Valery Chernoray | Chalmers University of Technology (original) (raw)
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Papers by Valery Chernoray
One of the major questions in fluid mechanics is the prediction of the mean flow and turbulence s... more One of the major questions in fluid mechanics is the prediction of the mean flow and turbulence structure of boundary layers over surfaces with different roughness types. The current paper shows a method to obtain the roughness function of different surface roughness by using a small-scale rig with rotating discs and long-distance microscopic PTV measurements in order to obtain submicron resolution inside the boundary layer of rotating disc flows. This rig has been designed and constructed for the optical measurements and consists of an electric motor driving the discs that are rotating inside of a 20-liter water tank. The PTV measurements are performed on surfaces with different degree of roughness and a smooth case. The rough cases correspond to two applications of a marine antifouling paint. The measurements are performed for two rotational speeds (300 and 600 RPM). Field mean velocity profiles are calculated by averaging vertical bins with 1 px width and every point of the mean ...
Volume 1: Aircraft Engine; Fans and Blowers; Marine; Honors and Awards, 2019
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.
The role of streamwise structures during transition to turbulence both in near-wall and in free s... more The role of streamwise structures during transition to turbulence both in near-wall and in free shear flows in many eases is determinative. The purpose of present study is the analysis of results of experimental researches of mechanisms of origin development and transition to turbulent state of the various shear flows with the streamwise structures which have been carried out of late.
Computational Methods in Multiphase Flow VI, 2011
EPJ Web of Conferences, 2012
EPJ Web of Conferences, 2012
A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency... more A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency and reducing emissions from aero-engines. This paper presents a detailed experimental evaluation of an engine realistic TRS which was studied in an engine-realistic rig at Chalmers University of Technology, Sweden. The TRS test section was equipped with three types of outlet guide vanes (OGVs) which are typical of modern state-of-the-art TRS: regular vanes, thickened vanes, and vanes with an engine mount recess (a shroud bump). Each of the three vane geometries was studied under on-design and off-design conditions at a fixed flow Reynolds number of 235,000. The study shows that the off-design performance of the TRS strongly depends on the presence of the local flow separation on the OGV suction side near the hub, which is greatly affected by the vane pressure distribution and inlet conditions. Similarly, the OGVs with increased thickness and with a vane shroud bump are shown to affect t...
Gears inside the gearbox are cooled and lubricated by oil. If the amount of oil is too little, th... more Gears inside the gearbox are cooled and lubricated by oil. If the amount of oil is too little, the lifetime of the gears is shorter due to insufficient heat dissipation, but if the amount of oil inside the gearbox is too much, it creates significant load for the gears when they are rotating, due to the shear of the oil. To find appropriate oil level inside a gearbox, understanding of the flow is needed. This study is to add understanding of the oil flow inside a gearbox and the data that has been generated will become a validation tool for numerical calculation. Two regions were chosen and measured. First region is below the gear. This region was chosen to understand the oil flow around the gear while the gear is immersed with the oil. And the second region is at the gear meshing. This region was chosen to study the squeezed oil when the gear is in contact. For measurement below the gear, five measurement planes with 5 mm apart were used to capture and measure 3D streamlines of the ...
Multihole pressure probes are widely used as accurate, robust, and versatile flowmeasuring instru... more Multihole pressure probes are widely used as accurate, robust, and versatile flowmeasuring instruments with numerous advantages over other flow measuring devices. Surprising though that a very few experimentalists, which use the multihole pressure probes in strong gradient fields, apply the spatial resolution and downwash velocity corrections. In recent experiments performed at Chalmers1 extensive measurements were performed using both the five-hole probes and cross hot-wires. During data analysis it was found that the crossflow velocity components measured by the five-hole pressure probes disagreed with those obtained using the cross hot-wires. Differences between these two measurement data sets were observed in zones of vane wakes and sidewall boundary layers where the velocity gradients are strong. Our subsequent research has revealed that a modified version of correction by Ligrani et al.2 can be used to compensate for the 5-hole probe errors caused by the velocity gradients. Th...
Thermophysics and Aeromechanics, 2004
Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear ... more Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear stage of the laminar-turbulent process in shear flows are presented. The flow behavior in the course of spatial evolution of streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical and numerical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaky structure are demonstrated, such as transverse and streamwise modulation of the structure by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-type structures localized in space in both cases.
A number of MEMS (Micro Electro Mechanical Systems) wall mounted hot wire sensors have been devel... more A number of MEMS (Micro Electro Mechanical Systems) wall mounted hot wire sensors have been developed at the Thermo and Fluid Dynamics department (TFD) at Chalmers University of Technology. The sensors were used to investigate the fluctuations of the velocity within the viscous sublayer of a zero-pressure-gradient turbulent boundary layer flow. The measurements performed at Reynolds numbers, Rθ ranging between 1000 and 15000 are discussed and compared to other relevant data collected from literature.
