Search

The Particle Image Velocimetry was used to investigate the coherent structures behind a cylinder under moderate Reynolds number. Dynamical decomposition method was used to detect flow patterns having similar frequency as the vortex shedding frequency which is given by Strouhal number. The flow field has two-dimensional nature only for time-averaged flow. The instantaneous snapshots are fully 3-D. The wake is full of spanwise as well as streamwise oriented vortical structures causing periodical changing in the pressure field.

The blown down wind tunnel tube has been developed. It provides a high degree of air flow laminarization. The uniqueness of this design is the presence of a system of air vortices destruction. This system contains a complex of metal grids, honeycomb straightener and contraction nozzle. The combination of these elements allows for low turbulence level and promote the air flow relative to its axis. The complex of measuring equipment for the establishment of operational characteristics in the test section has been performed. A four-channel probe has been developed to analyze the total pressure and air flow velocity in the measuring tunnel area. The design of this probe makes possible to analyze the boundary layers of air flow in a wind tunnel. The corrective algorithm of recombination for the obtained data and software for their analysis is developed. A prerequisite for developing an algorithm for the recombination of the obtained data and their subsequent visualization is the idea of sectoral analysis and averaging of the data of common areas of the measuring area. Besides the developed algorithm, the correction function for leveling the aerodynamic resistance of the design of the four-channel probe was included. Whereas it approaches the nozzle of static pressure, there is a distortion of the real data distribution on each of the probe tube. To confirm the adequacy of the developed algorithm and the correct functioning of the software developed on its basis, a series of experimental studies was conducted, which were based on the measurement of total pressure when placing objects that create aerodynamic resistance in the measuring section. A profile analysis of the data allowed to visualize correctly the distribution of total pressure around the investigated bodies, even in the place of its sharp difference.

Reynolds number is the basic parameter determining the flow-field topology and its evolution in time unambiguously if only inertial, pressure and viscous effects are involved. However the Reynolds number definition is not unique and its physical meaning depends strongly on its actual definition. In the paper Reynolds number definition is given. Then, its role in typical situations in fluid dynamics is to be explained. The laminar flow, transition from laminar state to turbulence and fully turbulent flow are to be taken into account respectively. The physical meaning of Reynolds number vary accordingly. In conclusion the final statement is adopted, that the Reynolds number should be understood as a measure of convective and viscous effects in terms of length-, time- and/or velocity-scales presented in a given flow-field as a result of competing convection and diffusion effects.Reynolds number is the basic parameter determining the flow-field topology and its evolution in time unambiguously if only inertial, pressure and viscous effects are involved. However the Reynolds number definition is not unique and its physical meaning depends strongly on its actual definition. In the paper Reynolds number definition is given. Then, its role in typical situations in fluid dynamics is to be explained. The laminar flow, transition from laminar state to turbulence and fully turbulent flow are to be taken into account respectively. The physical meaning of Reynolds number vary accordingly. In conclusion the final statement is adopted, that the Reynolds number should be understood as a measure of convective and viscous effects in terms of length-, time- and/or velocity-scales presented in a given flow-field as a result of competing convection and diffusion effects.

We report observation of secondary flow in one corner of developing channel air flow. Length of the channel, i.e. length of boundary layer, is 400?mm, which is 3.2 times the channel cross-sectional size. Three components of velocity are measured by using a Stereo Particle Image Velocimetry (PIV) technique in the measurement area of size 24×22?mm, which is perpendicular to the direction of main flow in the channel. The Reynolds number based on the length of the channel ranged from 4·104 to 8·105 and has been controlled via imposed velocity. At low Reynolds number we observe a laminar corner vortex having at all velocities the same orientation. This symmetry breaking is probably caused by an imperfectness of the experimental device. At Reynolds number around 8·104 this vortex starts to slightly variate its strength and position causing transition of boundary layers into turbulence at Re = 1.1·105. At higher Re this laminar vortex disappears from the instantaneous velocity fields, but it is still apparent in the averaged ones. It gets smaller and another oppositely oriented vortex forms; note that the second vortex is not observed in the instantaneous velocity fields, only in the ensemble average. At even higher Re, this secondary flow structure is smaller than the turbulent boundary layers, but its shape of a pair of counter-rotating vortices is conserved probably being a seed for secondary flow between fully developed boundary layers reported in the literature for longer channels with fully developed flow.

