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Reynolds-Averaged Turbulence Model Assessment for a Highly Back-Pressured Isolator FlowfieldThe use of computational fluid dynamics in scramjet engine component development is widespread in the existing literature. Unfortunately, the quantification of model-form uncertainties is rarely addressed with anything other than sensitivity studies, requiring that the computational results be intimately tied to and calibrated against existing test data. This practice must be replaced with a formal uncertainty quantification process for computational fluid dynamics to play an expanded role in the system design, development, and flight certification process. Due to ground test facility limitations, this expanded role is believed to be a requirement by some in the test and evaluation community if scramjet engines are to be given serious consideration as a viable propulsion device. An effort has been initiated at the NASA Langley Research Center to validate several turbulence closure models used for Reynolds-averaged simulations of scramjet isolator flows. The turbulence models considered were the Menter BSL, Menter SST, Wilcox 1998, Wilcox 2006, and the Gatski-Speziale explicit algebraic Reynolds stress models. The simulations were carried out using the VULCAN computational fluid dynamics package developed at the NASA Langley Research Center. A procedure to quantify the numerical errors was developed to account for discretization errors in the validation process. This procedure utilized the grid convergence index defined by Roache as a bounding estimate for the numerical error. The validation data was collected from a mechanically back-pressured constant area (1 2 inch) isolator model with an isolator entrance Mach number of 2.5. As expected, the model-form uncertainty was substantial for the shock-dominated, massively separated flowfield within the isolator as evidenced by a 6 duct height variation in shock train length depending on the turbulence model employed. Generally speaking, the turbulence models that did not include an explicit stress limiter more closely matched the measured surface pressures. This observation is somewhat surprising, given that stress-limiting models have generally been developed to better predict shock-separated flows. All of the models considered also failed to properly predict the shape and extent of the separated flow region caused by the shock boundary layer interactions. However, the best performing models were able to predict the isolator shock train length (an important metric for isolator operability margin) to within 1 isolator duct height.
Document ID
20130000726
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Baurle, Robert A.
(NASA Langley Research Center Hampton, VA, United States)
Middleton, Troy F.
(NASA Langley Research Center Hampton, VA, United States)
Wilson, L. G.
(Analytical Mechanics Associates, Inc. Hampton, VA, United States)
Date Acquired
August 27, 2013
Publication Date
December 3, 2012
Subject Category
Spacecraft Propulsion And Power
Report/Patent Number
NF1676L-15654
Report Number: NF1676L-15654
Meeting Information
Meeting: 33rd Airbreathing Propulsion Joint Subcommittee Meeting
Location: Monterey, CA
Country: United States
Start Date: December 3, 2012
End Date: December 7, 2012
Sponsors: Department of the Navy, Department of the Air Force, NASA Headquarters, Department of the Army
Funding Number(s)
WBS: WBS 475122.02.07.09.03
Distribution Limits
Public
Copyright
Public Use Permitted.
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