Mechanism of Flow Drag Reduction on Non-Smooth Surface

2013 ◽  
Author(s):  
Beibei Feng ◽  
Darong Chen ◽  
Jiadao Wang ◽  
Xingtuan Yang
Keyword(s):  
Drag Reduction ◽  
Smooth Surface ◽  
Reynolds Shear Stress ◽  
Dominant Factor ◽  
Adjacent Area ◽  
Flow Shear ◽  
Outer Flow ◽  
Flow Alteration ◽  
Pressure Drag ◽  
Flow Drag

Numerical simulations of air flow were carried out on non-smooth surface where microriblets were distributed uniformly at only one of the walls. An accurate numerical treatment based on k-ε turbulence model was adopted to study flow alteration and to analyze drag reduction and increasing mechanism on non-smooth surface. A modified calculation unit was used to estimate characteristics of flow at the reformed cells. With the microriblets aligned on the surface, the Reynolds shear stress was significantly decreased which was considered the dominant factor resulting in drag reduction. An additional force generating from the deviation of static pressure on the front and rear end of the riblet grooves caused pressure drag increasing exhibiting exponential growth with the flow rate, which was closely related to vortices induced by momentum transfer at the adjacent area of flow inside the grooves and the outer flow. Shear action at groove walls was greatly degraded due to the gradually variational velocity of vortices. Flow alteration on non-smooth surface compared with smooth surface was also analyzed in detail.

Transition to turbulence in pipe flow for water and dilute solutions of polyethylene oxide

1972 ◽  
Vol 51 (1) ◽  
pp. 177-185 ◽  
Author(s):  
R. W. Paterson ◽  
F. H. Abernathy
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Polyethylene Oxide ◽  
Transition To Turbulence ◽  
Small Scale ◽  
Outer Flow ◽  
Pure Solvent ◽  
Inlet Conditions ◽  
Scale Turbulence ◽  
Flow Drag

An experimental study of the transition from laminar to turbulent flow in a long 0·248in. I.D. pipe is reported for both water and dilute water solutions of polyethylene oxide which exhibit turbulent flow drag reduction (the Toms phenomenon). The drag-reducing solutions, ranging in effectiveness from near zero to the maximum attainable, are observed to undergo transition in a similar way to the Newtonian solvent in that the solutions exhibit intermittency and the growth rates of the turbulent patches are essentially equal to those of the pure solvent. The growth rate of turbulent patches indicates that drag reduction is associated with the small-scale structure of the turbulence near the pipe wall while patch growth is associated with the larger-scale turbulence in the outer flow. For low-disturbance pipe inlet conditions the strong drag-reducing solutions are observed to undergo transition at lower Reynolds numbers than the pure solvent.

Automotive Drag Reduction through Distributed Base Roughness Elements

2014 ◽  
Vol 553 ◽  
pp. 267-272
Author(s):  
Iain Robertson ◽  
Adrien Becot ◽  
Adrian Gaylard ◽  
Ben Thornber
Keyword(s):  
Drag Reduction ◽  
Reference Model ◽  
Detailed Examination ◽  
Rear Face ◽  
Cfd Simulations ◽  
Near Wake ◽  
Wake Structure ◽  
Pressure Drag ◽  
Roughness Elements ◽  
Baseline Case

This paper focuses on the effect of base roughness added to the rear of an automotive reference model, the Windsor model. This roughness addition was found to reduce both the drag and the lift of the model. RANS CFD simulations presented here replicate the experimentally observed drag reduction and enable a detailed examination of the mechanisms behind this effect. Investigations into the wake structure of the configurations with base roughness and the baseline case without base roughness showed the main changes to the wake to include a reduction in the overall size of the wake with base roughness present. Furthermore a reduction in the near wall velocities at the rear of the model caused stretching of the upper and lower vortices, a more turbulent near wake and pressure recovery over much of the rear face. This leads to reduce levels of pressure drag on the model.

scholarly journals Effects of Side Walls on Pipe Inlet Flow (Drag Reduction by Separated Flow Control Using Ring Shaped Small Obstacle)

2009 ◽  
Vol 4 (2) ◽  
pp. 468-478 ◽  
Author(s):  
Toshitake ANDO ◽  
Toshihiko SHAKOUCHI ◽  
Hiroyuki YAMAMOTO ◽  
Koichi TSUJIMOTO
Keyword(s):  
Drag Reduction ◽  
Flow Control ◽  
Separated Flow ◽  
Inlet Flow ◽  
Side Walls ◽  
Flow Drag ◽  
Small Obstacle ◽  
Pipe Inlet

On the Effects of Aero Boundary Layer Control on Pressure Drag Reduction in Supercavitating Bodies

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Pressure Distribution ◽  
Constant Pressure ◽  
Viscous Drag ◽  
Cavity Surface ◽  
Gradient Flows ◽  
Supercavitating Vehicles ◽  
Pressure Drag ◽  
Layer Control

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we’ll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present some approaches by which this probable separation can be controlled. Comparisons of several conditions exhibits that at very low cavitation numbers, constant pressure assumption fails particularly for gradient shaped profiles and separation is probable if the flow is sufficiently turbulent. Air injection into the NATURALLY FORMED supercavity is found as an effective way to delay probable separation and so significant pressure drag reduction is achieved. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered. Moreover, electromagnetic forces cause to delay or even prevent separation in high pressure gradient flows and interesting results obtained in this regard shows significant drag reduction in supercavitating vehicles.

