F-1521 Numerical Simulations of Boat-tail Drag Reduction

2001 ◽  
Vol IV.01.1 (0) ◽  
pp. 355-356
Author(s):  
Hideyo Negishi ◽  
Kozo Fujii ◽  
Osamu Nakabep
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations

scholarly journals Aerodynamic Study of a Tricycle Wheel Subsystem for Drag Reduction

2012 ◽  
Author(s):  
Thomas Driant ◽  
Lakhdar Remaki ◽  
Stéphane Moreau ◽  
Alain Desrochers ◽  
Hachimi Fellouah
Keyword(s):  
Wind Tunnel ◽  
Drag Reduction ◽  
Numerical Simulations ◽  
Experimental Results ◽  
Flow Conditions ◽  
Commercial Code ◽  
Drag Analysis

This paper deals with a CFD and experimental drag analysis on an isolated rotating wheel subsystem (including its accessories: tire, suspension, A-arms and fender) of a tricycle vehicle. The main goal of the present work is to study the effect of the fender on the wheel subsystem drag and its optimization. The Star CCM+ commercial code was used for the numerical simulations. Different flow conditions were simulated and some results were validated by comparison to wind tunnel experimental results. To perform drag optimization, several aerodynamic fender shapes were designed and simulated as part of the subsystem. A drastic drag reduction up to 30.6% compared to the original wheel subsystem was achieved through numerical simulations.

scholarly journals Numerical Simulation of Supersonic Carman Curve Bodies with Aerospike

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
HaiLong Zhao ◽  
Ke Peng ◽  
ZePing Wu ◽  
WeiHua Zhang ◽  
JiaWei Yang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Mach Number ◽  
Supersonic Flow ◽  
Drag Reduction ◽  
Numerical Simulations ◽  
Reduction Methods ◽  
Reduction Effect ◽  
Supersonic Vehicles

Drag reduction is one of the important problems for the supersonic vehicles. As one of the drag reduction methods, aerospike has been used in some equipment because of its good drag reduction effect. In this paper, the numerical simulations of Carman curve bodies with different lengths of the aerospike and different radius of the flat cylindrical aerodisk in supersonic flow freestream are investigated. Based on the numerical simulations, the mechanism of drag reduction of the aerospike is discussed. The drag reduction effect influence of the parameters of the aerodisk radius and the aerospike length on the Carman curve body is analyzed. The aerodisk radius within a certain range is helpful for the drag reduction. The change of length of the aerospike has little effect on the drag of Carmen curve bodies. The drag reduction effect of the same aerospike becomes worse with the increase of the incoming Mach number.

scholarly journals Turbulent drag reduction by anisotropic permeable substrates – analysis and direct numerical simulations

2019 ◽  
Vol 875 ◽  
pp. 124-172 ◽  
Author(s):  
G. Gómez-de-Segura ◽  
R. García-Mayoral
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Critical Value ◽  
Direct Numerical Simulations ◽  
Mean Flow ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Theoretical Predictions ◽  
The Mean ◽  
The Difference

We explore the ability of anisotropic permeable substrates to reduce turbulent skin friction, studying the influence that these substrates have on the overlying turbulence. For this, we perform direct numerical simulations of channel flows bounded by permeable substrates. The results confirm theoretical predictions, and the resulting drag curves are similar to those of riblets. For small permeabilities, the drag reduction is proportional to the difference between the streamwise and spanwise permeabilities. This linear regime breaks down for a critical value of the wall-normal permeability, beyond which the performance begins to degrade. We observe that the degradation is associated with the appearance of spanwise-coherent structures, attributed to a Kelvin–Helmholtz-like instability of the mean flow. This feature is common to a variety of obstructed flows, and linear stability analysis can be used to predict it. For large permeabilities, these structures become prevalent in the flow, outweighing the drag-reducing effect of slip and eventually leading to an increase of drag. For the substrate configurations considered, the largest drag reduction observed is ${\approx}$20–25 % at a friction Reynolds number $\unicode[STIX]{x1D6FF}^{+}=180$.

