Numerical investigation of hydrodynamic characteristics of fish-like undulation using the adaptive dynamic-grid method

2021 ◽  
pp. 2150299
Author(s):  
Zeyu Guo ◽  
Gucheng Zhu ◽  
Zuogang Chen ◽  
Yukun Feng
Keyword(s):  
Frictional Force ◽  
Control Method ◽  
Turbulent Viscosity ◽  
Flow Characteristics ◽  
Grid Method ◽  
Wave Number ◽  
Hydrodynamic Characteristics ◽  
Substantial Impact ◽  
Vortex Patterns ◽  
Undulatory Swimming

To investigate the hydrodynamics of undulatory swimming, a key issue in numerical analysis is to determine the correlation between undulatory locomotion and the flow characteristics. In this study, a novel dynamic-grid generation method, the adaptive control method, is implemented to deal with the moving and morphing boundaries in an unsteady flow field at all Reynolds numbers. This method, based on structured grids, can ensure the orthogonality and absolute controllability of the grids and is performed to precisely simulate the wake and the boundary layer. The NACA0010 wing is employed as a two-dimensional (2D) body model of a fish in the simulations. To maintain the calculation stability, the increase stage of the amplitude is defined as a smooth transitional stage. Analysis of hydrodynamic coefficients reveals that undulation results in a significant increase of frictional force in laminar flow [Formula: see text]. However, the undulation also results in a reduction of the frictional force when the fish swims in turbulent flow [Formula: see text]. The vorticity distribution and the [Formula: see text]-criterion are both used to accurately capture the shedding vortexes in the wake. Furthermore, these vortex pairs have a substantial impact on the turbulence and the wake, in which the turbulent kinetic energy and the turbulent viscosity ratio both decrease at [Formula: see text]. The wake of an undulatory fish presents different vortex patterns with various kinematic parameters. When the phase velocity is greater than the incoming velocity and the wave number is sufficiently large, thrust is yielded, accompanying the distinct reverse Karman Street in the wake.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

scholarly journals Study on the 3D Hydrodynamic Characteristics and Velocity Uniformity of a Gravity Flow Circular Flume

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 927
Author(s):  
Yi Zhang ◽  
Longxi Han ◽  
Lina Chen ◽  
Chenfang Wang ◽  
Bo Chen ◽  
...  
Keyword(s):  
Flow Field ◽  
Environmental Science ◽  
Structural Characteristics ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Science Research ◽  
Hydrodynamic Characteristics ◽  
Straight Channel ◽  
Uniformity Coefficient ◽  
Annular Flume

Flumes have been widely used in water conservancy science and environmental science research. It is of great significance to obtain the hydrodynamic characteristics and flow field uniformity in the flume. In this study, a new type of annular flume was taken as an example. The 3D flow field was simulated by using a commercial computational fluid dynamics (CFD) code, and was also measured by acoustic doppler velocimeter (ADV) to verify the simulation results. The average relative error range was between 8.37% and 9.95%, the simulated results basically reflected the actual situation of the flow field. On this basis, the structural characteristics of flow field were analyzed. A new calculation method of flow velocity uniformity was presented according to the flow characteristics of natural open channels. The velocity uniformity in the straight channel was calculated and analyzed based on this method, and the influence of speed on the velocity uniformity was further discussed. The length of uniform section was negatively correlated with the rotational speed (average velocity), which was between 39 cm and 101 cm in the straight, and the uniformity coefficient was less than 10%. Finally, the water flow characteristics in the straight channel without wheel were compared with the natural open channel flow. The longitudinal velocity was well fitted with the Prandtl logarithmic distribution formula (R2 > 0.977), and the application feasibility of the flume was analyzed. This study can provide technical support for the development and application of annular flume.

