Reynolds-Averaged Simulation of the Fully Developed Turbulent Drag Reduction Flow in Concentric Annuli

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Xiao Xiong ◽  
Yan Zhang ◽  
Mohammad Azizur Rahman
Keyword(s):  
Drag Reduction ◽  
Numerical Approach ◽  
Weissenberg Number ◽  
Rheological Parameters ◽  
Turbulent Regime ◽  
Ansys Fluent ◽  
Commercial Code ◽  
Turbulent Statistics ◽  
The Difference ◽  
Nonlinear Elastic

Abstract Reynolds-averaged modeling is performed for polymer-induced drag reduction (DR) fluid at the fully developed turbulent regime in a concentric annulus by using the commercial code, ansys-fluent. The numerical approach adopted in this study relies on a modified k–ε–v2¯–f model to characterize the turbulence and the finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model to represent the rheological behavior of the polymer solution. The near-wall axial velocity, Reynolds stress, and turbulent kinetic energy (TKE) budget near both walls of the annulus (fixed radius ratio of 0.4) are compared in detail at a constant Reynolds number (Re=10,587) and various rheological parameters (Weissenberg number We in the range of 1–7 and the maximum polymer elongation L = 30 and 100). Current simulation has predicted the redistributions of turbulent statistics in the annulus, where the two turbulent boundary layers (TBLs) of the DR flow differ more compared to those of its Newtonian counterpart. The difference is also found to be highly dependent on the rheological properties of the viscoelastic fluid.

Effect of Slit Inclusions in Drag Reduction of Flow over Cylinders

2016 ◽  
Vol 846 ◽  
pp. 18-22
Author(s):  
Rohit Bhattacharya ◽  
Abouzar Moshfegh ◽  
Ahmad Jabbarzadeh
Keyword(s):  
Fluid Flow ◽  
Drag Reduction ◽  
Drag Coefficient ◽  
Finite Volume ◽  
Lattice Boltzmann ◽  
Circular Cross Section ◽  
Finite Volume Methods ◽  
Turbulent Regime ◽  
Ansys Fluent ◽  
Comparison Of The Results

The flow over bluff bodies is separated compared to the flow over streamlined bodies. The investigation of the fluid flow over a cylinder with a streamwise slit has received little attention in the past, however there is some experimental evidence that show for turbulent regime it reduces the drag coefficient. This work helps in understanding the fluid flow over such cylinders in the laminar regime. As the width of the slit increases the drag coefficient keeps on reducing resulting in a narrower wake as compared to what is expected for flow over a cylinder. In this work we have used two different approaches in modelling a 2D flow for Re=10 to compare the results for CFD using finite volume method (ANSYS FLUENTTM) and Lattice Boltzmann methods. In all cases cylinders of circular cross section have been considered while slit width changing from 10% to 40% of the cylinder diameter. . It will be shown that drag coefficient decreases as the slit ratio increases. The effect of slit size on drag reduction is studied and discussed in detail in the paper. We have also made comparison of the results obtained from Lattice Boltzmann and finite volume methods.

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.

Improved Power for Wind Farm Savonius Rotors: Effect of Blade Shape and Rotors Position

2020 ◽  
Author(s):  
Abdelkader Filali ◽  
Lyes Khezzar ◽  
Hamza Semmari
Keyword(s):  
Wind Farm ◽  
Numerical Data ◽  
Numerical Approach ◽  
Rotor Blades ◽  
Power Coefficient ◽  
Total Power ◽  
Ansys Fluent ◽  
Commercial Code ◽  
Field Efficiency ◽  
Wake Zone

Abstract In the present study the effect of distance between five vertical Savonius rotors « Gap » on the total performance of the wind farm rotors is investigated. Numerical computations are conducted for a single Savonius turbine, and for the five clustered turbines aligned in perpendicular direction with respect to the upstream wind velocity. The study is carried out using ANSYS FLUENT commercial code and the moving mesh approach for the rotating zones is used. The turbulence model adopted in this work is the k-ω shear stress transport (SST) model. Numerical approach was first validated with previously published experimental and numerical data for a single rotating Savonius rotor case with semi-circular blades. Then, an improvement process based on the modification of the blades profiles to an elliptical shape was adopted. Subsequently, the change in distance between the five vertical Savonius rotors « Gap » has been considered with values of 0.25, 1 and 1.4 times the rotor radius (R). Results show that the Gap = 1R provides the optimum power coefficient for the wind farm rotors. However, the generated wake zone behind the five aligned rotors for this value is more important in particular for the 90 ° angle of the advanced and returned rotor blades. The field efficiency defined by the total power ratio of the five isolated rotors to the total power of the wind farm with five Savonius rotors is around 67%. All these geometrical considerations and propositions made it possible to define an optimal wind farm rotors arrangement.

scholarly journals Effect of finite Weissenberg number on turbulent channel flows of an elastoviscoplastic fluid

2021 ◽  
Vol 927 ◽  
Author(s):  
Daulet Izbassarov ◽  
Marco E. Rosti ◽  
Luca Brandt ◽  
Outi Tammisola
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Weissenberg Number ◽  
Channel Flows ◽  
Viscoplastic Flow ◽  
Turbulent Structures ◽  
Turbulent Dissipation ◽  
Flow Equations ◽  
Turbulent Channel Flows ◽  
Nonlinear Elastic

