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Christian Klein - One of the best experts on this subject based on the ideXlab platform.
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skin friction based identification of the critical lines in a transonic high reynolds number flow via Temperature Sensitive Paint
Sensors, 2021Co-Authors: Marco Costantini, Christian Klein, Ulrich Henne, Massimo MiozziAbstract:In this contribution, three methodologies based on Temperature-Sensitive Paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface Temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of Temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Gottingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.
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application of the Temperature Sensitive Paint method for quantitative measurements in water
Measurement Science and Technology, 2021Co-Authors: Jonathan Lemarechal, Christian Klein, Dominik K Puckert, Ulrich RistAbstract:In this paper the characteristics of a Europium-based Temperature-Sensitive Paint (TSP) in polyurethane (PUR) clear coat submerged in water are investigated. It is shown that the Temperature sensitivity is not affected by water. However, the optical transmission of the PUR is reduced, which reduces the measurable emission of the TSP. Furthermore, a TSP measurement in the laminar water channel at the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, was set up. In this experiment the skin friction field for two types of roughness elements, i.e., a truncated cylinder and an array of cuboids, in a Blasius like boundary layer is investigated. Additionally, the Temperature field was recorded with sub-millimeter resolution while an artificial heat flux was applied. A modification of the Colburn analogy is used to derive the skin friction from the Temperature measurement. Skin friction results derived from velocity measurements are in good agreement with the TSP results. The experimental setup provides a resolution of the Temperature and skin friction measurement of (∆T )min < 0:007 K and (∆τ)min ≤ 4:01 × 10−5 N=m2 (≤1 %), respectively. Additionally the uncertainty of the Temperature and skin friction measurement is analyzed.
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taylor hypothesis applied to direct measurement of skin friction using data from Temperature Sensitive Paint
Experimental Thermal and Fluid Science, 2020Co-Authors: Massimo Miozzi, Christian Klein, Fabio Di Felice, Marco CostantiniAbstract:Abstract We report about the feasibility of two criteria for the direct measurement of the skin friction τ which are based on the investigation of the passive transport of Temperature fluctuations, as obtained from Temperature-Sensitive Paint (TSP) data. The first criterion represents a proof-of-concept about the reliability of the use of the passive transport of Temperature fluctuations T w for the estimation of u τ . It relies on the identification of the time lag corresponding to the correlation peak between Temperature time histories taken at points separated by fixed streamwise distance from the investigated location. The second criterion expands the former to check the feasibility of the skin friction measurement by means of T w propagation celerity in a wider range of flow conditions. It is derived by minimizing the deviation from the Taylor hypothesis of the equation of transport of Temperature fluctuations, which corresponds to the energy equation for incompressible flows at the investigated conditions. Firstly, a common rule about the relationships between propagation celerity U T of the Temperature disturbances at the wall beneath a turbulent boundary layer and friction velocity u τ is assessed from literature. Starting from this theoretical basis, the focus is placed on the flow over the suction side of a NACA 0015 hydrofoil model and in particular on the laminar separation bubble developing on this model surface, investigated experimentally at a chord Reynolds number of Re = 1.8 × 10 5 and angles of attack AoA = [ 1 ° , 3 ° , 5 ° , 7 ° , 10 ° ] . The profiles of time- and spanwise-averaged U T ( x ) and C f ( x ) (friction coefficient) are proposed and critically analyzed. Time averaged maps of the same quantities are then reported and commented as well. Paper topics are focused on: • The relationship between the propagation celerity of the velocity disturbances U U and the friction velocity u τ • The relationship between the propagation celerity of the Temperature disturbances U T and U U • The algorithms for the extraction of the propagation celerity of Temperature perturbations U T based on both the time lag of the correlation peak occurrence and the minimization of the deviation of transport equation for Temperature fluctuations from the Taylor’s hypothesis. • The resulting profiles and maps of friction quantities u τ and C f .
