NASA Scientific and Technical Aerospace Reports

SCIENTIFIC AND TECHNICAL
AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 42, OCTOBER 8, 2004
02
AERODYNAMICS
Includes aerodynamics of flight vehicles, test bodies, airframe components and combinations, wings, and control surfaces. Also includes
aerodynamics of rotors, stators, fans, and other elements of turbomachinery. For related information see also 34 Fluid Mechanics and
Thermodynamics.
20040111309 NASA Langley Research Center, Hampton, VA, USA
Control and Identification of Turbulent Boundary Layer Separation
Seifert, Avi; Pack-Melton, La Tunia; [2004]; 11 pp.; In English; International Union of Theoretical and Applied Mechanics
2004, 12-14 Aug. 2004, Gottingen, Germany
Contract(s)/Grant(s): 23-719-55-MG; No Copyright; Avail: CASI; A03, Hardcopy
Effective delay of turbulent boundary layer separation could be achieved via closed-loop control. Constructing such a
system requires that sensor data be processed, real-time, and fed into the controller to determine the output. Current methods
for detection of turbulent boundary layer separation are lacking the capability of localized, fast and reliable identification of
the boundary layer state. A method is proposed for short-time FFT processing of time series, measured by hot-film sensors,
with the purpose of identifying the alternation of the balance between small and large scales as the boundary layer separates,
favoring the large scales. The method has been validated by comparison to other criteria of separation detection and over a
range of baseline and controlled flow conditions on a simplified high-lift system, incorporating active flow control.
Derived from text
Turbulent Boundary Layer; Flow Distribution; Active Control; Boundary Layer Separation; Time Series Analysis
20040111369 North Carolina State Univ., Raleigh, NC, USA
Role of Turbulent Prandtl Number on Heat Flux at Hypersonic Mach Number
Xiao, X.; Edwards, J. R.; Hassan, H. A.; [2004]; 5 pp.; In English
Contract(s)/Grant(s): NAG1-03030; Copyright; Avail: CASI; A01, Hardcopy
Present simulation of turbulent flows involving shock wave/boundary layer interaction invariably overestimates heat flux
by almost a factor of two. One possible reason for such a performance is a result of the fact that the turbulence models
employed make use of Morkovin’s hypothesis. This hypothesis is valid for non-hypersonic Mach numbers and moderate rates
of heat transfer. At hypersonic Mach numbers, high rates of heat transfer exist in regions where shock wave/boundary layer
interactions are important. As a result, one should not expect traditional turbulence models to yield accurate results. The goal
of this investigation is to explore the role of a variable Prandtl number formulation in predicting heat flux in flows dominated
by strong shock wave/boundary layer interactions. The intended applications involve external flows in the absence of
combustion such as those encountered in supersonic inlets. This can be achieved by adding equations for the temperature
variance and its dissipation rate. Such equations can be derived from the exact Navier-Stokes equations. Traditionally, modeled
equations are based on the low speed energy equation where the pressure gradient term and the term responsible for energy
dissipation are ignored. It is clear that such assumptions are not valid for hypersonic flows. The approach used here is based
on the procedure used in deriving the k-zeta model, in which the exact equations that governed k, the variance of velocity,
and zeta, the variance of vorticity, were derived and modeled. For the variable turbulent Prandtl number, the exact equations
that govern the temperature variance and its dissipation rate are derived and modeled term by term. The resulting set of
equations are free of damping and wall functions and are coordinate-system independent. Moreover, modeled correlations are
tensorially consistent and invariant under Galilean transformation. The final set of equations will be given in the paper.
Author
Prandtl Number; Heat Flux; Hypersonic Speed
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