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Andreas Jocksch

Direct Numerical Simulation of
Turbulent Spots in High-Speed
Boundary Layers

Reprint of Diss. ETH No. 18104

1st edition Konstanz 2009, VI, 134 pages. EURO 64,00.
ISBN 3-86628-275-3 and 978-3-86628-275-9

We investigate the development of isolated turbulent spots in boundary layers at Mach numbers M = 1.1 and M = 5 for adiabatic and cooled walls by direct numerical simulations. The turbulent spots show typical properties known from the incompressible regime, e. g., the arrowhead-like shape of the spot with the downstream overhang region and streaks in the tail region. At M = 5 spanwise structures close to the wall appear in the front region. Strong wall cooling leads to elongated turbulent spots. Besides the Mach number also the Reynolds number affects the spot growth.

In the core region of the turbulent spots velocity profiles, skin friction and heat transfer are evaluated. For one parameter set at M = 1.1 turbulence statistics are analysed by considering an ensemble of turbulent spots with slightly varying initial disturbances. For M = 5 the asymptotic spreading of linear instabilities and its relation to the growth of turbulent spots are investigated. The downstream spreading of the turbulent spots is faster than for linear instabilities. In contrast to the adiabatic wall case, the slow tail velocity of the cooled-wall spots seems to be related to the spreading of linear instabilities. The near-field reveals waves propagating away from the spots. In the freestream they are spherical and propagate according to classical acoustics, while within the boundary layer they appear as distinct semi-circular patterns.


Keywords: Turbulent spots, Transition to turbulence, Compressible boundary, layer, Supersonic flow.

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