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Surface Temperature Effects on Boundary-Layer Transition at Various Subsonic Mach Numbers and Streamwise Pressure Gradients
New Results in Numerical and Experimental Fluid Mechanics XII, 2020Co-Authors: Marco Costantini, Steffen Risius, Christian KleinAbstract:The effect on transition of a non-adiabatic surface was systematically studied in the present experimental work in combination with the influence of variations in Mach number and pressure gradient. The investigations were carried out in a (quasi-) two-dimensional flow at four different subsonic Mach numbers and chord Reynolds numbers up to 13 million. Various streamwise pressure gradients and wall Temperature ratios were examined. The experiments were conducted in the low-turbulence Cryogenic Ludwieg-Tube Göttingen on a two-dimensional flat-plate configuration designed for an essentially uniform pressure gradient on the model upper surface. The model was instrumented with a Temperature-Sensitive Paint to measure globally and non-intrusively the surface Temperature and thus the boundary-layer transition. A marked influence of a variation in the wall Temperature ratio on transition was observed for all considered Mach numbers, being this effect more pronounced at lower Mach numbers. The measured transition locations were also correlated with the results of linear local stability analysis. Smaller disturbance amplification factors were found at transition for larger Mach numbers and, in most of the examined cases, for smaller wall Temperature ratios and stronger flow acceleration.
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investigation of stationary crossflow instability induced transition with the Temperature Sensitive Paint method
Experimental Thermal and Fluid Science, 2019Co-Authors: Jonathan Lemarechal, Marco Costantini, Christian Klein, Markus J Kloker, W Wurz, Holger B E Kurz, Thomas Streit, Sven SchaberAbstract:Abstract The Temperature-Sensitive Paint (TSP) method is used for surface-based flow visualizations on a swept-wing wind-tunnel model with a generic natural laminar-flow airfoil. Within the investigated parameter range the stationary crossflow instability is the dominating instability mechanism. Based on the TSP results the location of the laminar-turbulent transition and the most amplified wavenumber of the stationary crossflow instability are determined. The test is performed with three different conditions of the leading-edge surface: highly polished, unpolished, and highly polished with discrete roughness elements applied. The Temperature-Sensitive Paint method has proven to have sufficient spatial resolution and Temperature sensitivity to resolve skin friction variations to detect the footprint of stationary crossflow vortices even inside of turbulent wedges. With the discrete roughness elements, i.e. cylindrical elements with micron-sized height, the transition could be delayed successfully for certain conditions. Local low-frequency movement of the beginning of turbulent wedges was detected for some data points with an unpolished leading edge.
Marco Costantini - One of the best experts on this subject based on the ideXlab platform.
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skin friction based identification of the critical lines in a transonic high reynolds number flow via Temperature Sensitive Paint
Sensors, 2021Co-Authors: Marco Costantini, Christian Klein, Ulrich Henne, Massimo MiozziAbstract:In this contribution, three methodologies based on Temperature-Sensitive Paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface Temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of Temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Gottingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.
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Surface Temperature Effects on Boundary-Layer Transition at Various Subsonic Mach Numbers and Streamwise Pressure Gradients
New Results in Numerical and Experimental Fluid Mechanics XII, 2020Co-Authors: Marco Costantini, Steffen Risius, Christian KleinAbstract:The effect on transition of a non-adiabatic surface was systematically studied in the present experimental work in combination with the influence of variations in Mach number and pressure gradient. The investigations were carried out in a (quasi-) two-dimensional flow at four different subsonic Mach numbers and chord Reynolds numbers up to 13 million. Various streamwise pressure gradients and wall Temperature ratios were examined. The experiments were conducted in the low-turbulence Cryogenic Ludwieg-Tube Göttingen on a two-dimensional flat-plate configuration designed for an essentially uniform pressure gradient on the model upper surface. The model was instrumented with a Temperature-Sensitive Paint to measure globally and non-intrusively the surface Temperature and thus the boundary-layer transition. A marked influence of a variation in the wall Temperature ratio on transition was observed for all considered Mach numbers, being this effect more pronounced at lower Mach numbers. The measured transition locations were also correlated with the results of linear local stability analysis. Smaller disturbance amplification factors were found at transition for larger Mach numbers and, in most of the examined cases, for smaller wall Temperature ratios and stronger flow acceleration.
