scholarly journals On the aerodynamic flow around a cyclist model at the hoods position

2019 ◽  
Vol 23 (1) ◽  
pp. 35-47 ◽  
Author(s):  
Jiun-Jih Miau ◽  
Shang-Ru Li ◽  
Zong-Xiu Tsai ◽  
Mai Van Phung ◽  
San-Yi Lin
Keyword(s):  
Wind Tunnel ◽  
Water Channel ◽  
Three Dimensional ◽  
Simulation Method ◽  
Reynolds Numbers ◽  
Numerical Results ◽  
Wake Flow ◽  
Model Surface ◽  
Eddy Simulation ◽  
Separation Pattern

Abstract Aerodynamic flow around an 1/5 scale cyclist model was studied experimentally and numerically. First, measurements of drag force were performed for the model in a low-speed wind tunnel at Reynolds numbers from $$5.5 \times 10^{4}$$5.5×104 to $$1.8 \times 10^{5}$$1.8×105. Meanwhile, numerical computation using a large eddy simulation method was performed at three Reynolds numbers of $$1.1 \times 10^{4}$$1.1×104, $$6.5 \times 10^{4}$$6.5×104 and $$1.5 \times 10^{5}$$1.5×105 to obtain the drag coefficients for comparison. Second, flow visualization was made in a water channel and the wind tunnel mentioned to examine the three-dimensional flow separation pattern on the model surface, which could also be realized from the numerical results. Finally, a wake flow survey based on the hot-wire measurements in the wind tunnel showed that in the near-wake region, the flow was featured with the formation of multiple streamwise vortices. The numerical results further indicated that these vortices were evolved from the separated flows occurred on the model surface. Graphic Abstract

scholarly journals Transient flows past arrays of yawed finite prisms

2017 ◽  
Vol 95 (12) ◽  
pp. 1285-1298 ◽  
Author(s):  
I-Han Liu ◽  
Bashar Attiya ◽  
Alparslan Oztekin
Keyword(s):  
Drag Coefficient ◽  
Three Dimensional ◽  
Simulation Method ◽  
Offshore Structures ◽  
Wake Flow ◽  
Transient Flows ◽  
Eddy Simulation ◽  
Marine Current ◽  
Yaw Angle ◽  
Energy Harvesting Devices

Transient flows past arrays of yawed finite-length prisms in tandem and staggered arrangements are simulated. Large eddy simulation method is employed to characterize spatial and temporal characteristics of flows in the vicinity of prisms. Drag coefficients of prisms are determined for different spacing and yaw angle of prisms. Three-dimensional effects are investigated for different spacings of prisms in a tandem array. Drag coefficient of downstream prism is significantly lower compared to that of upstream prism when prisms are tightly spaced. Drag coefficient of downstream prism predicted by simulations in three-dimensional geometry is recovered fully as spacing approaches 10 times the height of the prism while drag coefficient predicted by simulations in two-dimensional geometry is only about 30% of the upstream prism even when two prisms are separated by 20 times the height of the prism. The wake flow patterns do not influence the drag coefficient strongly for the staggered arrays of yawed prisms. Prisms can be placed in a tighter arrangement without a significant penalty of drag reduction. Mathematical models and numerical methods employed are validated by comparing simulation results against experimental results. Drag exerted on these prisms can directly be related to power generation by devices containing translating blades of marine-current applications. This study demonstrates that arrangement, spacing, and yaw angle can be used to design and optimize energy harvesting devices and other offshore structures.

scholarly journals Aerodynamic analysis of a generic wing featuring an elasto-flexible lifting surface

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
J. Piquee ◽  
I. López Canalejo ◽  
C. Breitsamter ◽  
R. Wüchner ◽  
K.-U. Bletzinger
Keyword(s):  
Performance Analysis ◽  
Wind Tunnel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Abrupt Decrease ◽  
Structure Interaction ◽  
Lifting Surface ◽  
Gradual Loss ◽  
Lifting Capacity ◽  
Membrane Type

AbstractA three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments. An analysis for three Reynolds numbers is conducted at various angles of attack. The computations are performed by means of the TAU-Code and the FEM Carat++ solver. Wind-tunnel tests are carried out for performance analysis and to estimate the accuracy of the computations. In the results, the advantages of an elasto-flexible-lifting-surface concept are highlighted by comparing the formvariable surface to its rigid counterpart. The flexibility of the material and its adaptivity to the freestream allow the membrane to adjust its shape to the pressure distribution. For positive angles of attack, the airfoil’s camber increases resulting in an increase in the wing lifting capacity. Furthermore, the stall onset is postponed to higher angles of attack and the abrupt decrease in the lift is replaced by a gradual loss of it.

