scholarly journals Development of an Algebraic Model of Empirical Parameterization of Near Wakes around a Vehicle

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 75
Author(s):  
Arata Kimura ◽  
Mitsufumi Asami ◽  
Hideyuki Oka ◽  
Yasushi Oka
Keyword(s):  
Flow Model ◽  
Flow Patterns ◽  
Algebraic Model ◽  
Wake Region ◽  
Cfd Model ◽  
Steady State Flow ◽  
Wind Tunnel Experiments ◽  
Near Wake ◽  
Proposed Model ◽  
Modelling Approach

In this paper, we describe and evaluate an algebraic model that has been adopted in a diagnostic wind flow model. Our numerical model is based on the Röckle’s wind modelling approach and we intend to reproduce the steady-state flow patterns of recirculation vortices that are generated in the near-wake region behind a vehicle. The evaluation of the practicality of our proposed model is performed by comparing the wind tunnel experiments of the flow around a vehicle conducted by the Loughborough University. We also compare the numerical results of our model with the CFD model. The proposed model reproduces the flow patterns behind a vehicle and it has significant advantages, such as low numerical costs. We expect that further improvements in the algebraic model when considering the vehicle’s shape will improve its practicality for the numerical analysis of flow fields around a vehicle.

Transient growth in the near wake region of the flow past a finite span wing

2019 ◽  
Vol 866 ◽  
pp. 399-430 ◽  
Author(s):  
Navrose ◽  
V. Brion ◽  
L. Jacquin
Keyword(s):  
Periodic Structures ◽  
Time Integration ◽  
Tip Vortex ◽  
Wake Region ◽  
Wind Tunnel Experiments ◽  
Near Wake ◽  
Optimal Perturbation ◽  
Tip Vortices ◽  
Naca0012 Airfoil ◽  
Flow Past

We investigate optimal perturbation in the flow past a finite aspect ratio ($AR$) wing. The optimization is carried out in the regime where the fully developed flow is steady. Parametric study over time horizon ($T$), Reynolds number ($Re$), $AR$, angle of attack and geometry of the wing cross-section (flat plate and NACA0012 airfoil) shows that the general shape of linear optimal perturbation remains the same over the explored parameter space. Optimal perturbation is located near the surface of the wing in the form of chord-wise periodic structures whose strength decreases from the root towards the tip. Direct time integration of the disturbance equations, with and without nonlinear terms, is carried out with linear optimal perturbation as initial condition. In both cases, the optimal perturbation evolves as a downstream travelling wavepacket whose speed is nearly the same as that of the free stream. The energy of the wavepacket increases in the near wake region, and is found to remain nearly constant beyond the vortex roll-up distance in nonlinear simulations. The nonlinear wavepacket results in displacement of the tip vortex. In this situation, the motion of the tip vortex resembles that observed during vortex meandering/wandering in wind tunnel experiments. Results from computation carried out at higher $Re$ suggest that, even beyond the steady flow regime, a perturbation wavepacket originating near the wing might cause meandering of tip vortices.

Simple explicit model of liquid mean flow in region above axial impeller

1985 ◽  
Vol 50 (11) ◽  
pp. 2396-2410
Author(s):  
Miloslav Hošťálek ◽  
Ivan Fořt
Keyword(s):  
Vortex Flow ◽  
Flow Model ◽  
Quantitative Agreement ◽  
Mean Flow ◽  
Flat Bottom ◽  
Proposed Model ◽  
Minimum Number ◽  
The Mean ◽  
Model Equations ◽  
Radial Circulation

The study describes a method of modelling axial-radial circulation in a tank with an axial impeller and radial baffles. The proposed model is based on the analytical solution of the equation for vortex transport in the mean flow of turbulent liquid. The obtained vortex flow model is tested by the results of experiments carried out in a tank of diameter 1 m and with the bottom in the shape of truncated cone as well as by the data published for the vessel of diameter 0.29 m with flat bottom. Though the model equations are expressed in a simple form, good qualitative and even quantitative agreement of the model with reality is stated. Apart from its simplicity, the model has other advantages: minimum number of experimental data necessary for the completion of boundary conditions and integral nature of these data.