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taylor hypothesis applied to direct measurement of skin friction using data from Temperature Sensitive Paint
Experimental Thermal and Fluid Science, 2020Co-Authors: Massimo Miozzi, Christian Klein, Fabio Di Felice, Marco CostantiniAbstract:Abstract We report about the feasibility of two criteria for the direct measurement of the skin friction τ which are based on the investigation of the passive transport of Temperature fluctuations, as obtained from Temperature-Sensitive Paint (TSP) data. The first criterion represents a proof-of-concept about the reliability of the use of the passive transport of Temperature fluctuations T w for the estimation of u τ . It relies on the identification of the time lag corresponding to the correlation peak between Temperature time histories taken at points separated by fixed streamwise distance from the investigated location. The second criterion expands the former to check the feasibility of the skin friction measurement by means of T w propagation celerity in a wider range of flow conditions. It is derived by minimizing the deviation from the Taylor hypothesis of the equation of transport of Temperature fluctuations, which corresponds to the energy equation for incompressible flows at the investigated conditions. Firstly, a common rule about the relationships between propagation celerity U T of the Temperature disturbances at the wall beneath a turbulent boundary layer and friction velocity u τ is assessed from literature. Starting from this theoretical basis, the focus is placed on the flow over the suction side of a NACA 0015 hydrofoil model and in particular on the laminar separation bubble developing on this model surface, investigated experimentally at a chord Reynolds number of Re = 1.8 × 10 5 and angles of attack AoA = [ 1 ° , 3 ° , 5 ° , 7 ° , 10 ° ] . The profiles of time- and spanwise-averaged U T ( x ) and C f ( x ) (friction coefficient) are proposed and critically analyzed. Time averaged maps of the same quantities are then reported and commented as well. Paper topics are focused on: • The relationship between the propagation celerity of the velocity disturbances U U and the friction velocity u τ • The relationship between the propagation celerity of the Temperature disturbances U T and U U • The algorithms for the extraction of the propagation celerity of Temperature perturbations U T based on both the time lag of the correlation peak occurrence and the minimization of the deviation of transport equation for Temperature fluctuations from the Taylor’s hypothesis. • The resulting profiles and maps of friction quantities u τ and C f .
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investigation of stationary crossflow instability induced transition with the Temperature Sensitive Paint method
Experimental Thermal and Fluid Science, 2019Co-Authors: Jonathan Lemarechal, Marco Costantini, Christian Klein, Markus J Kloker, W Wurz, Holger B E Kurz, Thomas Streit, Sven SchaberAbstract:Abstract The Temperature-Sensitive Paint (TSP) method is used for surface-based flow visualizations on a swept-wing wind-tunnel model with a generic natural laminar-flow airfoil. Within the investigated parameter range the stationary crossflow instability is the dominating instability mechanism. Based on the TSP results the location of the laminar-turbulent transition and the most amplified wavenumber of the stationary crossflow instability are determined. The test is performed with three different conditions of the leading-edge surface: highly polished, unpolished, and highly polished with discrete roughness elements applied. The Temperature-Sensitive Paint method has proven to have sufficient spatial resolution and Temperature sensitivity to resolve skin friction variations to detect the footprint of stationary crossflow vortices even inside of turbulent wedges. With the discrete roughness elements, i.e. cylindrical elements with micron-sized height, the transition could be delayed successfully for certain conditions. Local low-frequency movement of the beginning of turbulent wedges was detected for some data points with an unpolished leading edge.
