Wyniki wyszukiwania - BazTech

1

Eﬀect of turbulence model, turbulence length scale and wall roughness on the laminar-turbulence transition and temperature distribution of a convectively cooled C3X turbine vane

Banaś K., Badur J.

Transactions of the Institute of Fluid-Flow Machinery

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2017

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nr 138

13--32

EN

Our paper demonstrates the ability of Favre-averaged Navier–Stokes (FANS) turbulence models to predict the laminar-turbulent transition and shows the inﬂuence of the models on the wall temperature distribution. The investigations were based on conjugate heat transfer analyses of a convectively cooled C3X turbine vane, which were performed using commercial ﬂow simulation software. We compared several eddy-viscosity models: shear stress transport (SST), γ-Reθ SSTtransition, v2-f, k-ε, realizable, k-kl-ω transition, and second-order closure ε-based Reynolds stress model (RSM) with a linear pressure-strain model. The turbulence length scale (TLS) was not measured during the experiment, so its inﬂuence on the location of the transition onset and wall temperature distribution is presented. We also examined the inﬂuence of the roughness of the airfoil wall on the location of turbulence initialization and the wall temperature distribution.

2

Numerical simulation of 3D flow in VKI-Genoa turbine cascade including laminar-turbulent transition

Yerschov S., Derevyanko A., Yakovlev V., Gryzun M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2016

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Vol. 20, No 1

43--61

EN

This study presents a numerical simulation of a 3D viscous flow in the VKI-Genoa cascade taking into account the laminar-turbulent transition. The numerical simulation is performed using the Reynolds-averaged Navier-Stokes equations and the two-equation k-ω SST turbulence model. The algebraic Production Term Modification model is used for modeling the laminar-turbulent transition. Computations of both fully turbulent and transitional flows are carried out. The Mach number contours, the turbulence kinetic energy, the entropy function as well as the limiting streamlines are presented. Our numerical results demonstrate the influence of the laminar-turbulent transition on the secondary flow pattern. The comparison between the present computational results and the existing experimental and numerical data shows that the proposed approach reflects sufficiently the physics of the laminar-turbulent transition in turbine cascades.

3

Analysis of effects of shape and location of micro-turbulators on unsteady shockwave-boundary layer interactions in transonic flow

Sznajder J., Kwiatkowski T.

Journal of KONES

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2016

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Vol. 23, No. 2

373--380

EN

Solutions for turbulisation of a part of laminar boundary layer upstream of shockwave on laminar airfoil in transonic flow were investigated by means of solution of Unsteady Reynolds-Averagd Navier-Stokes equations using as a closure the four-variable Transition SST turbulence model of ANSYS FLUENT solver. This turbulence model has the capability of resolving laminar-turbulent transition occurring in undisturbed flow as well as under the influence of flow-control devices. The aim of the work was to investigate possibilities of improvement of aerodynamic characteristics of laminar wing of a prospective transport aircraft in adverse conditions characterised by occurrence of a shockwave over a laminar-turbulent transition region with separation of laminar flow under the shockwave. The subject is important for application of laminar flow technology, offering economic and environmental advantages due to decreased friction drag, into civil transport aviation. Natural laminar-turbulent transition in the investigated conditions takes place with occurrence of “laminar separation bubble” under the foot of a shockwave and the resulting shockwave is intensive and prone to unsteady oscillations, the “buffet” phenomenon, limiting operational range of flight parameters. In order to counteract the harmful effects of natural laminar-turbulent transition in transonic flow two types of turbulators, placed upstream of the shockwave, were investigated. One of them consisted of delta-shaped vortex generators, producing chordwise-oriented vortices. The other consisted of rectangular micro-vanes, perpendicular to flow and to airfoil surface producing vortices of rotation axes oriented spanwise. Effectiveness of both types of turbulators was investigated for varying height and their location on airfoil chord. Both types of turbulators have proved their effectiveness in tripping laminar boundary layer. The specific effects of the tutbulators, different for each type occurred in the region where laminar separation takes place on clean airfoil. As a result, the changes of lift and drag were different for each type of turbulators.