The wake behind an inclined plate simulating airfoil is to be studied experimentally. The vortical structures are identified eventually. Theirs topology and dynamical behaviour is to be studied in details using the Proper Orthogonal Decomposition method. The stereo time resolved Particle Image Velocimetry technique is used for the experimental research. The vortex trains with oblique orientation and chequered topology have been detected.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEE [ADD1_IRSTEA]Sûreté alimentaire; International audience; This article describes the planning, set-up, turbulence characterization and analysis of measurements of a passive grid turbulence experiment that was carried out in the S1MA wind-tunnel from ONERA in Modane, in the context of the ESWIRP European project. This experiment aims at a detailed investigation of the statistical properties of turbulent flows at large Reynolds numbers. The primary goal is to take advantage of the unequaled large-scale dimensions of the ONERA S1MA wind-tunnel facility, to make available to the broad turbulence community high-quality experimental turbulence data with unprecendented resolution (both spatial and temporal) and accuracy (in terms of statistical convergence). With this goal, we designed the largest grid-generated turbulence experiment planned and performed to date. Grid turbulence is a canonical flow known to produce almost perfectly homogeneous and isotropic turbulence (HIT) which remains a unique framework to investigate fundamental physics of turbulent flows. Here, we present a brief description of the measurements, in particular those based on hot-wire diagnosis. By comparing results from classical hot-wires and from a nano-fabricated wire (developed at Princeton University), we show that our goal of resolving down to the smallest dissipative scales of the flow has been achieved. We also present the full characterization of the turbulence here, in terms of turbulent energy dissipation rate, injection and dissipation scales (both spatial and temporal) and Reynolds number. © 2017, Deutsches Zentrum f

Flow around steady and vibrating airfoil NACA 0012 with a 10° angle of attack has been studied experimentally, using a time-resolved PIV technique at Reynolds number of 65 000. In this situation, a strong interaction between the airfoil and the flow-field is typically observed. Dynamics of flow in the airfoil wake has been investigated in details. Besides statistical analysis of the flow field point-by-point in space, we have explored complex spatial dynamics of the flow using the Oscillation Pattern Decomposition (OPD) method applied on the entire velocity vector field. The flow field spatial dynamics is characterized by the OPD modes of oscillating and non-oscillating characters, capturing traveling and pulsating patterns. Topology and frequencies of dynamical modes are to be shown. The unsteady velocity field is affected by both wing vibrations and inherent flow dynamics. Role of the airfoil vibrations in the flow dynamics is demonstrated.

Experimental study of the structure of the boundary layer on the suction side of a plate is to be presented. The flat plate with rounded edges and angle of attack of 7° is used. The boundary layer flow will be explored using the time-resolved PIV technique, measuring plane was located very close to the wall. Analysis of the flow dynamics is to be presented using the POD technique applied on both velocity and vorticity fields.

2D3C TR-PIV technique was utilized to investigate streamwise-oriented vortical structures behind an inclined flat plate. The angle of attack was set to 7 deg, several fields of view in the wake were investigated. The instantaneous velocity vector fields were captured, dynamics of the flow was studied using POD method. The streamwise structures are determined by vorticity and low- and high-velocity streaks are defined. The acquired results are in a good agreement with the new hypothesis of a principle of flight.

The stereo PIV measurement were performed behind a wing in the plane perpendicular to the flow to study the vortical structures oriented in the streamwise direction, which take place both in suction and pressure sides of the wing. The Reynolds numbers during the experiments in the 3 m wind tunnel range from 0.5 million up to 1.5 million.