Compressor Drum Aerodynamic Experiments and Analysis With Coolant Injected at Selected Locations

1991 ◽  
Vol 113 (2) ◽  
pp. 272-280 ◽  
Author(s):  
B. V. Johnson ◽  
W. A. Daniels ◽  
E. J. Kawecki ◽  
R. J. Martin
Keyword(s):  
Turbulent Viscosity ◽  
Tangential Velocity ◽  
Flow Characteristics ◽  
Aircraft Engine ◽  
Reynolds Numbers ◽  
Coolant Flow ◽  
Pressure Distributions ◽  
Coolant Injection ◽  
High Pressure Compressor ◽  
Momentum Integral

Experiments were conducted to determine the pressure distributions within a multicavity compressor drum model for two coolant injection locations and a range of flow conditions. Flow was injected through the upstream conical wall or through the cylindrical wall of the rotating model. The coolant flow, the drum rotational rate, and the model pressure were varied to produce a range of tangential and coolant flow Reynolds numbers, typical of large aircraft engine high-pressure compressor drums. The experimental results were used to evaluate analytical procedures for predicting flow characteristics in rotating annular cavities with radially inward flow and for correlating flow characteristics in multiple-rotating annular cavities, which are not currently predicted. Swirling flows, radially inward between compressor disks and within rotating annular cavities with no net flow, were analyzed with a procedure that coupled a viscous solution for the rotating core flow with a momentum integral analysis for the boundary layers on the disks. Constant viscosity and variable turbulent viscosity models were used in the analysis. Results from the analysis and the experiments were used to estimate the tangential velocity distribution in trapped cavities for two coolant injection configurations and a range of flow rates.

Experimental Study on Hydrodynamic Characteristics of Hydrofoil of the Birds Embedded in Marine Seismic Streamers

2010 ◽  
Author(s):  
Xiaoqing Zhang ◽  
Weijing Zhang ◽  
Jun Chen
Keyword(s):  
Control Strategy ◽  
Control Method ◽  
Reference Value ◽  
Attack Angle ◽  
Hydrodynamic Characteristics ◽  
Oil Exploitation ◽  
Exact Position ◽  
Marine Seismic ◽  
And Control ◽  
Important Significance

A “bird” is a device usually being used to control the depth and position of marine seismic streamers. Exact position of the streamers can effectively promote the precision, reduce the measured times and save the costs for marine seismic exploitation. So the “birds” have important significance to marine oil exploitation. A Hydrodynamic characters test concerning a new embedded bird has been introduced in this paper. And some useful hydrodynamic character-data of the hydrofoil are obtained, such as lift-attack angle diagram, resistance-attack angle diagram, torque-attack angle diagram. These data and diagrams are more helpful for studying on the embedded bird, including the control method and control strategy etc. Above all, the results of the test have significant reference value for the control of birds and marine seismic streamers.

Numerical investigation for flow over a square rod through a passive control method at various Reynolds numbers

2020 ◽  
Vol 98 (5) ◽  
pp. 425-432
Author(s):  
A. Ahmed ◽  
R. Manzoor ◽  
S.U. Islam ◽  
H. Rahman
Keyword(s):  
Flow Regime ◽  
Passive Control ◽  
Control Method ◽  
Sudden Change ◽  
Flow Characteristics ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Spacing Ratio ◽  
Boltzmann Method ◽  
Control Rods

This work presents a numerical simulation performed to study the effect of Reynolds number (Re = 80–200) on fluid flow over a square rod attached to two small controlling rods using the Lattice Boltzmann method. For this reason, the spacing ratio between the control rods and main rod varies systematically from g = 0.5–5. Flow has been subdivided into three flow regimes based on spacing ratios. The first flow regime is considered at a small gap (g = 0.5, 1, and 1.5), the second flow regime is obtained at a moderate gap (g = 2, 2.5, and 3), and the third flow regime is considered a at large gap (g = 4–5). Five different types of flow modes were noticed in the given flow regimes. The values Re = 200 and g = 5 were found to be critical due to a sudden change in flow characteristics. The maximum value of Cdmean is 0.869 and the largest percent reduction (65.15%) in the mean drag coefficient was found at Re = 200 and g = 2.