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experimental investigation of surface imperfection effects on boundary layer transition using Temperature Sensitive Paints
2017Co-Authors: Marco Costantini, Steffen Risius, Carsten Fuchs, Christian KleinAbstract:The effect of sharp forward-facing steps and sinusoidal bumps on boundary-layer transition was systematically investigated in this experimental work in combination with the influence of variations in the following parameters: streamwise pressure gradient, Reynolds number and Mach number. The experiments were conducted in a quasi-two-dimensional flow at high Reynolds numbers and at both low and high subsonic Mach numbers in the Cryogenic Ludwieg-Tube Gottingen. The adopted experimental setup enabled an independent variation of the aforementioned parameters and allowed a decoupling of their respective effects on the boundary-layer transition. Transition, measured non-intrusively by means of Temperature-Sensitive Paint, was found to move gradually upstream towards the imperfection location with increaslng non-dimensional imperfection parameters. Stronger flow acceleration led to an increase in the transltlon Reynolds number even in the presence of forward-facing steps and bumps; this favorable influence became, however, less pronounced at larger values of the non-dimensional lmperfection parameters.
Massimo Miozzi - One of the best experts on this subject based on the ideXlab platform.
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skin friction based identification of the critical lines in a transonic high reynolds number flow via Temperature Sensitive Paint
Sensors, 2021Co-Authors: Marco Costantini, Christian Klein, Ulrich Henne, Massimo MiozziAbstract:In this contribution, three methodologies based on Temperature-Sensitive Paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface Temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of Temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Gottingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.
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taylor hypothesis applied to direct measurement of skin friction using data from Temperature Sensitive Paint
Experimental Thermal and Fluid Science, 2020Co-Authors: Massimo Miozzi, Christian Klein, Fabio Di Felice, Marco CostantiniAbstract:Abstract We report about the feasibility of two criteria for the direct measurement of the skin friction τ which are based on the investigation of the passive transport of Temperature fluctuations, as obtained from Temperature-Sensitive Paint (TSP) data. The first criterion represents a proof-of-concept about the reliability of the use of the passive transport of Temperature fluctuations T w for the estimation of u τ . It relies on the identification of the time lag corresponding to the correlation peak between Temperature time histories taken at points separated by fixed streamwise distance from the investigated location. The second criterion expands the former to check the feasibility of the skin friction measurement by means of T w propagation celerity in a wider range of flow conditions. It is derived by minimizing the deviation from the Taylor hypothesis of the equation of transport of Temperature fluctuations, which corresponds to the energy equation for incompressible flows at the investigated conditions. Firstly, a common rule about the relationships between propagation celerity U T of the Temperature disturbances at the wall beneath a turbulent boundary layer and friction velocity u τ is assessed from literature. Starting from this theoretical basis, the focus is placed on the flow over the suction side of a NACA 0015 hydrofoil model and in particular on the laminar separation bubble developing on this model surface, investigated experimentally at a chord Reynolds number of Re = 1.8 × 10 5 and angles of attack AoA = [ 1 ° , 3 ° , 5 ° , 7 ° , 10 ° ] . The profiles of time- and spanwise-averaged U T ( x ) and C f ( x ) (friction coefficient) are proposed and critically analyzed. Time averaged maps of the same quantities are then reported and commented as well. Paper topics are focused on: • The relationship between the propagation celerity of the velocity disturbances U U and the friction velocity u τ • The relationship between the propagation celerity of the Temperature disturbances U T and U U • The algorithms for the extraction of the propagation celerity of Temperature perturbations U T based on both the time lag of the correlation peak occurrence and the minimization of the deviation of transport equation for Temperature fluctuations from the Taylor’s hypothesis. • The resulting profiles and maps of friction quantities u τ and C f .
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global and local skin friction diagnostics from tsp surface patterns on an underwater cylinder in crossflow
Physics of Fluids, 2016Co-Authors: Massimo Miozzi, Alessandro Capone, Fabio Di Felice, Christian KleinAbstract:A systematical method is formulated for extracting skin-friction fields from Temperature Sensitive Paint (TSP) images in the sense of time-averaging and phase-averaging. The method is applied to an underwater cylinder in crossflow at two subcritical regimes (Re = 72 000 and 144 000). TSP maps are decomposed in a time-averaged, a phase-averaged, and a random component. The asymptotic form of the energy equation at the wall provides an Euler-Lagrange equation set that is solved numerically to gain the relative skin friction time- and phase-averaged fields from the TSP surface Temperature maps. The comparison of the time averaged relative skin-friction profiles with the literature data shows an excellent agreement on the whole laminar boundary layer up to the laminar separation line. Downstream of separation, time averaged results identify the secondary reattachment/separation events, which are lost in the available literature data. The periodic behavior of the skin-friction is taken, describing how the lami...