Direct Numerical Simulations of Turbulent Channel Flow With Polymer Additives

2020 ◽  
Vol 36 (5) ◽  
pp. 691-698
Author(s):  
Che-Yu Lin ◽  
Chao-An Lin
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Weissenberg Number ◽  
Direct Numerical Simulations ◽  
Polymer Additives ◽  
Boundary Treatments ◽  
Conformation Tensor ◽  
Nonlinear Elastic

ABSTRACTDirect numerical simulations have been applied to simulate flows with polymer additives. FENE-P (finite-extensible-nonlinear-elastic-Peterlin) dumbbell model solving for the conformation tensor is adopted to investigate the influence of the polymer on the flowfield. Boundary treatments of the conformation tensor on the flowfield are examined first, where boundary condition based on the linear extrapolation scheme provides more accurate results with second-order accurate error norms. Further simulations of the turbulent channel flow at different Weissenberg numbers are also conducted to investigate the influence on drag reduction. Drag reduction increases in tandem with the increase of Weissenberg number and the increase saturates at Weτ~200, where the drag reduction is close to the maximum drag reduction (MDR) limit. At the regime of y+ > 5, the viscous layer thickens with the increase of the Weissenberg number showing a departure from the traditional log-law profile, and the velocity profiles approach the MDR line at high Weissenberg number. The Reynolds stress decreases in tandem with the increase of Weτ, whereas the levels of laminar stress and polymer stress act adversely. However, as the Weissenberg number increases, the proportion of the laminar stress in the total stress increases, and this contributes to the drag reduction of the polymer flow.

Predictions of the effective slip length and drag reduction with a lubricated micro-groove surface in a turbulent channel flow

2019 ◽  
Vol 874 ◽  
pp. 797-820 ◽  
Author(s):  
Jaehee Chang ◽  
Taeyong Jung ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Aspect Ratio ◽  
Drag Reduction ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Slip Length ◽  
Turbulent Channel Flow ◽  
Solid Substrate ◽  
Direct Numerical Simulations ◽  
Effective Slip ◽  
Lubricant Viscosity

We perform direct numerical simulations of a turbulent channel flow with a lubricated micro-grooved surface to investigate the effects of this surface on the slip characteristics at the interface and the friction drag. The interface between water and lubricant is assumed to be flat, i.e. the surface-tension effect is neglected. The solid substrate, where a lubricant is infused, is composed of straight longitudinal grooves. The flow rate of water inside the channel is maintained constant, and a lubricant layer under the interface is shear driven by the turbulent water flow above. A turbulent channel flow with a superhydrophobic (i.e. air-lubricated) surface having the same solid substrate configuration is also simulated for comparison. The results show that the drag reduction with the liquid-infused surface highly depends on the lubricant viscosity as well as the groove width and aspect ratio. The amounts of drag reduction with the liquid-infused surfaces are not as good as those with superhydrophobic surfaces, but are still meaningfully large. For instance, the maximum drag reduction by the heptane-infused surface is approximately 13 % for a rectangular groove whose spanwise width and depth in wall units are 12 and 14.4, respectively, whereas a superhydrophobic surface with the same geometry results in a drag reduction of 21 %. The mean slip length normalized by the viscosity ratio and groove depth depends on the groove aspect ratio. The ratio of fluctuating spanwise slip length to the streamwise one is between 0.25 (ideal surface without groove structures) and 1 (i.e. isotropic slip), indicating that the slip is anisotropic. Using the Stokes flow assumption, the effective streamwise and spanwise slip lengths are expressed as a function of groove geometric parameters and lubricant viscosity. We also suggest a predictive model for drag reduction with the heptane-lubricated surface by combining the predicted effective slip lengths with the drag reduction formula used for riblets (Luchini et al., J. Fluid Mech., vol. 228, 1991, pp. 87–109). The predicted drag reductions are in good agreements with those from the present and previous direct numerical simulations.

Bubble Effects on Wall Shear in Vortical Flows

2003 ◽  
Author(s):  
Arturo Ferna´ndez ◽  
Jiacai Lu ◽  
Gre´tar Tryggvason
Keyword(s):  
Surface Tension ◽  
Drag Reduction ◽  
Numerical Simulations ◽  
Turbulent Flows ◽  
Front Tracking ◽  
Direct Numerical Simulations ◽  
Fluid Inertia ◽  
Fundamental Interaction ◽  
Turbulent Structures ◽  
Simplified Models

Direct numerical simulations of the motion of bubbles in turbulent flows are being carried out, using a finite volume/front tracking technique that accounts fully for the effect of fluid inertia, viscosity, bubble deformability, and surface tension. The objective of the simulations is both to address the fundamental interaction mechanisms between the bubbles and the flow and how the bubbles modify the wall turbulent structures, as well as to provide data for validation of simplified models. Results for bubbles placed in the so-called “minimum turbulent channel” show significant drag reduction as the bubbles disrupt the near-wall turbulent flow.

Direct and Large Eddy Numerical Simulations of Turbulent Viscoelastic Drag Reduction

2011 ◽  
pp. 421-428
Author(s):  
Laurent Thais ◽  
Andres E. Tejada-Martínez ◽  
Thomas B. Gatski ◽  
Gilmar Mompean ◽  
Hassan Naji
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Large Eddy
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