The presented study is focused on experimental investigation of a boundary layer on a flat plate in adverse pressure gradient. The flat plate is placed in regular flow, the pressure gradient is generated by the plate inclination. The study [9] deals with structure of the wake behind the plate, the presented study concentrates on structure of the flow close to the suction surface of the plate. Dynamical behaviour of the flow structures is studied in details with respect to the streamwise topology changes. In spite of the fact that the time-mean flow field is 2D, constant along the span, the instantaneous structures topology is fully 3D.

The flow-field behind an inclined plate was investigated experimentally using stereo PIV method providing all 3 velocity vector components in the measuring plane. Flow structure in several measuring planes perpendicular to the main flow was studied. Statistical characteristics were evaluated in the measuring planes. The downwash angle was assessed as well to consider its effect on the lift generation mechanism. The dynamical behavior was studied using Proper Orthogonal Decomposition of velocity fields in measuring planes. The dominant (most energetic) structures were evaluated and presented. The detected structures are of the form of streamwise vortices combined with high-and low-velocity streaks.

The experimental method of PIV (Particle image velocimetry) is used to study the air flow over a forward facing step creating shear layer between the outer flow and the recirculation bubble. This layer decays into vortices, which are highlighted by using Reynolds (temporal) decomposition or Agrawal (spatial) decomposition. The later can be tuned to different-sized structures, and, additionally, their energies roughly follow the Kolmogorov -5/3 law.

The motivation of the presented study is supporting new ideas about principle of flight by Hoffman and Johnson, see [1]. The new hypothesis of physical mechanism of flight relies on existence of streamwise vortical structures on the suction side of the airfoil and within its wake. The vortices origin is supposed to be the instability of the boundary layer subjected to adverse pressure gradient. The vortices are of highly dynamical nature, changing theirs position, size and other parameters in time very rapidly. For this experiment the simplest airfoil possible was chosen represented by a flat plate in uniform flow and moderate angle of attack. In the suggested paper detailed measurement of the zone of interest will be carried out using stereo PIV method. System of measuring planes perpendicular to the flow will be explored. POD analysis is to be utilized.

Stereo PIV measurements has been performed behind the inclined plate, angle of attack 5 and 10 deg. Occurrence and dynamics of streamwise structures behind the plate trailing edge have been studied in details using POD method. The streamwise structures are represented by vortices and low- and highvelocity regions, probably streaks. The obtained results support the hypothesis of an airfoil-flow force interaction by Hoffman and Johnson [1,2].

Coanda effect takes place in flow within valves diffuser for certain conditions. The valve plug in half-closed position forms wall-jet, which could be stable or instable, depending on geometry and other conditions. This phenomenon was subject of experimental study using time-resolved PIV technique. For the acquired data analysis the special spatio-temporal methods have been used.

The problem of flow field in the urban boundary-layer (UBL) in aspects of wind comfort around buildings and pollutant dispersion has grown in importance since human activity has become so intense that it started to have considerable impact on environment. The issue of wind comfort in urban areas is the result of complex interactions of many flow phenomena and for a long time it arouses a great interest of the research centres. The aim of article is to study urban atmospheric flow at the local scale, which allows for both a detailed reproduction of the flow phenomena and the development of wind comfort criteria. The proposed methodology involves the use of PIV wind tunnel experiments as well as numerical simulations (Computational Fluid Dynamics, CFD) in order to enhance understanding of the flow phenomena at this particular scale in urban environments. The analysis has been performed for the 3D case of two surface-mounted buildings arranged in tandem, which were placed with one face normal to the oncoming flow. The local characteristics of flow were obtained by the use of commercial CFD code (ANSYS Fluent). The validation was carried out with reference to the PIV results.

