Comments on Hypersonic Boundary-Layer Transition

Abstract

OTIC FLIGHT DYNAIMICS LABORATORY WRIGHT RESEARCH AND DEVELOPMENT CENTER AIR FORCE SYSPThS COW~hANDThis is a survey paper on the subject of hypersonic boundary-layer transition. Part 1 discusses boundary-layer stability theory, hypersonic boundary-layer stability experiments, and a comparison between theory and experiment. Part 2 contains comments on how many configuration and flow parameters influence transition. Part 3 discusses some additional general aspects of transition. Part 4 discusses problems of predicting transition and comments on three prediction methods. Part 5 contains some general guidelines for prediction methodology. Thus, much hvpersonic transition guidance must be speculated from subsonic and supersonic results and old hypersonic data must be retrieved and re-evaluated. E-1 S4AE AS RPTNot that it helps with the boundarv-layer transition prediction problems, but there is some small gratification in knowing that design uncertainties are been a considerable number of hypersonic transition experiments; however, these data generally provide only parametric trends (e.g. , the effects of nosetip bluntness on transition location). When the only information obtalned is the location of transition it is impossible to determine details of the boundary-layer disturbance mechanisms which caused the transition. In order to obtain fundamental information about hypersonic boundary-layer instability phenomena it is necessary to perform stability experiments which describe the disturbances in the laminar boundary layer prior to transition. It is unfor-tunate that such an important topic as hypersonic stability has received so little attention. -n understanding of hypersonic instability phenomena is __ortant for obtaining a better understanding of hypersonic transition and is esserclal for analytical prediction methods. The following discus.'ion will briefly discuss our current understanding of hypersonic boundary-layer instabilities. (I.b) STABILITY THEORYIt is now generally believed that the onset of boundary-layer turbulence is the result of instability waves in the laminar boundary layer; however, the direct relationship between instability and transition is unknown. Stability theory provides a means of understanding the characteristics of instability waves and, consequently, a better understanding of transition. Numerical solutions of the stability equations can provide important details of boundarylayer instability; such as, the identity of those disturbance frequencies which are stable and those which are unstable, the minimum critical ReynoldR number at which disturbances scart to grow, their growth rates, their return to a stable condition, the particular disturbance frequency which will cbtain the maximum distuibance amplitude, and the effect of various parameters (e.g., Mach number, pressure gradient, wall temperature, etc.) Stability theory can povIde much valuable information about boundary-layer disturbances, but it cannot predict transition. This Is an inportant point.There is no transition 3 t...

Direct numerical simulation of hypersonic boundary layer transition over a blunt cone with a small angle of attack

“…Limited by computer resource, only the flow around the leeward and the windward sections is simulated in the DNS, 13 while the whole distribution of transition locations on the cone surface is not studied. Stetson's experiment 12 shows that the transition location shows a nonmonotonic curve on the cone surface in the condition of small angle of attack. However, the mechanism of this nonmonotonic transition location is still unclear and needs further study.…”

“…Experimental researches show that even a very small angle of attack ͑such as 1°͒ can affect the transition locations of cone boundary layer significantly. 8,12 The authors 13 performed the DNS of boundary transition over a blunt cone with free-stream Mach 6 and 1°angle of attack, trying to answer the question why transition is early in the leeward section and is delayed in the windward section. Limited by computer resource, only the flow around the leeward and the windward sections is simulated in the DNS, 13 while the whole distribution of transition locations on the cone surface is not studied.…”

Experimental investigation of a three dimensional scramjet engine at hypervelocity conditions

“…There are very few things about transition that are known for certain other than that it occurs if the Reynolds number is high enough. This lack of knowledge is due to the fact that the process is complex and is influenced by many contributing factors (Stetson, 1990).…”

“…"Even though some of these parameters play only a minor role in the transition process, the effects of the major parameters are usually interrelated and difficult to interpret (Stetson, 1990)." This makes it very difficult to develop empirical relations that can be used widely to predict transition, it is simply impossible to include enough parameters.…”

Discrete Roughness Transition for Hypersonic Flight Vehicles

“…All of the experimental results were correlated using a proven computational approach (LATCH), applied to flight in a manner consistent with the development. 3 Also, critical to the establishment of an uncertainty value in applying a ground-based correlation to flight, an in-depth review of Orbiter flight data was initiated to establish credible flight calibration cases. A complete set of results leading up to the initial version of the BLT Tool were compiled into an informal technical note provided to the Orbiter program and then subsequently in a series of conference papers (Refs.…”