Spectral measurements of hypervelocity flow in an expansion tunnel

Atmospheric reentry vehicles and planetary probes fly through the atmosphere at hypervelocity speed. At such speed, there is a significant proportion of heat load to the vehicle surface due to radiative heating. Accurate prediction needs a good knowledge of the radiation spectrum properties. In this paper, a high-speed camera and spectrograph coupled to an intensified charge-coupled device have bee n impleme nted to inv estigate the rad i at io n flow over a semi-cylinder model. The experiments were carried out in the JF16 expansi on timnel with secondary shock velocity of 7.9 km·s^-1. Results show that the emissio n spectrum comprises several atomic lines and molecular band systems. We give detailed data of the radiation spectrum, shock shape, shock detached distance and radiation intensity varying with space and wavelength. This valuable experimental dataset will be helpful to validate computational fluid dynamics codes and radiation models, which equates to increased prediction accuracy of radiation heating. Also, some suggestions for spectral measurement in hypervelocity flow field were list in the end.

Simulation of Wave-Flow-Cavitation Interaction Using a Compressible Homogenous Flow Method

A numerical method based on a homogeneous single-phase flow model is presented to simulate the interaction between pressure wave and flow cavitation.To account for compressibility effects of liquid water,cavitating flow is assumed to be compressible and governed by time-dependent Euler equations with proper equation of state(EOS).The isentropic one-fluid formulation is employed to model the cavitation inception and evolution,while pure liquid phase is modeled by Tait equation of state.Because of large stiffness of Tait EOS and great variation of sound speed in flow field,some of conventional compressible gasdynamics solvers are unstable and even not applicable when extended to calculation of flow cavitation.To overcome the difficulties,a Godunov-type,cell-centered finite volume method is generalized to numerically integrate the governing equations on triangular mesh.The boundary is treated specially to ensure stability of the approach.The method proves to be stable,robust,accurate,time-efficient and oscillation-free.Novel numerical experiments are designed to investigate unsteady dynamics of the cavitating flow impacted by pressure wave,which is of great interest in engineering applications but has not been studied systematically so far.Numerical simulation indicates that cavity over cylinder can be induced to collapse if the object is accelerated suddenly and extremely high pressure pulse results almost instantaneously.This,however,may be avoided by changing the traveling speed smoothly.The accompanying huge pressure increasemay damage underwater devices.However,cavity formed at relatively high upstream speed may be less distorted or affected by shock wave and can recover fully from the initial deformation.It is observed that the cavitating flow starting from a higher freestream velocity is more stable and more resilient with respect to perturbation than the flow with lower background speed.These findings may shed some light on how to control cavitation development to avoid possible damage to operating devices.