scholarly journals Flow Turbulence Characteristics and Mass Transport in the Near-Wake Region of an Aquaculture Cage Net Panel

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 294
Author(s):  
Dongdong Shao ◽  
Li Huang ◽  
Ruo-Qian Wang ◽  
Carlo Gualtieri ◽  
Alan Cuthbertson
Keyword(s):  
Mass Transport ◽  
Near Field ◽  
Lateral Spreading ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Turbulence Characteristics ◽  
Macro Scale ◽  
Flow Turbulence ◽  
Fish Cages

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal embayments or fjords, significantly affecting flow and mass transport in the surrounding waters. Existing studies have focused primarily on the macro-scale flow blockage effects of fish cages, and the complex wake flow and associated near-field mass transport in the presence of the cages remain largely unclear. As a first step toward resolving this knowledge gap, this study employed the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) flow imaging technique to measure turbulence characteristics and associated mass transport in the near wake of a steady current through an aquaculture cage net panel in parametric flume experiments. In the near-wake region, defined as ~3M (mesh size) downstream of the net, the flow turbulence was observed to be highly inhomogeneous and anisotropic in nature. Further downstream, the turbulent intensity followed a power-law decay after the turbulence production region, albeit with a decay exponent much smaller than reported values for analogous grid-generated turbulence. Overall, the presence of the net panel slightly enhanced the lateral spreading of the scalar plume, but the lateral distribution of the scalar concentration, concentration fluctuation and transverse turbulent scalar flux exhibited self-similarity from the near-wake region where the flow was still strongly inhomogeneous. The apparent turbulent diffusivity estimated from the gross plume parameters was found to be in reasonable agreement with the Taylor diffusivity calculated as the product of the transverse velocity fluctuation and integral length scale, even when the plume development was still transitioning from a turbulent-convective to turbulent-diffusive regime. The findings of this study provide references to the near-field scalar transport of fish cages, which has important implications in the assessment of the environmental impacts and environmental carrying capacity of cage-based aquaculture.

Study of the Laminar Free-Convection Wake Above an Isothermal Vertical Plate

1973 ◽  
Vol 95 (3) ◽  
pp. 289-294 ◽  
Author(s):  
N. E. Hardwick ◽  
E. K. Levy
Keyword(s):  
Free Convection ◽  
Vertical Plate ◽  
Fluid Motion ◽  
Heated Plate ◽  
Two Dimensional ◽  
Wake Region ◽  
Hot Wire ◽  
Near Wake ◽  
Steady Laminar ◽  
Finite Difference Techniques

The steady, laminar, two-dimensional wake above a thin vertical isothermal heated plate cooled by free convection was investigated theoretically and experimentally. The system of partial differential equations governing the fluid motion and heat transfer in the vicinity of the plate and in the near wake region was formulated and solved using finite difference techniques. Using air, the temperature and velocity profiles in the wake region were measured experimentally using a laser holographic interferometer and a constant temperature hot wire anemometer.

scholarly journals A Multidimensional and Multiscale Model for Pressure Analysis in a Reservoir-Pipe-Valve System

2018 ◽  
Author(s):  
Feng Jie Zheng ◽  
Fu Zheng Qu ◽  
Xue Guan Song
Keyword(s):  
Pressure Fluctuation ◽  
Large Scale ◽  
Three Dimensional ◽  
Industrial Process ◽  
Multiscale Model ◽  
Computational Time ◽  
Small Scale ◽  
Cfd Model ◽  
Computationally Efficient ◽  
Proposed Model