4

Influence of limiting walls on shock wave structure in single passage test section with compressor profile

Piotrowicz M., Flaszyński P., Szwaba R.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2015

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Vol. 19, No 2

141--152

EN

The shock wave boundary layer interaction on the suction side of a transonic compressor blade is one of the main objectives of the TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to look more closely into the flow structure on the suction side of the blade, a design of a turbine passage model in a rectilinear transonic wind tunnel was proposed. The model which could reproduce the flow structure, the shock wave location, the pressure distribution and the boundary layer development similar to the obtained in a reference cascade profile is the main objective of the design presented here. The design of the proposed test section is very challenging, because of the existence of a shock wave, its interaction with the boundary layer and its influence on the 3-D flow structure in the test section. The paper presents the influence of the test section geometry configuration on the flow structure as an effect of the shock wave boundary layer interaction.

5

Effects of turbulence induced by micro vortex generators on shockwave : boundary layer interactions

Sznajder J., Kwiatkowski T.

Journal of KONES

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2015

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Vol. 22, No. 2

241--248

EN

Interactions between viscous and transonic effects in air flow around a laminar wing were investigated computationally by means of the solution of unsteady Reynolds-averaged Navier-Stokes Equations. The subject is important from the point of view of applications of Natural Laminar Flow technology in modern, economically efficient passenger aircraft. The research was focused on simulations and analyses of influence of turbulence induced by micro vortex generators on intensity of harmful transonic phenomena like strong shock waves and buffet. Two ways of modelling of the effects of turbulators – the micro vortex generators were taken into consideration. The first way consisted in resolving the shape and inclination angle of the generator in the grid over airfoil and setting the non-slip wall boundary condition on the surface of the generator. The second way, taking advantage of the BAY model of vortex generator, was implemented on orthogonal grid without the need of resolving the shape of the vortex generator in the grid. Calibration of the BAY model was aimed at producing similar distribution of vorticity and velocity circulation behind the model of the vortex generator, as obtained for the grid-resolved model of the vortex generator. The calibration procedure resulted, however, in overestimated turbulisation of the boundary layer in the BAY model, compared to the effects of the grid-resolved vortex generator. The flow simulations indicated, however, that turbulisation of boundary layer induced by micro vortex generators can reduce or eliminate the oscillation of strong shock wave and buffet in off-design conditions and that further adjusting of the BAY model is an efficient strategy for modelling the interactions between viscous and transonic effects in air flow around a laminar wing.

6

Numerical Investigations of Taylor-Couette Flow Using DNS/SVV Method

Tuliszka-Sznitko E., Kiełczewski K.

Computational Methods in Science and Technology

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2015

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Vol. 21, No. 4

211--219

EN

In the paper the authors present the results obtained during a numerical investigation (Direct Numerical Simulation/ Spectral Vanishing Viscosity method – DNS/SVV) of a Taylor-Couette flow, i.e. the flow between two concentric disks and two concentric cylinders. The Taylor-Couette flow is one of paradigmatical systems in hydrodynamics, widely used for studying the primary instability, pattern formation, transitional flows and fully turbulent flows. Simultaneously, the flows in rotating cavities appear in numerous machines in the field of mechanics and chemistry, e.g., in cooling systems of gas turbines and axial compressors. In the paper, attention is focused on the laminar-turbulent transition region of the Taylor-Couette flow. The main purpose of the computations is to investigate the influence of different parameters (the aspect ratio, the end-wall boundary conditions, temperature gradient) on the flow structure and on flow characteristics.

7

Stability of supersonic boundary layer on permeable surface

Gaponov S. A., Ermolaev Yu. G., Kosinov A. D., Lysenko V. I., Semionov N. V., Smorodsky B. V.

Archives of Mechanics

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2014

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Vol. 66, nr 6

453--466

EN

In the present study we have performed combined theoretical and experimental investigation of the surface permeability influence on the linear stability of the supersonic flat-plate boundary layer at free-stream Mach number M = 2. Good quantitative agreement was obtained between the data calculated by the linear theory of stability and the data obtained in experiments with artificially generated disturbances performed on models with various porous inserts.

8

Numerical simulation of turbulent heat and momentum transport in rotating cavity

Tuliszka-Sznitko E., Majchrowski W., Kiełczewski K.

