Accuracy of the Gamma Re-Theta Transition Model for Simulating the DU-91-W2-250 Airfoil at High Reynolds Numbers

Accurate computation of the performance of a horizontal-axis wind turbine (HAWT) using Blade Element Momentum (BEM) based codes requires good quality aerodynamic characteristics of airfoils. This paper shows a numerical investigation of transitional flow over the DU 91-W2-250 airfoil with chord-based Reynolds number ranging from 3 × 106 to 6 × 106. The primary goal of the present paper is to validate the unsteady Reynolds averaged Navier-Stokes (URANS) approach together with the four-equation transition SST turbulence model with experimental data from a wind tunnel. The main computational fluid dynamics (CFD) code used in this work was ANSYS Fluent. For comparison, two more CFD codes with the Transition SST model were used: FLOWer and STAR-CCM +. The obtained airfoil characteristics were also compared with the results of fully turbulent models published in other works. The XFOIL approach was also used in this work for comparison. The aerodynamic force coefficients obtained with the Transition SST model implemented in different CFD codes do not differ significantly from each other despite the different mesh distributions used. The drag coefficients obtained with fully turbulent models are too high. With the lowest Reynolds numbers analyzed in this work, the error in estimating the location of the transition was significant. This error decreases as the Reynolds number increases. The applicability of the uncalibrated transition SST approach for a two-dimensional thick airfoil is up to the critical angle of attack.

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A Numerical Investigation of Co-flow Jet Effects on Airfoil Aerodynamic Characteristics

10.21203/rs.3.rs-672095/v1 ◽

2021 ◽

Author(s):

Shima Yazdani ◽

Erfan Salimipour ◽

Ayoob Salimipour

Keyword(s):

Reynolds Number ◽

Stokes Equations ◽

Active Flow Control ◽

Lift Coefficient ◽

Reynolds Numbers ◽

Aerodynamic Characteristics ◽

Dynamic Stall ◽

Navier Stokes ◽

Navier Stokes Equations ◽

Momentum Coefficient

Abstract The present paper numerically investigates the performance of a Co-Flow Jet (CFJ) on the static and dynamic stall control of the NACA 0024 airfoil at Reynolds number 1.5 × 105. The two-dimensional Reynolds-averaged Navier-Stokes equations are solved using the SST k-ω turbulence model. The results show that the lift coefficients at the low angles of attack (up to α = 15̊) are significantly increased at Cµ = 0.06, however for the higher momentum coefficients, it is not seen an improvement in the aerodynamic characteristics. Also, the dynamic stall for a range of α between 0̊ and 20̊ at the mentioned Reynolds number and with the reduced frequency of 0.15 for two CFJ cases with Cµ = 0.05 and 0.07 are investigated. For the case with Cµ = 0.07, the lift coefficient curve did not present a noticeable stall feature compared to Cµ = 0.05. The effect of this active flow control by increasing the Reynolds numbers from 0.5 × 105 to 3 × 105 is also investigated. At all studied Reynolds numbers, the lift coefficient enhances as the momentum coefficient increases where its best performance is obtained at the angle of attack α = 15̊.

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Numerical Simulation of Fountain Formation due to Normal and Inclined Twin-Jet Impingement on Ground

Fluids ◽

10.3390/fluids5030132 ◽

2020 ◽

Vol 5 (3) ◽

pp. 132 ◽

Cited By ~ 1

Author(s):

Xiang Zhang ◽

Ramesh K. Agarwal

Keyword(s):

Reynolds Number ◽

Numerical Simulations ◽

Jet Impingement ◽

Reynolds Numbers ◽

Navier Stokes ◽

Ansys Fluent ◽

Flow Physics ◽

Flow Parameters ◽

Twin Jets ◽

Two Jets

The goal of this paper is to study numerically the flow physics of a fountain formed by twin-jet impingement on ground. The incompressible Reynolds-Averaged Navier-Stokes (RANS) equations with realizable k-ε and WA (Wray-Agarwal) turbulence model are employed in the numerical simulations with ANSYS Fluent. A series of numerical simulations for straight and inclined fountain formations are conducted by changing the geometric and flow parameters of twin jets and distance between them. The changes in parameters include variations in the jet Reynolds number from 2 × 104 to 8 × 104, impingement height, distance between the centerlines of the two jets from 1.4D to 16D where D is the jet diameter, and ratio of the Reynolds number of the two jets from 1 to 4. It is shown that different Reynolds numbers of the two jets can result in a fountain that inclines towards the jet with smaller Reynolds number. Detailed flow field simulations for a large number of cases are presented, and the flow physics of fountain formation is analyzed for the first time in the literature.

