Valery Chernoray | Chalmers University of Technology (original) (raw)

Papers by Valery Chernoray

Vestnik Novosibirskogo gosudarstvennogo universiteta, Jul 1, 2009

The structure of a plane wall jet by means of smoke visualization and PIV measurements is investi... more The structure of a plane wall jet by means of smoke visualization and PIV measurements is investigated experimentally. Instantaneous and ensemble-averaged the flow fields for different cross-sections are presented. Features of the development and interaction of the Kelvin-Helmholz vortex and longitudinal structures are shown.

IOP conference series, Mar 1, 2014

Improvements in ventilation and cooling offer means to run hydro power generators at higher power... more Improvements in ventilation and cooling offer means to run hydro power generators at higher power output and at varying operating conditions. The electromagnetic, frictional and windage losses generate heat. The heat is removed by an air flow that is driven by fans and/or the rotor itself. The air flow goes through ventilation channels in the stator, to limit the electrical insulation temperatures. The temperature should be kept limited and uniform in both time and space, avoiding thermal stresses and hot-spots. For that purpose it is important that the flow of cooling air is distributed uniformly, and that flow separation and recirculation are minimized. Improvements of the air flow properties also lead to an improvement of the overall efficiency of the machine. A significant part of the windage losses occurs at the entrance of the stator ventilation channels, where the air flow turns abruptly from tangential to radial. The present work focuses exclusively on the air flow inside a generator model, and in particular on the flow inside the stator channels. The generator model design of the present work is based on a real generator that was previously studied. The model is manufactured taking into consideration the needs of both the experimental and numerical methodologies. Computational Fluid Dynamics (CFD) results have been used in the process of designing the experimental setup. The rotor and stator are manufactured using rapid-prototyping and plexi-glass, yielding a high geometrical accuracy, and optical experimental access. A special inlet section is designed for accurate air flow rate and inlet velocity profile measurements. The experimental measurements include Particle Image Velocimetry (PIV) and total pressure measurements inside the generator. The CFD simulations are performed based on the OpenFOAM CFD toolbox, and the steady-state frozen rotor approach. Specific studies are performed, on the effect of adding "pick-up" to spacers, and the effects of the inlet fan blades on the flow rate through the model. The CFD results capture the experimental flow details to a reasonable level of accuracy.

A turbine rear structure (TRS) is typically used to deswirl the flow from the low pressure turbin... more A turbine rear structure (TRS) is typically used to deswirl the flow from the low pressure turbine (LPT) and hence maximize the axial thrust. It is important to study the effect of surface roughness on aerodynamic performance of TRS. Numerical simulations with surface roughness are performed and results are compared with the data from experiments. Comparisons show that the trends between the numerical analysis and the experiments are in line with one another. Further understanding of numerical analysis shows that, at higher Reynolds number, the effect of surface roughness is more significant when compared to the effects at low-Reynolds number. An attempt has been made to study the transition behavior in the presence of surface roughness. Since boundary layer measurements are planned for the rig, this numerical study provides good inputs in order to plan instrumentation.

To study the time-mean and temporal characteristics of secondary flow within a linear GE-E 3 high... more To study the time-mean and temporal characteristics of secondary flow within a linear GE-E 3 high pressure turbine cascade, a planar Time-Resolved Particle Image Velocimetry (TR-PIV) system is used. In the double-passage cascade, a row of six converging slot-holes is placed upstream of center blade to generate film cooling effect, and different turbulence grids are replaced to create various free-stream turbulence (Tu in) levels. In this experiment, the time-mean characteristics of secondary flow, the fast switch process of unsteady leading edge horseshoe vortex (LEHV), and the temporal characteristics of corner vortices (CVs) are completely exhibited by the TR-PIV technique. The influences of the upstream coolant injection and Tu in level on the flow characteristics of LEHV and passage vortex (PV) are discussed. The discussion reveals that: (1) in the case of no coolant injection, a high Tu in level slightly moves the LEHV toward the blade, changes the shape of the PV, increases the fluctuations of the LEHV and PV, and reduces the frequency of the LEHV switch process; (2) at various Tu in levels, the coolant injections suppress the formation of the LEHV, and the LEHV disappears at a high coolant-to-mainstream blowing ratio (BR) of 1.5; (3) a high BR of 1.5 can greatly weaken the PV at various Tu in levels, and relative to the case of low Tu in , the high Tu in level induces a larger reduction; (4) for a low BR, at various Tu in levels, a slight change in the LEHV results in a distinct difference of the PV characteristics; (5) for a high BR, since the LEHV disappears, the Tu in effect on the secondary flow characteristics is slight.