Journal of Theoretical and Applied Mechanics

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2011

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Vol. 49 nr 4

1217-1232

EN

The paper gives the results of the Direct Numerical Simulation (DNS) and Large Eddy simulation (LES) which were performed to investigate the 3D transitional non-isothermal flows within a rotor/stator cavity. A Lagrangean version of the dynamic Smagorinsky eddy viscosity model was used. Computations were performed for the cavity of the aspect ratio L=3.0-5.0, curvature parameters Rm=1.8-5.0, for the Reynolds number Re=(1.0-2.5)105 and for defferent Prandtl numbers. The results were obtained for coupled momentum and thermal transport in the rotor/stator cavity flows. The obtained distributions of the turbulent heat flux tensor components, the Reynolds stress tensor components, the turbulent Prandtl numer and other structural parameters coincide with the experimental data (published in the literature).

PL

W atykule przedstawiono wyniki symulacji przepływu (z wymianą ciepła) w obszarze pomiędzy stojanem i wirnikiem oraz dwoma pierścieniami uzyskane z zastosowaniem metod DNS i LES. Badania przeprowadzono dla rozciagłości obszaru L=3.0-5.0 oraz dla współczynnika krzywizny Rm=1.8-5.0. Badano struktury niestabilnościowe występujące w warstwie przyściennej wirnika i stojana oraz profile osiowe naprężeń reynoldsowskich, fluktuacji temperatury, turbulentnej liczby Prandtla, profile parametrów strukturalnych i korelacyjnych. Obliczenia przeprowadzono dla różnych liczb Reynoldsa i Prandtla. Uzyskane rozwiązania porównano z wynikami badań eksperymentalnych Elkinsa i Eatona (2000) uzyskanymi podczas badania przepływu wokół pojedynczego wirującego dysku podgrzewanego jednorodnym strumieniem. Rezultaty badań porównywano również z wynikami uzyskanymi dla dwuwymiarowych turbulentnych warstw przyściennych.

9

LES and DNS of the Flow with Heat Transfer in Rotating Cavity

Tuliszka-Sznitko E., Majchrowski W.

Computational Methods in Science and Technology

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2010

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Vol. 16, No. 1

105-114

EN

In the present paper we summarized our numerical investigations on the flow with heat transfer in rotating cavity performed by DNS (Direct Numerical Simulation) and LES (Large Eddy Simulation). We considered different geometrical configurations and different flow and thermal conditions. All presented computations have been performed in Poznań Supercomputing and Networking Center. The objective of our investigations was to analyze the coherent structures of transitional and turbulent flows and to compute statistical parameters, i.e. turbulent heat fluxes, the Reynolds stress tensor components, the turbulent Prandtl number and others. In the LES we used a version of the dynamic Smagorinsky eddy viscosity model proposed by Meneveau et al. (A Lagrangian dynamic subgrid-scale model of turbulence, J. Fluid Mech., vol. 319, 1996), in which the Smagorinsky coefficient at a given position x depends on the history of the flow along the fluid particle pathline.

10

Influence of the negative and positive jet of wake on laminar-turbulent transition in a boundary layer

Żabski J., Wierciński Z.

Journal of Theoretical and Applied Mechanics

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2009

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Vol. 47 nr 4

797-814

EN

In this paper, the results of experimental investigations relating to the influence of negative and positive jet of the wake on laminar-turbulent transition in the boundary layer on a flat plate are described. Using the technique of phase averaging and wavelet analysis, the investigations were carried out in an aerodynamic tunnel with a low level of turbulence in the external stream. The existence of serious differences was noted between the influence of the negative and positive jets due to strong velocity impulses appearing in the area behind the negative jet in the place of the local minimum of the velocity. However, behind the positive jet such strong disturbances appear later, not directly in the region behind the jet. These impulses do not show any signs of chaos and fortuity, therefore they should be rather classified as determined disorder. Moreover, the region of calm behind the positive jet, well-known in the literature, remains also in the area of entirely disturbed flow.

PL

W pracy przedstawiono badania eksperymentalne dotyczące wpływu ujemnego i dodatniego strumienia śladu spływowego na przejście laminarno-turbulentne w warstwie przyściennej na płaskiej płycie. Badania przeprowadzono w tunelu aerodynamicznym o niskim poziomie turbulencji przepływu zewnętrznego, wykorzystując technikę fazowego uśredniania i analizy falkowej. Stwierdzono istnienie poważnych różnic między oddziaływaniem ujemnego i dodatniego strumienia w postaci silnych impulsów prędkości pojawiających się w obszarze za ujemnym strumieniem w miejscu o lokalnego minimum prędkości. Za dodatnim strumieniem takie silne zaburzenia pojawiają się później i nie bezpośrednio za nim. Ponadto regiony uspokojenia za dodatnim strumieniem, dobrze znane z literatury, są dobrze widoczne także w rejonie całkowicie zaburzonego przepływu.

