Stanislaw Gepner

Warsaw University of Technology · Institute of Aeronautics and Applied Mechanics (IAAM)

Pressure-gradient-driven flows through sinusoidal channels have been studied. The analysis was carried out up to the formation of secondary nonlinear states and spanned a range of low and moderate Reynolds numbers. Direct numerical simulations were used to identify and determine the properties of steady as well as non-stationary, two-dimensional (2...

Couette–Poiseuille (CP) flow in the presence of longitudinal grooves is studied by means of numerical analysis. The flow is actuated by movement of the flat wall and pressure imposed in the opposite direction. The stationary wall features longitudinal grooves that modify the flow, change hydrodynamic drag on the driving wall and cause onset of hydr...

Flows through narrow, rectangular ducts, with width to height aspect ratio below the established linear stability threshold of 3.2 and modified with grooves on top and bottom walls, are investigated. The primary objective of the current work lies in reintroduction of the linear destabilization mechanism, which is not present for the case of low asp...

Flow through a channel equipped with plane, longitudinal grooves is investigated. We focus on determining changes to the flow dynamics due to applied wall manipulations, especially the possibility of drag-reduction, potential for hydrodynamic destabilization and onset of secondary, nonlinear flow solutions. Considered patterns of geometrical manipu...

We demonstrate that an intensive stirring can be achieved in laminar channel flows in a passive manner by utilizing the recently discovered instability waves which lead to chaotic particle movements. The stirring is suitable for mixtures made of delicate constituents prone to mechanical damage, such as bacteria and DNA samples, as collisions betwee...

Flow in a longitudinally grooved channel is analysed with the primary objective of quantifying intensification of transport mechanism due to the onset of secondary flows resulting from hydrodynamic instability and amplification of unstable modes into the nonlinear regime. Considered geometry consists of a channel whose walls are fitted with sinusoi...

Flow in a finite-width rectangular duct with a corrugated top-bottom wall has been studied. The primary goal is to establish geometries that allow early flow destabilization at a possibly low drag increase. The flow is assumed periodic in the streamwise direction and bounded by the duct sidewalls in the spanwise direction; the top and bottom wall c...

Flow in a channel with corrugated walls has been studied, with the primary goal of establishing channel geometries that enhance achievable mixing at possibly low drag increase. The wall corrugation has the form of a sinusoidal wave oriented transversely, i.e., the lines of constant elevation (or phase) are parallel to the direction of the flow. The...

The present paper discusses an effective adaptive methods suited for use in parallel environment. An in-house, parallel flow solver based on the residual distribution method is used for the solution of flow problems. Simulation is parallelized based on the domain decomposition approach. Adaptive changes to the mesh are achieved by two distinctive t...

An analysis of flows in converging–diverging channels has been carried out with the primary goal of identifying geometries which result in increased mixing. The model geometry consists of a channel whose walls are fitted with spanwise grooves of moderate amplitudes (up to 10 % of the mean channel opening) and of sinusoidal shape. The groove systems...

Flow in a diverging-converging channel of moderate amplitudes has been studied. The analysis is carried out up to Reynolds numbers resulting in the formation of secondary states. The first part of the analysis is based on a two-dimensional model and demonstrates that reducing the corrugation wavelength results in the appearance of an unsteady separ...

Direct Numerical Simulation of a flow in a channel with grooves parallel to the flow direction has been studied. Analysis is performed up to the Reynolds numbers resulting in the formation of secondary instability states. The analysis includes investigations of the drag reducing properties of the transversely-oriented wall corrugation. Linear stabi...

Flow in a corrugated channel has been studied. The analysis is carried out up to Reynolds numbers resulting in the formation of secondary states. The first part of the analysis is based on a two-dimensional model and demonstrates that reducing the corrugation wavelength results in the appearance of an unsteady separation. In the second part a three...

This paper considers a problem of generation of high-order anisotropic hybrid grids to be used for simulation of high-Reynolds number compressible turbulent flows around 3D geometries. The algorithm relies on generating a curvilinear structural grid in the boundary layer region, separately from the usual low-order unstructured grid in the rest of t...

Computations in Fluid Dynamics require minimisation of time in which the result could be obtained. While parallel techniques allow for handling of large problems, it is the adaptivity that ensures that computational effort is focused on interesting regions in time and space. Parallel efficiency, in a domain decomposition based approach, strongly de...

Adaptive algorithms require some driving mechanism to trigger computational mesh modification.

Mesh Adaptation is a technique allowing to solve of complex problems by limiting the use of computational resources. In parallel simulation, adaptivity causes perturbation in numerical load balance leading to decrease in overall parallel efficiency. It is therefore vital to allow for dynamic load balancing if adaptive algoritms are to be run in par...

Parallel efficiency, in a domain decomposition based approach, strongly depends on a partitioning quality. For an adaptive simulation partitioning quality is lost due to the dynamic modification of the computational mesh. Maintaining high efficiency of parallelization requires rebalancing of the numerical load. This paper presents numerical experim...

Parallelization of adaptive algorithms leads to problems with parallel efficiency. Adaptation is a method which introduces dynamic perturbations to computational environment. This in turn causes problems with proper load balance. To ensure proper efficiency of a parallel simulation it is necessary to perform load balancing whenever certain threshol...

Large scale computing requires parallelization in order to arrive at solution at reasonable time. Today parallelization is a standard in fluid problems simulation. On the other hand adaptation is a technique that allows for dynamic modification of the mesh as the need for locally higher resolution arises. Adaptation used during parallel simulation...