Prediction of laminarturbulent transition at high level of free-stream turbulence in boundary lay... more Prediction of laminarturbulent transition at high level of free-stream turbulence in boundary layers of airfoil geometries with external pressure gradient changeover is in focus. The aim is a validation of a transition model for transition prediction in turbomachinery applications. Numerical simulations have been performed by using a transition model by Langtry and Menter for a number of di¨erent cases of pressure gradient, at Reynolds-number range, based on the airfoil chord, 50 000 ≤ Re ≤ 500 000, and free-stream turbulence intensities 2% and 4%. The validation of the computational results against the experimental data showed good performance of used turbulence model for all test cases. 1 INTRODUCTION Components of an aeroengine operate in a Reynolds-number range between 5•10 4 and 1 • 10 6 [1]. For this range of Reynolds numbers, the laminarturbulent transition in a boundary layer and separation play an important role in determining the §ow and heat transfer. In order to predict the aerodynamic and heat transfer performance of aeroengine components accurately, one needs to predict the location and length of the regions with laminarturbulent transition and separation. This prediction is a challenging task due to the presence of varying pressure gradients and high level of free-stream turbulence. Except for the fan, the level of turbulence in an aeroengine is high, above 1%, and classic transition scenario is seldom realized. The typical transition regimes are the bypass transition and separated §ow transition. An overview of di¨erent scenarios of laminarturbulent transition at high free-stream turbulence and presence of pressure gradient can be found in studies [26]. On an airfoil, if the Reynolds number is high enough so that the transition is complete before a laminar separation can occur or if the boundary layer does not separate because the §ow deceleration is slight, then an attached §ow transition occurs. If the

International Journal of Fluid Machinery and Systems, Jun 30, 2015

Tribology International, Oct 1, 2023

Implementation of an engineering method for wind turbine aerodynamics was the objective of the pr... more Implementation of an engineering method for wind turbine aerodynamics was the objective of the project work. The Blade Element Momentum (BEM) method was implemented to calculate the aerodynamic loads and the results were validated with given values from the vortex method. The computational benefits of BEM over vortex method was realized and deviation of results at every stage were quantified. The blade of the wind turbine is discretized using cosine, half-cosine and equidistant mesh types. A convergence study was made for the three mesh types, where cosine and half cosine mesh gave the better convergence to consider for further studies on account of better resolution of higher gradient of forces near the tip of the blade. The classical BEM method was first implemented with no yaw misalignment involved and then compared with vortex method and BEM code of National Technical University of Athens (NTUA) for the NREL 5MW wind turbine. A series of yaw misalignments were introduced and the impact of sign and magnitude of the same on the power and thrust generated were studied and compared with the vortex method. The pitch angles were found crucial in higher velocities as for the yaw misalignment case, the pitch angles used for no yaw misalignment case were over-pitching the blades, producing less than the rated power. The normal and tangential forces were computed across the section of the blade for different velocities with and without yaw misalignment and were compared to the results from vortex method. In attempt to make BEM model replicate reality more, loss factors were associated to the calculations and it was striking to notice that the hub and the tip loss factor could not contribute commendably to help BEM results match the results of vortex method. The load dependence on the azimuth angle in yawed inflow condition opened the possibility of extending the current work to dynamic structural analysis and the impact of blade pitch angles were studied. iii FIGURE 4.5: Thrust with ±yaw.

In modern commercial aviation engines, the low-pressure turbine (LPT) has a high outlet swirl to ... more In modern commercial aviation engines, the low-pressure turbine (LPT) has a high outlet swirl to maximize turbine power to weight ratio. Downstream of the last LPT rotor is the turbine rear structure (TRS) that with relatively few low-aspect-ratio outlet guide vanes (OGV), de-swirls the flow to maximize the thrust. In the wide operational envelope of the TRS, both transition location and mode can change during a normal operating cycle. Hence, accurately predicting transition is critical for the development of future TRS modules. This work discusses the experimental method and results of laminar-turbulent transition in a TRS module at engine representative conditions at Reynolds Number of 235,000. This was done in Chalmers 1.5 stage LPT-OGV facility. The transition was measured on the entire span using IR-thermography. The technique was specially developed at Chalmers for this particular purpose and validated by boundary layer hot-wire measurements. The technique provides both steady-state heat transfer with high confidence of 2-8% and time-resolved temperature fluctuations. This paper describes a collection of how this data can be used for transition detection, how it compares to fundamental correlations and as a tool for flow visualization. The facility was built thanks to the financial support of Energimyndigheten, Nationella flygtekniska forskningsprogrammet, the EU Commission, GKN Aerospace Sweden AB and the department of Mechanics and Maritime Sciences at Chalmers. The aerosurface of the LPT and TRS is designed by GKN Aerospace solely for the experimental rig and is not related to any GKN Aerospace product characteristics.

