplets in high-speed air flows. In this work the analysis of the experiments of water droplet breakup in the supersonic flow with Mach numbers up to M = 3 was carried out. The influence of shock wave presence in the flow on the intensity of droplets gas-dynamic breakup is shown. A developed empirical model is presented. It allows to predict the distribution of droplet diameters and velocities depending on the gas flow conditions, as well as the physical properties of the liquid. The effect of the Weber and Reynolds numbers on the rate of droplets gas-dynamic breakup at various Mach numbers is shown. The obtained data can be useful in the development of mathematical models for the numerical simulation of two-phase flows in the combined Lagrange-Euler formulation.

Numerical Study on the Biomimetic Trailing Edge of a Turbine Blade Under a Wide Range of Outlet Mach Numbers

This study was carried out to investigate the loss mechanism of a blade with a harbor seal whisker structure on the trailing edge under different Mach numbers. The loss of high-pressure turbine blades with four different trailing edge geometries, including a prototype, an elliptical trailing edge (ETE), a sinusoidal trailing edge (STE), and a biomimetic trailing edge (BTE) at Mach numbers of 0.38–1.21 is studied. The delayed detached-eddy simulation method is used to predict the detailed flow of the four cascades. The result shows that, when the Mach number is less than 0.9, the BTE can effectively reduce the energy loss coefficient compared with the other three cases. As the Mach number increases, the three-dimensional characteristics of the wake behind the BTE weaken. The energy loss coefficient of the blade with the BTE is close to that of the blade with the ETE and STE when the Mach number is greater than 0.9. Besides this, by controlling the wake, the BTE can effectively suppress the dynamic movement of shock waves in the cascade at high Mach numbers.

Improved theory for shock waves using the OBurnett equations

The main goal of the present study is to thoroughly test the recently derived OBurnett equations for the normal shock wave flow problem for a wide range of Mach number ( $3 \leq Ma \leq 9$ ). A dilute gas system composed of hard-sphere molecules is considered and the numerical results of the OBurnett equations are validated against in-house results from the direct simulation Monte Carlo method. The primary focus is to study the orbital structures in the phase space (velocity–temperature plane) and the variation of hydrodynamic fields across the shock. From the orbital structures, we observe that the heteroclinic trajectory exists for the OBurnett equations for all the Mach numbers considered, unlike the conventional Burnett equations. The thermodynamic consistency of the equations is also established by showing positive entropy generation across the shock. Further, the equations give smooth shock structures at all Mach numbers and significantly improve upon the results of the Navier–Stokes equations. With no tweaking of the equations in any way, the present work makes two important contributions by putting forward an improved theory of shock waves and establishing the validity of the OBurnett equations for solving complex flow problems.