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.

Experimental investigation of hypersonic flight-duplicated shock tunnel characteristics

Hypersonic air-breathing propulsion is one of the key techniques for future aviation and the ground aerodynamic testing for full scale test models with sufficient test time at flight conditions is of fundamental importance for verifying hypersonic air-breathing engines.Based on the backward detonation-driven concept,the hypersonic flight-duplicated shock tunnel(or JF-12 shock tunnel)has been successfully constructed and calibrated.This facility is capable of reproducing airflow for Mach numbers ranging from 5 to 9 at an altitude of 25-50 km,with a test duration of more than 100 ms.To quantify the performance of the shock tunnel,experiments were conducted to investigate the aerodynamic characteristics of the test flows and the effects of several critical techniques that play important roles in the operation of the shock tunnel.The stagnation pressure was constant within士5%and the average stagnation pressure varied by less than 0.048%/ms.The variation of the stagnation pressure in repeated experiments is less than 2.0%,indicating the good repeatability of the wind tunnel.The non-uniformity of the Mach number in the core flow field at the nozzle exit was within士2.5%.Additional,a uniform flow field is established upstream of the nozzle exit.The axial gradients of the flow field are small since the Mach number varies less than 1.7%/m.Findings regarding the ignition technology,diaphragm ruptures,detonation driver capacity,incident shock-wave decay,and tunnel operation mode are also presented.The findings of this study are not only helpful for operating the shock tunnel,but can also assist the future development of hypersonic wind tunnels.