Recent Advances in Wake Dynamics and Active Drag Reduction of Simple Automotive Bodies

2021 ◽  
Author(s):  
Yu Zhou ◽  
Bingfu Zhang
Keyword(s):  
Machine Learning ◽  
Drag Reduction ◽  
Closed Loop ◽  
Three Dimensional ◽  
The Body ◽  
Flow Structures ◽  
Slant Angle ◽  
Reduction Mechanisms ◽  
Reduction Methods ◽  
Active Drag

Abstract This is a compendium of recent progresses in the development of wake dynamics and active drag reduction of three-dimensional simple automotive models, largely focused on the generic Ahmed body. It covers our new understanding of involved instabilities, predominant frequencies, pressure distribution and unsteady flow structures in the high- (12.5° < f < 30°) and low-drag (f > 30°) bodies and the square-back body (f = 0°), where f is the rear slant angle of the body. Various drag reduction methods and their performances are reviewed, including open- and closed-loop controls along with machine-learning control. The involving drag reduction mechanisms, net saving and efficiencies are discussed. Comments are made for the areas that deserve more attention and future investigation.

Active drag reduction of a high-drag Ahmed body based on steady blowing

2018 ◽  
Vol 856 ◽  
pp. 351-396 ◽  
Author(s):  
B. F. Zhang ◽  
K. Liu ◽  
Y. Zhou ◽  
S. To ◽  
J. Y. Tu
Keyword(s):  
Drag Reduction ◽  
The Body ◽  
Force Balance ◽  
Effective Control ◽  
Rear Window ◽  
Flow Measurements ◽  
Slant Angle ◽  
Vertical Base ◽  
Active Drag ◽  
Ahmed Body

Active drag reduction of an Ahmed body with a slant angle of $25^{\circ }$, corresponding to the high-drag regime, has been experimentally investigated at Reynolds number $Re=1.7\times 10^{5}$, based on the square root of the model cross-sectional area. Four individual actuations, produced by steady blowing, are applied separately around the edges of the rear window and vertical base, producing a drag reduction of up to 6–14 %. However, the combination of the individual actuations results in a drag reduction 29 %, higher than any previous drag reductions achieved experimentally and very close to the target (30 %) set by automotive industries. Extensive flow measurements are performed, with and without control, using force balance, pressure scanner, hot-wire, flow visualization and particle image velocimetry techniques. A marked change in the flow structure is captured in the wake of the body under control, including the flow separation bubbles, over the rear window or behind the vertical base, and the pair of C-pillar vortices at the two side edges of the rear window. The change is linked to the pressure rise on the slanted surface and the base. The mechanisms behind the effective control are proposed. The control efficiency is also estimated.

Study of Drag Reduction Devices for a Square Back Vehicle Configuration Using RANS CFD Simulations

2012 ◽  
Author(s):  
Bahram Khalighi ◽  
Kuo-Huey Chen ◽  
Gianluca Iaccarino
Keyword(s):  
Drag Reduction ◽  
Three Dimensional ◽  
Common Element ◽  
Flow Structures ◽  
Vehicle Model ◽  
Cfd Simulations ◽  
Upward Deflection ◽  
Unsteady Rans ◽  
The Common ◽  
Shedding Frequency

The aerodynamic flow around a simplified road vehicle model with and without drag reduction devices is investigated. The simulations are carried out using the unsteady RANS in conjunction with the ν2-f turbulence model. The corresponding experiments are performed in a small wind tunnel which includes pressure and velocity fields measurements. The devices are add-on geometry parts (a box with a cavity and, boat-tail without a cavity) which are attached to the back of the square-back model to improve the pressure recovery and reduce the flow unsteadiness. The results show that the recirculation regions at the base are shortened and weakened and the base pressure is significantly increased by the devices which lead to lower drag coefficients (up to 30% reduction in drag). Also, the results indicate a reduction of the turbulence intensities in the wake as well as a rapid upward deflection of the underbody flow with the devices in place. A suppression or damping of the unsteadiness is the common element of the devices studied. The baseline configuration (square-back) exhibits strong three-dimensional flapping of the wake. The main shedding frequency captured agrees well with the available experimental data. Comparisons with the measurements show that the simulations agree reasonably well with the experiments in terms of drag and the flow structures.