Study on Cooperative Control Method among Large Flow and Long-Distance Intersections

2015 ◽  
Vol 744-746 ◽  
pp. 2006-2011
Author(s):  
Jian Lu ◽  
Jin Gang Gu ◽  
Qiang Fu ◽  
Ya Li
Keyword(s):  
Traffic Flow ◽  
Cooperative Control ◽  
Control Method ◽  
Flow Characteristics ◽  
Signal Control ◽  
Coordination Control ◽  
Long Distance ◽  
Average Delay ◽  
Traffic Flow Characteristics ◽  
Large Flow

Large flow and long distance intersections are very difficult to bring out coordination control and very easy to emerge traffic problems such as traffic congestion due to the large flow and long distance and traffic discrete. It’s necessary to analysis the traffic flow characteristics among large flow and long distance intersections and take measure to improve the signal control. This paper analyzed the traffic flow characteristics of the large flow and long distance intersections, such as the speed would be faster than the normal road between near distance intersection, the headway between cars would be increased, and long traffic queue would be easily occurred at the downstream intersection. In order to realize the coordination control between far intersections, measures for example puts forward signal light at an appropriate position between the intersections, set up fences between vehicles and bicycles, and intersection channelized were put forward to rebuild the traffic flow to adjust the signal control. Those measures were applied to the intersections in Danyang which located in Jiangsu province, the results shows that the queue length was reduced by 67.4% at downstream intersection, the average delay was reduced by 60.3%, the traffic flow saturation was reduced to0.67, and the travel speed and travel time would all become better than before. It suggested that those methods could realize the coordination control and its effect was good, and have good feasibility and practicability.

Influence of non-uniform inflow on unsteady internal flow characteristics of waterjet pump

2021 ◽  
Author(s):  
Chao Liu ◽  
Hongxun Chen ◽  
Zheng Ma
Keyword(s):  
High Speed ◽  
Pressure Pulsation ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Energy Performance ◽  
Hydrodynamic Characteristics ◽  
Area Formula ◽  
Low Speed ◽  
Waterjet Pump

Waterjet propulsion has many advantages when operating at high-speed conditions. As a special way of navigation, it is mostly used in high-speed ships and shallow draft ships. In this paper, a mixed-flow waterjet pump was taken as the research object. For the two cases of non-uniform inflow and uniform inflow, a modified RANS/LES method was adopted for unsteady calculation of the whole channel, aiming at investigating the influence mechanism of the non-uniform inflow on the energy performance and pressure pulsation characteristics of the waterjet pump. The hydrodynamic characteristics of the waterjet pump were comprehensively analyzed such as head, efficiency, axial-force, internal flow and pressure pulsation. It is found that the non-uniform inflow will reduce the external characteristics of the waterjet pump and lead to the huge fluctuation of energy performance with time. Low-speed swirls occur locally in the intake duct for non-uniform inflow, in which condition the vorticity is much higher than that for uniform inflow. In terms of the low-speed area, [Formula: see text] and [Formula: see text], the values under non-uniform inflow condition are generally larger than those under uniform flow condition when in the impeller and guide vane zone. The dominant frequencies of pressure pulsation are, respectively, [Formula: see text], 7[Formula: see text] and 4[Formula: see text] in the intake duct, impeller and diffuser, which are almost consitent for the two cases. However, the frequency features are more diverse, and the amplitudes corresponding to the same frequencies are more intense for non-uniform inflow.

ADOMIAN DECOMPOSITION METHOD FOR MAGNETOHYDRODYNAMIC FLOW OF BLOOD INDUCED BY PERISTALTIC WAVES

2017 ◽  
Vol 17 (01) ◽  
pp. 1750007 ◽  
Author(s):  
G. C. SHIT ◽  
N. K. RANJIT ◽  
A. SINHA
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Decomposition Method ◽  
Flow Characteristics ◽  
Adomian Decomposition Method ◽  
Velocity Slip ◽  
Wave Number ◽  
Axial Velocity Component ◽  
Adomian Decomposition ◽  
Small Change

