An Investigation of the Forces on Three Dimensional Bluff Bodies in Rough Wall Turbulent Boundary Layers

1977 ◽  
Vol 99 (3) ◽  
pp. 503-509 ◽  
Author(s):  
B. E. Lee ◽  
B. F. Soliman
Keyword(s):  
Three Dimensional ◽  
The Body ◽  
Bluff Bodies ◽  
Drag Forces ◽  
Pressure Distributions ◽  
Mean Pressure ◽  
Flow Phenomena ◽  
The Mean ◽  
Building Ventilation ◽  
Group Density

A study has been made of the influence of grouping parameters on the mean pressure distributions experienced by three dimensional bluff bodies immersed in a turbulent boundary layer. The range of variable parameters has included group density, group pattern and incident flow type and direction for a simple cuboid element form. The three flow regimes associated with increasing group density are reflected in both the mean drag forces acting on the body and their associated pressure distributions. A comparison of both pressure distributions and velocity profile parameters with established work on two dimensional bodies shows close agreement in identifying these flow regime changes. It is considered that the application of these results may enhance our understanding of some common flow phenomena, including turbulent flow over rough surfaces, building ventilation studies and environmental wind around buildings.

Laminar Fluid Flow Around Two Wall-Mounted Blocks of Different Size

2009 ◽  
Author(s):  
Mohammad Mehdi Tavakol ◽  
Mohammad Eslami
Keyword(s):  
Fluid Flow ◽  
Free Stream ◽  
Three Dimensional ◽  
Simple Algorithm ◽  
Bluff Bodies ◽  
Wake Region ◽  
Science And Engineering ◽  
Vortical Structures ◽  
Laminar Fluid Flow ◽  
Pressure Distributions

Fluid flow around single or multiple bluff bodies mounted on a surface has great significance in science and engineering. Understanding the characteristics of different vortices formed around wall-mounted bodies is quite necessary for different applications. Although the case of a single surface mounted cube has been studied extensively, only little attention has been paid to the flow around two or more rectangular blocks in array. Therefore, a CFD code is developed to calculate three dimensional steady state laminar fluid flow around two cuboids of arbitrary size and configuration mounted on a surface in free stream conditions. The employed numerical scheme is finite volume and SIMPLE algorithm is used to treat pressure and velocity coupling. Results are presented for two rectangular blocks of the different size mounted on a surface in various inline arrangements. Streamlines are plotted for blocks of different size ratio. Velocity and pressure distributions are also plotted in the wake region behind the obstacles. It is shown that how the behavior of flow field and vortical structures depend on the respective size and location of the larger block in comparison with the case of two inline wall mounted cubes of the same size.

CFD Solution of a Two-Canopy Parachute in a Top-to-Top Formation With a Vent of Air From One of Its Canopy

2008 ◽  
Author(s):  
Mohammad J. Izadi
Keyword(s):  
Cross Sectional Area ◽  
The Body ◽  
The Other ◽  
Bluff Bodies ◽  
Variable Cross ◽  
Sectional Area ◽  
Cross Sectional ◽  
Drag Forces ◽  
Varied Form ◽  
Two Bodies

A CFD study of a 3 Dimensional flow field around two bodies (Two Canopies of a Parachutes) as two bluff bodies in an incompressible fluid (Air) is modeled here. Formations of these two bodies are top-to-top (One on the top of the other) with respect to the center of each other. One canopy with a constant cross sectional area with a vent of air at its apex, and the other with a variable cross sectional area with no vent is studied here. Vertical distances of these two bodies are varied form zero to half, equal, double and triple radius of the body with a vent on it. The flow condition is considered to be 3-D, unsteady, turbulent, and incompressible. The vertical distances between the bluff bodies, cross sectional area, and also vent ratio of bluff bodies are varied here. The drag forces with static pressures around the two bodies are calculated. From the numerical results, it can be seen that, the drag coefficient is constant on the range of zero to twenty percent of the vent ratio and it decreases for higher vent ratios for when the upper parachute is smaller than the lower one, and it increases for when the upper parachute is larger than the lower one. Both Steady and Unsteady cases gave similar results especially when the distance between the canopies is increased.