Effect of Base Slant on Flow in the Near Wake of an Axisymmetric Cylinder

1980 ◽  
Vol 31 (2) ◽  
pp. 132-147 ◽  
Author(s):  
Thomas Morel
Keyword(s):  
Drag Coefficient ◽  
Three Dimensional ◽  
Local Maximum ◽  
The Body ◽  
Wake Flow ◽  
Force Measurements ◽  
Near Wake ◽  
Slant Angle ◽  
Cylinder Length ◽  
Axisymmetric Bodies

SummaryThe effects of slanting the base of a slender axisymmetric cylinder (length/diameter ratio of 9), aligned with the flow, was studied experimentally. The body was equipped with interchangeable rear ends covering a range of slant angles between 0° (vertical) and 70°. It was found that the base slant has a very dramatic effect on body drag, particularly in a relatively narrow range of slant angles where the drag coefficient exhibits a large local maximum (over-shoot). Detailed study of the flow showed that the drag overshoot is related to the existence of two very different Separation patterns on the slanted base. One pattern is similar to that found behind axisymmetric bodies with no base slant, and its main feature is the presence of a closed Separation region adjacent to the base. The other pattern is highly three-dimensional with two streamwise vortices forming along the sides of the slanted base. This pattern sets in very abruptly at a “critical” slant angle α ∼ 47°. Drag force measurements showed that, at first, the drag coefficient slowly increases with the slant angle, but then jumps suddenly upwards to more than double its baseline value (from CD = 0.24 to CD = 0.625) at the critical angle. At angles higher than that CD decreases again, and at 70° it is about equal to the baseline value. Further effects of the slant angle are the generation of a large side force and a significant increase in near-wake flow periodicity.

scholarly journals An overview of passive and active drag reduction methods for bluff body of road vehicles

2018 ◽  
Vol 7 (4.13) ◽  
pp. 53
Author(s):  
Lay Chuan Eun ◽  
Azmin Shakrine Mohd Rafie ◽  
Surjatin Wiriadidjaja ◽  
Omar Faruqi Marzuki
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Smooth Surface ◽  
Bluff Body ◽  
Rotation Speed ◽  
Rotating Cylinder ◽  
Road Vehicles ◽  
Reduction Methods ◽  
Base Drag ◽  
Active Drag

This paper is an overview of results done on bluff body road vehicle’s base drag reduction either by experimental or numerical methods. Two categories of devices are divided that prove certain degrees of effectiveness in reducing the base drag, namely passive and active. The reduction of drag coefficient achieved in existing research ranging from 5% to 50%, which varies for each method and device. However, the higher the achieved drag reduction is, the greater the compensation required is. The compensation comes in various forms to achieve the desirable drag reduction. For passive drag reduction, hump shaped bluff body with boat-tail shows significant drag reduction by 50.9% compared to the other methods. Meanwhile, one of the potential of active drag reductions is by utilizing rotating cylinder. The rotating can reduce the drag on the bluff body by influencing the separation of boundary layer. The drag can be further reduced by enhancing the rotating cylinder with surface roughness and rotation speed. A notable 23% reduction of drag coefficient using rough surface on bluff body vehicle’s is achieved compared to the smooth surface.  

Computational and Neuro-Fuzzy Study of the Effect of Small Objects on the Flow and Thermal Fields of Bluff Bodies

2006 ◽  
Author(s):  
Ahmed F. Abdel Gawad
Keyword(s):  
Drag Reduction ◽  
Bluff Body ◽  
Three Dimensional ◽  
The Body ◽  
Bluff Bodies ◽  
Small Object ◽  
Two Dimensional ◽  
Neuro Fuzzy ◽  
Body Cooling ◽  
Two Dimensional Flows

