scholarly journals Active Flow Control on a Square-Back Road Vehicle

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 55 ◽  
Author(s):  
Juan José Cerutti ◽  
Costantino Sardu ◽  
Gioacchino Cafiero ◽  
Gaetano Iuso
Keyword(s):  
Drag Reduction ◽  
Active Flow Control ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Wake Structure ◽  
Rectangular Slot ◽  
Natural Case ◽  
Image Velocimetry ◽  
Dimensional Reconstruction ◽  
Maximum Drag Reduction

An experimental investigation focused on the manipulation of the wake generated by a square back car model is presented. Four continuously-blowing rectangular slot jets were mounted on the rear face of a 1:10 commercial van model. Load cell measurements evidence drag reduction for different forcing configurations, reaching a maximum of 12% for lateral and bottom jets blowing. The spectral analysis of the pressure fluctuations evidence, for all forced cases, an energy attenuation with respect to the natural case, especially close to the shedding frequency. An energy budget highlighted the most efficient forcing configurations accounting for both the drag reduction and the power required to feed the blowing system. Two main configurations are considered: the maximum drag reduction and the best compromise, yielding 5% drag reduction and a convenient energy balance. Particle Image Velocimetry (pPIV) and stereoscopic PIV (sPIV) experiments were performed allowing the three-dimensional reconstruction of the wake in the three considered configurations. Consistently with static and fluctuating pressure measurements, sPIV results reveal a dramatic change in the wake structure when the jets blow in the maximum drag reduction configuration. Conversely, the best compromise configuration reveals a wake structure similar to the natural one.

Three-Dimensional Bubble Reconstruction in a Pipe Flow Using Shadow Technique

2002 ◽  
Author(s):  
Javier Ortiz-Villafuerte ◽  
Yassin A. Hassan ◽  
Toru Furukawa
Keyword(s):  
Pipe Flow ◽  
Particle Image ◽  
Three Dimensional ◽  
Bubbly Flows ◽  
Three Dimensional Reconstruction ◽  
Two Phase ◽  
Generalized Hough Transform ◽  
Image Velocimetry ◽  
Dimensional Reconstruction ◽  
Shadow Image Velocimetry

Two different three-dimensional reconstruction techniques for the shape of gas bubbles flowing in a liquid are presented. The first technique is based on the Dynamic Generalized Hough Transform Algorithm, and the second on the Metaball Model. These techniques are suitable for analysis of turbulent two-phase bubbly flows. Both techniques require at least two views of the bubble intended for three-dimensional reconstruction, and can be used in either stereoscopic or orthogonal camera setups. Once the reconstruction is accomplished, the bubble images can be accurately removed from the images acquired during Particle Image Velocimtery or Shadow Image Velocimetry measurements. After removing the bubble images from PIV images, a typical analysis of the liquid phase can be performed. This improves the accuracy of the statistical analysis of the parameters of each phase.

Experimental Study on Drag-Reduction Effect of a New Sinusoidal Riblet

2012 ◽  
Author(s):  
Monami Sasamori ◽  
Kaoru Iwamoto ◽  
Akira Murata
Keyword(s):  
Experimental Study ◽  
Drag Reduction ◽  
Flat Surface ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Reduction Rate ◽  
Physical Mechanisms ◽  
Image Velocimetry ◽  
Reduction Effect ◽  
Riblet Surface

An experimental study of a new three-dimensional (3-D) riblet has been carried out. The lateral spacing of our 3-D riblet surface is sinusoidally varied in the streamwise direction (see Fig. 3). In the comparison of the optimal two-dimensional (2-D) blade riblet which shows 9.9% drag reduction rate [1], the riblet height, thickness and averaged lateral spacing are respectively 0.83, 5 and 2.5 times larger than those of the optimal 2-D riblet in wall units. The net drag reduction rate of 11.7% has been confirmed in a low-speed wind channel at the bulk Reynolds number of 3400. The flow structure over the 3-D riblet mounted a wall was also analyzed in the velocity field by using 2-D Particle Image Velocimetry and was compared with the corresponding flow over the flat surface in an attempt to identify the physical mechanisms for the drag reduction. The normal turbulent intensities on the present riblet are almost same as those of the flat surface, whereas the Reynolds shear stress is much decreased, and especially becomes negative near the riblet height. These are different phenomena from those of all the previous riblets [1–7].

