Search

The aerodynamic interaction between the wake flow structure behind a single spire with a smooth wall boundary layer at a long streamwise location was observed in a wind tunnel experiment. The application of a single spire is intended to generate a wake flow similar to the one generated behind a skyscraper. A quarter elliptic wedge spire was used and a long streamwise distance of up to 26 times the spire’s height was adopted to ensure the development of the boundary layer and the wake recovery. To grasp how the smooth wall boundary layer interacts with the wake as well as how the wake recovers downstream, vertical and lateral velocity profiles were examined. Despite only one spire being utilized, it was found that the role of the spire as a vortex generator was confirmed the boundary layer height in the with-spire case increased compared to that of the without-spire case. Moreover, the velocity deficit recovery process was observed vertically and streamwise. However, within the boundary layer, the recovery rate in the streamwise direction was lower compared to the above it. This finding indicates that within the boundary, the turbulence generated can sustain the wake caused by the spire, reducing the recovery rate. Based on the current lateral velocity analysis, the final streamwise distance required by the wake to fully recover could not be predicted due to the large velocity deviation of 2.15% at the end of the streamwise distance.

The aerodynamic interaction between the wake flow structure behind a single spire with a smooth wall boundary layer at a long streamwise location was observed in a wind tunnel experiment. The application of a single spire is intended to generate a wake flow similar to the one generated behind a skyscraper. A quarter elliptic wedge spire was used and a long streamwise distance of up to 26 times the spire's height was adopted to ensure the development of the boundary layer and the wake recovery. To grasp how the smooth wall boundary layer interacts with the wake as well as how the wake recovers downstream, vertical and lateral velocity profiles were examined. Despite only one spire being utilized, it was found that the role of the spire as a vortex generator was confirmed the boundary layer height in the with-spire case increased compared to that of the without-spire case. Moreover, the velocity deficit recovery process was observed vertically and streamwise. However, within the boundary layer, the recovery rate in the streamwise direction was lower compared to the above it. This finding indicates that within the boundary, the turbulence generated can sustain the wake caused by the spire, reducing the recovery rate. Based on the current lateral velocity analysis, the final streamwise distance required by the wake to fully recover could not be predicted due to the large velocity deviation of 2.15% at the end of the streamwise distance. [ABSTRACT FROM AUTHOR]

The purpose of this study is to determine whether it is possible to reduce the upstream and downstream length of a measuring pipeline by installing different types of air flow conditioners. The main goal is to investigate the distance position of these flow conditioners and thus analyze their impact on flow conditions within the pipeline. To improve the current conditions in the pipeline, an analysis was performed of how measurement accuracy was impacted by installing different types of air flow conditioners. Measurement accuracy would also be improved. The preliminary analysis included two different types of flow conditioners: Zanker and NEL. Both were inserted into a measuring pipeline for measuring velocity field and profiles, and thus reduce uncertainty during measurements. A CFD model was built for each type of the air flow conditioner that simulated its impact on velocity fields in the measuring pipeline using the ANSYS Fluent software package. Numerical results of velocity profiles were validated and compared with experimental result. The Zanker flow conditioner was selected for the installation in the measuring pipeline due to better results compared to NEL. Based on the numerical results, the air flow conditioner was optimized and the most suitable conditioner was selected, in this case D/10-V3.