The present investigation deals with the application of Adomian decomposition method (ADM) to blood flow through an asymmetric non-uniform channel induced by peristaltic wave in the presence of magnetic field and the velocity slip at the wall. The ADM is applied with an aim to avoid any simplifications and restrictions, which changes non-linearity of the problem as well as to provide analytical solution. The blood flowing through the vessel is assumed to be Newtonian and incompressible with constant viscosity. The analytical expressions for the axial velocity component, streamlines and wall shear stress are presented. The numerical results of these physical quantities are obtained for different values of the Reynolds number, wave number and Hartmann number. The results obtained for different values of the parameters involved in the problem under consideration show that the flow is appreciably influenced by the presence of slip velocity as well as magnetic field. From this study, we conclude that the assumption of long wavelength and low Reynolds number overestimates the flow characteristics even for a small change in the parameters.

An improved turbulence model for predicting unsteady cavitating flows in centrifugal pump

2015 ◽  
Vol 25 (5) ◽  
pp. 1198-1213 ◽  
Author(s):  
Jian Wang ◽  
Yong Wang ◽  
Houlin Liu ◽  
Haoqin Huang ◽  
Linglin Jiang
Keyword(s):  
Centrifugal Pump ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulent Viscosity ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Content Type ◽  
Cavitation Inception ◽  
Cavitation Performance ◽  
Unsteady Rans

Purpose – The purpose of this paper is to study the unsteady caivitating flows in centrifugal pump, especially for improving the turbulence model to obtain highly resolution results-capable of predicting the cavitation inception, shedding off and collapse procedures. Design/methodology/approach – Both numerical simulations and experimental visualizations were performed in the present paper. An improved RCD turbulence models was proposed by considering three corrected methods: the rotating corrected method, the compressible corrected method and the turbulent viscosity corrected method. Unsteady RANS computations were conducted to compare with the experiments. Findings – The comparison of pump cavitation performance showed that the RCD turbulence model obtained better performance both in non-cavitation and cavitation conditions. The visualization of the cavitation evolution was recorded to validate the unsteady simulations. Good agreement was noticed between calculations and visualizations. It is indicated the RCD model can successfully capture the bubbles detachment and collapse at the rear of the cavity region, since it effectively reduces the eddy viscosity in the multiphase region of liquid and vapor. Furthermore, the eddy viscosity, the instantaneous pressure and density distribution were investigated. The effectiveness of the compressibility was found. Meanwhile, the influence of the rotating corrected method on prediction was explored. It is found that the RCD model solved more unsteady flow characteristics. Originality/value – The current work presented a turbulence model which was much more suitable for predicting the cavitating flow in centrifugal pump.

scholarly journals Basal-flow characteristics of a linear medium sliding frictionless over small bedrock undulations

1997 ◽  
Vol 43 (143) ◽  
pp. 71-79 ◽  
Author(s):  
G. Hilmar Gudmundsson
Keyword(s):  
Flow Characteristics ◽  
Local Maximum ◽  
Critical Value ◽  
Two Dimensions ◽  
Creeping Flow ◽  
Wave Number ◽  
Vertical Position ◽  
Gravity Driven ◽  
The Mean ◽  
Basal Flow

AbstractThe basal deformation of a gravity-driven linear creeping flow sliding frictionless over slowly varying bed undulations in two dimensions is analysed analytically, using results from second-order perturbation theory. One of the key results is that, close to sinusoidal bedrock undulations, up to two different spatial regions of local extrusion flow may arise. The offset and onset of extrusion flow is controlled primarily by the amplitude-to-wavelength ratio. Above the crest of a sinusoidal bed line, a local maximum of the surface-parallel velocity develops for ε : =ak< 0.138, whereais the amplitude andkis the wave number. Asεincreases from zerо to this critical value, the vertical position of the velocity maximum moves fromkz= 1 tokz≈ 1.98, wherezis the vertical distance above the mean bed line. Within and above the trough of a sinusoid, a region of local minimum of the surface-parallel velocity component develops, which shifts fromkz= 1 towards the bed line asεincreases front zero to 1/2. Below this velocity minimum, and for some distance above the velocity maximum, the surface-parallel velocity increases with depth. This type of extrusion flow will cause a reversal of borehole-inclination profiles close to the bedrock.

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