Costantini Marco - One of the best experts on this subject based on the ideXlab platform.
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A Robust Method for Reliable Transition Detection in Temperature-Sensitive Paint Data
'Elsevier BV', 2021Co-Authors: Costantini Marco, Henne Ulrich, Risius Steffen, Klein ChristianAbstract:This work presents a method to automatically detect boundary-layer transition on thermographic images of aerodynamic surfaces, acquired using the Temperature-Sensitive Paint measurement technique. It is applied to surface Temperature distributions mapped onto three-dimensional grids representing the surfaces of interest. Motivated and substantiated by earlier work, the transition location is determined at the location corresponding to the maximal value of the streamwise gradient of the surface Temperature in the transitional region. The robustness of the transition detection method was proven for a challenging case with low signal to-noise ratio and moderate streamwise Temperature gradients. Moreover, the present method was validated against transition data obtained using an uncorrelated transition detection method based on the measurement of surface pressure fluctuations. The developed transition detection algorithm enabled the accurate, reliable, and consistent detection of the transition location under a variety of test conditions, including experiments on natural laminar flow airfoil and wing models at high Reynolds numbers and high subsonic Mach numbers
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Taylor hypothesis applied to direct measurement of skin friction using data from Temperature Sensitive Paint
'Elsevier BV', 2020Co-Authors: Miozzi Massimo, Di Felice Fabio, Klein Christian, Costantini MarcoAbstract:We report about the feasibility of two criteria for the direct measurement of the skin friction which ground on the investigation of the passive transport of Temperature fluctuations, as obtained from Temperature-Sensitive Paint (TSP) data. To this aim, the relationships between the propagation velocity of the Temperature disturbances at the wall beneath a turbulent boundary layer and the friction velocity is firstly assessed from literature as a common rule of these reverse strategies. The first criterion represents a proof-of-concept of the reliability of the use of the passive transport of Temperature fluctuations for the estimation of the friction velocity. It relies on the identification of the time lag corresponding to the correlation peak between Temperature time histories taken at points separated by fixed streamwise distance from the investigated location. The second criterion is derived by minimizing the deviation from the Taylor hypothesis of the equation of transport of Temperature fluctuations (energy equation for incompressible flows at investigated conditions). Starting from these theoretical basis, the focus is placed on the flow around the suction side of a NACA 0015 hydrofoil model and on the Laminar Separation Bubble beneath, investigated experimentally at chord Reynolds number Re = 180000 and angles of attack AoA = [1°; 3°; 5°; 7°; 10°]. The time- and spanwise-averaged propagation velocity of the Temperature disturbances and friction coefficient are proposed and criticized. Averaged maps of the same quantities are then reported and commented as well
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Skin friction on a NACA0015 profile in the wake of a marine propeller
Hydro-Testing Forum, 2019Co-Authors: Miozzi Massimo, Dubbioso Giulio, Muscari Roberto, Costantini MarcoAbstract:We report about the feasibility to experimentally characterize the interaction between a propeller and a hydrofoil model at incidence in its wake by using a Temperature-Sensitive Paint. The experiments were conducted in a cavitation water tunnel at a freestream speed of 3.4 m/s and at a propeller rotational speed of 17 rps for two model angles of attack (4° and 8°). Time-resolved maps of the Temperature evolution on both suction and pressure sides of the model obtained by means of the Temperature-Sensitive Paint allow to take advantage of the direct link between friction velocity and celerity of propagation of Temperature disturbances. By minimizing the dissimilarity between the observed propagation and that of the ideal wave suggested by the Taylor hypothesis, a quantitative estimation of the friction velocity vector field is gained. Detached eddy simulations are also conducted for the examined problem in the case of a model angle of attack of 4°, providing numerical data that are compared with the experimental results. The analysis of time-averaged results unveil the existence of laminar separation bubbles, stretched and folded according to the constructive / destructive coupling of the pressure fields induced by the hydrofoil incidence and by the propeller streamtube
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Incipient stall characterization from skin friction maps