This paper presents a detailed experimental evaluation of the flow field in a state of the art li... more This paper presents a detailed experimental evaluation of the flow field in a state of the art linear cascade with boundary-layer suction. The linear cascade was designed using a new design-process as described by Hjarne et al. [1]. From the measurements presented in this paper it can be concluded that all of the features of the test-rig work as expected. Hence the measurements validate the design process presented by Hjarne et al. in [1].The intention with the test facility is to provide high quality benchmark cases for the flow field around aggressive designs of Low Pressure Turbine/Outlet Guide Vanes (LPT/OGV's) to be used for validation of numerical codes. The flow quality is assessed by measuring inlet uniformity, boundary-layer heights, periodicity of the static pressure distribution around the OGV's and uniformity of the outlet flow.
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. The performance of the TRS is strongly connected to secondary flow structures, which in turn are strongly influenced by the laminar-turbulent transition. Transition can be challenging to predict in turbomachinery due to the highly complex flow present. At the design point the TRS can have both by-pass transition and laminar separation with transition and a following turbulent reattachment. In addition, a TRS needs to perform well in a large off-design envelope, with large variations of the inlet swirl angle. Accurately predicting transition, both at the design point and in important off-design points, is critical for the development of future TRS modules. In modern geared ...
Active flow control can be applied using a various number of approaches. The general, yet ultimat... more Active flow control 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 experiments presented in this paper show the achievements of a synthetic jet used to mitigate and eventually suppress the recirculation bubble occurring at the A-pillars of a truck, Fig. 1a. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillars of a real truck. Figures and dimensions of the model are presented in Figs. 1 (b and c), 2, and Tab. 1, respectively. Time resolved PIV was employed to investigate the flow (Re = 5 × 10 5 ), Fig. 3. The s...
During manufacturing and in-service of the outlet guide vanes various irregularities on the vane ... more During manufacturing and in-service of the outlet guide vanes various irregularities on the vane surface can occur. These irregular shapes are surface non-conformances in the form of welds, traces or repairs of various forms. Improvement of the aerodynamic performance of the guide vanes requires understanding of the impact of these technological features on the flow field and aerodynamics. Experimental study is performed in a linear cascade facility at Chalmers University. In focus of current work are non-conformances in form of welding traces. The model welding traces were placed at different locations on the suction side of the vane. The influence of these non-conformances on the cascade aerodynamics is evaluated and validation of CFD results obtained by the k-e realizable and k-ω SST turbulence models is performed.
One of the major questions in fluid mechanics is the prediction of the mean flow and turbulence s... more One of the major questions in fluid mechanics is the prediction of the mean flow and turbulence structure of boundary layers over surfaces with different roughness types. The current paper shows a method to obtain the roughness function of different surface roughness by using a small-scale rig with rotating discs and long-distance microscopic PTV measurements in order to obtain submicron resolution inside the boundary layer of rotating disc flows. This rig has been designed and constructed for the optical measurements and consists of an electric motor driving the discs that are rotating inside of a 20-liter water tank. The PTV measurements are performed on surfaces with different degree of roughness and a smooth case. The rough cases correspond to two applications of a marine antifouling paint. The measurements are performed for two rotational speeds (300 and 600 RPM). Field mean velocity profiles are calculated by averaging vertical bins with 1 px width and every point of the mean ...
Volume 1: Aircraft Engine; Fans and Blowers; Marine; Honors and Awards, 2019
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.
The role of streamwise structures during transition to turbulence both in near-wall and in free s... more The role of streamwise structures during transition to turbulence both in near-wall and in free shear flows in many eases is determinative. The purpose of present study is the analysis of results of experimental researches of mechanisms of origin development and transition to turbulent state of the various shear flows with the streamwise structures which have been carried out of late.
Computational Methods in Multiphase Flow VI, 2011
EPJ Web of Conferences, 2012
EPJ Web of Conferences, 2012
A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency... more A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency and reducing emissions from aero-engines. This paper presents a detailed experimental evaluation of an engine realistic TRS which was studied in an engine-realistic rig at Chalmers University of Technology, Sweden. The TRS test section was equipped with three types of outlet guide vanes (OGVs) which are typical of modern state-of-the-art TRS: regular vanes, thickened vanes, and vanes with an engine mount recess (a shroud bump). Each of the three vane geometries was studied under on-design and off-design conditions at a fixed flow Reynolds number of 235,000. The study shows that the off-design performance of the TRS strongly depends on the presence of the local flow separation on the OGV suction side near the hub, which is greatly affected by the vane pressure distribution and inlet conditions. Similarly, the OGVs with increased thickness and with a vane shroud bump are shown to affect t...