All vessels operating in water will experience marine growth on the hull. These marine growth can... more All vessels operating in water will experience marine growth on the hull. These marine growth can be classified into macro biofouling (barnacles, seaweed, etc) and micro biofouling (slime or biofilm) . Biofouling will increase the weight and surface roughness of the hull, increasing ship resistance (Haslbeck and Bohlander 1992) and thereby increasing fuel consumption (Schultz, Bendick et al. 2011).

Buildings

There is a need to shield from the wind to improve pedestrian comfort in urban environments. Perf... more There is a need to shield from the wind to improve pedestrian comfort in urban environments. Perforated windbreaks, such as fences, vegetation or textile nets, have proven to be an efficient solution, whereas knitted textiles have not yet been explored. The purpose of this study was to evaluate the capacity of knitted textile windbreaks to reduce wind velocities, to inform further research and promote wider architectural applications. Five custom-knitted textile prototypes, representing fragments of textile windbreaks, were tested in a wind tunnel and compared against a perforated and a nonperforated solid board. Forces on the models, as well as upstream and downstream velocities, were measured. The results indicate that the optimal optical porosity of knitted windbreaks should be around 10%, which differs from the porosity for perforated windbreaks recommended by prior studies. Moreover, it was observed that a textile windbreak knitted using the drop-stitch technique efficiently re...

3rd ECATS Conference, Making Aviation Environmentally Sustainable,, 2020

Applied Thermal Engineering, 2018

The majority of the numerical studies conducted on the thermochemical conversion of solid fuels i... more The majority of the numerical studies conducted on the thermochemical conversion of solid fuels in a fluidized bed have ignored the bed materials inside the bed and just considered the effect of hot air passing the fuel particle. In this study, a sub-bituminous coal particle hydrodynamics during the devolatilization process is modeled inside a 2D fluidized bed in two different cases. In the first case, the energy exchange of inert phase with the fuel particle is included in the simulation and, in the second case, it is ignored. The coal particle's motion is modeled including the drag force from the bed and the heat and the mass transfer are also simulated during the devolatilization process while the fuel particle is heated up using the chemical percolation devolatilization model. The simulation successfully predicted the motion of the particle inside the bed as well as the temperature increase and volatile release from the particle during the simulation time. The mass loss and temperature history of the fuel particle resulting from the simulation show good agreement with the experimental results. The simulation also indicates that inert particles have a great effect on the heat transfer coefficient inside the bed and ignoring them will cause a difference in the devolatilization time, and this difference will also increase significantly with the increase of the fuel particle's diameter.

Journal of Wind Engineering and Industrial Aerodynamics, 2017

This paper presents a drag reduction study using active flow control (AFC) on a generic bluff bod... more This paper presents a drag reduction study using active flow control (AFC) on a generic bluff body. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the two other rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck [1]. The prediction of the flow field by partially averaged Navier-Stokes (PANS) simulations, conducted on a relatively coarse mesh, is validated against wind tunnel data (pressure measurements and particle image velocimetry (PIV)) and resolved large eddy simulations (LES) data. The Reynolds number for both simulations and experiments is Re = 5 × 10 5 (which corresponds to 1/6 of a full scale truck Re) based on the inlet velocity U inf and the width of the model W = 0.4m. A validation of PANS results is followed by a CFD study on the actuation frequency that minimizes the aerodynamic drag and suppresses the side recirculation bubbles. PANS accurately predicts the flow field measured in experiments and predicted by a resolved LES. The side recirculation bubble of a simplified truck cabin model is suppressed almost completely and a notable drag reduction by means of AFC is observed.

