The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Masahito Asai - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of influences of roughness receptivity on Protuberance noise
Journal of the Physical Society of Japan, 2015Co-Authors: Masashi Kobayashi, Masahito AsaiAbstract:When a two-dimensional Protuberance is set in a laminar boundary layer, tonal sound is radiated through a feedback-loop mechanism between sound radiation from the Protuberance and generation of Tollmien–Schlichting (T–S) waves in the receptivity region. In this paper, influences of a small-height roughness glued upstream of the Protuberance on the feedback mechanism were examined experimentally in a zero-pressure-gradient laminar boundary layer at low Mach numbers. The results showed that depending on the location and height of roughness, competition between leading-edge-generated and roughness-generated T–S waves occurred and consequently governed sound radiation. Even when the roughness height was on the order of one-tenth the displacement thickness, tonal sound due to the feedback-loop between the roughness and Protuberance could be more dominant than that between the leading edge and Protuberance. It was also shown that the roughness receptivity reduced the critical Protuberance height for the occurre...
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experimental investigation of sound generation by a Protuberance in a laminar boundary layer
Physics of Fluids, 2014Co-Authors: Masashi Kobayashi, Masahito Asai, Ayumu InasawaAbstract:Sound radiation from a two-dimensional Protuberance glued on the wall in a laminar boundary layer was investigated experimentally at low Mach numbers. When the Protuberance was as high as the boundary-layer thickness, a feedback-loop mechanism set in between Protuberance-generated sound and Tollmien-Schlichting (T-S) waves generated by the leading-edge receptivity to the upstream-propagating sound. Although occurrence of a separation bubble immediately upstream of the Protuberance played important roles in the evolution of instability waves into vortices interacting with the Protuberance, the frequency of tonal vortex sound was determined by the selective amplification of T-S waves in the linear instability stage upstream of the separation bubble and was not affected by the instability of the separation bubble.
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flow recovery downstream from a surface Protuberance
Theoretical and Computational Fluid Dynamics, 2014Co-Authors: Ayumu Inasawa, J M Floryan, Masahito AsaiAbstract:A single roughness element and the beginning/end of a roughness patch represent common surface Protuberances. The flow recovers from disruptions caused by such Protuberances either by returning to its original state or by approaching a new state downstream from a Protuberance. Understanding of the recovery process is important in the determination of the sensitivity of the laminar–turbulent transition to surface Protuberances. The beginning/end of a roughness patch has been modeled as a small-height channel expansion/contraction, while a rectangular Protuberance has been used in the analysis of disruptions caused by a single roughness element. The recovery process has been studied using semi-analytical methods, direct numerical simulations as well as experiments. The size of the recovery zone has been measured using two types of criteria, one based on the properties of the stationary flow and the other one based on the characteristics of the linear instability. It has been found that the flow remains stationary without any unsteady separation at the subcritical Reynolds number Re = 5000 of interest. The effects of the step persist very far in the downstream direction; for the step height of 1 % of the channel half-height, the two-dimensional TS wave reaches asymptotic form at about 500 channels half-heights (50,000 step’s heights) downstream from the step. The length of the recovery zone is reduced by an order of magnitude if the channel returns to its upstream form downstream from the Protuberance, as demonstrated through analysis of a single roughness element. Smoothing of the downstream side of the Protuberance eliminates flow separation but does not affect the flow characteristics.
Ayumu Inasawa - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of sound generation by a Protuberance in a laminar boundary layer
Physics of Fluids, 2014Co-Authors: Masashi Kobayashi, Masahito Asai, Ayumu InasawaAbstract:Sound radiation from a two-dimensional Protuberance glued on the wall in a laminar boundary layer was investigated experimentally at low Mach numbers. When the Protuberance was as high as the boundary-layer thickness, a feedback-loop mechanism set in between Protuberance-generated sound and Tollmien-Schlichting (T-S) waves generated by the leading-edge receptivity to the upstream-propagating sound. Although occurrence of a separation bubble immediately upstream of the Protuberance played important roles in the evolution of instability waves into vortices interacting with the Protuberance, the frequency of tonal vortex sound was determined by the selective amplification of T-S waves in the linear instability stage upstream of the separation bubble and was not affected by the instability of the separation bubble.
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flow recovery downstream from a surface Protuberance
Theoretical and Computational Fluid Dynamics, 2014Co-Authors: Ayumu Inasawa, J M Floryan, Masahito AsaiAbstract:A single roughness element and the beginning/end of a roughness patch represent common surface Protuberances. The flow recovers from disruptions caused by such Protuberances either by returning to its original state or by approaching a new state downstream from a Protuberance. Understanding of the recovery process is important in the determination of the sensitivity of the laminar–turbulent transition to surface Protuberances. The beginning/end of a roughness patch has been modeled as a small-height channel expansion/contraction, while a rectangular Protuberance has been used in the analysis of disruptions caused by a single roughness element. The recovery process has been studied using semi-analytical methods, direct numerical simulations as well as experiments. The size of the recovery zone has been measured using two types of criteria, one based on the properties of the stationary flow and the other one based on the characteristics of the linear instability. It has been found that the flow remains stationary without any unsteady separation at the subcritical Reynolds number Re = 5000 of interest. The effects of the step persist very far in the downstream direction; for the step height of 1 % of the channel half-height, the two-dimensional TS wave reaches asymptotic form at about 500 channels half-heights (50,000 step’s heights) downstream from the step. The length of the recovery zone is reduced by an order of magnitude if the channel returns to its upstream form downstream from the Protuberance, as demonstrated through analysis of a single roughness element. Smoothing of the downstream side of the Protuberance eliminates flow separation but does not affect the flow characteristics.