Flow Past Circular Cylinder With Different Surface Configurations

1992 ◽  
Vol 114 (2) ◽  
pp. 170-177 ◽  
Author(s):  
Y. C. Leung ◽  
N. W. M. Ko ◽  
K. M. Tang
Keyword(s):  
Reynolds Number ◽  
Groove Surface ◽  
Number Range ◽  
Pressure Distributions ◽  
Downward Shift ◽  
Reynolds Number Range ◽  
Lower Reynolds Number ◽  
Smooth Cylinder ◽  
Mean Pressure ◽  
The Mean

Measurements of the mean pressure distributions and Strouhal numbers on partially grooved cylinders with different groove subtend angles were made over a Reynolds number range of 2.0×104 to 1.3×105 which was within the subcritical regime of smooth cylinder. The Strouhal number, pressure distributions, and their respective coefficients were found to be a function of the groove subtend angles. In general, a progressive shift of the flow regime to lower Reynolds number was observed with higher subtend angle and a subtend angle of 75 deg was found for optimum drag reduction. With the configuration of asymmetrical groove surface, lower drag, and higher lift coefficients were obtained within the same Reynolds number range. Wake traverse and boundary layer results of the asymmetric grooved cylinder indicated that the flows at the smooth and groove surfaces lied within different flow regimes and a downward shift of the wake.

Laminar Fluid Flow around Two Wall-Mounted Cubes of Arbitrary Configuration

2010 ◽  
Vol 224 (11) ◽  
pp. 2396-2407 ◽  
Author(s):  
M Eslami ◽  
M M Tavakol ◽  
E Goshtasbirad
Keyword(s):  
Fluid Flow ◽  
Flow Field ◽  
Free Stream ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Vortical Structures ◽  
Laminar Fluid Flow ◽  
Pressure Distributions ◽  
Arbitrary Configuration ◽  
Computational Fluid Dynamics Cfd

The problem of flow field around multiple bluff bodies mounted on a surface is of great significance in different fields of engineering. In this study, a computational fluid dynamics (CFD) code is developed to calculate three-dimensional (3D) steady state laminar fluid flow around two cuboids of arbitrary size and configuration mounted on a surface in free stream conditions. This study presents the results for two cubes of the same size mounted on a surface in both inline and staggered arrangements. Streamlines are plotted for various combinations of the distance between the two cubes and Reynolds number. Moreover, the effects of different parameters on vortical structures, separation, and reattachment points are discussed. Also, velocity and pressure distributions are plotted in the wake region behind the two cubes. It is clearly shown that how the presence of the second cube changes the flow field and the vortical structures in comparison with the case of a single cube.

PRESSURE DISTRIBUTION ON WHEELCHAIR CUSHIONS IN STATIC SITTING AND DURING MANUAL PROPULSION

2001 ◽  
Vol 01 (01) ◽  
pp. 33-44 ◽  
Author(s):  
GIUSEPPE ANDREONI ◽  
ANTONIO PEDOTTI ◽  
MAURIZIO FERRARIN
Keyword(s):  
The Body ◽  
Biomechanical Analysis ◽  
Pressure Sores ◽  
Wheelchair Propulsion ◽  
Wheelchair User ◽  
Sitting Posture ◽  
Manual Propulsion ◽  
Mean Pressure ◽  
Biomechanical Parameters ◽  
The Mean

Quantification of biomechanical parameters by describing interactions between a wheelchair user and his cushion is important to prevent pressure sores in a better way and to match the needs of the subjects in terms of comfort and mobility. This paper presents the method and the results of a biomechanical analysis through the pressure maps at the body–seat interface of a antidecubitus wheelchair cushion on a group of eight patients (affected by SCI or Multiple Sclerosis) during autonomous wheelchair propulsion. In general, our results confirm that mobility is an important factor for ulcer prevention because passing from the static sitting posture to propulsion the mean pressure decreases and there is a redistribution of the load at lower pressure values. Moreover this represents a useful approach for the customized choice and adaptation of the antidecubitus aids.

scholarly journals TO THE THEORY OF n-DIMENSIONAL BRACHISTOCHRONE

2020 ◽  
pp. 53-60
Author(s):  
Gladkov S.O. ◽  
◽  
Bogdanova S.B. ◽  
Keyword(s):  
Three Dimensional ◽  
Plane Curve ◽  
Viscous Friction ◽  
Analytical Description ◽  
The Body ◽  
Viscous Drag ◽  
Friction Forces ◽  
Drag Forces ◽  
Moving Body ◽  
Plane Shape