Numerical investigation of near-wake characteristics of cavitating flow over a circular cylinder

2016 ◽  
Vol 790 ◽  
pp. 453-491 ◽  
Author(s):  
Aswin Gnanaskandan ◽  
Krishnan Mahesh
Keyword(s):  
Circular Cylinder ◽  
Single Phase ◽  
Three Dimensional ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Cavitating Flow ◽  
Cylinder Surface ◽  
Near Wake ◽  
Eddy Simulation ◽  
Wake Characteristics

A homogeneous mixture model is used to study cavitation over a circular cylinder at two different Reynolds numbers ($Re=200$ and 3900) and four different cavitation numbers (${\it\sigma}=2.0$, 1.0, 0.7 and 0.5). It is observed that the simulated cases fall into two different cavitation regimes: cyclic and transitional. Cavitation is seen to significantly influence the evolution of pressure, boundary layer and loads on the cylinder surface. The cavitated shear layer rolls up into vortices, which are then shed from the cylinder, similar to a single-phase flow. However, the Strouhal number corresponding to vortex shedding decreases as the flow cavitates, and vorticity dilatation is found to play an important role in this reduction. At lower cavitation numbers, the entire vapour cavity detaches from the cylinder, leaving the wake cavitation-free for a small period of time. This low-frequency cavity detachment is found to occur due to a propagating condensation front and is discussed in detail. The effect of initial void fraction is assessed. The speed of sound in the free stream is altered as a result and the associated changes in the wake characteristics are discussed in detail. Finally, a large-eddy simulation of cavitating flow at $Re=3900$ and ${\it\sigma}=1.0$ is studied and a higher mean cavity length is obtained when compared to the cavitating flow at $Re=200$ and ${\it\sigma}=1.0$. The wake characteristics are compared to the single-phase results at the same Reynolds number and it is observed that cavitation suppresses turbulence in the near wake and delays three-dimensional breakdown of the vortices.

Three-Dimensional Numerical Simulation of the Flow around Two Side-by-Side Cylinders of Different Diameters

2014 ◽  
Vol 721 ◽  
pp. 199-202
Author(s):  
Zhen Xiao Bi ◽  
Zhi Han Zhu
Keyword(s):  
Numerical Simulation ◽  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Simulation Method ◽  
Scale Model ◽  
Hydrodynamic Characteristics ◽  
Eddy Simulation ◽  
Drag And Lift ◽  
Different Diameters

This paper presents the calculation of hydrodynamic characteristics of two side-by-side cylinders of different diameters in three dimensional incompressible uniform cross flow by using Large-eddy simulation method based on dynamical Smagorinsky-Lilly sub-grid scale model. Solution of the three dimensional N-S equations were obtained by the finite volume method. The numerical simulation focused on investigating the characteristic of the pressure distribution (drag and lift force), vorticity field and turbulence Re=. Results shows that, the asymmetry of the time –averaged velocity distribution in the flow direction behind the two cylinders is very obvious; the frequency of eddy shedding of the small cylinder is about twice of the large one. The turbulence of cylinders is more obvious.

Flow separation on a spheroid at incidence

1979 ◽  
Vol 92 (4) ◽  
pp. 643-657 ◽  
Author(s):  
Taeyoung Han ◽  
V. C. Patel
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Surface Flow ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Turbulent Separation

Surface streamline patterns on a spheroid have been examined at several angles of attack. Most of the tests were performed at low Reynolds numbers in a hydraulic flume using coloured dye to make the surface flow visible. A limited number of experiments was also carried out in a wind tunnel, using wool tufts, to study the influence of Reynolds number and turbulent separation. The study has verified some of the important qualitative features of three-dimensional separation criteria proposed earlier by Maskell, Wang and others. The observed locations of laminar separation lines on a spheroid at various incidences have been compared with the numerical solutions of Wang and show qualitative agreement. The quantitative differences are attributed largely to the significant viscous-inviscid flow interaction which is present, especially at large incidences.

Three-dimensional study of separated flow over a square cylinder by large eddy simulation

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
M Farhadi ◽  
M Rahnama
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Mean Flow ◽  
Central Difference ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy

Large eddy simulation of flow over a square cylinder in a channel is performed at Reynolds numbers of 22 000 and 21 400. The selective structure function (SSF) modelling of the subgrid-scale stress terms is used and the convective terms are discretized using quadratic upstream interpolation for convective kinematics (QUICK) and central difference (CD) schemes. A series of time-averaged velocities, turbulent stresses, and some global flow parameters such as lift and drag coefficients and their fluctuations are computed and compared with experimental data. The suitability of SSF model has been shown by comparing the computed mean flow velocities and turbulent quantities with experiments. Results show negligible variation in the flow parameters for the two Reynolds numbers used in the present computations. It was observed that both QUICK and CD schemes are capable of obtaining results close to those of the experiments with some minor differences.