Reservoir-pipe-valve (RPV) systems are widely used in many industrial process. The pressure in an RPV system plays an important role in the safe operation of the system, especially during the sudden operation such as rapid valve opening/closing. To investigate the pressure especially the pressure fluctuation in an RPV system, a multidimensional and multiscale model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the model, the reservoir is modeled by a zero-dimensional virtual point, the pipe is modeled by a one-dimensional MOC, and the valve is modeled by a three-dimensional CFD model. An interface model is used to connect the multidimensional and multiscale model. Based on the model, a transient simulation of the turbulent flow in an RPV system is conducted, in which not only the pressure fluctuation in the pipe but also the detailed pressure distribution in the valve are obtained. The results show that the proposed model is in good agreement with the full CFD model in both large-scale and small-scale spaces. Moreover, the proposed model is more computationally efficient than the CFD model, which provides a feasibility in the analysis of complex RPV system within an affordable computational time.

scholarly journals A Multidimensional and Multiscale Model for Pressure Analysis in a Reservoir-Pipe-Valve System

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Feng Jie Zheng ◽  
Chao Yong Zong ◽  
William Dempster ◽  
Fu Zheng Qu ◽  
Xue Guan Song
Keyword(s):  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Multiscale Model ◽  
Computational Time ◽  
Small Scale ◽  
Dimensional System ◽  
Cfd Model ◽  
Computationally Efficient ◽  
Proposed Model

Reservoir-pipe-valve (RPV) systems are widely used in many industrial processes. The pressure in an RPV system plays an important role in the safe operation of the system, especially during the sudden operations such as rapid valve opening or closing. To investigate the pressure response, with particular interest in the pressure fluctuations in an RPV system, a multidimensional and multiscale model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the model, the reservoir is modeled as a zero-dimensional virtual point, the pipe is modeled as a one-dimensional system using the MOC, and the valve is modeled using a three-dimensional CFD model. An interface model is used to connect the multidimensional and multiscale model. Based on the model, a transient simulation of the turbulent flow in an RPV system is conducted in which not only the pressure fluctuation in the pipe but also the detailed pressure distribution in the valve is obtained. The results show that the proposed model is in good agreement when compared with a high fidelity CFD model used to represent both large-scale and small-scale spaces. As expected, the proposed model is significantly more computationally efficient than the CFD model. This demonstrates the feasibility of analyzing complex RPV systems within an affordable computational time.

Flow Unsteadiness and Stability Characteristics of Low-Re Flow Past an Inclined Triangular Cylinder

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Wei Zhang ◽  
Hui Yang ◽  
Hua-Shu Dou ◽  
Zuchao Zhu
Keyword(s):  
Growth Rate ◽  
Sensitivity Analysis ◽  
Unsteady Flow ◽  
Maximum Velocity ◽  
Flow Patterns ◽  
Wake Flow ◽  
Near Wake ◽  
Flow Unsteadiness ◽  
Flow Past ◽  
Far Wake

The present study investigates the two-dimensional flow past an inclined triangular cylinder at Re = 100. Numerical simulation is performed to explore the effect of cylinder inclination on the aerodynamic quantities, unsteady flow patterns, time-averaged flow characteristics, and flow unsteadiness. We also provide the first global linear stability analysis and sensitivity analysis on the targeted physical problem for the potential application of flow control. The objective of this work is to quantitatively identify the effect of cylinder inclination on the characteristic quantities and unsteady flow patterns, with emphasis on the flow unsteadiness and instability. Numerical results reveal that the flow unsteadiness is generally more pronounced for the base-facing-like cylinders (α → 60 deg) where separation occurs at the front corners. The inclined cylinder reduces the velocity deficiency in the near-wake, and the reduction in far-wake is the most notable for the α = 30 deg cylinder. The transverse distributions of several quantities are shifted toward the negative y-direction, such as the maximum velocity deficiency and maximum/minimum velocity fluctuation. Finally, the global stability and sensitivity analysis show that the spatial structures of perturbed velocities are quite similar for α ≤ 30 deg and the temporal growth rate of perturbation is sensitive to the near-wake flow, while for α ≥ 40 deg there are remarkable transverse expansion and streamwise elongation of the perturbed velocities, and the growth rate is sensitive to the far-wake flow.

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