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Václav Uruba - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of turbulent flow in a channel with the backward-facing inclined step
EPJ Web of Conferences, 2012Co-Authors: Jaromír Příhoda, Václav Uruba, Michal Kotek, Václav Kopecký, Ondřej HladíkAbstract: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 H mm 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 Reynolds number was obtained for various step angles. 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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Stability and Dynamics of Flow in a Turbulent Boundary Layer Separation Region
Springer Proceedings in Physics, 2012Co-Authors: Václav UrubaAbstract:Separation of a turbulent boundary layer on a flat plate under adverse pressure gradient was studied experimentally using Time-Resolved PIV technique. The results of spatio-temporal analysis of the flow-field in the Separation zone are presented. For this purpose, the Proper Orthogonal Decomposition method is used to perform the dynamical system reduction which is then analyzed using Principal Oscillation Patterns method. The study contributes to understanding mechanisms of a boundary layer Separation process. The acquired information could be used to improve strategies of a boundary layer Separation control.
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Separation bubbles dynamics in turbulent boundary layer Separation Region
2010Co-Authors: Vladislav Janecek, Václav UrubaAbstract:Dynamical behavior of a turbulent boundary layer Separation is analyzed from experimental data acquired using Time-Resolved Particle Image Velocimetry method. Special attention is paid to occurrence and behavior of Separation bubbles. The analysis of those structures is carried out with respect to both space and time features.
V. M. Molochnikov - One of the best experts on this subject based on the ideXlab platform.
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Turbulent flow Separation and characteristics of heat transfer under unsteady hydrodynamic conditions
Thermal Engineering, 2011Co-Authors: I. A. Davletshin, Nikolay I. Mikheev, O. A. Dushina, F. S. Zan’ko, V. M. MolochnikovAbstract:Results from an experimental study of hydrodynamics and heat transfer in turbulent Separation flow under the conditions of its periodic pulsations are presented. It is found that an essential change occurs in the spatial and timing structure of Separation flow under the effect of superimposed unsteadiness. Phenomena involving reduction of the longitudinal dimensions of the Separation Region and essential enhancement of heat transfer in the Separation Region of pulsating flow are revealed. The physical mechanism of these phenomena is described.
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Heat transfer in a turbulent Separation Region with superimposed stream pulsations
Thermophysics and Aeromechanics, 2008Co-Authors: I. A. Davletshin, Nikolay I. Mikheev, V. M. MolochnikovAbstract:Experimental data on heat transfer in turbulent Separation Region behind obstacle in a broad frequency range of superimposed free-stream pulsations are reported. The heat-transfer coefficient was determined by solving an inverse non-stationary heat conduction problem based on experimentally measured wall transient temperature. Substantial heat-transfer intensification in the Separation Region of the pulsating flow was identified.
I. A. Davletshin - One of the best experts on this subject based on the ideXlab platform.
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Heat transfer in turbulent Separation Region of pulsating flow behind a backward-facing step
Thermophysics and Aeromechanics, 2019Co-Authors: I. A. Davletshin, Nikolay I. Mikheev, A. K. Aslaev, A. A. PaereliyAbstract:Heat transfer in a pulsating air flow was studied experimentally in the Separation Region behind a backward-facing step. The data on distributions of heat transfer coefficient have been obtained. At the distance of more than ten step heights away from the step edge, the heat transfer coefficient in pulsating flow deviated by no more than ±10 % from the steady flow values. Towards the step, heat transfer became more intensive relative to the steady regimes. Immediately beyond the Separation edge, flow pulsations led to local twofold enhancement of heat transfer and even higher. In general, heat transfer augmentation in the Separation Region behind the step reached a maximum (70 %) at the Strouhal number Sh ~ 1.