Direct numerical simulations are carried out to study the effect of finite Weissenberg number up to $Wi=16$ on laminar and turbulent channel flows of an elastoviscoplastic (EVP) fluid, at a fixed bulk Reynolds number of $2800$ . The incompressible flow equations are coupled with the evolution equation for the EVP stress tensor by a modified Saramito model that extends both the Bingham viscoplastic and the finite extensible nonlinear elastic-Peterlin (FENE-P) viscoelastic models. In turbulent flow, we find that drag decreases with both the Bingham and Weissenberg numbers, until the flow laminarises at high enough elastic and yield stresses. Hence, a higher drag reduction is achieved than in the viscoelastic flow at the same Weissenberg number. The drag reduction persists at Bingham numbers up to 20, in contrast to viscoplastic flow, where the drag increases in the laminar regime compared with a Newtonian flow. Moreover, elasticity affects the laminarisation of an EVP flow in a non-monotonic fashion, delaying it at lower and promoting it at higher Weissenberg numbers. A hibernation phenomenon is observed in the EVP flow, leading to large changes in the unyielded regions. Finally, plasticity is observed to affect both low- and high-speed streaks equally, attenuating the turbulent dissipation and the fragmentation of turbulent structures.

scholarly journals A FENE-P k–ε Viscoelastic Turbulence Model Valid up to High Drag Reduction without Friction Velocity Dependence

2020 ◽  
Vol 10 (22) ◽  
pp. 8140
Author(s):  
Michael McDermott ◽  
Pedro Resende ◽  
Thibaut Charpentier ◽  
Mark Wilson ◽  
Alexandre Afonso ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Turbulence Model ◽  
Friction Velocity ◽  
Model Performance ◽  
Reynolds Numbers ◽  
Rheological Parameters ◽  
Velocity Dependence ◽  
Polymeric Solutions ◽  
Conformation Tensor ◽  
Nonlinear Elastic

A viscoelastic turbulence model in a fully-developed drag reducing channel flow is improved, with turbulent eddies modelled under a k–ε representation, along with polymeric solutions described by the finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model. The model performance is evaluated against a wide variety of direct numerical simulation data, described by different combinations of rheological parameters, which is able to predict all drag reduction (low, intermediate and high) regimes with good accuracy. Three main contributions are proposed: one with a simplified viscoelastic closure for the NLTij term (which accounts for the interactions between the fluctuating components of the conformation tensor and the velocity gradient tensor), by removing additional damping functions and reducing complexity compared with previous models; second through a reformulation for the closure of the viscoelastic destruction term, Eτp, which removes all friction velocity dependence; lastly by an improved modified damping function capable of predicting the reduction in the eddy viscosity and thus accurately capturing the turbulent kinetic energy throughout the channel. The main advantage is the capacity to predict all flow fields for low, intermediate and high friction Reynolds numbers, up to high drag reduction without friction velocity dependence.

scholarly journals Numerical Investigation of an Optimized Rotor Head Fairing for the RACER Compound Helicopter in Cruise Flight

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 66
Author(s):  
Patrick Pölzlbauer ◽  
Andreas Kümmel ◽  
Damien Desvigne ◽  
Christian Breitsamter
Keyword(s):  
Drag Reduction ◽  
Design Optimization ◽  
Cost Effective ◽  
Aerodynamic Design ◽  
Ansys Fluent ◽  
Aerodynamic Design Optimization ◽  
Flow Phenomena ◽  
Compound Helicopter ◽  
Rotor Head ◽  
Cruise Flight

The present work is part of the Clean Sky 2 project Full-Fairing Rotor Head Aerodynamic Design Optimization (FURADO), which deals with the aerodynamic design optimization of a full-fairing rotor head for the Rapid And Cost-Effective Rotorcraft (RACER) compound helicopter. The rotor head is a major drag source and previous investigations have revealed that the application of rotor head fairings can be an effective drag reduction measure. As part of the full-fairing concept, a new blade-sleeve fairing was aerodynamically optimized for cruise flight. Within this publication, the newly developed blade-sleeve fairing is put to test on an isolated, five-bladed rotor head and compared to an already existing reference blade-sleeve fairing, which was developed at Airbus Helicopters. Numerical flow simulations are performed with ANSYS Fluent 2019 R2 considering a rotating rotor head with cyclic pitch movement. The aerodynamic forces of the isolated rotor head are analyzed to determine the performance benefit of the newly developed blade-sleeve fairing. A drag reduction of 4.7% and a lift increase of 20% are obtained in comparison to the Airbus Helicopters reference configuration. Furthermore, selected surface and flow field quantities are presented to give an overview on the occurring flow phenomena.

scholarly journals Turbulent drag reduction by polymer additives in parallel-shear flows

