Markus Klöker
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View article: Direct numerical simulation of complete transition to turbulence with a fluid at supercritical pressure
Direct numerical simulation of complete transition to turbulence with a fluid at supercritical pressure Open
The objective of this work is to investigate the unexplored laminar-to-turbulent transition of a heated flat-plate boundary layer with a fluid at supercritical pressure. Two temperature ranges are considered: a subcritical case, where the …
View article: Boundary-layer transition in the age of data: from a comprehensive dataset to fine-grained prediction
Boundary-layer transition in the age of data: from a comprehensive dataset to fine-grained prediction Open
The laminar-to-turbulent transition remains a fundamental and enduring challenge in fluid mechanics. Its complexity arises from the intrinsic nonlinearity and extreme sensitivity to external disturbances. This transition is critical in a w…
View article: Boundary-layer transition in the age of data: from a comprehensive dataset to fine-grained prediction
Boundary-layer transition in the age of data: from a comprehensive dataset to fine-grained prediction Open
The laminar-to-turbulent transition remains a fundamental and enduring challenge in fluid mechanics. Its complexity arises from the intrinsic nonlinearity and extreme sensitivity to external disturbances. This transition is critical in a w…
View article: Sensitivity of three-dimensional boundary layer stability to intrinsic uncertainties of fluid properties: a study on supercritical CO<sub>2</sub>
Sensitivity of three-dimensional boundary layer stability to intrinsic uncertainties of fluid properties: a study on supercritical CO<sub>2</sub> Open
The intrinsic uncertainty of fluid properties, including the equation-of-state, viscosity and thermal conductivity, on boundary layer stability has scarcely been addressed. When a fluid is operating in the vicinity of the Widom line (defin…
View article: On the Origin of Sediment Ripples
On the Origin of Sediment Ripples Open
As soon as a granular sediment has been set in motion by the currents of droppable fluids or by wind, sand waves form as smaller ripples or larger dunes. The relevance of this phenomenon lies in the roughness effect against the currents an…
View article: Transpiration cooling in hypersonic flow and mutual effect on turbulent transition and cooling performance
Transpiration cooling in hypersonic flow and mutual effect on turbulent transition and cooling performance Open
This work presents recent advancements in the study of film cooling in hypersonic flows, considering experimental and numerical investigations, with the aim to characterize the wall-cooling performance in different coolant injection and ba…
View article: A systematic DNS approach to isolate wall-curvature effects in spatially developing boundary layers
A systematic DNS approach to isolate wall-curvature effects in spatially developing boundary layers Open
A methodology to numerically assess wall-curvature effects in boundary layers is introduced. Wall curvature, which directly induces streamline curvature, is associated with several changes in boundary-layer flow. By necessity, a local radi…
View article: Experimental investigation on boundary-layer streaks induced by grid-generated free-stream turbulence in a water channel
Experimental investigation on boundary-layer streaks induced by grid-generated free-stream turbulence in a water channel Open
In this study, the influence of various turbulence-grid configurations is analysed on both the induced free-stream turbulence (FST) and the resulting Klebanoff modes/streaks developing in a laminar flat-plate boundary layer downstream in a…
View article: Direct Numerical Simulations of K-type transition in a flat-plate boundary layer with supercritical fluids
Direct Numerical Simulations of K-type transition in a flat-plate boundary layer with supercritical fluids Open
We investigate the controlled K-type breakdown of a flat-plate boundary-layer with highly non-ideal supercritical fluid at a reduced pressure of $p_{r,\infty}=1.10$. Direct numerical simulations are performed at a Mach number of $M_\infty=…
View article: Heat-transfer effects in compressible turbulent boundary layers – a regime diagram
Heat-transfer effects in compressible turbulent boundary layers – a regime diagram Open
As shown by Wenzel et al. ( J. Fluid Mech. , vol. 930, 2022, A1), the Eckert number $Ec$ defined using the difference between recovery temperature $\bar{T}_r$ and wall temperature $\bar{T}_w$ can be understood as a meaningful quantity to c…