Turbulent flow inside a street canyon was investigated in a wind-channel. Velocity measurements were performed in vertical planes by means of particle image velocimetry (PIV) at the repetition rate 500 Hz. Two geometries were used for comparison purposes: buildings with pitched roofs and with flat roofs. Both induce different dynamic regimes in the street, so that the generated turbulent flows are of different categories. Velocity data were analysed by proper orthogonal decomposition (POD). POD identifies the most dominant modes with high coherency in the flow and also evaluates the relative contributions of each mode to the overall kinetic energy of turbulence. Rigorous analysis of correctness of the physical interpretation of such decomposition was carried out. POD reconstruction of the original vector field was performed and the accuracy of the method was evaluated. Wavelet analysis was applied to the time-series of the POD expansion coefficients in order to reveal the dynamics of the modes. Vorticity, calculated from the original velocity data, was decomposed by POD as well. Finally, the correlation between the vorticity and other methods for vortex detection was assessed.

We present a educational poster supporting the subject „Mechanics of fluids I“, which the students evaluate to be difficult mainly due to abstractness. Our goal is to show in vivo the behavior, especially the non-linearity, of various flows transiting into turbulence. The fluid motion is visualized by using the rheoscopic fluid, which consist of water and the dust of mica, whose particles are longitudinal and shiny resulting into easily observable reflections, when the particles coherently orient along the maximum stress. This happens mainly in shear layers, e.g. at the boundary between vortex core and envelope. An example of flow transiting into turbulence is the Taylor-Couette flow between two concentric cylinders, which with increasing Taylor number passes through various regimes from fully laminar bearing flow through the Taylor vortex flow (TVF) and later Wavy vortex flow (WVF) up to Turbulent Taylor vortices regime (TTV) and, finally, the regime of featureless turbulence.

The aim of this paper is to study the physics related to lift generation on an airfoil. A new hypothesis [1] of physical mechanism of flight relies on existence of streamwise vortical structures above the wing and inside the wake. The vortices origin as a consequence of flow instability inside the boundary layer developed under adverse pressure gradient. These structures are highly dynamical in nature, they change position and size very rapidly. A simple airfoil in the form of a flat plate with moderate angle of attack is considered in the presented research that generates suitable flow at rather low Reynolds number. Stereo PIV time resolved measurement technique is used to capture high-dynamic data in several planes which are located in the wake and are perpendicular to freestream or parallel to the airfoil. The overall image of the flow field dynamics will be created using POD decomposition. Distinct flow patterns with associated kinetic energy are to be described as well as their role in the studied case. Existence of streamwise vorticity is proved, topology and other parameters are estimated in the paper; however related pressures and forces are not evaluated.

Bypass boundary layer transition in flows on flat plate by adverse pressure gradient was investigated experimentally. It was measuered cases with combination of adverse pressure gradient by different free stream turbulence intenzity. Hot wire anemometry technique was used. Measuerement were made on flat plate in closed wind tunnel. Adverse pressure gradient was set by diffuser in tested section of wind tunnel. Grid turbulence of free stream was controlled by screen. Hot wire anemometry technique was used, intermitency factor was evaluated. Results were compared wih cases with simpliest conditions.

The global flow-field around an airfoil will be studied using time-resolved PIV technique. Interactions between pressure and suction sides flows will be studied in detail. Spanwise structures dynamics is to be analysed.

The canonical case of cross-flow behind prismatic circular cylinder is analyzed from the point of view of 3D instabilities appearance. Various flow conditions defined by various Reynolds number values are considered. All cases in question exhibit significant 3D features in close wake playing significant role in physical mechanisms of force generation.

The effect of ionic wind generated by plasma actuator on developed boundary layer inside a narrow channel was investigated recently. Since the main investigated plane was parallel to the channel axis, the description of flow field was not evaluated credibly. This paper is dealing with cross-section planes downstream the actuator measured via 3D time-resolved PIV. The actuator position is in spanwise or in streamwise orientation so that ionic wind is blown in the same direction as the main flow or in opposite direction or perpendicularly. The interaction between boundary layer and ionic wind is evaluated for three different velocities of main flow and several parameters of plasma actuation (steady and unsteady regime, frequency etc.). Statistical properties of the flow are shown as well as dynamical behaviour of arising longitudinal vortices are discussed via phase-locked measurement and decomposition method.