Experimental Study of the Spanwise Wake Compression of a Trapezoidal Pitching Panel

2015 ◽  
Author(s):  
Justin T. King ◽  
Melissa A. Green
Keyword(s):  
Strouhal Number ◽  
Particle Image ◽  
Three Dimensional ◽  
Stereoscopic Particle Image Velocimetry ◽  
Current Work ◽  
Wake Structure ◽  
Number Range ◽  
Screw Propeller ◽  
Image Velocimetry ◽  
Engineering Designs

Aquatic animals can maneuver and propel themselves through a variety of means. Among these means, are the oscillation and undulation of the flukes and fins of different cetaceans and fishes. The motions of these species can be employed to develop thrust-producing, highly three-dimensional wakes. Recently, a great deal of interest in incorporating certain biological propulsion schemes into engineering designs has been generated. Experiments have shown that bio-inspired propulsors can develop large efficiencies, with some efficiencies being greater than those of a screw-propeller propulsion system. In the current work, stereoscopic particle image velocimetry (PIV) was used to characterize the wake produced by a rigid, trapezoidal pitching panel. Prior work has shown that one of the dominant parameters governing wake structure is the Strouhal number. Detailed analysis in terms of Strouhal number is the focus of the current work, and the Strouhal number range tested was from 0.17 to 0.56.

Drag reduction of circular cylinders by porous coating on the leeward side

2017 ◽  
Vol 813 ◽  
pp. 382-411 ◽  
Author(s):  
Katharina Klausmann ◽  
Bodo Ruck
Keyword(s):  
Drag Reduction ◽  
Pressure Fluctuations ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Porous Coating ◽  
Leeward Side ◽  
Cylinder Surface ◽  
Amplitude Damping ◽  
Image Velocimetry

The present paper describes the effect of drag reduction of circular cylinders due to a porous coating on their leeward sides. To investigate the coating effect, experiments were conducted in a wind tunnel of Goettingen type. Systematic drag measurements were carried out for different cylinder configurations and flow velocities. The drag measurements were complemented by pressure and particle image velocimetry (PIV) flow field measurements around selected cylinders. The Reynolds numbers were varied in the subcritical range of $3\times 10^{4}<Re<1.4\times 10^{5}$. The results show that a thin porous layer on the leeward side, either incorporated in the cylinder shape or applied on the cylinder surface, leads to an increase of base pressure on the leeward side of the cylinder. It causes a reduction of drag and dampens oscillation amplitudes when compared to a cylinder without coating. Results obtained for different configurations with varying key parameters (coating angles, layer thicknesses and pore sizes of the porous material) clearly indicate the drag-reducing and amplitude-damping potential of leeward coating. The amount of drag reduction and amplitude damping depends on the combination of key parameters. It was demonstrated that the lowered drag coefficients $c_{d}$ were almost constant in the tested range of Reynolds numbers. A maximum reduction of drag of 13.2 % was measured. In addition, the results revealed a strong reduction of the pressure fluctuations around cylinders with a leeward coating due to the shift of the vortex region further downstream.

scholarly journals Drag Reduction by Application of Aerodynamic Devices in a Race Car

2020 ◽  
Author(s):  
Devang S. Nath ◽  
Prashant Chandra Pujari ◽  
Amit Jain ◽  
Vikas Rastogi
Keyword(s):  
Drag Reduction ◽  
Drag Force ◽  
High Speed ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Fuel Prices ◽  
Race Car ◽  
High Speeds ◽  
Maximum Drag Reduction ◽  
Computational Fluid Dynamics Cfd

Abstract In this era of fast-depleting natural resources, the hike in fuel prices is ever-growing. With stringent norms over environmental policies, the automotive manufacturers are on a voyage to produce efficient vehicles with lower emissions. High-speed cars are at a stake to provide uncompromised performance but having strict rules over emissions drives the companies to approach through a different route to keep the demands of performance intact. One of the most sought-after ways is to improve the aerodynamics of the vehicles. Drag force is one of the major setbacks when it comes to achieving high speeds when the vehicle is in motion. This research aims to examine the effects of different add on devices on the vehicle to reduce drag and make the vehicle aerodynamically streamlined. A more streamlined vehicle will be able to achieve high speeds and consequently, the fuel economy is also improved. The three-dimensional car model is developed in SOLIDWORKS v17. Computational Fluid Dynamics (CFD) is performed to understand the effects of these add on devices. CFD is carried out in the ANSYSTM 17.0 Fluent module. Drag Coefficient (CD), Lift Coefficient (CL), Drag Force and Lift Force are calculated and compared in different cases. The result of the simulations were analyzed and it was observed that different devices posed several different functionalities, but maximum drag reduction was found in the case of GT with spoiler and diffuser with a maximum reduction of 16.53%.

scholarly journals Drag reduction by application of aerodynamic devices in a race car

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Devang S. Nath ◽  
Prashant Chandra Pujari ◽  
Amit Jain ◽  
Vikas Rastogi
Keyword(s):  
Drag Reduction ◽  
Drag Force ◽  
High Speed ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Fuel Prices ◽  
Race Car ◽  
High Speeds ◽  
Maximum Drag Reduction ◽  
Computational Fluid Dynamics Cfd