11

Modelling of Influence of Turbulent Transition on Heat Transfer Conditions

Bochon K., Wróblewski W., Dykas S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2008

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Vol. 12, No 3-4

173-184

EN

This article deals with the turbulent transition phenomenon modelling and its influence on heat transfer. The purpose of the analyses was to verify the transition modelling implemented in the ANSYS CFX 11 commercial code for popular test cases (low flow speed) described in literature, and then use it for verification of the in-house CFD code (created for compressible flows). The inhouse CFD code has been extended lately for the Conjugate Heat Transfer modelling (CHT) as well, taking into account important flow effects, especially the turbulent transition. A Wilcox k-omega turbulence model with the Low-Reynolds modification was used in the in-house code. The calculations in ANSYS CFX were made using an SST turbulence model and a gamma-theta transition model. A fully turbulent flow was modelled by means of both codes, and the results were compared with the available experimental data. Then, the turbulent transition for several test cases was analysed with ANSYS CFX. Afterwards, the in-house CFD code was verified by means of ANSYS CFX for a higher flow speed (Mach numbers). The CHT modelling was analysed by means of both codes and the results were compared and discussed. The conducted analyses show that the results obtained by means of both codes are comparable, but the turbulence model used in the in-house CFD code is simpler and requires less computation time. A modification of two equations turbulence models can be an alternative for design problems in more developed laminar/turbulent flows.

12

Instability of the flow in rotating cavity

Tuliszka-Sznitko E., Zieliński A.

Journal of Theoretical and Applied Mechanics

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2007

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Vol. 45 nr 3

685-704

EN

The transitional flow in rotating cavity is investigated numerically by Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and theoretical (LSA) methods. LSA results coupled with accurate numerical DNS and LES computations based on an efficient pseudo-spectral Chebyshev-Fourier method, brings new insight into the spatio-temporal characteristics of the isothermal and not- isothermal flows in the rotating cavities. DNS and LES computations have been performed for a wid e range of Reynolds numbers to analyze different stages of the transition process. Computations have been performed for different geometrical configurations, including co- and counter-rotating cavities with throughflow.

PL

W pracy dokonano analizy wyników dotychczasowych prac własnych nad statecznością przepływów w wirujących przestrzeniach. Badania te prowadzono metodą liniową, metodą DNS i LES. Do trójwymiarowych obliczeń numerycznych zastosowano metodę spektralnej kolokacji bazującą na szeregach Czebyszewa i szeregu Fouriera. Do metody LES zastosowano metodę Lagrangea zaproponowaną przez Meneveau. Głównym celem było zbadanie struktur niestabilnościowych występujących w wirujących przestrzeniach. Wyniki te porównano z wynikami prac eksperymentalnych innych autorów. Badano wpływ termicznej liczby Rossbiego na rozkłady liczb Nusselta wzdłuż promienia tarcz oraz efektywność chłodzenia promieniowego tarcz za pomocą napływającego chłodnego czynnika.

13

Numerical investigation of transitional flow in co- and counter-rotating annular cavity

Tuliszka-Sznitko E., Zieliński A.

Journal of Theoretical and Applied Mechanics

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2006

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Vol. 44 nr 2

405-420

EN

A 3D direct numerical simulation is performed to study the transitional flow in co- and counter-rotating annular cavity of the aspect ratio 5. The identification and characterization of mechanisms related to the laminar-turbulent process in rotating cavities should improve the prediction methods and lead to new, more effective boundary layer control strategies. Numerical computations are based on the pseudo-spectral Chebyshev-Fourier method for solving the incompressible Navier-Stokes equation. The numerical computations allow one to describe the steady axisymmetric basic state and 3D instability structures which appear in the transitional flow. The DNS computations are interpreted in the light of our LSA results. Moreover, the absolute instability regions are theoretically identified and the critical Reynolds numbers of the convective/absolute transition in both layers are given.