2019Co-Authors: Miozzi Massimo, Di Felice Fabio, Klein Christian, Costantini MarcoAbstract:We experimentally characterize the incipient stall condition which develops on the suction side of a NACA 0015 hydrofoil model at Re = 180000, by observing the skin friction evolution on the model surface. Grounding on Temperature data acquired via Temperature Sensitive Paint (TSP), the proposed approach adopts a two-fold point of view. From one side, the relative skin-friction vector fields, extracted from Temperature maps by means of an optical-flow-based algorithm, provide flow topology at the wall and feed a physics-based criterion for the identification of flow separation and reattachment. From the other side, a direct link between friction velocity and celerity of propagation of Temperature disturbances is established on the basis of currently available results in scientific literature. Then, the time averaged streamwise component of velocity of passive transport of Temperature disturbances is estimated after minimization of the dissimilarity between observed and ideal wave behavior suggested by the Taylor hypothesis. Eventually, a quantitative estimation of time averaged friction-velocity maps is gained. We describe, through the synergistic application of the proposed methods, the incipient stall evolution by firstly identifying the trailing edge separation at an angle-of-attack AoA = 11.5° and then by capturing the onset of upstream oriented mushroom-like structures at AoA = 13°. The concomitant occurrence of both scenarios is reported as well (AoA = 12.2°)
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Experimental Analysis of a Wind-Turbine Rotor Blade Airfoil by means of Temperature-Sensitive Paint
'American Institute of Aeronautics and Astronautics (AIAA)', 2019Co-Authors: Costantini Marco, Klein Christian, Henne Ulrich, Ondrus Vladimir, Fuchs Carsten, Bruse Martin, Löhr Markus, Jacobs MarkusAbstract:Knowledge on the boundary-layer transition location at large chord Reynolds numbers (Re ≥ 3 million) is essential to evaluate the performance of airfoils designed for modern wind-turbine rotor blades, which rotor diameters can be of the order of hundred meters. In the present work, a Temperature-Sensitive Paint (TSP) was used to systematically study boundary-layer transition on the suction side of a DU 91-W2-250 airfoil. The experiments were performed in the High-Pressure Wind Tunnel Göttingen at chord Reynolds numbers up to Re = 12 million and angles-of-attack from -14° to 20°. The coefficients of airfoil lift, drag, and pitching moment were also obtained after integration of the pressure distributions measured on the wind-tunnel model surface and in the model wake. The surface data obtained by means of TSP enabled not only to analyze the evolution of the transition location with varying angle-of-attack and chord Reynolds number, but also to provide an explanation for the evolution of the aerodynamic coefficients measured at stall and post-stall conditions. The stability of the laminar boundary layers investigated in the experiments was analyzed according to linear stability theory. The results of the stability computations supported the experimentally observed variations in the transition location. The amplification factors of boundary-layer disturbances at transition were also determined by correlating the experimental and numerical results
Yingzheng Liu - One of the best experts on this subject based on the ideXlab platform.
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assessment of film cooling s surface quantities using pressure and Temperature Sensitive Paint comparisons between shaped and sand dune inspired holes
Experimental Thermal and Fluid Science, 2019Co-Authors: Wenwu Zhou, Di Peng, Yingzheng LiuAbstract:Abstract Following the previous work (Zhou and Hu, 2017), a comprehensive assessment was performed to further evaluate the film cooling’s surface quantities behind shaped and sand dune-inspired holes. Adiabatic film cooling effectiveness, heat transfer coefficient, and net heat flux reduction (NHFR) were measured at four blowing ratios (M = 0.40, 0.90, 1.40, and 2.00). The measured quantities were compared side-by-side between the shaped and sand dune-inspired holes. The pressure-Sensitive Paint (PSP) technique was used to acquire high-resolution adiabatic effectiveness and the Temperature-Sensitive Paint (TSP) technique was used to map the corresponding heat transfer coefficient over the surface. Nitrogen and air, with a density ratio of about one, were used as the coolant for the PSP and TSP tests respectively. The measured results showed that the adiabatic effectiveness of the Barchan dune-shaped injection compound (BDSIC) was significantly higher than that of the shaped hole. Improvements of 20–150% in the centerline and 30–400% in the laterally averaged effectiveness were observed behind the BDSIC compared to the shaped hole. As for the heat transfer performance, although the BDSIC showed 10–20% higher heat transfer coefficient, hf/h0, the measured spatially averaged NHFR still demonstrated an augmentation of 50–150% in heat flux reduction in comparison to the shaped hole. This paper represents the first effort to comprehensively evaluate the surface quantities behind BDSIC film cooling concept using both PSP and TSP techniques.