The aim of the present study is to find computationally the optimum parameters that affect the drag reduction of bluff bodies using a small object (obstacle). These parameters include the size of the obstacle as well as the gap between the obstacle and the bluff body. Two- and three-dimensional bodies were investigated in turbulent flow fields. The research was focused on the cases of the rectangular-section obstacle. Four values of the obstacle size were studied, namely: 4%, 10%, 35%, and 100% of the size of the bluff body. The effect of the obstacle on the thermal field of the two-dimensional body was also studied. Comparisons were carried out with the available experimental measurements. A proposed neuro-fuzzy approach was used to predict the drag reduction of the entire system. Results showed that system drag reductions up to 62% (two-dimensional flows) and 48% (three-dimensional flows) can be obtained. Also, enhancement of the body cooling up to 75% (two-dimensional flows) may be achieved. Generally, useful comments and suggestions are stated.

scholarly journals Flow Structures in Three-Dimensional Fish-Like Swimming

2010 ◽  
Author(s):  
Xing Zhang ◽  
Shizhao Wang ◽  
Guowei He
Keyword(s):  
Three Dimensional ◽  
The Body ◽  
Flow Structures

The swimming of a fish-like body is numerical simulated. The wake structures consist of a series of hairpin-like vortices braided together. The caudal fins generated vorticity interacts constructively with the body-bounded vorticity.

Unsteady flow structures around a high-drag Ahmed body

2015 ◽  
Vol 777 ◽  
pp. 291-326 ◽  
Author(s):  
B. F. Zhang ◽  
Y. Zhou ◽  
S. To
Keyword(s):  
Coherent Structures ◽  
Leading Edge ◽  
Side Surface ◽  
The Body ◽  
Flow Structures ◽  
Rear Window ◽  
Hairpin Vortices ◽  
Recirculation Bubble ◽  
Slant Angle ◽  
Ahmed Body

This work aims to gain a relatively thorough understanding of unsteady predominant coherent structures around an Ahmed body with a slant angle of $25^{\circ }$, corresponding to the high-drag regime. Extensive hot-wire, flow visualization and particle image velocimetry measurements were conducted in a wind tunnel at $\mathit{Re}=(0.45{-}2.4)\times 10^{5}$ around the Ahmed body. A number of distinct Strouhal numbers (St) have been found, two over the rear window, three behind the vertical base and two above the roof. The origin of every St has been identified. The two detected above the roof are ascribed to the hairpin vortices that emanate from the recirculation bubble formed near the leading edge and to the oscillation of the core of longitudinal vortices that originate from bubble pulsation, respectively. The two captured over the window originate from the hairpin vortices and the shear layers over the roof and side surface, respectively. One measured in the wake results from the structures emanating alternately from the upper and lower recirculation bubbles. The remaining two detected behind the lower edge of the base are connected to the cylindrical struts, respectively, which simulate wheels. These unsteady structures and corresponding St reconcile the widely scattered St data in the literature. The dependence on Re of these Strouhal numbers is also addressed, along with the effect of the turbulent intensity of oncoming flow on the flow structures. A conceptual model is proposed for the first time, which embraces both steady and unsteady coherent structures around the body.

Scanning electron microscopy of freeze-fractured prescapular lymph node of caprine

1984 ◽  
Vol 42 ◽  
pp. 244-245
Author(s):  
O. Faroon ◽  
F. Al-Bagdadi ◽  
T. G. Snider ◽  
C. Titkemeyer
Keyword(s):  
Lymph Node ◽  
Lymph Nodes ◽  
Lymphatic System ◽  
Three Dimensional ◽  
Meat Products ◽  
The Body ◽  
Morphological Data ◽  
The World ◽  
Cellular Constituent ◽  
Scanning Electron

The lymphatic system is very important in the immunological activities of the body. Clinicians confirm the diagnosis of infectious diseases by palpating the involved cutaneous lymph node for changes in size, heat, and consistency. Clinical pathologists diagnose systemic diseases through biopsies of superficial lymph nodes. In many parts of the world the goat is considered as an important source of milk and meat products.The lymphatic system has been studied extensively. These studies lack precise information on the natural morphology of the lymph nodes and their vascular and cellular constituent. This is due to using improper technique for such studies. A few studies used the SEM, conducted by cutting the lymph node with a blade. The morphological data collected by this method are artificial and do not reflect the normal three dimensional surface of the examined area of the lymph node. SEM has been used to study the lymph vessels and lymph nodes of different animals. No information on the cutaneous lymph nodes of the goat has ever been collected using the scanning electron microscope.

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