The classical approach to analysis of forces exerted on a body in flow is based on 2D and inviscid mathematical model. Obviously, it fails in explanation of physical mechanism behind this phenomenon. The new hypothesis proposed by Hoffmann and Johnson [1, 2] based on 3D flow structure physical model is to be presented and analyzed here. The results of experiments and mathematical modelling shown in the paper support the new theory, however the real flow-field is even more complex, it contains structures not presented in the model.

The article deals with the effects of the inlet flow parameters on the flow field structures in axial turbine stage. The experiment was performed on the axial turbine stage rig with an air as a working medium. The variable inlet channel produced the different inlet turbulence intensity and different inlet end-wall boundary layer thickness, resp. different inlet velocity distribution was applied. The turbulence was measured by CTA probes. The measured parameters of the inlet velocity distribution and turbulence intensity across the inlet channel height are presented. Based on the experimental inlet parameters the CFD fully turbulent calculation of the flow field was made. The differences in outlet kinetic energy loss, outlet vane angle and the turbulence distribution in the vane mid-span section are depicted. Changes of secondary flow structures with the different inlet end-wall boundary layer thickness were observed on the vane outlet parameters.

Results of the experimental investigation on control of narrow channel flow behind a backward-facing step by blowing/suction near the step foot are presented. The slots differ in both the orifice shape (rectangle or serrated) and area (50–375 · 10 −6 m 2 ) of its cross-section. The intensity of flow control is characterized by the suction/blowing flow coefficient (mass flow through the slot over mass flow above the step, suction: negative values) that varies from −0.035 up to 0.035 at Reynolds number 5 · 10 4 (defined on the basis of the hydraulic diameter and volume velocity). Preliminary results indicate that both blowing and suction are able to reduce the length of the separation zone down to one third of its value without control. Control effectiveness is given by absolute value of the flow coefficient. The other parameters (slot area and shape) are important only for blowing, in this case small cross-section with serrated edge is the most effective. The existing three-dimensional vortex structures near the step (resulting from interaction of boundary layers near the step edge) are influenced by suction more then by blowing. The experiments are still in progress.

Flow in a branched channel is studied experimentally using the PIV technique. The branches are issuing from the main channel perpendicularly, all channels are of rectangular cross-section. The flow dynamics in one particular branch is investigated using the OPD method.

The motivation of this paper is the continual development of the blades for the last stage of the steam turbine. The biggest problem is the slenderness of such blades and the extreme sensitivity to aeroelastic vibrations (flutter) caused by the instabilities present in the flow. This experimental research is dealing with the aeroelastic binding of the moving blades located in the blade grid with the flow field and vice versa. A parallelogram is used to ensure one order of freedom of the blade. The grid has five blades in total, three of them are driven by force control using three shakers. The deviation as well as force response is measured by strain gauges and dynamometers. The flow field statistical as well as dynamical characteristics are measured by optical method Particle Image Velocimetry. The grid is connected to the blow-down wind tunnel with velocity range up to 40 m/s. The aeroelastic binding is investigated in dependency on used actuation frequency and maximal amplitude (the intensity of force actuation) and on different Reynolds numbers. The flow field and the wake behind each individual blade are studied and the maximal interaction is examined for individual inter-blade phase angle of the grid.

The flow-field in the vicinity of tandem building model in a wind tunnel will be subjected to analysis of dynamics. The model is 3D consisting of the two blocks of different sizes arranged in a streamwise direction. Experiments were performed using time-resolved PIV technique in several measuring planes to capture both spatial and dynamical features.

Wavelet analysis is applied to data from PIV measurement in order to recognize a specific structure in the flow. The PIV snaphots achieved on the model of the street canyon was used as a test case. Four flow characteristics that are at disposal from one-point simultaneous two-components measurement (e.g. from 2D LDA) were analyzed by Wavelet method: longitudinal and vertical velocity, momentum flux u’w’ and δS – the difference between momentum fluxes associated with a sweep and an ejection. Each of characteristic is useful for detection of certain type of event. We have focused on the sweep and the ejection that seem to be the most convenient for investigation of a significant inflow or an outflow from the street canyon.

Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time resolved PIV technique. Secondary flow represented by vortical structures is studied using Oscillation Pattern decomposition technique. The low-frequency quasi-periodical structures appearing in the region just behind the step close to the channel bottom are studied. Typical dynamics of vortex structures involving contra-rotating vortex pair train, vortices coalescence and splitting have been observed.

The effect of length scale on flat-plate by-pass boundary layer transition under free stream turbulence conditions has been investigated. Plane grids generated a constant value of 3 percent intensity turbulent fluctuations and five values of the dissipation length parameter in the range of 2.2 mm to 33.3 mm at 5 m/s flow velocity in the plane of the leading edge of the flat plate. The investigated boundary layer corresponds to the ERCOFTAC Test Case T3A+. Distributions of integral parameters as well as the statistical characteristics of the turbulent fluctuations were measured. They document a significant effect of turbulence length scale on the onset and the end of by-pass transition. It was found that the onset of the final stage of transition comes on later in `fine-grained' turbulence than in the case of large free stream turbulence length scale. At the same time, the extent of the transition region shortens with decreasing length scale. Nevertheless, the transition process terminates sooner in a flow with a large turbulence length scale than in a flow with a small one. An attempt has been made to describe these observations quantitatively.

Dynamics of the flow reattachment behind the backward-facing step in a narrow channel is studied experimentally with help of the PIV technique. Reattachment region is detected using statistical characteristics of the flow velocity close to the channel bottom. Two methods of reattachment definition are applied. The reattachment region structure and extent is shown.

Previously, the DBD (dielectric barrier discharge) plasma actuator was used in rectangular channel to modify the properties of the boundary layer in spanwise and in streamwise orientation. The actuator was redesigned for using on the surface of the Glauert-Goldschmied body in different position to influence the point of the separation and the reattachment point as well as the total extent of the separation bubble. The most intensive effect occurs when the actuator takes effect in the point of separation. Further downstream, the ionic wind produced by DBD causes complex coherent structures in the wake for spanwise orientation in both direction. The effect of streamwise orientation is studied also. Actuator is operated in steady regime to produces continuous ionic wind as well as in unsteady regime when the vortex street is generated. The properties of vortex street is given by modulation parameters (frequency and duty cycle). The effect of these parameters on the wake is evaluated. This experiment is realized in the perspex channel connected to the blow-down wind tunnel. The HUMP profile is flush-mounted to the bottom side. The wire electrode of the actuator is situated in x/L = 0.63, 0.66, 0.69 and 0.72 of the chord length. The time-resolved PIV (Particle Image Velocimetry) is used as a main measurement technique. The flow field behind the profile is captured in longitudinal plane as well as in cross-section planes using 3D PIV. The results based on statistical quantities will be presented in this paper. More, next part will be devoted to the decomposition analysis of the flow dynamics (BOD, OPD).

Proper orthogonal decomposition (POD) of a very turbulent flow inside a street canyon is performed. The energy contribution of each mode is obtained. Also, physical meaning of the POD result is clarified. Particular modes of POD are assigned to the particular flow events like a sweep event, a vortex behind a roof or a vortex at the bottom of a street. Test of POD sensitivity to the acquisition time of data records is done. Test with decreasing sample frequency is also executed. Fur- ther, interpolation of POD expansion coefficient is performed in order to test possible increase in sample frequency and get new information about the flow from the POD analysis. We tested a linear and a spline type of the interpolation and the linear one carried out a slightly better result.

Infrared camera, 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 numbers transition mechanism. Airfoils of Wortmann FX66 series and FX66 series wing-fuselage interaction, as well as modern airfoils and their wing-fuselage geometry were subject to study. The presence of previously identified structures in the CFD modelling, such as horse-shoe vortices, was confirmed in the flow. Wind-tunnels and in-flight measurements on sailplanes were carried out and effect of passive flow control devices - vortex generators - was surveyed; namely counter-rotating vortex generators and Zig-zag type turbulators were applied. Separation suppression and consequent drag coefficient reduction of test aircrafts was reached. PIV investigation was further extended by Time-Resolved techniques. An important study on structure of the turbulent flow in the lower atmosphere, creating an environment of the soaring flight, was presented.