PL

W pracy badany jest metodą bezpośrednią przepływ nieściśliwy w przestrzeni pomiędzy dwoma wirującymi tarczami i dwoma wirującymi pierścieniami. Do obliczeń numerycznych zastosowano metodę spektralnej kolokacji bazującą na szeregach Czebyszewa i szeregu Fouriera. Obliczenia przeprowadzono dla współczynnika rozciągłości obszaru L = 5 i współczynnika krzywizny Rm = 1.5 i 3.0. Badania wykazały olbrzymią złożoność badanego przepływu i różnorodność struktur niestabilnościowych występujących w obszarze przejścia laminarno-turbulentnego. Badania bezpośrednie (DNS) uzupełnione zostały badaniami teoretycznymi (LSA), które umożliwiły między innymi wyznaczenia w przestrzeni pomiędzy wirującymi tarczami obszarów o niestabilności absolutnej .

14

Instability of the flow in rotating annular cavity of aspect ratio 9

Tuliszka-Sznitko E., Zieliński A.

Turbulence : international journal

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2005

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Vol. 11

213-220

EN

The 3D direct numerical simulation is performed to study the isothermal and non-isothermal flow in the rotating disks annular cavity of aspect ratio 9. Identification and characterization of mechanisms, related to the laminar-turbulent process in rotating cavities, should improve the prediction methods and lead to new, more effective boundary layer control strategies. Numerical computations are based on a pseudo-spectral Chebyshev-Fourier method for solving the governing equations. The numerical computations allowed us to describe the steady axisymmetric basic state and 3D instability structures which appear in the transitional flow. The preliminary results obtained for the not-isothermal flow arc presented.

15

Numerical investigation of instability of an annular rotating cavity

Tuliszka-Sznitko E., Zieliński A., Polus J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 1

5-15

EN

A direct two-dimensional numerical simulation has been performed to study the transition flow in an annual rotating cavity. The spectral collocation method based on the Chebyshev polynomial is used to solve the incompressible Navier-Stokes equation. The time scheme is semi-implicit and second-order accurate; it corresponds to a combination of the second-order backward differentiation formula for the viscous diffusion term and the Adams-Bashforth scheme for the non-linear terms. The method uses a projection scheme to maintain the incompressibility constrain. The numerical computations, performed for an annular cavity of the aspect ratio L=2 and 5 and for the curvature parameters Rm=(R1+R0)/(R1-R0)=5, exhibit instability structures in the form of circular rolls. These structures are in good agreement with the other investigations, both experimental and theoretical.

16

Application of artificial neural networks (ANN) as multiple degradation classifiers in thermal and flow diagnostics

Głuch J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 2

199-210

EN

Application of a neural network of the classifier type for diagnostic purposes is presented. The described ANN solves the task of recognizing causes of degradation of power units' thermal cycle components. Verification of the applied ANN responses is based on the presented research in the numerical simulation of selected power installations. The obtained results stand for a diagnosis worked out under condition of power cycle proper measurements. Considerably good obtained results prove that the ANN technique can be applied as an automatic detector of operational faults. Thus an ANN can serve as a support tool for operational decisions. The present work also offers a way of reducing training time.

17

Numerical investigations of the nature of the first bifurcation for the flow in an annular rotor/stator cavity

Tuliszka-Sznitko E., Zieliński A.

Journal of Theoretical and Applied Mechanics

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2005

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Vol. 43 nr 1

135--155

EN

Direct numerical simulation is performed to study a transitional flow in an annual rotating cavity of different aspect ratios L = 4.0, 5.0 and different curvature parameters Rm = (R1+ R0)/(R1-R0) = 1.5 - 6.0.This paper reports on the influence of the curvature parameter Rm and end-wall boundary layers on the nature of the first bifurcation to unsteadiness and on instability structures in the rotor and stator boundary layers. For all considered end-wall boundary conditions, we have observed cleary supercritical transition to unsteadiness for larger Rm and direct transition from a steady flow to chaotic one for small Rm. A spectral collocation method based on the Chebyshev polynomial is used for solving the incompressible Navier-Stokes equations. The time scheme is semi-implicit and second-order accurate; it corresponds to a combination of the second-order backward differentiation formula for the viscous diffusion terms and the Adams-Bashforth scheme for the non-linear terms. The method uses a projection scheme to maintain the incompressibility contraint.

