Stanisław Drobniak

Quality of LES Predictions of Isothermal and Hot Round Jet

The paper presents results of LES computations performed for isothermal and non-isothermal variable density jets using high order numerical code. According to the experimental data and linear stability theory the range of the density ratios between jet and the ambient fluids considered in this work encloses the regimes of absolute and convective type of instability. Much attention is paid to the quality of the solutions depending on the mesh resolution and turbulence intensity imposed at the inlet velocity profile. The differences between the solutions obtained using different (advective/conservative) form of the Navier–Stokes equations are also mentioned.

A comparative analysis of correction method for total-head probes in large velocity-gradient flows

Abstract The paper presents a comparative analysis of already published correction methods for the readings of Pitot tubes under conditions of strong velocity and pressure gradients. The results obtained suggest the superior performance of these formulae which take into account the actual value of velocity gradient in measuring point.

Self-sustained oscillations in a homogeneous-density round jet

The paper is devoted to a new phenomenon of self-sustained oscillations triggered in a round free homogeneous-density jet. It was shown by the experimental investigations supported by the numerical approach based on extensive-Large Eddy Simulations studies that such a self-sustained regime can be established in a homogeneous-density jet, provided that the boundary layer at the nozzle exit is sufficiently thin and the perturbation level sufficiently low. The growth rate of the naturally amplified unstable modes is high enough to induce backflow leading to self-excited oscillations.

Modelling liquid redistribution in a packed bed

The paper is devoted to the computational fluid dynamics (CFD) simulation of liquid spreading process in a packed bed. The volume of fluid (VOF) approach was applied to simulate the flow in a realistic porous region composed of 6mm Raschig rings. Modelling results were used to determine the probability density function (PDF) distribution of liquid velocity vector orientation angle which was then implemented into 2-fluid Euler-Euler multiphase model of packing column. The simulation showed that the model is capable to simulate adequately the liquid redistribution in a porous region being, however, much more efficient computationally than the VOF method.

Experimental Analysis and Prediction of Wake-Induced Transition in Turbomachinery

The paper presents an experimental and numerical analysis of the interaction between wakes and boundary layers on aerodynamic blade profiles. The experiment revealed that incoming wakes interact with boundary layers and cause the significant increase of velocity fluctuations in the boundary layer and in consequence shift the transition zone towards the leading edge. The full time evolution of periodic wake induced transition was reproduced from measurements. The numerical simulation of the flow around the blade profile has been performed with the use of the adaptive grid viscous flow unNEWT PUIM solver with a prescribed unsteady intermittency method (PUIM) developed at Cambridge University, UK. The results obtained give evidence that the turbulence transported within the wake is mainly responsible for the transition process. The applied CFD solver was able to reproduce some essential flow features related to the bypass and wake-induced transitions and the simulations reveal good agreement with the experimental results in terms of localisation and extent of wake-induced transition.Copyright

Experimental analysis of internal energy transport in the presence of coherent motion

Abstract The paper presents the internal energy budget in the initial region of the slightly heated free round jet in the presence of column-mode coherent structures. The budget was obtained by the quantitative evaluation of the shares of particular streams of internal energy transported in the flow-field considered. The input data for calculations have been obtained by the hot-wire measurements of three components of instantaneous velocity and instantaneous temperature. All the terms of the internal energy budget have been determined experimentally except the pressure-velocity term which was treated as a closing quantity. The results of the study suggest, that the internal energy of the flow is determined by the mutual balance of convection realized by the mean, oscillatory and random components of motion accompanied by the work of pressure-velocity correlations. It appears furthermore, that the heat transfer in the initial jet area is realized mainly by random fluctuations of proper turbulence motion, generated, however, in substantial part by coherent structures existing in the flow-field considered.

Experimental Analysis of Turbulent Boundary Layer with Adverse Pressure Gradient Corresponding to Turbomachinery Conditions

The paper deals with the experimental analysis of turbulent boundary layer at the flat plate for Reynolds number Re θ ≈3000. The adverse pressure gradient generated by curvature of the upper wall corresponded to the case of pressure distribution in axial compressor. The fully developed turbulence structure was achieved by proper triggering of the boundary layer. The mean and turbulent flow-fields were investigated with the use of hot-wire technique. A substantial effort has been devoted to the precise definition of inlet boundary conditions as well as consistency of measurements obtained with different HWA sensors. The analysis in the paper was concentrated on the problem of scaling of turbulent boundary layer and on the physical background behind scaling laws being compared.

Transition Prediction on Turbine Blade Profile With Intermittency Transport Equation

The paper presents the results of tests and validations of γ-Reθ model proposed by Menter at al [10], which was extended by in-house correlations on onset location and transition length. The tests performed were based on experimental data on the flat plate Test Cases available at ERCOFTAC Data Base as well as on experimental data of turbine blade profile investigated at Czestochowa University of Technology. Further on, the model was applied for unsteady calculations of the blade profile test case, where chosen inlet conditions (turbulent intensity, wake parameters) were applied. For the selected case numerical results were compared not only with the experimental data, but also with the results obtained with other transition models. It was shown that the applied model was able to reproduce some essential flow features related to the bypass and wake-induced transitions and the simulations reveal good agreement with the experimental results in terms of localisation and extent of wake-induced transition.Copyright

Analysis of Development of Vortical Structures in a Turbulent Boundary Layer under Adverse Pressure Gradient Based on VITA Method

The paper concerns experimental investigation of a turbulent boundary layer (TBL) developing on a flat plate under an adverse pressure gradient (APG) for a Re θ ≈ 3000. In particular, the paper deals with the analysis of bursting phenomena in TBL with the use of VITA technique. For interpretation of structure behaviour the shape of conditionally averaged velocity traces recorded by X-wire probe were analysed. It was found that bursting process under the influence of APG is damped near the wall and this phenomenon is emphasized in the outer region of TBL.

Numerical and Experimental Investigations of Momentum and Heat Transfer in Microchannels

The paper presents the results of a research performed during recent years at LEGI Grenoble with joint participation of CzUT researchers. The special attention is devoted to experimental and numerical studies devoted to three cases involving various aspects of microchannel flow physics (range of microchannel sizes corresponds to the classification of Kandlikar [19]). The first aspect is related to hydraulic properties of a network of parallel triangular microchannels, where experimental investigations revealed the rapid increase of pressure drop for Re exceeding value of 10. The second aspect of the research was the influence of surface roughness, which was investigated both experimentally and numerically for periodically and randomly distributed surface elements. The third research case was devoted to the numerical modelling of heat transfer. As a result, experimental and numerical analyses showed that there was no scale effect for the microchannels considered, i.e. the relevance of the classical continuum flow model was confirmed.© 2008 ASME