Gears inside the gearbox are cooled and lubricated by oil. If the amount of oil is too little, th... more Gears inside the gearbox are cooled and lubricated by oil. If the amount of oil is too little, the lifetime of the gears is shorter due to insufficient heat dissipation, but if the amount of oil inside the gearbox is too much, it creates significant load for the gears when they are rotating, due to the shear of the oil. To find appropriate oil level inside a gearbox, understanding of the flow is needed. This study is to add understanding of the oil flow inside a gearbox and the data that has been generated will become a validation tool for numerical calculation. Two regions were chosen and measured. First region is below the gear. This region was chosen to understand the oil flow around the gear while the gear is immersed with the oil. And the second region is at the gear meshing. This region was chosen to study the squeezed oil when the gear is in contact. For measurement below the gear, five measurement planes with 5 mm apart were used to capture and measure 3D streamlines of the ...
Multihole pressure probes are widely used as accurate, robust, and versatile flowmeasuring instru... more Multihole pressure probes are widely used as accurate, robust, and versatile flowmeasuring instruments with numerous advantages over other flow measuring devices. Surprising though that a very few experimentalists, which use the multihole pressure probes in strong gradient fields, apply the spatial resolution and downwash velocity corrections. In recent experiments performed at Chalmers1 extensive measurements were performed using both the five-hole probes and cross hot-wires. During data analysis it was found that the crossflow velocity components measured by the five-hole pressure probes disagreed with those obtained using the cross hot-wires. Differences between these two measurement data sets were observed in zones of vane wakes and sidewall boundary layers where the velocity gradients are strong. Our subsequent research has revealed that a modified version of correction by Ligrani et al.2 can be used to compensate for the 5-hole probe errors caused by the velocity gradients. Th...
Thermophysics and Aeromechanics, 2004
Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear ... more Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear stage of the laminar-turbulent process in shear flows are presented. The flow behavior in the course of spatial evolution of streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical and numerical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaky structure are demonstrated, such as transverse and streamwise modulation of the structure by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-type structures localized in space in both cases.
A number of MEMS (Micro Electro Mechanical Systems) wall mounted hot wire sensors have been devel... more A number of MEMS (Micro Electro Mechanical Systems) wall mounted hot wire sensors have been developed at the Thermo and Fluid Dynamics department (TFD) at Chalmers University of Technology. The sensors were used to investigate the fluctuations of the velocity within the viscous sublayer of a zero-pressure-gradient turbulent boundary layer flow. The measurements performed at Reynolds numbers, Rθ ranging between 1000 and 15000 are discussed and compared to other relevant data collected from literature.
This paper presents a detailed experimental evaluation of the flow field in a state of the art li... more This paper presents a detailed experimental evaluation of the flow field in a state of the art linear cascade with boundary-layer suction. The linear cascade was designed using a new design-process as described by Hjarne et al. [1]. From the measurements presented in this paper it can be concluded that all of the features of the test-rig work as expected. Hence the measurements validate the design process presented by Hjarne et al. in [1].The intention with the test facility is to provide high quality benchmark cases for the flow field around aggressive designs of Low Pressure Turbine/Outlet Guide Vanes (LPT/OGV's) to be used for validation of numerical codes. The flow quality is assessed by measuring inlet uniformity, boundary-layer heights, periodicity of the static pressure distribution around the OGV's and uniformity of the outlet flow.
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. The performance of the TRS is strongly connected to secondary flow structures, which in turn are strongly influenced by the laminar-turbulent transition. Transition can be challenging to predict in turbomachinery due to the highly complex flow present. At the design point the TRS can have both by-pass transition and laminar separation with transition and a following turbulent reattachment. In addition, a TRS needs to perform well in a large off-design envelope, with large variations of the inlet swirl angle. Accurately predicting transition, both at the design point and in important off-design points, is critical for the development of future TRS modules. In modern geared ...
Active flow control can be applied using a various number of approaches. The general, yet ultimat... more Active flow control 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 experiments presented in this paper show the achievements of a synthetic jet used to mitigate and eventually suppress the recirculation bubble occurring at the A-pillars of a truck, Fig. 1a. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillars of a real truck. Figures and dimensions of the model are presented in Figs. 1 (b and c), 2, and Tab. 1, respectively. Time resolved PIV was employed to investigate the flow (Re = 5 × 10 5 ), Fig. 3. The s...
During manufacturing and in-service of the outlet guide vanes various irregularities on the vane ... more During manufacturing and in-service of the outlet guide vanes various irregularities on the vane surface can occur. These irregular shapes are surface non-conformances in the form of welds, traces or repairs of various forms. Improvement of the aerodynamic performance of the guide vanes requires understanding of the impact of these technological features on the flow field and aerodynamics. Experimental study is performed in a linear cascade facility at Chalmers University. In focus of current work are non-conformances in form of welding traces. The model welding traces were placed at different locations on the suction side of the vane. The influence of these non-conformances on the cascade aerodynamics is evaluated and validation of CFD results obtained by the k-e realizable and k-ω SST turbulence models is performed.