The corrugated lobed nozzle is an emerging research topic in jet flow dynamics, and little investigation has been conducted on its effect on flow characteristics. Thus, in this study, the effects of lobe count and lobe length of corrugated lobed nozzles on subsonic jet characteristics were experimentally investigated by analyzing the velocity profiles of the jets emanating from the nozzles. The Pitot tube readings were obtained by varying the count (4 ≤ N ≤ 8) and length (10 mm ≤ L ≤ 20 mm) of corrugated lobes. These measurements were then compared with the experimental readings obtained for a baseline circular nozzle. The nozzle pressure ratio (NPR) and exit nozzle area were kept identical at 1.5 and 600 mm2, respectively, for all nozzle configurations. The most striking observation was the ‘W’-shaped radial velocity profile of the corrugated nozzle, which differed from the ‘Top hat’ profile of the baseline circular nozzle. Additionally, the length of the potential central region of the corrugated nozzle was always shorter than that of the baseline circular nozzle, indicating the early occurrence of turbulence in the former. It was found that the lobe length had a meagre effect on the velocity variation in the jet issuing from the corrugated nozzle, whereas the lobe count had a significant effect on the velocity profile. However, as the lobe count increased, the velocity profile of the corrugated nozzle gradually resembled that of the circular nozzle. The findings of this study would be beneficial for selecting a proper lobe count and lobe length while designing and implementing a corrugated lobed nozzle.

The purpose of this study is to determine whether it is possible to reduce the upstream and downstream length of a measuring pipeline by installing different types of air flow conditioners. The main goal is to investigate the distance position of these flow conditioners and thus analyze their impact on flow conditions within the pipeline. To improve the current conditions in the pipeline, an analysis was performed of how measurement accuracy was impacted by installing different types of air flow conditioners. Measurement accuracy would also be improved. The preliminary analysis included two different types of flow conditioners: Zanker and NEL. Both were inserted into a measuring pipeline for measuring velocity field and profiles, and thus reduce uncertainty during measurements. A CFD model was built for each type of the air flow conditioner that simulated its impact on velocity fields in the measuring pipeline using the ANSYS Fluent software package. Numerical results of velocity profiles were validated and compared with experimental result. The Zanker flow conditioner was selected for the installation in the measuring pipeline due to better results compared to NEL. Based on the numerical results, the air flow conditioner was optimized and the most suitable conditioner was selected, in this case D/10-V3. [ABSTRACT FROM AUTHOR]

The corrugated lobed nozzle is an emerging research topic in jet flow dynamics, and little investigation has been conducted on its effect on flow characteristics. Thus, in this study, the effects of lobe count and lobe length of corrugated lobed nozzles on subsonic jet characteristics were experimentally investigated by analyzing the velocity profiles of the jets emanating from the nozzles. The Pitot tube readings were obtained by varying the count (4 = N = 8) and length (10 mm = L = 20 mm) of corrugated lobes. These measurements were then compared with the experimental readings obtained for a baseline circular nozzle. The nozzle pressure ratio (NPR) and exit nozzle area were kept identical at 1.5 and 600 mm², respectively, for all nozzle configurations. The most striking observation was the 'W'-shaped radial velocity profile of the corrugated nozzle, which differed from the 'Top hat' profile of the baseline circular nozzle. Additionally, the length of the potential central region of the corrugated nozzle was always shorter than that of the baseline circular nozzle, indicating the early occurrence of turbulence in the former. It was found that the lobe length had a meagre effect on the velocity variation in the jet issuing from the corrugated nozzle, whereas the lobe count had a significant effect on the velocity profile. However, as the lobe count increased, the velocity profile of the corrugated nozzle gradually resembled that of the circular nozzle. The findings of this study would be beneficial for selecting a proper lobe count and lobe length while designing and implementing a corrugated lobed nozzle. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of the porosity of a submerged breakwater on wave fields, including snapshots of the wave, velocity profiles of the water over the structure, and the kinetic energy of the wave. Two-dimensional experiments were conducted for submerged trapezoidal breakwaters with impermeable and permeable layers in a two-dimensional wave tank. The flow fields obtained by the particle image velocimetry (PIV) technique are presented to understand the flow characteristics due to the waves’ interactions with the submerged impermeable and permeable breakwaters, and these characteristics showed that the vertical velocity dominant flow occurred under the crest of the wave. In addition, the kinetic energies were compared for different porosities and wave conditions. The comparisons of the wave flow fields and kinetic energy distributions showed that the different pattern of the dissipated kinetic energy was dependent on the porosity. The dissipation of kinetic energy also was observed to increase as the wave period increased. The comparisons indicated that greater amounts of energy were dissipated for longer wave periods.

