Assessment of heat transfer and Mach number effects on high-speed turbulent boundary layers

High-speed vehicles experience a highly challenging environment in which the freestream Mach number and surface temperature greatly influence aerodynamic drag and heat transfer. The interplay of these two parameters strongly affects the near-wall dynamics of high-speed turbulent boundary layers (TBL...

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Bibliographic Details
Published in:Journal of fluid mechanics 2023-10, Vol.974, Article A10
Main Authors: Cogo, Michele, Baù, Umberto, Chinappi, Mauro, Bernardini, Matteo, Picano, Francesco
Format: Article
Language:English
Subjects:
Adiabatic
Adiabatic flow
Aerodynamic drag
Boundary layers
Compressibility
Cooling
Decoupling
Direct numerical simulation
Flow distribution
Flow pattern
Free flow
Heat transfer
High Mach number
High speed
JFM Papers
Parameters
Reynolds number
Surface temperature
Temperature
Temperature fields
Turbulence
Turbulence intensity
Turbulent boundary layer
Velocity
Viscosity
Viscous sublayers
Wall temperature
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Summary:High-speed vehicles experience a highly challenging environment in which the freestream Mach number and surface temperature greatly influence aerodynamic drag and heat transfer. The interplay of these two parameters strongly affects the near-wall dynamics of high-speed turbulent boundary layers (TBLs) in a non-trivial way, breaking similarity arguments on velocity and temperature fields, typically derived for adiabatic cases. We present direct numerical simulations of flat-plate zero-pressure-gradient TBLs spanning three freestream Mach numbers $[2,4,6]$ and four wall temperature conditions (from adiabatic to very cold walls), emphasising the choice of the wall-cooling parameter to recover a similar flow organisation at different Mach numbers. We link qualitative observations on flow patterns to first- and second-order statistics to explain the decoupling of temperature–velocity fluctuations that occurs at reduced wall temperatures and high Mach numbers. For these cases, we discuss the formation of a secondary peak of thermal production in the viscous sublayer, which is in contrast with the monotonic behaviour of adiabatic profiles. We propose different physical mechanisms induced by wall-cooling and compressibility that result in apparently similar flow features, such as a higher peak in the streamwise velocity turbulence intensity, and distinct features, such as the separation of turbulent scales.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.791