Magnetohydrodynamic Turbulent Model for LMFRs

2004 ◽  
Author(s):  
Hiroaki Ohira ◽  
Kuniaki Ara
Keyword(s):  
Average Velocity ◽  
Simulation Method ◽  
Reynolds Numbers ◽  
Flow Meters ◽  
Law Of The Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Calculation Results ◽  
Mhd Channel ◽  
Good Agreement

In order to study magnetohydrodynamic behavior in electromagnetic pumps, electromagnetic flow meters, etc. for Liquid Metal Fast Reactors (LMFRs), a large eddy simulation method using an artificial wall boundary condition was developed. In this study, Spalding’s law of the wall and the eddy viscosity for uniform magnetic fields, which was proposed by Shimomura, was applied to Finite Element Method of Generalized Simplified Marker and Cell (GSMAC-FEM). We calculated MHD channel flow in various element sizes on the conditions of Hartmann numbers of 0, 52.5 and 125, whose Reynolds numbers based on the average velocity were all about 29,000. These results showed the average velocity profiles were in good agreement with both the experimental results by Brouillette-Lykoudis and the detail calculation results by Shimomura, although farther calculations were needed to verify the turbulence intensities.

Numerical investigation of wake flow regimes behind a high-speed rotating circular cylinder in steady flow

2019 ◽  
Vol 878 ◽  
pp. 875-906
Author(s):  
Adnan Munir ◽  
Ming Zhao ◽  
Helen Wu ◽  
Lin Lu
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Rotation Rate ◽  
High Speed ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Rotating Circular Cylinder

Flow around a high-speed rotating circular cylinder for $Re\leqslant 500$ is investigated numerically. The Reynolds number is defined as $UD/\unicode[STIX]{x1D708}$ with $U$, $D$ and $\unicode[STIX]{x1D708}$ being the free-stream flow velocity, the diameter of the cylinder and the kinematic viscosity of the fluid, respectively. The aim of this study is to investigate the effect of a high rotation rate on the wake flow for a range of Reynolds numbers. Simulations are performed for Reynolds numbers of 100, 150, 200, 250 and 500 and a wide range of rotation rates from 1.6 to 6 with an increment of 0.2. Rotation rate is the ratio of the rotational speed of the cylinder surface to the incoming fluid velocity. A systematic study is performed to investigate the effect of rotation rate on the flow transition to different flow regimes. It is found that there is a transition from a two-dimensional vortex shedding mode to no vortex shedding mode when the rotation rate is increased beyond a critical value for Reynolds numbers between 100 and 200. Further increase in rotation rate results in a transition to three-dimensional flow which is characterized by the presence of finger-shaped (FV) vortices that elongate in the wake of the cylinder and very weak ring-shaped vortices (RV) that wrap the surface of the cylinder. The no vortex shedding mode is not observed at Reynolds numbers greater than or equal to 250 since the flow remains three-dimensional. As the rotation rate is increased further, the occurrence frequency and size of the ring-shaped vortices increases and the flow is dominated by RVs. The RVs become bigger in size and the flow becomes chaotic with increasing rotation rate. A detailed analysis of the flow structures shows that the vortices always exist in pairs and the strength of separated shear layers increases with the increase of rotation rate. A map of flow regimes on a plane of Reynolds number and rotation rate is presented.

LES of the Slipstream of a Rotating Train

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Hassan Hemida ◽  
Nahia Gil ◽  
Chris Baker
Keyword(s):  
High Speed ◽  
Reynolds Numbers ◽  
Radial Component ◽  
Wake Flow ◽  
Upstream Region ◽  
Outer Side ◽  
Tail Region ◽  
Long Distance ◽  
Eddy Simulation ◽  
Fine Mesh

The slipstream of a high-speed train was investigated using large-eddy simulation (LES). The subgrid stresses were modeled using the standard Smagorinsky model. The train model consisted of a four-coach of a 1/25 scale of the ICE2 train. The model was attached to a 3.61 m diameter rotating rig. The LES was made at two Reynolds numbers of 77,000 and 94,000 based on the height of the train and its speed. Three different computational meshes were used in the simulations: course, medium and fine. The coarse, medium, and fine meshes consisted of 6×106, 10×106, and 15×106 nodes, respectively. The results of the fine mesh are in fairly agreement with the experimental data. Different flow regions were obtained using the LES: upstream region, nose region, boundary layer region, intercarriage gap region, tail region, and wake region. Localized velocity peak was obtained near the nose of the train. The maximum and minimum pressure values are also noticed near to the nose tip. Coherent structures were born at the nose and roof of the train. These structures were swept by the radial component of the velocity toward the outer side of the train. These structures extended for a long distance behind the train in the far wake flow. The intercarriage gaps and the underbody complexities, in the form of supporting cylinders, were shown to have large influences on the slipstream velocity. The results showed that the slipstream velocity is linearly proportional to the speed of the train in the range of our moderate Reynolds numbers.

Sign in / Sign up

Export Citation Format

Share Document