An electrified liquid sheet was investigated by the linear analysis method. The sheet was injected into a dielectric viscous gas bounded by two horizontal parallel flat plates with a transverse electric field. To take into account the gas boundary layer thickness, the velocity profile of the liquid sheet must be considered and derived. By analyzing the liquid and gas domain, the relation between the growth rate and the wavenumbers for electrified liquid sheets was derived, and solved using the spectral method whose accuracy is higher than those of the finite element method and the finite difference method. Two modes, namely the sinuous mode and varicose mode were also investigated. The results revealed that the maximum growth rate of the sinuous disturbance wave is greater than that of the varicose one for the electrified liquid sheet. Moreover, the effects of the electrified Euler number and other parameters on the instability of the electrified liquid sheets have been tested. It is found that the growth rate is faster for an electrified liquid sheet than a non-electrified one. The electrical Euler number, the liquid Reynolds number, the Weber number and the momentum flux ratio can promote the breakup of a liquid sheet. However, the increase in the ratio l of the distance between the liquid sheet and flat plate to the liquid sheet thickness has an opposite influence with the other parameters. [ABSTRACT FROM AUTHOR]

In order to solve the velocity profile and pressure gradient of the unsteady unidirectional slip flow of Voigt fluid, Laplace transform method is adopted in this research. Between the parallel microgap plates, the flow motion is induced by a prescribed arbitrary inlet volume flow rate which varies with time. The velocity slip condition on the wall and the flow conditions are known. In this paper, two basic flow situations are solved, which are a suddenly started and a constant acceleration flow respectively. Based on the above solutions, linear acceleration and oscillatory flow are also considered.

The modified log-wake law, which was developed for turbulent boundary layers and pipe flows, is extended to turbulent flows in open-channels. Turbulent velocity profiles in open-channels can be approximated with three components: (1) the law of the wall that results from the constant bed shear stress; (2) the law of the wake that reflects the effects of gravity, secondary currents and bed roughness; and (3) the cubic correction near the maximum velocity. A procedure to determine the four model parameters from velocity measurements while keeping k = 0.41 is presented. The modified log-wake law compares very well with experimental data from Coleman, Lyn, Kironoto and Graf and Sarma et al. It also replicates the measured velocity profiles of the Mississippi River. In particular, it can well fit the velocity dip phenomenon in openchannels where the conventional log-wake law fails.

This paper was presented at the Eleventh Asian Congress of Fluid Mechanics as an invited/keynote lecture. The lecture summarizes development of physical model for transfer processes in turbulent separated flows. Attention is focused on the factors that have led to significant advances in understanding of the mechanisms of transfer processes in separated flows, which differs from those in traditional attached turbulent flows in channels and zero pressure gradient turbulent flows. The physical model of transfer processes in the near-wall region of turbulent separated and reattached flows based on the assumption of the governing role of generated local pressure gradient that takes place in the immediate vicinity of the wall in separated flow as a result of intense instantaneous accelerations induced by large-scale vortex flow structures is discussed. Similarity laws for mean velocity and temperature profiles and spectral characteristics of the transfer processes resulting in the physical model are confirmed by the available experimental data. The physical model has provided explanations of the well-known empirical heat and mass transfer correlations for turbulent separated flows and other types of flows close in their structure to those of turbulent separated flows.

The purpose of this study was to investigate the effect of the porosity of a submerged breakwater on wave fields, including snapshots of the wave, velocity profiles of the water over the structure, and the kinetic energy of the wave. Two-dimensional experiments were conducted for submerged trapezoidal breakwaters with impermeable and permeable layers in a two-dimensional wave tank. The flow fields obtained by the particle image velocimetry (PIV) technique are presented to understand the flow characteristics due to the waves' interactions with the submerged impermeable and permeable breakwaters, and these characteristics showed that the vertical velocity dominant flow occurred under the crest of the wave. In addition, the kinetic energies were compared for different porosities and wave conditions. The comparisons of the wave flow fields and kinetic energy distributions showed that the different pattern of the dissipated kinetic energy was dependent on the porosity. The dissipation of kinetic energy also was observed to increase as the wave period increased. The comparisons indicated that greater amounts of energy were dissipated for longer wave periods. [ABSTRACT FROM AUTHOR]