Stephen T. Mcclain - One of the best experts on this subject based on the ideXlab platform.
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Protuberances in a Turbulent Thermal Boundary Layer
Journal of Heat Transfer-transactions of The Asme, 2011Co-Authors: Steven R. Mart, Stephen T. McclainAbstract:Recent efforts to evaluate the effects of isolated Protuberances within velocity and thermal boundary layers have been performed using transient heat transfer approaches. While these approaches provide accurate and highly resolved measurements of surface flux, measuring the state of the thermal boundary layer during transient tests with high spatial resolution presents several challenges. As such, the heat transfer enhancement evaluated during transient tests is presently correlated to a Reynolds number based either on the distance from the leading edge or on the momentum thickness. Heat flux and temperature variations along the surface of a turbine blade may cause significant differences between the shapes and sizes of the velocity and thermal boundary layer profiles. Therefore, correlations are needed which relate the states of both the velocity and thermal boundary layers to Protuberance and roughness distribution heat transfer. In this study, a series of three experiments are performed for various freestream velocities to investigate the local temperature details of Protuberances interacting with thermal boundary layers. The experimental measurements are performed using isolated Protuberances of varying thermal conductivity on a steadily heated, constant flux flat plate. In the first experiment, detailed surface temperature maps are recorded using infrared thermography. In the second experiment, the unperturbed velocity profile over the plate without heating is measured using hot-wire anemometry. Finally, the thermal boundary layer over the steadily heated plate is measured using a thermocouple probe. Because of the constant flux experimental configuration, the Protuberances provide negligible heat flux augmentation. Consequently, the variation in Protuberance temperature is investigated using the velocity boundary layer parameters, the thermal boundary layer parameters, and the local fluid temperature at the Protuberance apices. A comparison of results using plastic and steel Protuberances illuminates the importance of the shape of the thermal and velocity boundary layers in determining the minimum Protuberance temperatures.
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Protuberances in a Turbulent Thermal Boundary Layer
Volume 5: Heat Transfer Parts A and B, 2011Co-Authors: Steven R. Mart, Stephen T. McclainAbstract:Recent efforts to evaluate the effects of isolated Protuberances within velocity and thermal boundary layers have been performed using transient heat transfer approaches. While these approaches provide accurate and highly resolved measurements of surface flux, measuring the state of the thermal boundary-layer during transient tests with high spatial resolution presents several challenges. As such, the heat transfer enhancement evaluated during transient tests are presently correlated to a Reynolds number based either on the distance from the leading edge or on the momentum thickness. Heat flux and temperature variations along the surface of a turbine blade may cause significant differences between the shapes and sizes of the velocity and thermal boundary layer profiles. Therefore, correlations are needed which relate the states of both the velocity and thermal boundary layers to Protuberance and roughness distribution heat transfer. In this study, a series of three experiments are performed for various freestream velocities to investigate the local temperature details of Protuberances interacting with thermal boundary layers. The experimental measurements are performed using isolated Protuberances of varying thermal conductivity on a steadily-heated, constant flux flat plate. In the first experiment, detailed surface temperature maps are recorded using infrared thermography. In the second experiment, the unperturbed velocity profile over the plate without heating is measured using hot-wire anemometry. Finally, the thermal boundary layer over the steadily heated plate is measured using a thermocouple probe. Because of the constant flux experimental configuration, the Protuberances provide negligible heat flux augmentation. Consequently, the variation in Protuberance temperature is investigated using the velocity boundary layer parameters, the thermal boundary layer parameters, and the local fluid temperature at the Protuberance apices. A comparison of results using plastic and steel Protuberances illuminates the importance of the shape of the thermal and velocity boundary layers in determining the minimum Protuberance temperatures.Copyright © 2011 by ASME
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Heat Transfer from Protuberances
Journal of Thermophysics and Heat Transfer, 2007Co-Authors: Stephen T. Mcclain, Mario Vargas, Richard E. Kreeger, Jen-ching TsaoAbstract:An experiment by Henry et al. explored the heat transfer of flows over Protuberances in laminar and turbulent flow, simulating conditions during the beginning stages of glaze icing. This paper represents an effort to explain the heat transfer enhancement of roughness elements and Protuberances that was observed by Henry et aL In the experiments of Henry et al., a single roughness element was placed on a heated flat plate. The temperature along the flat plate and along the roughness element was measured using an infrared camera to determine the enhancement of heat transfer of the Protuberance as opposed to the smooth surface. A one-dimensional extended-surface (fin) analysis was performed to examine the results of Henry et al. Although significant assumptions were made using the extended-surface analysis, the important trends of the Henry et al. data were captured. The extended-surface analysis captured the trends of the apparent enhancement as reported by Henry et al. vs the Reynolds number based on the location from the leading edge of the surface and vs the ratio of the Protuberance height to the boundary-layer thickness. Although the absolute magnitudes of the apparent enhancement are overestimated by the extended-surface analysis, the matched trends indicate the importance of the thermal conductivity of the Protuberance, the importance of the interaction of the Protuberance with the thermal boundary layer, and the importance of radiation into the Protuberance.
