Review—Bluff Body Flows Applicable to Vehicle Aerodynamics

1980 ◽  
Vol 102 (3) ◽  
pp. 265-274 ◽  
Author(s):  
P. W. Bearman
Keyword(s):  
Bluff Body ◽  
Main Flow ◽  
Wind Tunnels ◽  
Prediction Methods ◽  
Bluff Bodies ◽  
Turbulence Level ◽  
Vehicle Aerodynamics ◽  
Body Shapes ◽  
Bluff Body Flows ◽  
Relative Wind

This paper attempts to review those aspects of bluff body aerodynamics that are relevant to the understanding of vehicle flows. Vehicles often have complex body shapes and are influenced by the proximity of the ground. The effect of the ground is discussed in some detail and results for bluff bodies mounted in wind tunnels above fixed and moving ground planes are presented. It is concluded that drag is little affected by ground proximity and ground representation whereas lift is often sensitive to both. The effect of slanting the base of a bluff body is discussed and the two main flow regimes that result are described. The influence of the wind on vehicle flows is investigated and it is found that vehicle mean flows are sensitive to the turbulence level in the relative wind. Finally numerical prediction methods are considered.

Vortex Shedding in a Linear Shear Flow From a Vibrating Marine Cable With Attached Bluff Bodies

1985 ◽  
Vol 107 (1) ◽  
pp. 61-66 ◽  
Author(s):  
R. D. Peltzer ◽  
D. M. Rooney
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Bluff Bodies ◽  
Near Wake ◽  
Cable System ◽  
Sheared Flow ◽  
Linear Shear ◽  
Body Shapes ◽  
Marine Cable

The present study examines the vortex street wake behavior of a flexible, helically wound, high aspect ratio marine cable in a linear shear flow. Particular attention is paid to the lock-on phenomena associated with uniform and sheared flow past the cable when it is forced to vibrate in the first mode, normal to the flow. An analysis is given of the effects on the vortex shedding and synchronization phenomena that are generated by placing distributions of spherical bluff body shapes along the span of the cable in uniform and sheared flow. The latter geometry is representative of a number of cable system deployments and has special consequencies for strumming in a shear flow. The effectiveness of these attached spheres as strumming-suppression devices is evaluated. Synchronized vibration and/or the presence of the bluff bodies significantly affected the spanwise character of the near wake cellular vortex shedding structure. The spanwise extent of the resonant, vortex-excited oscillations was significantly extended by the presence of the spheres along the cable span. This finding was particularly significant because it meant that the undesirable effects that accompanied synchronization would be extended over a longer portion of the cable span.

Generalized Airloads Prediction for Bluff Bodies Transported as Slung Loads

2015 ◽  
Author(s):  
Nicholas Motahari ◽  
Nandeesh Hiremath ◽  
Dhwanil Shukla ◽  
Brandon Liberi ◽  
Nikolaus Thorell ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Bluff Body ◽  
Flight Speed ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Aerodynamic Loads ◽  
Rotation Method ◽  
Continuous Rotation ◽  
Speed Prediction ◽  
Body Shapes

Objects of arbitrary shapes have to be carried as slung loads under aircraft, particularly rotorcraft. The flight speed is limited by the possibility of slung loads going into divergent oscillations. In 2014 we presented a testing-based approach to predict the safe flight speed, applicable to bluff bodies of arbitrary shape. Since then, an extensive variety of bluff-body shapes has been tested, and we venture further towards generalized airload prediction, required for generalized divergence speed prediction. Extending recent work, the Continuous Rotation method is applied to obtain aerodynamic loads on generic shapes: a circular cylinder and a rectangular prism, both with aspect ratio varied systematically. The genesis of the side force on the yawed cylinder, and the differences between rough and smooth cylinders, have been derived from comparisons between experiments and diagnostic computations with an unsteady Navier-Stokes solver. Interpolating Fourier coefficients of the azimuthal load variation appears to be viable to generalize loads on cylinders of varying aspect ratio for both the generic shapes.

Large eddy simulation of flows around ground vehicles and other bluff bodies

2009 ◽  
Vol 367 (1899) ◽  
pp. 2917-2930 ◽  
Author(s):  
Siniša Krajnović
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Three Dimensional ◽  
Finite Cylinder ◽  
Bluff Bodies ◽  
Ground Vehicles ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Bluff Body Flows ◽  
Near Wall

A brief review of large eddy simulation (LES) applications for different bluff-body flows performed by the author and his co-workers is presented. Examples of flows range from simple cube flows characterized by sharp edge separation over a three-dimensional hill where LES relies on good near-wall resolution, to complex flows of a tall, finite cylinder that contains several flow regimes that cause different challenges to LES. The second part of the paper is devoted to flows around ground vehicles at moderate Reynolds numbers. Although the present review proves the applicability of LES for various bluff-body flows, an increase of the Reynolds number towards the operational speeds of ground vehicles requires accurate near-wall modelling for a successful LES.

