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Preliminary experimental investigation of boundary layer in decelerating flow
Hladík, Ondřej ; Jonáš, Pavel ; Příhoda, Jaromír
Investigations of characteristics of turbulence inside boundary layer under decelerating flow were studied by means of constant temperature anemometer. The decelerating flow was simulated in the closed circuit wind tunnel 0.9 m × 0.5 m at IT AS CR. The free stream turbulence was either natural or risen up by square mesh plane grid. The details of experimental settings and measurement procedures of the instantaneous longitudinal velocity component are described and the distributions of intensity, skewness and kurtosis of turbulent fluctuations are discussed in the contribution.
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Experimental investigation of turbulent flow in a channel with the backward-facing inclined step
Příhoda, Jaromír ; Kotek, M. ; Uruba, Václav ; Kopecký, V. ; Hladík, Ondřej
The work deals with the experimental investigation of turbulent flow in a closed channel with the backward-facing inclined step. Experiments were carried by means of the PIV optical measuring method in the channel of the rectangular cross-section in the inlet part and with inclined steps of the constant height and various inclination angles for a wide range of the Reynolds number. The attention was paid especially to the separation region behind the step and to the relaxation of the shear layer after the reattachment in the outlet part of the channel. The dependence of the length of the separation region on the inclination step angle. Optical measurements were completed by the measurement of static pressure distribution in the inlet and outlet part of the channel to estimate energy losses.
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Numerické modelování přechodu do turbulence v odtržené mezní vrstvě na profilu
Ďuriš, M. ; Příhoda, Jaromír ; Maršík, František
Práce se zabývá numerickým modelováním přechodu do turbulence v odtržené mezní vrstvě při dvourozměrném proudění stlačitelné tekutiny. Výpočet je založen na řešení středovaných Navier-Stokesových rovnic uzavřených k-omega modelem turbulence a algebraickým modelem zkráceného přechodu. Výpočet je proveden komerčním softwarem ANSYS FLUENT 6.3.26 doplněným funkcemi definovanými uživatelem. Navržený model je porovnán s experimentálními výsledky, získanými pro obtékání leteckých profilů NACA 63A421 a XIS40MOD při různých úhlech náběhu
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Modelling of supercritical turbulent flow over an inclined backward-facing step in a open channel
Příhoda, Jaromír ; Zubík, P. ; Šulc, J. ; Sedlář, M.
The contribution deals with the experimental and numerical modelling of supercritical turbulent flow in an open channel with an inclined backward-facing step on its bottom. The step with the height 100 mm and the inclination angle 20 deg was placed in the water channel of the cross-section 200x200 mm. Experiments were carried out by means of the PIV and LDA measuring techniques. Numerical simulations were executed by the commercial software ANSYS CFX 12.0. Numerical results obtained by the two-equation SST model and the EARSM model completed by transport equations for turbulent energy and specific dissipation rate were compared with experimental data. The modelling was concentrated particularly on the flow pattern near the step including the possible flow separation and the corresponding changes of free surface. The agreement of numerical results obtained by means of the EARSM model with experimental data is quite good.
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Numerical and experimental modelling of transition in a separated boundary layer on the NACA63A421 airfoil
Ďuriš, M. ; Popelka, Lukáš ; Příhoda, Jaromír ; Šimurda, David
The paper is concerned with numerical modelling of transition in a separated boundary layer. A transition model is based on the combination of empirical terms determining position of the transition and averaged Navier–Stokes equations closed by SST turbulence model. The model of transition is applied in computation of 2D flow past NACA63A421 airfoil. Computation is performed using commercial code Fluent 6.3.26, in which the transition model is implemented as a User-Defined-Function. Computed distributions of the pressure coefficient along the airfoil are verified by comparison with experimental data, which were obtained by measurements in a closed circuit wind tunnel at the constant Reynolds number and several angles of attack. The comparison proves the applicability of the implemented transition model.
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An influence of amplitude modulation of the synthetic jet to the flow
Matějka, M. ; Popelka, Lukáš
The paper deals with an experimental research of an active boundary layer control achieved by using periodic excitation of a synthetic jet. An influence of amplitude modulation of the synthetic jet flow control to the flow field of the wake was studied. It summarizes the influence of the basic factors that affect the design of the synthetic jet actuator. The principle of a flow control with and without amplitude modulation was used. Flow visualization of the flow field was done.
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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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Experimentální a numerické modelování proudění kapaliny s odtržením
Zubík, P. ; Šulc, J. ; Příhoda, Jaromír ; Sedlář, M.
Příspěvek se zabývá experimentálním a numerickým modelováním tlakového, podkritického a nadkritického turbulentního proudění s rozsáhlým odtržením vlivem náhlého rozšíření průřezu (obtékání šikmého schodu). Experimenty byly provedeny ve vodním kanálu s průřezem 200x200 mm pomocí PIV a LDA měřicí techniky. Pro numerickou simulaci byla použita VOF metoda a komerční sotfware ANSYS CFX-12.0. Numerické výsledky byly porovnány s experimentálními daty.
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Visualization of Flow Separation and Control by Vortex Generators on an Single Flap in Landing Configuration
Součková, Natálie ; Kuklová, J. ; Popelka, Lukáš ; Matějka, Milan
This paper focuses on a suppression of the flow separation, which occurs on a deflected flap, by means of vortex generators (VG's). An airfoil NACA 63A421 with a simple flap and vane-type vortex generators were used. The investigation was carried out by using experimental and numerical methods. The data from the numerical simulation of the flapped airfoil without VG's control were used for the vortex generator design. Two sizes, two different shapes and various spacing of the vortex generators were tested. The flow past the airfoil was visualized through three methods, namely tuft filaments technique, oil and thermo camera visualization. The experiments were performed in closed circuit wind tunnels with closed and open test sections. The lift curves for both cases without and with vortex generators were acquired for a lift coefficient improvement determination. The improvement was achieved for several cases by means all of the applied methods.
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Infrared Thermography as a Visualization Tool of Flow Control by Vortex Generators
Součková, Natálie ; Kuklová, J. ; Popelka, Lukáš ; Matějka, M.
This paper focuses on a suppression of the flow separation, which occurs on a deflected flap, by means of vortex generators (VG's). An airfoil NACA 63A421 with a simple flap and vane-type vortex generators were used. The investigation was carried out by using experimental and numerical methods. The data from the numerical simulation of the flapped airfoil without VG's control were used for the vortex generator design. Two sizes, two different shapes and various spacing of the vortex generators were tested. The flow past the airfoil was visualized through two methods, namely oil and infrared thermography visualization. The lift curves for both cases without and with vortex generators were acquired for a lift coefficient improvement determination. . The experiments were performed in closed circuit wind tunnels with open and close test sections. The improvement was achieved for several cases by means all of the applied methods.
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