The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Hideki Tsuruta - One of the best experts on this subject based on the ideXlab platform.
-
experiments on vortex shedding from Flat Plates with square leading and trailing edges
Journal of Fluid Mechanics, 1991Co-Authors: Y Nakamura, Yuji Ohya, Hideki TsurutaAbstract:Vortex shedding from Flat Plates with square leading and trailing edges having chord-to-thickness ratios 3–16 at Reynolds numbers (1–3) × 10 3 is investigated experimentally in low-speed wind tunnels. It is shown that vortex shedding from Flat Plates with square leading and trailing edges is characterized by the impinging-shear-layer instability where the separated shear layer becomes unstable in the presence of a sharp trailing edge corner. The Strouhal number which is based on the plate's chord is approximately constant and equal to 0.6 for chord-to-thickness ratios 3–5. With further increase in the ratio it increases stepwise to values that are approximately equal to integral multiples of 0.6.
Changhwan Choi - One of the best experts on this subject based on the ideXlab platform.
-
experimental study of skin friction drag reduction on superhydrophobic Flat Plates in high reynolds number boundary layer flow
Physics of Fluids, 2013Co-Authors: Elias Aljallis, Mohammad Amin Sarshar, Raju Datla, Andrew K Jones, Vinod K Sikka, Changhwan ChoiAbstract:In this paper, we report the measurement of skin friction drag on superhydrophobic-coated Flat Plates in high Reynolds (Re) number boundary layer flows, using a high-speed towing tank system. Aluminum Flat Plates with a large area (4 feet × 2 feet, 3/8 in. thick) and sharpened leading/trailing edges (1 in. long) were prepared as a boundary layer flow model. Spray coating of hydrophobic nanoparticles was applied to make two different types of superhydrophobic coatings: one with low contact angle and high contact angle hysteresis, and the other with high contact angle and low contact angle hysteresis. Skin friction drag of the superhydrophobic Plates was measured in the flow speed up to 30 ft/s to cover transition and turbulent flow regimes (105 < ReL < 107), and was compared to that of an uncoated bare aluminum plate. A significant drag reduction was observed on the superhydrophobic plate with high contact angle and low contact angle hysteresis up to ∼30% in transition regime (105 < ReL < 106), which is at...
-
experimental study of skin friction drag reduction on superhydrophobic Flat Plates in high reynolds number boundary layer flow
Physics of Fluids, 2013Co-Authors: Elias Aljallis, Mohammad Amin Sarshar, Raju Datla, Andrew K Jones, Vinod K Sikka, Changhwan ChoiAbstract:In this paper, we report the measurement of skin friction drag on superhydrophobic-coated Flat Plates in high Reynolds (Re) number boundary layer flows, using a high-speed towing tank system. Aluminum Flat Plates with a large area (4 feet × 2 feet, 3/8 in. thick) and sharpened leading/trailing edges (1 in. long) were prepared as a boundary layer flow model. Spray coating of hydrophobic nanoparticles was applied to make two different types of superhydrophobic coatings: one with low contact angle and high contact angle hysteresis, and the other with high contact angle and low contact angle hysteresis. Skin friction drag of the superhydrophobic Plates was measured in the flow speed up to 30 ft/s to cover transition and turbulent flow regimes (105 < ReL < 107), and was compared to that of an uncoated bare aluminum plate. A significant drag reduction was observed on the superhydrophobic plate with high contact angle and low contact angle hysteresis up to ∼30% in transition regime (105 < ReL < 106), which is attributed to the shear-reducing air layer entrapped on the superhydrophobic surface. However, in fully turbulence regime (106 < ReL < 107), an increase of drag was observed, which is ascribed to the morphology of the surface air layer and its depletion by high shear flow. The texture of superhydrophobic coatings led to form a rugged morphology of the entrapped air layer, which would behave like microscale roughness to the liquid flow and offset the drag-reducing effects in the turbulent flow. Moreover, when the superhydrophobic coating became wet due to the removal of air by high shear at the boundary, it would amplify the surface roughness of solid wall and increase the drag in the turbulent flow. The results illustrate that drag reduction is not solely dependent on the superhydrophobicity of a surface (e.g., contact angle and air fraction), but the morphology and stability of the surface air layer are also critical for the effective drag reduction using superhydrophobic surfaces, especially in high Re number turbulent flow regimes.
Luis P Bernal - One of the best experts on this subject based on the ideXlab platform.
-
effects of pivot location and reduced pitch rate on pitching rectangular Flat Plates
AIAA Journal, 2017Co-Authors: Luis P BernalAbstract:This paper presents the results of an experimental investigation of the unsteady flow about pitching Flat Plates. Hydrodynamic force and two-dimensional particle image velocimetry measurements are reported for three pivot locations (leading edge, midchord, and trailing edge), reduced pitch rates from 0.022 to 0.39, and in still water, which corresponds to infinite reduced pitch rate. The wing has rectangular planform with effective aspect ratio 4, and the wing pitching motion is from 0 to 45 deg angle of attack. The relation between hydrodynamic force and vortical flow development as a function of pivot location and reduced pitch rate is discussed. Reasonable agreement is found between measured hydrodynamic force and quasi-steady potential flow theoretical results. Several vortical flow features are identified and discussed, including 1) the effect of pivot location and pitch acceleration on formation and evolution of vortical structures, 2) the impact of interaction between vortical flow structures on hy...