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Turbulent flow Separation and characteristics of heat transfer under unsteady hydrodynamic conditions
Thermal Engineering, 2011Co-Authors: I. A. Davletshin, Nikolay I. Mikheev, O. A. Dushina, F. S. Zan’ko, V. M. MolochnikovAbstract:Results from an experimental study of hydrodynamics and heat transfer in turbulent Separation flow under the conditions of its periodic pulsations are presented. It is found that an essential change occurs in the spatial and timing structure of Separation flow under the effect of superimposed unsteadiness. Phenomena involving reduction of the longitudinal dimensions of the Separation Region and essential enhancement of heat transfer in the Separation Region of pulsating flow are revealed. The physical mechanism of these phenomena is described.
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Heat transfer in a turbulent Separation Region with superimposed stream pulsations
Thermophysics and Aeromechanics, 2008Co-Authors: I. A. Davletshin, Nikolay I. Mikheev, V. M. MolochnikovAbstract:Experimental data on heat transfer in turbulent Separation Region behind obstacle in a broad frequency range of superimposed free-stream pulsations are reported. The heat-transfer coefficient was determined by solving an inverse non-stationary heat conduction problem based on experimentally measured wall transient temperature. Substantial heat-transfer intensification in the Separation Region of the pulsating flow was identified.
Viktor I. Terekhov - One of the best experts on this subject based on the ideXlab platform.
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Influence of the PreSeparation Flow Structure on the Characteristics of the Separation Region Behind a Backward-Facing Step
Journal of Engineering Physics and Thermophysics, 2018Co-Authors: V. L. Zhdanov, D. A. Ivanov, Ya. I. Smul’skii, Viktor I. TerekhovAbstract:This paper presents the results of investigations of the influence of the separated flow structure behind a rib located before the edge of the backward-facing step on the parameters of the Separation Region behind it. Numerical investigations were carried out by the method of large eddy similution in a plane air channel. The velocity of the developed turbulent flow at the inlet to the channel was assumed to be 25 m/s with a level of initial turbulence for three velocity components of 5%. The Reynolds number calculated by the initial velocity and the step height was 15,500. It has been shown that the creation of a preSeparation Region causes the two-dimensional flow to transform into a three-dimensional one before the edge of the back-facing step with the formation of nonuniform verticity along its length. This restructuring of the flow leads to an increase in the inhomogeneity of velocity parameters in the separated mixing layer. The flow expansion behind the step increased and was accompanied by local Separation on the upper wall of the channel. The two Separation Regions caused a rapid growth of pulsations throughout the channel behind the step.
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RANS and LES analysis of a Separation Region in front of a backward-facing step
Journal of Physics: Conference Series, 2018Co-Authors: T A Baranova, V. L. Zhdanov, D. A. Ivanov, Ja I Smulsky, Viktor I. TerekhovAbstract:Turbulent characteristics of a reattached flow separated from a rib ahead of a backward-facing step in a flat air channel were numerically analyzed by RANS and LES methods. The Separation Region ended just before the step edge. The both methods showed low pressure Regions in corners, formed by the rib and the channel walls that caused a vorticity tube forming along the rib. Nevertheless in RANS, a separated flow was identified as two-dimensional with a thicker shear layer at the step edge. In LES, the low pressure Regions caused both redistributions between velocity components, Reynolds stresses, and a thicker shear layer at the step edge. The flow structure behind the rib has been, thus, identified as three-dimensional.
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Effect of surface permeability on the structure of a separated turbulent flow and heat transfer behind a backward-facing step
Journal of Applied Mechanics and Technical Physics, 2017Co-Authors: V. V. Terekhov, Viktor I. TerekhovAbstract:The structure and heat transfer in a turbulent separated flow in a suddenly expanding channel with injection (suction) through a porous wall are numerically simulated with the use of two-dimensional averaged Navier–Stokes equations, energy equations, and v 2–f turbulence model. It is shown that enhancement of the intensity of the transverse mass flux on the wall reduces the Separation Region length in the case of suction and increases the Separation Region length in the case of injection up to complete boundary layer displacement. The maximum heat transfer coefficient as a function of permeability is accurately described by the asymptotic theory of a turbulent boundary layer.