In order to solve the velocity profile and pressure gradient of the unsteady unidirectional slip flow of Voigt fluid, Laplace transform method is adopted in this research. Between the parallel microgap plates, the flow motion is induced by a prescribed arbitrary inlet volume flow rate which varies with time. The velocity slip condition on the wall and the flow conditions are known. In this paper, two basic flow situations are solved, which are a suddenly started and a constant acceleration flow respectively. Based on the above solutions, linear acceleration and oscillatory flow are also considered. [ABSTRACT FROM AUTHOR]

An experimental investigation of pulsatile flow through a tapered 180° curved tube, i.e., a U-tube, was performed to study the blood flow in the aorta. The experiments were carried out in a U-tube with a curvature radius ratio of 3.5 and a 50% reduction in the cross-sectional area from the entrance to the exit of the curved section. Velocity measurements were conducted by a laser Doppler velocimetry (LDV) for a Womersley number of 10, a mean Dean number of 400 and a flow rate ratio of 1. Additionally, flow was visualized to qualitatively investigate the nature of the flow, complementing the quantitative LDV measurements. The velocity profiles for steady and pulsatile flows in the tapered U-tube were compared with the corresponding results in a U-tube having a uniform cross-sectional area. The striking effects of the tapering on the flow are exhibited in the axial velocity profiles in the section from the latter half of the bend to the downstream tangent immediately behind the bend exit. A depression in the velocity profile appears at a smaller turn angle Ω in the case of tapering, although the magnitude of the depression relative to the cross-sectional average velocity decreases. Near the bend exit, strong secondary-flow motion occurs, leading to a weak depression in the velocity profile in the downstream tangent immediately behind the bend exit. The value of β, which indicates the uniformity in the velocity profile over the cross section, decreases with increasing Ω, whereas it rapidly increases immediately behind the bend exit. [ABSTRACT FROM AUTHOR]

The modified log-wake law, which was developed for turbulent boundary layers and pipe flows, is extended to turbulent flows in open-channels. Turbulent velocity profiles in open-channels can be approximated with three components: (1) the law of the wall that results from the constant bed shear stress: (2) the law of the wake that reflects the effects of gravity, secondary currents and bed roughness; and (3) the cubic correction near the maximum velocity. A procedure to determine the four model parameters from velocity measurements while keeping &kapha; = 0.41 is presented. The modified log-wake law compares very well with experimental data from Coleman, Lyn. Kironoto and Graf and Sarma et al. It also replicates the measured velocity profiles of the Mississippi River. In particular, it can well fit the velocity dip phenomenon in open-channels where the conventional log-wake law fails. [ABSTRACT FROM AUTHOR]

This paper was presented at the Eleventh Asian Congress of Fluid Mechanics as an invited/keynote lecture. The lecture summarizes development of physical model for transfer processes in turbulent separated flows. Atlention is focused on the factors that have led to significant advances in understanding of the mechanisms of transfer processes in separated flows, which differs from those in traditional attached turbulent flows in channels and zero pressure gradient turbulent flows. The physical model of transfer processes in the near-wall region of turbulent separated and reattached flows based on the assumption of the governing role of generated local pressure gradient that takes place in the immediate vicinity of the wall in separated flow as a result of intense instantaneous accelerations induced by large-scale vortex flow structures is discussed. Similarity laws for mean velocity and temperature profiles and spectral characteristics of the transfer processes resulting in the physical model are confirmed by the available experimental data. The physical model has provided explanations of the well-known empirical heat and mass transfer correlations fur turbulent separated flows and other types of flows close in their structure to those of turbulent separated flows. [ABSTRACT FROM AUTHOR]