View article: Transient growth in diabatic boundary layers with fluids at supercritical pressure
Transient growth in diabatic boundary layers with fluids at supercritical pressure Open
In the region close to the thermodynamic critical point and in the proximity of the pseudo-boiling (Widom) line, strong property variations substantially alter the growth of modal instabilities, as revealed in Ren et al. (J. Fluid Mech., v…
View article: Instabilities in three-dimensional boundary-layer flows with a highly non-ideal fluid
Instabilities in three-dimensional boundary-layer flows with a highly non-ideal fluid Open
The present work investigates the linear instability of three-dimensional boundary layers in thermodynamically non-ideal regimes. As a representative fluid, we consider carbon dioxide at supercritical pressure (80 bar). The flow set-up is …
View article: Control of laminar breakdown in a supersonic boundary layer employing streaks
Control of laminar breakdown in a supersonic boundary layer employing streaks Open
In this study direct numerical simulations are employed to investigate the effects of various parameters on the laminar-flow-control capabilities of narrowly spaced streaks in a supersonic boundary layer at Mach $2.0$ . Previous work by Sh…
View article: About the influences of compressibility, heat transfer and pressure gradients in compressible turbulent boundary layers
About the influences of compressibility, heat transfer and pressure gradients in compressible turbulent boundary layers Open
This paper presents a comprehensive analysis of the momentum and energy transfer in compressible turbulent boundary layers based on integral identities. By considering data obtained from direct numerical simulations for a wide parameter ra…
View article: Reynolds analogy factor in self-similar compressible turbulent boundary layers with pressure gradients
Reynolds analogy factor in self-similar compressible turbulent boundary layers with pressure gradients Open
View article: Numerical Simulation of Film Cooling in Supersonic Flow
Numerical Simulation of Film Cooling in Supersonic Flow Open
High-order direct numerical simulations of film cooling by tangentially blowing cool helium at supersonic speeds into a hot turbulent boundary-layer flow of steam (gaseous H 2 O) at a free stream Mach number of 3.3 are presented. The stagn…
View article: Self-similar compressible turbulent boundary layers with pressure gradients. Part 1. Direct numerical simulation and assessment of Morkovin’s hypothesis
Self-similar compressible turbulent boundary layers with pressure gradients. Part 1. Direct numerical simulation and assessment of Morkovin’s hypothesis Open
A direct numerical simulation study of self-similar compressible flat-plate turbulent boundary layers (TBLs) with pressure gradients (PGs) has been performed for inflow Mach numbers of 0.5 and 2.0. All cases are computed with smooth PGs fo…
View article: Self-similar compressible turbulent boundary layers with pressure gradients. Part 2. Self-similarity analysis of the outer layer
Self-similar compressible turbulent boundary layers with pressure gradients. Part 2. Self-similarity analysis of the outer layer Open
A thorough self-similarity analysis is presented to investigate the properties of self-similarity for the outer layer of compressible turbulent boundary layers. The results are validated using the compressible and quasi-incompressible dire…
View article: Control of oblique-type breakdown in a supersonic boundary layer employing streaks
Control of oblique-type breakdown in a supersonic boundary layer employing streaks Open
The effectiveness of streak modes in controlling the oblique-type breakdown in a supersonic boundary-layer at Mach 2.0 is investigated using direct numerical simulations. Investigations in the literature have shown the effectiveness of str…
View article: Control of crossflow-vortex-induced transition by unsteady control vortices
Control of crossflow-vortex-induced transition by unsteady control vortices Open
The fundamental mechanisms of a hitherto unstudied approach to control the crossflow-induced transition in a three-dimensional boundary layer employing unsteady control vortices are investigated by means of direct numerical simulations. Us…
View article: Experimental control of swept-wing transition through base-flow modification by plasma actuators
Experimental control of swept-wing transition through base-flow modification by plasma actuators Open
Control of laminar-to-turbulent transition on a swept-wing is achieved by base-flow modification in an experimental framework, up to a chord Reynolds number of 2.5 million. This technique is based on the control strategy used in the numeri…