PL

W pracy badana jest stabilność przepływu w wirującej, pierścieniowej przestrzeni pomiędzy wirnikiem i stojanem metodą bezpośrednią. Zagadnienie przepływu w przestrzeniach pomiędzy tarczami wirującymi w różnych konfiguracjach jest istotne nie tylko ze względów poznawczych, ale również aplikacyjnych. Tego typu przepływy występują pomiędzy tarczami silników turbogazowych i sprężarek osiowych. Zagadnienie może zainteresować w szczególności inżynierów zajmujących się chłodzeniem tarcz silników turbogazowych. Z punktu widzenia teoretycznego jest bardzo interesujące poznanie szeregu kolejnych bifurkacji prowadzących w wirujących przestrzeniach od przepływu laminarnego do turbulentnego. Analizowany jest wpływ bezwymiarowych parametrów geometrycznych przestrzeni, tj. współczynnika rozciągłości obszaru L, parametru krzywizny Rm, jak i wpływ warunków brzegowych stawianych na pierścieniach ograniczających przestrzeń na charakter pierwszej bifurkacji. Badane są struktury niestabilnościowe występujące w warstwach przyściennych wirnika i stojana. Do badań zastosowano metodę spektralnej kolokacji bazującą na szeregach Czebyszewa. Zastosowany schemat po czasie jest kombinacją schematu wstecznego o dokładności drugiego rzędu i schematu Adamsa-Bashfortha.

18

Transient laminar-turbulent transition of thermal boundary layer after the change of incidence angle

Wierciński Z., Kaiser M.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 114

237-252

EN

Convective heat transfer problems occur in many technical application. Unsteady transition in the heated boundary layer is one of them. Heat transfer investigation of a flat plate in a low subsonic wind tunnel for flow velocity Uo=15 and 20 m/s was performed. The changes in time of the Stanton number distribution along the plate were observed after the incidence angle had been changed from - 0.8 to 0°. While for the incidence angle i= -0.8° the flow in boundary layer was laminar, for angle -0.67#176 the transition was observed, and for the angle -0.23° the flow was turbulent. After the sudden change of angle the transient bahaviour of the heat transfer between these three states were observed, e.g. for the change from -0.8 to -0.6° from laminar to transitional, so after the time of about 30 min the transition was perfect. This time is needed to achieve a new internal thermal balance of the plate and transition in thermal boundary is established.

19

Modeling of flow with periodic wakes

Wierciński Z., Epik Ya. T. E., Suprun T. T.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 114

267-276

EN

The flow through blade channels in turbomachinery is unsteady due to wakes from the blade rings placed upstream. The squirrel cage is one of the most spread generators for modeling the unsteady flow with wakes. By means of this kind of wake generator it is possible to investigate the influence of wakes on the development of boundary layer in the presence of transition under conditions typical for turbomachines. The aim of this paper is to compare the features of the external flow behind the squirrel cage generators and structure of boundary layers on the flat plates in installations used at IFFM, Gdańsk, and IET, kiev.

20

Absolute instability in the compressible flow around a rotating cone

Tuliszka-Sznitko E.

Journal of Theoretical and Applied Mechanics

|

1999

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nr 1

29-46

EN

In the present paper the character of instability of compressible viscous flow around geometries rotating in the uniform flow is analyzed. The linear local stability theory is used to investigate the boundary layer stability. Following the works of Briggs and Bers in the field of plasma physics, the absolute instability region is identified by the singularities of dispersion relation called pinch-points. The regions of absolute instability in boundary layers of a rotating cone have been found. Calculations have been made for different Mach numbers, wall temperatures and rotational speeds of the cone.

PL

W pracy badany jest charakter niestabilności przepływu wokół wirującego stożka. Do badania charakteru przepływu zastosowano kryterium fizyków plazmy Briggsa i Bersa, zgodnie z którym o charakterze niestabilności decydują osobliwości funkcji dyspersji zwane punktami styku. Obliczenia przeprowadzono stosując liniową teorię niestabilności. W pracy stwierdzono występowanie obszarów o niestabilności absolutnej w przepływie wokół wirującego stożka. Obliczenia zostały wykonane dla różnych liczb Macha i różnych temperatur ścianki. Wyznaczono krzywe neutralne ograniczające obszar przepływu o niestabilności abolutnej. Stwierdzono, że współczynnik wzmocnienia absolutnego maleje wraz z rosnącą liczbą Macha, jak również malejące pod wpływem chłodzenia ścianki. Nie stwierdzono występowania niestabilności absolutnej w przepływach naddźwiękowych.