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ACTIVITY_TITLE

Assessment of Predictive Capabilities for Aerothermodynamic Heating of Hypersonic Systems

ACTIVITY_NUMBER

AVT-205

CLASSIFICATION

NU

ACTIVITY_STATUS_LABEL

2

ACTIVITY_LABEL

RTG

START_DATE

01/01/2012

END_DATE

01/12/2014

ACTIVITY_OPEN_TO_PARTNERS

0

KEYWORDS

Hypersonic; CFD; shock waves; boundary layers; roughness; heat transfer

BACKGROUND

One of the primary technological challenges to the development of hypersonic capabilities is the management of the substantial thermal loads associated with the aerothermodynamic environment. Conservative approaches to thermal protection systems increase vehicle weight at the expense of performance, while aggressive, low-weight designs increase the potential risk for structural failure. At the heart of this problem lies the current inability to accurately predict the complex fluid dynamic, thermodynamic and chemical phenomena which dominate the development of thermal loads on hypersonic systems. Two examples of such critical phenomena include shock wave/boundary layer interactions and surface heating due to turbulent flow over both localized disturbances and distributed arbitrary roughness. Shock wave/ boundary layer interactions (denoted "shock interactions") are commonplace in hypersonic aerodynamics. They occur in the vicinity of deflected control surfaces, fuselage-wing junctures, corner flows in inlets and many other locations. Shock interactions can cause boundary layer separation with concommitant high heat transfer at reattachment which has a significant impact on the design of thermal protection systems. Accurate prediction of shock interactions is therefore essential for optimal design of hypersonic vehicles. Assessment of current predictive capabilities for shock interactions was a major focus of the activities of RTO AVT-136 during 2005-2009. As part of the effort, a set of two test configurations (i.e., a 25 deg - 55 deg cone and a circular cylinder) were computed by an international team of CFD experts from the US and Europe. The results indicate significant success in modeling shock interactions for non-equilibrium flows; however, results for one of the cases was indeed surprising (i.e., all six computations of one double-cone configuration indicated highly unsteady flow in direct contrast to the experiment which indicated steady flow). In addition, uncertainties regarding the proper surface boundary condition in the presence of catalytic surface conditions led to a substantial variation in predicted surface heat transfer. The AVT-136 effort also intended to assess the capability of current computational methods to predict the actual shock interactions characterized in recent flight research experiments such as HIFiRE 1. Unfortunately the HIFiRE 1 flight data was not available in time for it to be utilized by AVT-136. As a result of both the outstanding technical questions associated with the simulation of nonequilibrium interactions and the now realistic opportunity to utilize flight data from HIFiRE 1, the AVT-136 study recommended additional investigations of hypersonic shock interactions to further validate CFD model effectiveness by comparison with additional experimental data. While seemingly benign, the flow of a turbulent boundary layer over a localized perturbation or arbitrary distributed roughness remains a critical challenge to the efficient design of thermal protection systems due to the relatively large levels of uncertainty (on the order of 20%) associated with the prediction of surface heat transfer in these flows and the fact that such flows can compose much of the surface of a system. Factors contributing to the overall lack of progress in this area include a deficit of high-quality experimental data for high-Reynolds number hypersonic boundary layers over well-defined rough surfaces and limited insight into the physical phenomena that define the energy transfer between kinetic and thermal states in such flows. There is currently significant interest from a number of research agencies, including both the Air Force Research Laboratory and NASA, in efforts to characterize hypersonic turbulent flows over rough surfaces and improve the prediction of the resultant surface heat transfer. 

OBJECTIVES

This working group will assess the state-of-the-art in the prediction of critical phenomena driving aerothermodynamic loads on hypersonic systems, identify key technical challenges limiting current capabilities, and recommend approaches for the improvement of future capabilities. Specific objectives include the following. • Establish a high-quality database of experimental data through identification of suitable existing data and exploitation of current funded research, including the following: - shock wave/ boundary layer interactions in non-equilibrium hypersonic flow - flight research data for dynamic shock wave/ boundary layer interactions - high-Reynolds number hypersonic boundary layers over discrete and well-defined distributed rough surfaces • Define a matrix of test cases within the experimental database for validation of computational models. • Establish a multi-national team of participants to compute the test cases. • Evaluate the results of the computations to identify modeling strengths and weaknesses. • Assess the utility of the experimental database and identify key objectives for future experiments. 

TOPICS

The Task Group will focus on one or more of the following topics: • Non-equilibrium hypersonic shock-wave laminar boundary layer interactions including the effects of surface catalysis and ablation • Turbulent heating generated by high-Reynolds number tur

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Created at 01/10/2014 10:15 by System Account
Last modified at 02/11/2014 16:26 by System Account