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PASSIVE CONTROL OF BOUNDARY LAYER TRANSITION AND SEPARATION
Popelka, Lukáš ; Matějka, M. ; Šimurda, David ; Součková, Natálie
Particle Image Velocimetry, smoke-wire, tuft filaments and oil-flow visualization techniques were used for wind-tunnel and in-flight investigation of boundary layer separation, both stall and separation bubbles, related to the low-Reynolds number transition mechanism. Airfoils of three Czech-designed sailplanes and their wing-fuselage interaction were subject to study. Experimental data were coupled with numerical modeling and synthesis gained. Effect of passive flow control devices - vortex generators - was surveyed, counter-rotating vortex generators and Zig-zag type turbulators were applied. Separation suppression was reached and consequent drag coefficient reduction of test aircrafts measured in flight. Investigation was further extended by PIV Time-Resolved technique.
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SPATIO-TEMPORAL ANALYSIS OF SWIRLING JET UNSTEADY BREAKDOWN
Uruba, Václav ; Oberleithner, K. ; Sieber, M. ; Hladík, Ondřej
The swirling jet breakdown unsteady process has been examined experimentally using stereo PIV time resolved method. The experimental setup has been designed, build and prepared in HFI. It generates helical swirling jet and allows implementation of the jet breakdown. The Bi-Orthogonal Decomposition (BOD) method has been chosen for the data analysis the Proper Orthogonal Decomposition applied both in space and time. the BOD method offers decomposition into energetic modes in space (toposes) and in time (chronoses).
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Application of the algebraic bypass-transition model for internal and external flows
Straka, P. ; Příhoda, Jaromír
A modified algebraic model of bypass transition was implemented into the in-house numerical code for the simulation of 2D compressible turbulent flow using the RANS equations and the k-omega turbulence model. The intemittent character of flow in the transition region is described by the algebraic relation for the intermittency coefficient and by empirical relations for the onset and the length of the transition region. The modified algebraic model considers different intermittency coefficient in the boundary layer and in the outer turbulent stream. The proposed model was verified by means of test cases ERCOFTAC covering boundary-layer flow with various free-stream turbulence and pressure gradient. Further, the model was applied for the simulation of the transitional flow through a turbine blade cascade and around the NACA 0012 aerofoil.
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Transition modelling in blade cascades
Straka, P. ; Příhoda, Jaromír
A modified algebraic model of the laminar/turbulent bypass transition was implemented into the in-house numerical code for the simulation of 2D compressible turbulent flow using the RANS equations closed by the two-equation k-omega TNT turbulence model. The model was verified by the ERCOFTAC test cases for various boundary-layer flows and applied for the simulation of the transitional flow in turbine blade cascades.
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Modification of an algebraic bypass-transition model for internal flows
Straka, P. ; Příhoda, Jaromír
The contribution deals with testing of an algebraic bypass-transition model for shear flows characteristic for turbomachinery. The transition model based on the algebraic equation for the intermittency coefficient is added to the averaged Navier-Stokes equations with the SST turbulence model. The transition onset and length are given by empirical relations. The modified model considers different intermittency coefficient in the transitional boundary layer and in the outer turbulent stream. The model was verified by means of test cases ERCOFTAC covering boundary-layer flow with various free-stream turbulence and pressure gradient.
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