In this paper, a solution to the problem of the motion of a brachistochrone in the ndimensional Euclidean space is firstly presented. The very first formulation of the problem in a two-dimensional case was proposed by J. Bernoulli in 1696. It represented an analytical description of the trajectory for the fastest rolling down under gravitational force only. Thereafter, a number of problems devoted to a brachistochrone were considered with account for gravitational forces, dry and viscous drag forces, and a possible variation in the mass of a moving body. Analytical solution to the formulated problem is presented in details by an example of the body moving along a brachistochrone in three-dimensional Cartesian coordinates. The obtained parametric solution is confirmed by a graphical interpretation of the calculated result. The formulated problem is solved for an ideal case when drag forces are neglected. If dry and viscous friction forces are taken into account, the plane shape of the brachistochrone remains the same,while the analysis of the solution becomes more complicated. When, for example, a side air flow is taken into account, the plane curve is replaced by a three-dimensional brachistochrone.

scholarly journals Design of wireless device to measure plantar pressure and gait analysis

2019 ◽  
Vol 2 (1) ◽  
pp. 174-181
Author(s):  
Mahendra Khatri ◽  
Sambardhan Dabadi ◽  
Sandeep Kumar Shrestha ◽  
Saugat Acharya ◽  
Sudip Tamang ◽  
...  
Keyword(s):  
Hip Joint ◽  
Lower Limb ◽  
Plantar Pressure ◽  
Walking Speed ◽  
Pressure Sensors ◽  
The Body ◽  
Joint Movement ◽  
Significant Difference ◽  
Mean Pressure ◽  
The Mean

Foot plantar pressure is the pressure field that acts between the plantar region of the foot and supporting ground. The pressure exerted on the variable region of the foot can be determined using discrete pressure sensors. Information obtained from these sensors is useful in the measurement of gait and posture for diagnosing various problems associated with a lower limb, footwear design, and sports biomechanics. This project is aimed to design a portable in-shoe plantar pressure and gyroscope-based gait angle measurement system. Six Force Sensitive Resistor (FSR) placed in the sole (hallux, 1st, 5th metatarsal, midfoot lateral, midfoot medial and heel respectively) detects the plantar pressure and gyroscope placed at the ankle, knee and hip help measure the orientation and angle of joint movement during various phases of gait. The study among 16 male and 16 female subjects illustrated the significant pressure variation (p<0.0001, t=5.17 with α=95%). Similarly, there was a significant difference in pressure between normal and fast walking speed (p<0.0001, t=5.88) with mean values of 353Kpa and 426Kpa respectively. The mean pressure value for slow walking speed was 423Kpa while there was no significant variation between slow and normal walking speeds (p=0.62, t=1.98). Plantar pressure increased linearly with an increase in the body weight of a person as well. The mean pressure for the 45-50 age group was 313.25Kpa and that for 70-75 was 449Kpa. The study among 10 diabetics and 10 non-diabetic subjects illustrated significantly higher pressure on 1st and 5th metatarsal on diabetic subjects (p=0.0207 and t=2.536). The movement of ankle, knee and hip joint is visualized using the 3D model of a lower limb through processing software. The study illustrated the range of ankle joint movement between -60(dorsiflexion) to 200(plantarflexion), for knee joint was 00 to 300 (flexion) and that for hip joint was -50(extension) to 400(flexion). There was a significant difference in angular values for all three joints while climbing up and down the staircase as compared to walk in a level surface.

scholarly journals Observation of aerodynamic instability in the flow of a particle stream in a dilute gas

2019 ◽  
Vol 622 ◽  
pp. A151 ◽  
Author(s):  
Holly L. Capelo ◽  
Jan Moláček ◽  
Michiel Lambrechts ◽  
John Lawson ◽  
Anders Johansen ◽  
...  
Keyword(s):  
Local Density ◽  
Mass Density ◽  
Density Ratio ◽  
Three Dimensional ◽  
Particle Number Density ◽  
Solid Particles ◽  
Dust Particles ◽  
Drag Forces ◽  
Velocity Statistics ◽  
The Mean