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Heat Transfer from Roughness Elements and Protuberances Part II - Correlations for Protuberance Heat Transfer
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006Co-Authors: Stephen T. Mcclain, Mario Vargas, Richard E. Kreeger, Jen-ching TsaoAbstract:In Part II, fin effectiveness is identified as a better measure of heat transfer enhancement over large roughness elements as opposed to the minimum roughness element surface temperature. The Extended Surface–Discrete Element Method (ES-DEM) is extended to calculate fin effectiveness versus the ratio of the Protuberance height to the boundary layer thickness (k/δ) for Protuberance heights of 1.7 mm and 2.8 mm in laminar flow. The use of the thermal boundary layer thickness (δT) as a better length scale is discussed. For the same Protuberance heights, fin effectiveness versus k/δ in the range of 1.25 >1) in laminar and turbulent flow. The same analysis is repeated for Protuberances that are comparable or smaller than the thermal boundary layer thickness and a correlation is developed. The correlation indicates the important parameters for predicting the fin effectiveness for Protuberances, and includes a new parameter: the thermal boundary layer correction factor, K. A methodology based on the correlations is presented to calculate the fin efficiency for a hemispherical Protuberance in laminar boundary layer with constant heat flux. A correlation is also proposed to predict the heat enhancement for ordered distributions of roughness elements of the same shape in laminar flow. Predictions from the ES-DEM are compared to experimental data from Poinsatte. The results are the first step toward the development and validation of ES-DEM correlations that can be used in heat transfer models of ice accretion codes.
Masamichi Fujihira - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics simulations of friction between an ordered organic monolayer and a rigid slider with an atomic scale Protuberance
Physical Review B, 2000Co-Authors: Takuya Ohzono, Masamichi FujihiraAbstract:The atomic-scale friction between an ordered organic monolayer and a rigid probing slider with an atomic-scale Protuberance was investigated using a molecular dynamics method. The slider was used to model the tip apex used in atomic force microscopy. In order to control the normal load, three orthogonal springs and a feedback regulation unit were introduced. The Protuberance, composed of a small number of atoms, brought about local and collective deformation of the monolayer and generated a friction force. Various frictional properties were investigated in terms of the size of the Protuberance, the length of molecules in the monolayer, and the conditions, such as temperature, applied normal load, and some parameters of the external observation system. Lattice-resolved friction signals were obtained when the size of the Protuberance was comparable to the cross-sectional area of the molecule.
Masashi Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of influences of roughness receptivity on Protuberance noise
Journal of the Physical Society of Japan, 2015Co-Authors: Masashi Kobayashi, Masahito AsaiAbstract:When a two-dimensional Protuberance is set in a laminar boundary layer, tonal sound is radiated through a feedback-loop mechanism between sound radiation from the Protuberance and generation of Tollmien–Schlichting (T–S) waves in the receptivity region. In this paper, influences of a small-height roughness glued upstream of the Protuberance on the feedback mechanism were examined experimentally in a zero-pressure-gradient laminar boundary layer at low Mach numbers. The results showed that depending on the location and height of roughness, competition between leading-edge-generated and roughness-generated T–S waves occurred and consequently governed sound radiation. Even when the roughness height was on the order of one-tenth the displacement thickness, tonal sound due to the feedback-loop between the roughness and Protuberance could be more dominant than that between the leading edge and Protuberance. It was also shown that the roughness receptivity reduced the critical Protuberance height for the occurre...
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experimental investigation of sound generation by a Protuberance in a laminar boundary layer
Physics of Fluids, 2014Co-Authors: Masashi Kobayashi, Masahito Asai, Ayumu InasawaAbstract:Sound radiation from a two-dimensional Protuberance glued on the wall in a laminar boundary layer was investigated experimentally at low Mach numbers. When the Protuberance was as high as the boundary-layer thickness, a feedback-loop mechanism set in between Protuberance-generated sound and Tollmien-Schlichting (T-S) waves generated by the leading-edge receptivity to the upstream-propagating sound. Although occurrence of a separation bubble immediately upstream of the Protuberance played important roles in the evolution of instability waves into vortices interacting with the Protuberance, the frequency of tonal vortex sound was determined by the selective amplification of T-S waves in the linear instability stage upstream of the separation bubble and was not affected by the instability of the separation bubble.