Dimensionless mean flow characteristics and the location of the transitional region were investigated of flat plate boundary layers (smooth surface or covered by sandpaper 60 grit) at the external flow velocities about 5 m/s, 10 m/s and 14 m/s and with turbulence levels either natural (less than 0.003) or gained by a grid across the flow (FST level 0.03 at the leading edge). Preliminary comparison of the received results with those previously published [1] is presented. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of the flow reattachment behind the backward-facing step in a narrow channel is studied experimentally using the PIV technique. Reattachment region is detected by statistical characteristics of the flow velocity close to the channel bottom. Two methods of reattachment definition are applied. The reattachment region structure and extent is shown. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Previously, the vortical structures generated by plasma DBD actuator working in unsteady regime were investigated in detail. The generalized model describing the behaviour of these vortices in dependency on input power parameters was introduced. This paper should reveal how the wall-jet-like-flow generated by that actuator will affect the developed flow in a rectangular channel with cross-section dimension of 250 × 100 mm. The actuator is considered in spanwise configuration where the induced flow has the same or opposite orientation as the main flow. The flow control will be tested both for steady regime and for unsteady regime. The dynamic of that complex phenomenon will be studied and results in qualitatively and quantitatively meaning will be presented. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental investigation of the boundary layer development on the rough plate (80-grits sandpaper) under external turbulent flows with a grid turbulence of various turbulence scales proved existence of the laminar/transitional region, regardless the surface roughness. Both the outset and the length of the transitional region are affected by the external flow turbulence.

The effect of the free stream turbulence (FST) on the essential flow characteristics was investigated in the diverging 2D channel. The diverging channel was modelled in the closed type working section by fastening a displacement body above the flat plate that is parallel with the wind-tunnel axis. The angle of the channel expansion 11 degree induced the pressure gradient parameter with the flow velocity U0 30 m/s at the start of expansion, x = 0. The height of the channel is 0.15 m at x = 0. FST was either natural 0.3 percent or amplified by turbulence generating grids/screens with turbulence levels up to 5 percent. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

The conditional analysis of the instantaneous wall friction is applied on time records made in transitional boundary layers originating on smooth surface or surface covered by sand paper (grits 60) under turbulent free stream. The applied intermittency analysis of measurement allowed the evaluations of turbulent and non-turbulent zone averages. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

An interaction of the free turbulent shear flow and the steady temperature field, which develops to the homogeneity, was studied. The temperature field was generated by parallel thin heated wires. The isotropic grid turbulence is supposed. Heated wire generates large cross temperature gradients and development of the temperature field was investigated experimentally. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

It will be shown how plasma actuator can generate wall-jet-like flow or train of periodical vortices depending on the generator setting. For generation the high-frequency high-voltage AC is used. Low-frequency modulation of the supply voltage is required to generate vortices. Data acquisition will be performed using time-resolved PIV technique. Phase-averaging will be studied from two different perspectives. Firstly, sampling of phases will be ensured using trigger that is contained in the PIV software and, secondly, phase-averaged flow will be computed from two main modes of POD analysis. The generated flow patterns are to be applied for control of a boundary layer. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Flow structure behind the backward facing step in a narrow channel was studied in details. The step height was 25% of the channel width. The structure of the region just behind the step forming the back-flow region is studied in details using stereo PIV technique. Time-mean 3D structures behind the step are evaluated and shown in the paper. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Presented work is the next step after several experimental examinations of vortex generator influence on a flow separation occurring on a model of the NACA 63A421 airfoil with deflected simple flap. In this stage of research the vortices produced by vortex generators (VGs) were studied using Particle Image Velocimetry technique (PIV) and numerical simulations. Vane type VGs with two spacings among VGs pairs in straight channel with turbulent flow were tested. The average velocity flow field, peak of vorticity and circulation decay downstream of VGs were evaluated. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)