Transitional Flow Dynamics Behind a Micro-Ramp
J. Casacuberta, K.J. Groot, Q. Ye, S. Hickel (2020)
Flow Turbulence and Combustion 104: 533-552. doi: 10.1007/s10494-019-00085-1
Micro-ramps are popular passive flow control devices which can delay flow separation by re-energising the lower portion of the boundary layer. We compute the laminar base flow, the instantaneous transitional flow, and the mean flow around a micro-ramp immersed in a quasi-incompressible boundary layer at supercritical roughness Reynolds number.
Effectivity and efficiency of selective frequency damping for the computation of unstable steady-state solutions
J. Casacuberta, K.J. Groot, H.J. Tol, S. Hickel (2018)
Journal of Computational Physics 375: 481-497. doi: 10.1016/j.jcp.2018.08.056
Selective Frequency Damping (SFD) is a popular method for the computation of globally unstable steady-state solutions in fluid dynamics. The approach has two model parameters whose selection is generally unclear. In this article, a detailed analysis of the influence of these parameters is presented, answering several open questions with regard to the effectiveness, optimum efficiency and limitations of the method.
Validation of large-eddy simulation methods for gravity wave breaking
S. Remmler, S. Hickel, M.D. Fruman, U. Achatz (2015)
Journal of the Atmospheric Sciences 72: 3537-3562. doi: 10.1175/JAS-D-14-0321.1
To reduce the computational costs of numerical studies of gravity wave breaking in the atmosphere, the grid resolution has to be reduced as much as possible. Insufficient resolution of small-scale turbulence demands a proper turbulence parameterization in the framework of a large-eddy simulation (LES). We consider three different LES methods—the adaptive local deconvolution method (ALDM), the dynamic Smagorinsky method (DSM), and a naïve central discretization without turbulence parameterization (CDS4)—for three different cases of the breaking of well-defined monochromatic gravity waves.
On the transition between regular and irregular shock patterns of shock-wave/boundary-layer interactions
J. Matheis, S. Hickel (2015)
Journal of Fluid Mechanics 776: 200-234. doi: 10.1017/jfm.2015.319
The reflection of strong oblique shock waves at turbulent boundary layers is studied numerically and analytically. A particular emphasis is put on the transition between regular shock-wave/boundary-layer interaction (SWBLI) and Mach reflection (irregular SWBLI). The classical two- and three-shock theory and a generalised form of the free interaction theory are used for the analysis of well-resolved large-eddy simulations (LES) and for the derivation of stability criteria.
Benchmarking in a rotating annulus: A comparative experimental and numerical study of baroclinic wave dynamics
M. Vincze, S. Borchert, U. Achatz, T. von Larcher, M. Baumann, C. Liersch, S. Remmler, T. Beck, K.D. Alexandrov, C. Egbers, J. Fröhlich, V. Heuveline, S. Hickel, U. Harlander (2015)
Meteorologische Zeitschrift 23: 611-635. doi: 10.1127/metz/2014/0600
The differentially heated rotating annulus is a widely studied tabletop-size laboratory model of the general mid-latitude atmospheric circulation. The two most relevant factors of cyclogenesis, namely rotation and meridional temperature gradient are quite well captured in this simple arrangement. The radial temperature difference in the cylindrical tank and its rotation rate can be set so that the isothermal surfaces in the bulk tilt, leading to the formation of baroclinic waves.
On the construction of a direct numerical simulation of a breaking inertia-gravity wave in the upper-mesosphere
M.D. Fruman, S. Remmler, U. Achatz, S. Hickel (2014)
Journal of Geophysical Research 119: 11613-11640. doi: 10.1002/2014JD022046
A systematic approach to the direct numerical simulation (DNS) of breaking upper mesospheric inertia-gravity waves of amplitude close to or above the threshold for static instability is presented. Normal mode or singular vector analysis applied in a frame of reference moving with the phase velocity of the wave (in which the wave is a steady solution) is used to determine the most likely scale and structure of the primary instability
Large-eddy simulation of passive shock-wave/boundary-layer interaction control
V. Pasquariello, M. Grilli, S. Hickel, N.A. Adams (2014)
International Journal of Heat and Fluid Flow 49: 116-127. doi: 10.1016/j.ijheatfluidflow.2014.04.005
We investigate a passive flow-control technique for the interaction of an oblique shock generated by an 8.8° wedge with a turbulent boundary-layer at a free-stream Mach number of Ma∞ = 2.3 and a Reynolds number based on the incoming boundary-layer thickness of Reδ = 60 500 by means of large-eddy simulation (LES).
On the application of WKB theory for the simulation of the weakly nonlinear dynamics of gravity waves
J. Muraschko, M.D. Fruman, U. Achatz, S. Hickel, Y. Toledo (2015)
Quarterly Journal of the Royal Meteorological Society 141: 676-697. doi: 10.1002/qj.2381
The dynamics of internal gravity waves is modelled using Wentzel–Kramer–Brillouin (WKB) theory in position–wave number phase space. A transport equation for the phase-space wave-action density is derived for describing one-dimensional wave fields in a background with height-dependent stratification and height- and time-dependent horizontal-mean horizontal wind, where the mean wind is coupled to the waves through the divergence of the mean vertical flux of horizontal momentum associated with the waves.
Direct numerical simulation of a breaking inertia-gravity wave
S. Remmler, M.D. Fruman, S. Hickel (2013)
Journal of Fluid Mechanics 722: 424-436. doi: 10.1017/jfm.2013.108
We have performed fully resolved three-dimensional numerical simulations of a statically unstable monochromatic inertia–gravity wave using the Boussinesq equations on an f - plane with constant stratification. The chosen parameters represent a gravity wave with almost vertical direction of propagation and a wavelength of 3 km breaking in the middle atmosphere.