Effect of tube lip thickness on the performance of Hartmann–Sprenger tubes

Abstract

Experiments were carried out to investigate the effect of tube lip thickness on Hartmann--Sprenger (HS) tones in the moderately underexpanded conditions. It is found that the generation of jet regurgitant (JRG) tones and screech tones are independent of the tube lip thickness. The first shock cell length ( L c) and the correctly expanded speed of sound ( a j) are found to be the characteristic scale for length and velocity, respectively for both JRG and screech tones in the moderately underexpanded jets. The average normalized frequency, f L/ a j ( L is the length of the HS tube) of the JRG tones is 0.25. Two new families of tones are generated by the increase of tube lip thickness. The frequency of tones in one of the two families is the same as the general impingement (IG) tones generated by the supersonic jet impinging on flat plates. The frequency of tones of the other family (induced quarter wave) is equal to the frequency of the quarter wave mode of the tube and these tones are induced by IG tones. The end wall pressure (a measure of compression of the residual fluid) is decreased when the IG tone is present together with the JRG tone. Feedback experiments showed that an acoustic feedback to the nozzle has a role in the self-excitation of screech tones and IG tones but their self-excitation mechanism are found to be different. There is no role of an acoustic feedback in the self-excitation of JRG tones.