Computational Evaluation of a Novel Aerodynamic Road Vehicle Design and Drag Reduction Using Vortex Generators

2019 ◽  
Author(s):  
B. B. Arora ◽  
Ujjwal Suri ◽  
Utkarsh Garg ◽  
Shraman Das ◽  
Sushrut Kumar
Keyword(s):  
Drag Reduction ◽  
Fuel Efficiency ◽  
Vortex Generators ◽  
Vehicle Design ◽  
Design Data ◽  
Road Vehicle ◽  
Pressure Drag ◽  
Computational Evaluation ◽  
Vehicle Aerodynamics ◽  
Dynamics Simulations

Abstract Vehicle aerodynamics is a prime domain of research and development. Multiple active and passive aerodynamic systems have been applied for its enhancement. The reduction of drag plays a pivotal role in the improvement of vehicle aerodynamic performance. The present paper studies the innovative design of a road vehicle for a fuel efficiency challenge, implemented for optimal drag reduction. Vortex generators are utilized as a passive aerodynamic feature for further minimization of the wake region size and reduction of pressure drag. High fidelity computational fluid dynamics simulations were applied for the evaluation of this design. Data was collated from simulations for both the cases, with and without the usage of vortex generators and compared objectively. The results of the study establish that the vehicle design has an exceptionally low drag coefficient. It also exhibits a strong reduction in drag when the vortex generators are fitted. These results reveal that the design can be deployed for production as a worthy competition vehicle.

An Experimental Investigation of Turbulent Drag Reduction in Concentric Annulus Using Particle Image Velocimetry Technique

2013 ◽  
Author(s):  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Polymer Concentration ◽  
Mean Flow ◽  
Flow Loop ◽  
Mean Velocity ◽  
Image Velocimetry

Polymer drag reduction is investigated using the Particle Image Velocimetry (PIV) technique in fully developed turbulent flow through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The polymer used was a commercially available partially hydrolyzed polyacrylamide (PHPA). The polymer concentration was varied from 0.07 to 0.12% V/V. The drag reduction is enhanced by increasing polymer concentration until the concentration reaches an optimum value. After that, the drag reduction is decreased with the increasing polymer concentration. Optimum concentration value of PHPA was found to be around 0.1% V/V. Experiments were conducted at solvent Reynolds numbers of 38700, 46700 and 56400. The percent drag reduction was found to be increasing with the increasing Reynolds number. The study was also focused on analyzing the mean flow and turbulence statistics for fully-turbulent flow using the velocity measurements acquired by PIV. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ <10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ >30). In all cases of polymer application, the viscous sublayer (i.e., y+ <10) thickness was found to be higher than that of the water flow. Reynolds shear stress in the core flow region was found to be decreasing with the increase in polymer concentration.

Turbulent flow drag reduction and degradation with dilute polymer solutions

1970 ◽  
Vol 43 (4) ◽  
pp. 689-710 ◽  
Author(s):  
R. W. Paterson ◽  
F. H. Abernathy
Keyword(s):  
Molecular Weight ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Average Molecular Weight ◽  
Experimental Studies ◽  
Polymer Degradation ◽  
High Viscosity ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Flow Drag

Experimental studies of drag reduction and polymer degradation in turbulent pipe flow with dilute water solutions of unfractionated polyethylene oxide are described. Drag reduction results indicate that the magnitude of the reduction cannot be correlated on the basis of weight average molecular weight, rather the phenomenon depends strongly on the concentration of the highest molecular weight species present in the molecular weight distribution. Polymer degradation in turbulent flow is found to be severe for high molecular weight polymers causing appreciable changes in drag reduction and molecular weight with the duration of flow. Data indicates that drag reduction exists in the limit of infinite dilution suggesting that the phenomenon is due to the interaction of individual polymer molecules with the surrounding solvent and that the extent of reduction is relatively independent of pipe diameter when a comparison is carried out at equal solvent wall shear stresses. Consideration of the high viscosity obtained with solutions in an irrotational laminar flow field suggests this is due to polymer molecule deformation and that this phenomenon is central to the mechanism of turbulent flow drag reduction.

The Simulation Research on Air Drag Reduction of Tail Dome on Vans

2013 ◽  
Vol 345 ◽  
pp. 48-53
Author(s):  
Li Feng Cao ◽  
Xiao Peng Xie ◽  
Jian Hao Zeng ◽  
Heng Huang
Keyword(s):  
Drag Reduction ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Test Results ◽  
Three Dimensional Model ◽  
Simulation Test ◽  
Simulation Research ◽  
Wind Resistance ◽  
Pressure Drag ◽  
Variable Speed Motor

In this paper, three different types of tail domes were designed based on the mechanism of reducing pressure drag between the front and rear of vans, and it takes the van without a dome as a comparison to discuss the drag reduction effects of three different sizes. The three-dimensional model of the van is established in PRO/E, and the pressure and velocity distribution of the van model were analyzed in Fluent; In addition, the wind resistance test of the van model is proceed in the variable speed motor wind resistance simulation test device. The results of CFD simulation have good consistency with the experimental test results, and it verifies the conclusion that the tail dome is good for drag reduction. It provides basis and reference for the optimization of drag reduction for the vans.

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