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complementary Temperature Sensitive Paint measurements and cfd analysis of wall heat transfer of cubes in tandem in a turbulent channel flow
Experimental Thermal and Fluid Science, 2018Co-Authors: Zahra Ghorbanitari, Yujia Chen, Yingzheng LiuAbstract:Abstract The influence of cubes-in-tandem on wall heat transfer in turbulent channel flow is investigated using complementary methods of Temperature-Sensitive Paint (TSP) measurements and computational fluid dynamics (CFD). Three systems—a single cube and cubes-in-tandem at spacing-to-span-wise widths (S/d) of 3 and 4—were comparatively studied. For the single cube, a high level of turbulence in opposite-circulation vortices occurred for significant augmentation of convective heat transfer. For the tandem system at 3d, circulation was periodically advected downstream from two symmetric vortices, in alternating fashion; this mechanism was found to promote a high heat transfer rate across the leading face of the downstream cube. When the spacing was increased sufficiently, i.e., 4d, a new horseshoe vortex system occurred for substantial enhancement along the front face of the downstream cube. As such, the system at 4d promoted a distinct flow field in the wake region of the downstream cube, which was responsible for larger augmentation of the heat transfer area. The results showed that the heat transfer was enhanced in the inter-body space of the system at 4d as compared with the single cube. Behind the downstream cubes, the enhancement of heat transfer was pertinent to the unsteadiness of circulation vortices; meanwhile, the heat transfer monotonically decreased by the stream-wise distance for the single cube.
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jet impingement heat transfer of a lobed nozzle measurements using Temperature Sensitive Paint and particle image velocimetry
International Journal of Heat and Fluid Flow, 2018Co-Authors: Yingzheng LiuAbstract:Abstract The impingement jet issuing from the lobed nozzles constructed using three small circular orifices is intensively investigated; the heat transfer characteristics and flow fields are respectively determined using Temperature-Sensitive Paint (TSP) and particle image velocimetry (PIV). A piece of fluorine-doped tin oxide (FTO)-coated glass with uniform wall heat flux is used for optical access in TSP measurements. In particular, the effects of the geometrical variations are compared by varying the ratio of the orifice centre offset to the orifice radius, i.e., a/b = 0, 0.5, 0.8, 1.0, 1.1 and 1.15, at a constant equivalent diameter De for all configurations to ensure a constant cross-section area of the nozzles. The TSP measurements of the impingement heat transfer at Reynolds numbers R e = 10,000 and 40,000 are performed using different nozzle-to-wall distances, i.e., H / D e = 2, 4 and 6, to determine the mean Nusselt number distribution on the heated wall. The results show that the heat transfer is enhanced using lobed jets at H/De ≤ 4. At H / D e = 2, the optimal Nusselt number is obtained using a lobed nozzle a / b = 0.8 in the region 1 H / D e = 4, the azimuthal-averaged Nusselt number increases (up to 16%) consistently in the region r/De H / D e = 6, the Nusselt number in the entire measured region decays with an increase in a/b. Finally, the PIV measurements of the flow fields at R e = 10,000 are performed at H / D e = 2 and 4 and a / b = 0, 0.8 and 1.15. The results show that the heat transfer enhancement can be attributed to the increased turbulence level in the wall-jet zone at H / D e = 2 and in the stagnation region at H / D e = 4.