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Effect of Dynamic Prehistory on Aerodynamics of a Laminar Separated Flow in a Channel Behind a Rectangular Backward‐Facing Step
Journal of Applied Mechanics and Technical Physics, 2002Co-Authors: S. R. Batenko, Viktor I. TerekhovAbstract:The effect of dynamic prehistory of the flow and the channel‐expansion ratio on aerodynamics of a steady separated laminar flow behind a rectangular backward‐facing step located in a plane‐parallel channel is numerically studied. It is shown that the boundary layer upstream of the flow Separation exerts a strong effect on flow characteristics behind the step. A decrease in the boundary‐layer thickness in the cross section of the step leads to a decrease in the Separation‐Region length, and an increase in the channel‐expansion ratio with a fixed initial boundary‐layer thickness and Reynolds number leads to an increase in the Separation‐Region length.
Willert Christian - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of shock-induced Separation and flow control in a transonic compressor cascade
'Springer Science and Business Media LLC', 2019Co-Authors: Klinner Joachim, Hergt Alexander, Grund Sebastian, Willert ChristianAbstract:The influence of transition control on shock-induced flow Separation was investigated in a highly loaded transonic compressor cascade at an inlet Mach number of 1.21 and a chord based Reynolds number of 1.4×10^6. Transition was influenced by raising the free-stream turbulence from 0.5% to 2.5%. Two further cases employed either air jet vortex generators (AJVG) or a surface roughness patch as transition control devices. Velocity fields in the vicinity of the unsteady transonic Separation were captured by particle image velocimetry (PIV). Blade flexure induced by the unsteady aerodynamic loading was tracked for each image and compensated individually prior to PIV processing. The captured flow fields indicate shape variations of the Separation Region while the shock foot moves within a range of up to 20% of chord. The frequency of Separation for each investigated case was assessed on the number of vectors with negative velocity in each PIV sample. To further quantify the size of the Separation Region, the statistically independent PIV samples were conditionally averaged for various passage shock positions at a resolution of 1% chord length. Insight to the dynamics and frequency of the passage shock motion was further provided by high-speed shadowgraphy. Large bubble Separation occurs if the turbulence of the incoming flow is low. The size of Separation Region decreases when AJVGs are applied but still exhibits bubble Separation as the passage shock moves downstream. The size of the Separation Region is significantly reduced either if a roughness patch is applied or if the turbulence level of the incoming flow is high. The flow conditions showing bubble Separation in the mean flow also exhibit distinct spectral peaks indicating periodic shock oscillations
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Investigation of shock-induced flow Separation over a transonic compressor blade by conditionally averaged PIV and high-speed shadowgraphs
2018Co-Authors: Klinner Joachim, Hergt Alexander, Grund Sebastian, Willert ChristianAbstract:The impact of Separation control has been investigated in a highly loaded transonic compressor cascade at an inlet Mach number of 1.21 and a chord based Reynolds number of 1.4 × 106. Applied control devices are air jet vortex generators (AJVG) and a surface roughness patch. Comparative flows without transition control imply a variation of the upstream turbulence level from 0.5% to 2.5%. Above the suction side, velocities of the unsteady Separation Region have been captured by particle image velocimetry (PIV). The aerodynamic load alternation due to shock motion results in flexure of the blade surface which has been measured and compensated prior to PIV processing. Single PIV shots indicate shape variations of both the lambda shock system and the associated Separation Region while the shock foot position is fluctuating within a range of up to 23% of chord. Large sets of statistically independent PIV samples are conditionally averaged upon instantaneous passage shock positions at a resolution of 1% of chord length to quantify the size of flow Separation. Large bubble Separation occurs if the turbulence of the incoming flow is low. The Separation Region becomes smaller when AJVGs are applied but still exhibits bubble Separation at rear shock positions. The size of the Separation Region is significantly reduced either if a roughness patch is applied or if the turbulence level of the incoming flow is high. The frequency range of shock motion is analyzed by shock tracking on the basis of high speed shadowgraphs. A Fourier analysis of shock motion in the low frequency range (