AbstractIn this era of fast-depleting natural resources, the hike in fuel prices is ever-growing. With stringent norms over environmental policies, the automotive manufacturers are on a voyage to produce efficient vehicles with lower emissions. High-speed cars are at a stake to provide uncompromised performance but having strict rules over emissions drives the companies to approach through a different route to keep the demands of performance intact. One of the most sought-after ways is to improve the aerodynamics of the vehicles. Drag force is one of the major setbacks when it comes to achieving high speeds when the vehicle is in motion. This research aims to examine the effects of different add on devices on the vehicle to reduce drag and make the vehicle aerodynamically streamlined. A more streamlined vehicle will be able to achieve high speeds and consequently, the fuel economy is also improved. The three-dimensional car model is developed in SOLIDWORKS v17. Computational Fluid Dynamics (CFD) is performed to understand the effects of these add on devices. CFD is carried out in the ANSYS™ 17.0 Fluent module. Drag Coefficient (CD), Lift Coefficient (CL), Drag Force and Lift Force are calculated and compared in different cases. The result of the simulations was analyzed and it was observed that different devices posed several different functionalities, but maximum drag reduction was found in the case of GT with spoiler and diffuser with a maximum reduction of 16.53%.

The Torque and Turbulent Boundary Layer of Rotating Disks with Smooth and Rough Surfaces, and in Drag-Reducing Polymer Solutions

1973 ◽  
Vol 17 (04) ◽  
pp. 181-195
Author(s):  
Paul S. Granville
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Polymer Solutions ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Rotating Disks ◽  
Dimensional Boundary ◽  
Maximum Drag Reduction ◽  
Drag Reducing Polymer ◽  
Unbounded Fluid

The resisting torque of disks rotating in an unbounded fluid is analyzed on the basis of three-dimensional boundary-layer theory. Smooth and rough surfaces in ordinary fluids and in drag-reducing polymer solutions are considered. A general logarithmic relation is derived for the torque as a function of Reynolds number for arbitrary roughness and arbitrary drag reduction. Special formulas are obtained for smooth surfaces, fully rough surfaces, polymer solutions with a linear logarithmic drag-reduction characterization, and polymer solutions with maximum drag reduction. Relations are also obtained for boundary-layer parameters such as thickness and wall shearing stress. The computed results are in excellent agreement with experimental data available in the literature.

Three-Dimensional Reconstruction Using Stereo Pairs from Serial Thick Sections

1977 ◽  
Vol 35 ◽  
pp. 562-563
Author(s):  
Robert Glaeser ◽  
Thomas Bauer ◽  
David Grano
Keyword(s):  
Three Dimensional ◽  
Dimensional Structure ◽  
Serial Sections ◽  
Thin Sections ◽  
3 Dimensional ◽  
Transmission Electron ◽  
Freeze Dried ◽  
Dimensional Reconstruction ◽  
Stereo Imagery ◽  
Whole Mounts

In transmission electron microscopy, the 3-dimensional structure of an object is usually obtained in one of two ways. For objects which can be included in one specimen, as for example with elements included in freeze- dried whole mounts and examined with a high voltage microscope, stereo pairs can be obtained which exhibit the 3-D structure of the element. For objects which can not be included in one specimen, the 3-D shape is obtained by reconstruction from serial sections. However, without stereo imagery, only detail which remains constant within the thickness of the section can be used in the reconstruction; consequently, the choice is between a low resolution reconstruction using a few thick sections and a better resolution reconstruction using many thin sections, generally a tedious chore. This paper describes an approach to 3-D reconstruction which uses stereo images of serial thick sections to reconstruct an object including detail which changes within the depth of an individual thick section.

3-D reconstruction of molecular shape from microcrystal thin sections

1983 ◽  
Vol 41 ◽  
pp. 748-749
Author(s):  
S. Cusack ◽  
J.-C. Jésior
Keyword(s):  
Three Dimensional ◽  
Molecular Shape ◽  
Biological Molecules ◽  
Fourier Space ◽  
Single Particles ◽  
Thin Sections ◽  
Standard Methods ◽  
X Ray ◽  
X Ray Crystallography ◽  
Dimensional Reconstruction

Three-dimensional reconstruction techniques using electron microscopy have been principally developed for application to 2-D arrays (i.e. monolayers) of biological molecules and symmetrical single particles (e.g. helical viruses). However many biological molecules that crystallise form multilayered microcrystals which are unsuitable for study by either the standard methods of 3-D reconstruction or, because of their size, by X-ray crystallography. The grid sectioning technique enables a number of different projections of such microcrystals to be obtained in well defined directions (e.g. parallel to crystal axes) and poses the problem of how best these projections can be used to reconstruct the packing and shape of the molecules forming the microcrystal.Given sufficient projections there may be enough information to do a crystallographic reconstruction in Fourier space. We however have considered the situation where only a limited number of projections are available, as for example in the case of catalase platelets where three orthogonal and two diagonal projections have been obtained (Fig. 1).

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