Forming macroscopic solid bodies in circumstellar discs requires local dust concentration levels significantly higher than the mean. Interactions of the dust particles with the gas must serve to augment local particle densities, and facilitate growth past barriers in the metre size range. Amongst a number of mechanisms that can amplify the local density of solids, aerodynamic streaming instability (SI) is one of the most promising. This work tests the physical assumptions of models that lead to SI in protoplanetary discs (PPDs). We conduct laboratory experiments in which we track the three-dimensional motion of spherical solid particles fluidised in a low-pressure, laminar, incompressible, gas stream. The particle sizes span the Stokes–Epstein drag regime transition and the overall dust-to-gas mass density ratio,ϵ, is close to unity. A recently published study establishes the similarity of the laboratory flow to a simplified PPD model flow. We study velocity statistics and perform time-series analysis of the advected flow to obtain experimental results suggesting an instability due to particle-gas interaction: (i) there exist variations in particle concentration in the direction of the mean relative motion between the gas and the particles, that is the direction of the mean drag forces; (ii) the particles have a tendency to “catch up” to one another when they are in proximity; (iii) particle clumping occurs on very small scales, which implies local enhancements above the backgroundϵby factors of several tens; (iv) the presence of these density enhancements occurs for a meanϵapproaching or greater than 1; (v) we find evidence for collective particle drag reduction when the local particle number density becomes high and when the background gas pressure is high so that the drag is in the continuum regime. The experiments presented here are precedent-setting for observing SI under controlled conditions and may lead to a deeper understanding of how it operates in nature.

Prediction of Sheet Cavitation on a Rudder Subject to Propeller Flow

2007 ◽  
Vol 51 (01) ◽  
pp. 65-75
Author(s):  
Spyros A. Kinnas ◽  
Hanseong Lee ◽  
Hua Gu ◽  
Shreenaath Natarajan
Keyword(s):  
Velocity Field ◽  
Three Dimensional ◽  
Leading Edge ◽  
Slip Boundary Condition ◽  
The Body ◽  
Solid Boundary ◽  
Blade Surface ◽  
Lattice Method ◽  
Sheet Cavitation ◽  
Pressure Distributions

This paper presents two numerical methods, a vortex lattice method (MPUF-3A) coupled with a finite volume method (GBFLOW-3D) and a boundary element method (PROPCAV), which are applied to predict time-averaged sheet cavitation on rudders, including the effects of the propeller as well as of the tunnel walls. The coupled MPUF-3A and GBFLOW-3D determines the velocity field due to the propeller within the fluid domain bounded by tunnel walls. MPUF-3A solves the potential flow around the propeller by distributing the line vortices and sources on the blade mean camber surface and determines the pressure distributions on the blade surface. GBFLOW-3D solves Euler equations with the body force terms converted from the pressure distributions on the blade surface and determines the total velocity field inside the fluid domain. The tunnel walls are treated as a solid boundary by applying the slip boundary condition, and the propeller blades are modeled via body forces. The two methods are solved iteratively until the forces on the blade converge. The cavity prediction on the rudder is accomplished via PROPCAV, which can handle back and face leading edge or mid-chord cavitation, in the presence of the three-dimensional flow field determined by the coupled MPUF-3A and GBFLOW-3D. The present method is validated by comparing the cavity shapes and the cavity envelope with those observed and measured in experiment and computed by another method.

scholarly journals Simulation of blast lung injury induced by shock waves of five distances based on finite element modeling of a three-dimensional rat

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Chang Yang ◽  
Zhang Dong-hai ◽  
Liu Ling-ying ◽  
Yu Yong-hui ◽  
Wu Yang ◽  
...  
Keyword(s):  
Lung Injury ◽  
Computational Simulation ◽  
Three Dimensional ◽  
3D Models ◽  
The Body ◽  
Maximum Pressure ◽  
Strong Correlations ◽  
Lung Lobe ◽  
Pressure Distributions ◽  
Blast Lung Injury

Abstract Blast lung injury (BLI) caused by both military and civilian explosions has become the main cause of death for blast injury patients. By building three-dimensional (3D) models of rat explosion regions, we simulated the surface pressure of the skin and lung. The pressure distributions were performed at 5 distances from the detonation center to the center of the rat. When the distances were 40 cm, 50 cm, 60 cm, 70 cm and 80 cm, the maximum pressure of the body surface were 634.77kPa, 362.46kPa, 248.11kPa, 182.13kPa and 109.29kPa and the surfaces lung pressure ranges were 928–2916 Pa, 733–2254 Pa, 488–1236 Pa, 357–1189 Pa and 314–992 Pa. After setting 6 virtual points placed on the surface of each lung lobe model, simulated pressure measurement and corresponding pathological autopsies were then conducted to validate the accuracy of the modeling. For the both sides of the lung, when the distance were 40 cm, 50 cm and 60 cm, the Pearson’s values showed strong correlations. When the distances were 70 cm and 80 cm, the Pearson’s values showed weak linear correlations. This computational simulation provided dynamic anatomy as well as functional and biomechanical information.

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