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Prediction of Aerodynamic Characteristics of an Elliptic Airfoil at Low Reynolds Number

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2012-72389 ◽

2012 ◽

Cited By ~ 1

Author(s):

Varun Chitta ◽

D. Keith Walters

Keyword(s):

Experimental Data ◽

Reynolds Number ◽

Turbulence Models ◽

Leading Edge ◽

Aerodynamic Characteristics ◽

Transitional Flow ◽

Suction Surface ◽

Turbulent Models ◽

Lift And Drag ◽

Elliptic Airfoil

This study focuses on modeling the effects of transitional flow and surface curvature on aerodynamic characteristics of an elliptic airfoil. Numerical simulations have been performed on a 16% thick elliptic airfoil for a range of angle of attack (α) from 0° to 20° and flow Reynolds number (Re) of 3 × 105, using relatively new transition-sensitive and traditional fully turbulent eddy viscosity turbulence models. Test conditions were matched to experiments by Kwon and Park (2005) and numerical results were compared with available experimental data. Results indicate that the transition-sensitive models, namely k-kL-ω and Transition SST, accurately predict the laminar-to-turbulent transition locations and reproduce the laminar separation bubbles on the suction surface of the airfoil in agreement with the experimental data. Also, transition-sensitive models yield improved predictions of lift and drag performance when compared with results from fully turbulent models. The fully turbulent models; including SA and k-ω SST, and a newly developed curvature-sensitive model (SST k-ω-ν2) fail to capture the flow separation and reattachment locations near the leading edge of airfoil. However, the curvature-sensitive SST k-ω-ν2 model predicts the stall point of the airfoil close to experimental results, while all other tested RANS models failed to accurately predict the stall point. Taken as a whole, the results suggest that accurate aerodynamic predictions at both low and high angles of attack might be achieved by using a model that includes the effects of both transition and curvature.

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Entrainment by a Refrigerated Air Curtain Down a Wall

Journal of Fluids Engineering ◽

10.1115/1.1792263 ◽

2004 ◽

Vol 126 (5) ◽

pp. 871-879 ◽

Cited By ~ 7

Author(s):

Pratik Bhattacharjee ◽

Eric Loth

Keyword(s):

Reynolds Number ◽

Stokes Equations ◽

Reynolds Numbers ◽

Two Dimensions ◽

Transitional Flow ◽

Navier Stokes ◽

Wall Jets ◽

Adiabatic Wall ◽

Air Curtain ◽

Thermal Entrainment

Thermal entrainment is important as it adversely affects energy consumption and evaporator humidity levels of refrigerated air curtain display cases, often at transitional Reynolds numbers. In order to get a more fundamental understanding of the mean and unsteady thermal entrainment processes, the shelf structure of a display case has been idealized to that of a plane, adiabatic wall subjected to refrigerated wall jets at laminar and transitional flow conditions. The wall jets are studied at different inflow profiles, Reynolds numbers, and Richardson numbers to investigate the effect on thermal entrainment rates. The primary simulation technique was direct numerical simulation of the Navier–Stokes equations in two dimensions for the low and moderate Reynolds numbers (though three-dimensional simulations were also conducted). At higher Reynolds numbers, a conventional Reynolds averaged Navier–Stokes approach was employed, which was found to give reasonable agreement with the above approach at a wall jet (early-transitional) Reynolds number of 2000. In general, the results yielded a significant variation in entrainment as a function of Reynolds number, with a minimum occurring at flow speeds immediately prior to transition. The entrainment rates were also sensitive to the initial velocity distribution, whereby a constant gradient profile (where any local velocity-gradient peaks were minimized) provided the least entrainment. Entrainment was also found to decrease with increasing Richardson number.

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Plunging Airfoil: Reynolds Number and Angle of Attack Effects

Aerospace ◽

10.3390/aerospace8080216 ◽

2021 ◽

Vol 8 (8) ◽

pp. 216

Author(s):

Emanuel A. R. Camacho ◽

Fernando M. S. P. Neves ◽

André R. R. Silva ◽

Jorge M. M. Barata

Keyword(s):

Reynolds Number ◽

High Performance ◽

Angle Of Attack ◽

Systems Design ◽

Reynolds Numbers ◽

Navier Stokes ◽

Low Reynolds Numbers ◽

Operational Conditions ◽

Naca0012 Airfoil ◽

The Mean

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

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Finite-amplitude steady waves in plane viscous shear flows

Journal of Fluid Mechanics ◽

10.1017/s0022112085003482 ◽

1985 ◽

Vol 160 ◽

pp. 281-295 ◽

Cited By ~ 34

Author(s):