-
unsteady pitching Flat Plates
Bulletin of the American Physical Society, 2013Co-Authors: Kenneth Granlund, Luis P BernalAbstract:Direct force measurements and qualitative flow visualization were used to compare flow field evolution versus lift and drag for a nominally two-dimensional rigid Flat plate executing smoothed linear pitch ramp manoeuvres in a water tunnel. Nondimensional pitch rate was varied from 0.01 to 0.5, incidence angle from 0 to 90◦, and pitch pivot point from the leading to the trailing edge. For low pitch rates, the main unsteady effect is delay of stall beyond the steady incidence angle. Shifting the time base to account for different pivot points leads to collapse of both lift/drag history and flow field history. For higher rates, a leading edge vortex forms; its history also depends on pitch pivot point, but linear shift in time base is not successful in collapsing lift/drag history. Instead, a phenomenological algebraic relation, valid at the higher pitch rates, accounts for lift and drag for different rates and pivot points, through at least 45◦ incidence angle.
-
quasi steady response of free to pivot Flat Plates in hover
Journal of Fluids and Structures, 2013Co-Authors: Kenneth Granlund, Luis P BernalAbstract:Abstract Using force measurements and flow visualization in a water tunnel, we consider motions of rigid Flat Plates with square edges free to pivot about the leading edge between incidence angles of ±45°. The plate's leading edge undergoes a prescribed periodic rectilinear translation. During most of the translation semi-stroke, the plate rests against its incidence limiter to produce a positive angle of attack; this reverses on the opposite semi-stroke, producing a motion akin to normal-hover with delayed rotation. Three aspect ratios are considered: a nominally 2D, or wall-to-wall plate spanning the tunnel test section, and Plates of aspect ratios 3.4 and 5.5. Reynolds number effects in the range of 10 000–31 000 were not found to be significant. Aerodynamic force coefficient history was found to be aspect-ratio invariant, despite difference in flowfield evolution in the wake, and the force coefficients magnitude decreased for decreasing motion amplitudes. Flow visualization gives qualitative evidence for leading-edge and trailing-edge vortices, but no evidence was found of leading edge vortex stability or for contribution of vortices to aerodynamic loads, for sinusoidal or nonsinusoidal imposed motions of the plate. No evidence is found that the vortex system in the wake interacts with the plate during or after semi-stroke reversal. The main operative parameter governing aerodynamic force history is the ratio of semi-stroke amplitude to plate chord. Especially for the larger semi-stroke to chord ratios, aerodynamic response during the translational phase of motion is nearly quasi-steady, with decay in both thrust and force opposing the motion, in proceeding along each semi-stroke. The rotational phase of each semi-stroke is dominated by a loads spike as the plate approaches its incidence limiter. This spike largely disappears when the free-to-pivot plate is replaced with one with a prescribed rotational history. These findings offer favorable implications for analysis of flapping-wings using quasi-steady blade element models.
Y Nakamura - One of the best experts on this subject based on the ideXlab platform.
-
experiments on vortex shedding from Flat Plates with square leading and trailing edges
Journal of Fluid Mechanics, 1991Co-Authors: Y Nakamura, Yuji Ohya, Hideki TsurutaAbstract:Vortex shedding from Flat Plates with square leading and trailing edges having chord-to-thickness ratios 3–16 at Reynolds numbers (1–3) × 10 3 is investigated experimentally in low-speed wind tunnels. It is shown that vortex shedding from Flat Plates with square leading and trailing edges is characterized by the impinging-shear-layer instability where the separated shear layer becomes unstable in the presence of a sharp trailing edge corner. The Strouhal number which is based on the plate's chord is approximately constant and equal to 0.6 for chord-to-thickness ratios 3–5. With further increase in the ratio it increases stepwise to values that are approximately equal to integral multiples of 0.6.
Mehrdad Ahmadinejad - One of the best experts on this subject based on the ideXlab platform.
-
Experimental comparison of film-wise and drop-wise condensations of steam on vertical Flat Plates with the presence of air
International Communications in Heat and Mass Transfer, 2004Co-Authors: Chung Bum-jin, Kim Sin, Kim Min Chan, Mehrdad AhmadinejadAbstract:Abstract This paper presents experimental results comparing film-wise and drop-wise condensations. The condensing Plates were developed to promote film-wise or drop-wise condensation respectively. Rates of heat transfer have been measured on a single face of water-cooled Flat Plates suspended vertically in a cylindrical test section as steam and mixtures of steam and air flowed over it. In the pure steam cases, the drop-wise condensations showed much higher heat transfer rates than film-wise condensations, which showed good agreements with the Nusselt theory of natural convection condensation. However in the steam and air mixture cases, as expected, both modes of condensations fell in similar range of heat transfer rates. Due to the difference in the condensate flows, the drop-wise condensation showed even lower heat transfer rates than film-wise condensation with the presence of air.