2017 ◽  
Vol 827 ◽  
Author(s):  
Bayode E. Owolabi ◽  
David J. C. Dennis ◽  
Robert J. Poole
Keyword(s):  
Drag Reduction ◽  
Cross Sections ◽  
Shear Flows ◽  
Extensional Flow ◽  
Relaxation Times ◽  
Weissenberg Number ◽  
Mechanical Degradation ◽  
Turbulent Drag Reduction ◽  
Time Resolved ◽  
Turbulent Drag

In this study, we experimentally investigate the turbulent drag-reduction (DR) mechanism in flow through ducts of circular, rectangular and square cross-sections using two grades of polyacrylamide in aqueous solution having different molecular weights and various semidilute concentrations. Specifically, we explore the relationship between drag reduction and fluid elasticity, purposely exploiting the mechanical degradation of polymer molecules to vary their rheological properties. We also obtain time-resolved velocity data for various DR levels using particle image velocimetry and laser Doppler velocimetry. Elasticity is quantified via relaxation times determined from uniaxial extensional flow using a capillary breakup apparatus. A plot of DR against Weissenberg number ($Wi$) is found to approximately collapse the data, with the onset of DR occurring at $Wi\approx 0.5$ and the maximum drag-reduction asymptote being approached for $Wi\gtrsim 5$. Thus quantitative predictions of DR in a range of shear flows can be made from a single measurable material property of a polymer solution, at least for this particular flexible linear polymer.

Durability of a Drag Reducing Solution

2008 ◽  
Vol 18 (1) ◽  
pp. 12421-1-12421-5
Author(s):  
V. Mik ◽  
J. Myska ◽  
Z. Chara ◽  
P. Stern
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Turbulence Intensity ◽  
Surfactant Concentration ◽  
Surfactant Solution ◽  
Small Addition ◽  
Rheological Parameters ◽  
Aging Effects ◽  
Flow Disturbance ◽  
Solution Change

AbstractEffectiveness of drag reduction by small addition of a surfactant in the turbulent flow of water depends on the structure and concentration of the additive, temperature of the solution and turbulence intensity, possible flow disturbance by a mechanical obstacle and the content of ions in water, but also on the age of the surfactant solution. We show how important aging effects are in connection with total surfactant concentration, in particular how rheological parameters of the drag reducing solution change with time.

scholarly journals Drag reduction in a class 8 truck - scaled down model

2018 ◽  
Vol 172 ◽  
pp. 01003
Author(s):  
R Vishwa Krishna. ◽  
R Suwathy. ◽  
M Pragadeesh. ◽  
M Venkatesan.
Keyword(s):  
Numerical Model ◽  
Drag Coefficient ◽  
Heavy Duty ◽  
Commercial Vehicles ◽  
Heavy Load ◽  
Ansys Fluent ◽  
Commercial Code ◽  
Class 8 Truck ◽  
Gap Width ◽  
Front Radius

Trucks are heavy load vehicles used mainly for commercial transport operations. There are several classes of heavy duty commercial vehicles classified based on the weight loaded. More than 50% of the engine output power in such trucks is utilized to overcome the drag. Drag force in automobiles is the resistance offered by air on vehicles at higher speeds. Class 8 trucks suffer higher drag when compared to other classes. In the present work, a numerical model is developed using a commercial code ANSYS FLUENT to predict the drag coefficient value. The effects of gap width and cab front radius with a constant fairing is analysed using the numerical model developed. A Class 8 model truck with minimal drag coefficient having constant fairing and optimized gap width between the trailer and cab is proposed.

scholarly journals Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit

2019 ◽  
Vol 874 ◽  
pp. 699-719 ◽  
Author(s):  
Jose M. Lopez ◽  
George H. Choueiri ◽  
Björn Hof
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Pipe Flow ◽  
Domain Size ◽  
Reynolds Numbers ◽  
Weissenberg Number ◽  
Pipe Length ◽  
Low Reynolds Numbers ◽  
Maximum Drag Reduction ◽  
Low Reynolds

Polymer additives can substantially reduce the drag of turbulent flows and the upper limit, the so-called state of ‘maximum drag reduction’ (MDR), is to a good approximation independent of the type of polymer and solvent used. Until recently, the consensus was that, in this limit, flows are in a marginal state where only a minimal level of turbulence activity persists. Observations in direct numerical simulations at low Reynolds numbers ($Re$) using minimal sized channels appeared to support this view and reported long ‘hibernation’ periods where turbulence is marginalized. In simulations of pipe flow at $Re$ near transition we find that, indeed, with increasing Weissenberg number ($Wi$), turbulence expresses long periods of hibernation if the domain size is small. However, with increasing pipe length, the temporal hibernation continuously alters to spatio-temporal intermittency and here the flow consists of turbulent puffs surrounded by laminar flow. Moreover, upon an increase in $Wi$, the flow fully relaminarizes, in agreement with recent experiments. At even larger $Wi$, a different instability is encountered causing a drag increase towards MDR. Our findings hence link earlier minimal flow unit simulations with recent experiments and confirm that the addition of polymers initially suppresses Newtonian turbulence and leads to a reverse transition. The MDR state on the other hand results at these low$Re$ from a separate instability and the underlying dynamics corresponds to the recently proposed state of elasto-inertial turbulence.

Sign in / Sign up

Export Citation Format

Share Document