Surface Vorticity Modelling of Separated Flows from Two-Dimensional Bluff Bodies of Arbitrary Shape

1981 ◽  
Vol 23 (1) ◽  
pp. 1-12 ◽  
Author(s):  
R. I. Lewis
Keyword(s):  
Flat Plate ◽  
Arbitrary Shape ◽  
Bluff Body ◽  
The Body ◽  
Separated Flows ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Vorticity Generation ◽  
Convection Schemes ◽  
Bluff Body Flows

A method is presented for the computation of separated flows past two-dimensional bodies of arbitrary shape. The surface vorticity technique is used to model the body flow and is combined with vorticity generation, shedding, and convection schemes which simulate the separation regime. The method is applied here especially to bluff body flows and illustrative examples have been limited to symmetrical or half plane flows only. An extension of the technique to free streamline flows is described and illustrated by comparison with the classical solution for free streamline separation from a flat plate.

scholarly journals Parametric CFD study of micro-energy harvesting in a flow channel exploiting vortex shedding

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Dimitrios G. Koubogiannis
Keyword(s):  
Energy Harvesting ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Electrical Power ◽  
Bluff Bodies ◽  
Miniature Device ◽  
Parametric Studies ◽  
Body Shapes ◽  
Duration Of Operation ◽  
Energy Harvesting Devices

Abstract Miniature energy harvesting devices are increasingly used in various fields. For example, Wireless Sensor Networks have recently made great progress in many applications. However, their main drawback, i.e. the limited duration of operation, poses the requirement for an effective way to recharge their batteries. In this context, the presentwork focuses on the study of micro-energy harvesting from flow by exploiting vortex shedding behind bluff bodies, in order to cause oscillations to a piezoelectric film and generate the required electrical power. To this end, a Computational Fluid Dynamics (CFD) tool is validated on a particular miniature device configuration proposed in the literature and implemented for the numerical simulations of flow around bluff micro-bodies in a very small channel. Aiming to enhance vortex shedding, parametric studies corresponding to different bluff body shapes and arrangements for a fixed Reynolds number are performed, the main parameters involved in the phenomenon are highlighted and the potential for vortex shedding exploitation is qualitatively assessed.

A Novel Deep Learning Method for the Predictions of Current Forces on Bluff Bodies

2018 ◽  
Author(s):  
T. P. Miyanawala ◽  
Rajeev K. Jaiman
Keyword(s):  
Neural Network ◽  
Deep Learning ◽  
Bluff Body ◽  
The Body ◽  
Stochastic Gradient Descent ◽  
Approximation Procedure ◽  
Bluff Bodies ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Body Shapes

Unsteady separated flow behind a bluff body causes fluctuating drag and transverse forces on the body, which is of great significance in many offshore and marine engineering applications. While physical experimental and computational techniques provide valuable physics insight, they are generally time-consuming and expensive for design space exploration and flow control of such practical scenarios. We present an efficient Convolutional Neural Network (CNN) based deep-learning technique to predict the unsteady fluid forces for different bluff body shapes. The discrete convolution process with a non-linear rectification is employed to approximate the mapping between the bluff-body shape and the fluid forces. The deep neural network is fed by the Euclidean distance function as the input and the target data generated by the full-order Navier-Stokes computations for primitive bluff body shapes. The convolutional networks are iteratively trained using a stochastic gradient descent method to predict the fluid force coefficients of different geometries and the results are compared with the full-order computations. We have extended this CNN-based technique to predict the variation of force coefficients with the Reynolds number as well. Within the error threshold, the predictions based on our deep convolutional network have a speed-up nearly three orders of magnitude compared to the full-order results and consumes an insignificant fraction of computational resources. The deep CNN-based model can predict the hydrodynamic coefficients required for the well-known Lighthill’s force decomposition in almost real time which is extremely advantageous for offshore applications. Overall, the proposed CNN-based approximation procedure has a profound impact on the parametric design of bluff bodies and the feedback control of separated flows.

Wake periodicity in subsonic bluff-body flows

AIAA Journal ◽  
1986 ◽  
Vol 24 (10) ◽  
pp. 1703-1704 ◽  
Author(s):  
J. L. F. Porteiro
Keyword(s):  
Bluff Body ◽  
Bluff Body Flows

Aerodynamic Characteristics of Asymmetric Bluff Bodies

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
J. C. Hu ◽  
Y. Zhou
Keyword(s):  
Bluff Body ◽  
Laser Doppler Anemometry ◽  
Vortex Formation ◽  
Aerodynamic Characteristics ◽  
Bluff Bodies ◽  
Reynolds Stresses ◽  
Freestream Velocity ◽  
Drag And Lift ◽  
Particle Imaging ◽  
Visualization Techniques

The wake of asymmetric bluff bodies was experimentally measured using particle imaging velocimetry, laser Doppler anemometry, load cell, hotwire, and flow visualization techniques at Re=2600–8500 based on the freestream velocity and the characteristic height of the bluff bodies. Asymmetry is produced by rounding some corners of a square cylinder and leaving others unrounded. It is found that, with increasing corner radius, the flow reversal region is expanded, and the vortex formation length is prolonged. Accordingly, the vortex shedding frequency increases and the base pressure rises, resulting in a reduction in the mean drag as well as the fluctuating drag and lift. It is further found that, while the asymmetric cross section of the cylinder causes the wake centerline to shift toward the sharp corner side of the bluff body, the wake remains globally symmetric about the shifted centerline. The near wake of asymmetric bluff bodies is characterized in detail, including the Reynolds stresses, characteristic velocity, and length scale, and is further compared with that of the symmetric ones.

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