Nosetip Bluntness Effects on Transition at Hypersonic Speeds: Experimental and Numerical Analysis

Paredes, Pedro ; Choudhari, Meelan M [Point of Contact] ; Li, Fei ; Jewell, Joseph S ; Kimmel, Roger L ; Marineau, Eric C ; Grossir, Guillaume

关键词: AMPLIFICATION;    BOUNDARY LAYER STABILITY;    BOUNDARY LAYER TRANSITION;    CIRCULAR CONES;    DATA BASES;    ENTROPY;    FRUSTUMS;    HYPERSONIC SPEED;    HYPERSONICS;    NOSE CONES;    NOSE TIPS;    NUMERICAL ANALYSIS;    RADII;    REYNOLDS NUMBER;    SENSITIVITY;    SLENDER CONES;    STABILITY;    UPSTREAM;    WALLS;    WIND TUNNEL TESTS;   

RP-ID  :  NF1676L-29701

学科分类：航空航天科学

美国|英语

来源: NASA Technical Reports Server

【 摘 要 】

The existing database of transition measurements in hypersonic ground facilities has establishedthat the onset of boundary layer transition over a circular cone at zero angle of attackshifts downstream as the nosetip bluntness is increased with respect to a sharp cone. However,this trend is reversed at sufficiently large values of the nosetip Reynolds number, so that thetransition onset location eventually moves upstream with a further increase in nosetip bluntness.This transition reversal phenomenon, which cannot be explained on the basis of linearstability theory, was the focus of a collaborative investigation under the NATO STO groupAVT-240 on Hypersonic Boundary-Layer Transition Prediction. The current paper providesan overview of that effort, which included wind tunnel measurements in three different facilitiesand theoretical analysis related to modal and nonmodal amplification of boundary layerdisturbances. Because neither first and second-mode waves nor entropy-layer instabilities arefound to be substantially amplified to initiate transition at large bluntness values, transient(i.e., nonmodal) disturbance growth has been investigated as the potential basis for a physics basedmodel for the transition reversal phenomenon. Results of the transient growth analysisindicate that stationary disturbances that are initiated within the nosetip or in the vicinity ofthe juncture between the nosetip and the frustum can undergo relatively significant nonmodal amplification and that the maximum energy gain increases nonlinearly with the nose radius ofthe cone. This finding does not provide a definitive link between transient growth and the onsetof transition, but it is qualitatively consistent with the experimental observations that frustumtransition during the reversal regime was highly sensitive to wall roughness, and furthermore,was dominated by disturbances that originated near the nosetip. Furthermore, the presentanalysis shows significant nonmodal growth of traveling disturbances that peak within theentropy layer and could also play a role in the transition reversal phenomenon.