European Journal of Vascular and Endovascular Surgery, Aug 1, 2016

WHAT THIS PAPER ADDS Flow induced displacement forces were assessed in an experimental model in E... more WHAT THIS PAPER ADDS Flow induced displacement forces were assessed in an experimental model in EVAR iliac stent grafts in relation to distal diameter and asymmetric stent graft curvatures. Forces were particularly high at the distal end of bellbottom grafts. Patients treated with bell-bottom grafts may require more vigilant surveillance and improved graft fixation. Objectives: Long-term durability after endovascular aortic repair is influenced by stent graft migration causing types I and III endoleaks. Flow induced displacement forces have been shown to have the potential to cause migration. In this study, the influence of the distal diameter of iliac limb stent grafts and the shape of graft curvature on flow induced displacement forces, were investigated. Methods: In an experimental pulsatile flow model mimicking aortic conditions in vivo, flow induced displacement forces at the proximal and distal ends of iliac limb stent grafts were studied at different angles (0e90) and perfusion pressures (145/80, 170/90, 195/100 mmHg). Bell-bottomed, tapered, and non-tapered stent grafts and also asymmetric stent graft curvatures at 90 bend were studied. Measurements of graft movement were performed at all studied angulations and graft shapes. Results: For all stent graft diameters, flow induced displacement forces increased with higher pressure and increased stent graft angulation. Forces in the bell-bottom graft were considerably higher than in tapered and non-tapered grafts, with a markedly elevated peak force at the distal end (proximal end, 2.3 AE 0.06 N and distal end, 6.9 AE 0.05 N compared with 1.7 AE 0.08 N and 1.6 AE 0.08 N in non-tapered grafts; p < .001 both). Peak forces in tapered and non-tapered grafts were not significantly different between the proximal and distal end. In asymmetric stent graft curvatures, a significant increase in displacement forces was observed in the attachment zone that was closest to the stent graft bend. Graft movement increased with greater displacement forces. Conclusion: Flow induced displacement forces in iliac limb stent grafts are significant and are influenced by distal stent graft diameter and the shape of the graft curvature. The displacement forces are particularly high at the large distal end of bell-bottom grafts. Wide iliac arteries treated with bell-bottom stent grafts may require more vigilant surveillance and improved stent graft fixation.

LES simulations at Re = 1 × 10^5 and wind tunnel experiments at Re = 5 × 10^5 were conducted to i... more LES simulations at Re = 1 × 10^5 and wind tunnel experiments at Re = 5 × 10^5 were conducted to investigate the beneficial effect of an active flow control (AFC) technique on the aerodynamic performance of a simplified truck geometry. The paper involves the investigation of a synthetic jet actuator characterized by periodic blowing and suction that defines a zero net mass flux flow control mechanism. The actuation aims to suppress the flow separation occurring at the A-pillar (front rounded corner) of a truck cabin. The work flow is defined as follow. First, LES at low Reynolds number are conducted for different disposition of the actuation slots. The results show a beneficial effect when the actuation slots are positioned in streamwise direction compared to spanwise (vertical) direction. Second, based on the previous considerations, wind tunnel experiments are conducted to verify and support the numerical findings. Both numerical solutions and experimental data show the same trend and the superiority of streamwise aligned AFC slots.

Active Flow Control (AFC) can be applied using a various number of approaches. The general, yet u... more Active Flow Control (AFC) can be applied using a various number of approaches. The general, yet ultimate, goal is to use a control strategy able to actively manipulate a separated flow. Reattachment or deflection of the shear layer is of main importance to enhance the aerodynamic performance of blunt and aerodynamic bodies. The paper presents a numerical and experimental study of the suppression of the recirculation bubble occurring at the side of a generic truck cabin (A-pillar separation) at Re = 5 × 10 5 . In this work the hybrid Partially Averaged Navier-Stokes (PANS) method was used. The aim of the present study is twofold: to validate the PANS method against in-house experiments and a resolved LES simulation, and to simulate the effect of an AFC on a heavily separated turbulent flow. Figure 1 shows the dimension of the computational and experimental domains (a and b) and the observed window in both experiments and simulations (c and d). The results show a good flow prediction by PANS even when the computational domain is drastically coarsened, Fig. 2. Velocity and Reynolds stress profiles, as well as modal and frequency analysis will be compared for a full validation. The AFC effect shows a drastic decrease of the side recirculation bubble, Fig. 3. The separation is observed to be receptive to the control and it locks to the specific actuation frequency when the latter is in the "receptive band". The flow reaches a frequency independent behaviour when the actuation frequency exceeds this range.

Journal of Wind Engineering and Industrial Aerodynamics, May 1, 2021

This experimental work aims to investigate the manipulation of a bluff body flow with a yaw angle... more This experimental work aims to investigate the manipulation of a bluff body flow with a yaw angle of 10 based on a genetic algorithm optimization. Two loudspeakers are used to generate zero-net mass-flux jets through streamwise slots, which span a large portion of the rounded A-pillars of the bluff body. The actuations produce a maximum drag reduction of 17% and 2% for the leeward and windward side control, respectively. The genetic algorithm has found two typical frequencies to separately drive the actuators on the windward and leeward sides. The drag reduction is 20% under the optimal control law, 3% larger than the 17% attained from the reference single frequency control. In addition, a beneficial effect is observed when considering energy efficiency, which increases by 30% in the optimal control compared to the single frequency control. The drag spectra and velocity mapping in the wake are measured with and without control, and, based on the measurement, the underlying flow mechanism behind the control is proposed.