F. A. Milinazzo ◽

P. G. Saffman

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Stokes Equations ◽

Reynolds Numbers ◽

Finite Amplitude ◽

Linear Instability ◽

Navier Stokes ◽

Unidirectional Flow ◽

Viscous Shear ◽

Finite Amplitude Waves

Computations of two-dimensional solutions of the Navier–Stokes equations are carried out for finite-amplitude waves on steady unidirectional flow. Several cases are considered. The numerical method employs pseudospectral techniques in the streamwise direction and finite differences on a stretched grid in the transverse direction, with matching to asymptotic solutions when unbounded. Earlier results for Poiseuille flow in a channel are re-obtained, except that attention is drawn to the dependence of the minimum Reynolds number on the physical constraint of constant flux or constant pressure gradient. Attempts to calculate waves in Couette flow by continuation in the velocity of a channel wall fail. The asymptotic suction boundary layer is shown to possess finite-amplitude waves at Reynolds numbers orders of magnitude less than the critical Reynolds number for linear instability. Waves in the Blasius boundary layer and unsteady Rayleigh profile are calculated by employing the artifice of adding a body force to cancel the spatial or temporal growth. The results are verified by comparison with perturbation analysis in the vicinity of the linear-instability critical Reynolds numbers.

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Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at High Reynolds Numbers for Direct Fired Cycle Applications

10.1115/gt2021-59630 ◽

2021 ◽

Author(s):

Matthew Searle ◽

Arnab Roy ◽

James Black ◽

Doug Straub ◽

Sridharan Ramesh

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Nusselt Number ◽

Gas Turbines ◽

Cfd Simulation ◽

Reynolds Numbers ◽

Navier Stokes ◽

Process Conditions ◽

Internal Cooling ◽

Air Breathing

Abstract In this paper, experimental and numerical investigations of three variants of internal cooling configurations — dimples only, ribs only and ribs with dimples have been explored at process conditions (96°C and 207bar) with sCO2 as the coolant. The designs were chosen based on a review of advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described in this paper utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is calculated in the experiments utilizing the Wilson Plot method and three heat transfer characteristics — augmentation in Nusselt number, friction factor and overall Thermal Performance Factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline channel flow cases are considered — a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds Averaged Navier Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared to the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in presence of ribs.

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Power Augmentation of a HAWT by Mie-type Tip Vanes, considering Wind Tunnel Flow Visualisation, Blade-Aspect Ratios and Reynolds Number

Wind Engineering ◽

10.1260/030952403769016663 ◽

2003 ◽

Vol 27 (3) ◽

pp. 183-194 ◽

Cited By ~ 12

Author(s):

Yukimaru Shimizu ◽

Edmond Ismaili ◽

Yasunari Kamada ◽

Takao Maeda

Keyword(s):

Reynolds Number ◽

Wind Tunnel ◽

Aspect Ratio ◽

Reynolds Numbers ◽

Flow Visualisation ◽

Velocity Measurements ◽

Horizontal Axis Wind Turbine ◽

Aspect Ratios ◽

Detailed Surface ◽

Blade Tips

Wind tunnel results are reported concerning the effects of blade aspect ratio and Reynolds number on the performance of a horizontal axis wind turbine (HAWT) with Mie-type1 tip attachments. The flow behaviour around the blade tips and the Mie-type tip vanes is presented. Detailed surface oil film visualization and velocity measurements around the blade tips, with and without Mie vanes, were obtained with the two-dimensional, Laser-Doppler Velocimetry method. Experiments were performed with rotors having blades with different aspect ratio and operating at different Reynolds numbers. The properties of the vortices generated by the Mie vanes and the blade tips were carefully studied. It was found that increased power augmentation by Mie vanes is achieved with blades having smaller aspect ratio and smaller Reynolds number.

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2D Numerical Simulation Study of Airfoil Performance

10.5194/wes-2021-45 ◽

2021 ◽

Author(s):

Nasser Shelil

Keyword(s):

Experimental Data ◽

Wind Tunnel ◽

Air Temperature ◽

Wind Turbines ◽

Aerodynamic Force ◽

Angle Of Attack ◽

Turbulence Models ◽

Aerodynamic Characteristics ◽

Operating Conditions ◽

Ansys Fluent

Abstract. The aerodynamic characteristics of DTU-LN221 airfoil is studied. ANSYS Fluent is used to simulate the airfoil performance with seven different turbulence models. The simulation results for the airfoil with different turbulence models are compared with the wind tunnel experimental data performed under the same operating conditions. It is found that there is a good agreement between the computational fluid dynamics (CFD) predicted aerodynamic force coefficients with wind tunnel experimental data especially with angle of attack between −5° to 10°. RSM is chosen to investigate the flow field structure and the surface pressure coefficients under different angle of attack between −5° to 10°. Also the effect of changing air temperature, velocity and turbulence intensity on lift and drag coefficients/forces are examined. The results show that it is recommended to operate the wind turbines airfoil at low air temperature and high velocity to enhance the performance of the wind turbines.

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Nonlinear amplification in hydrodynamic turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.914 ◽

2021 ◽

Vol 930 ◽

Author(s):

Kartik P. Iyer ◽

Katepalli R. Sreenivasan ◽

P.K. Yeung

Keyword(s):

Reynolds Number ◽

Isotropic Turbulence ◽

Stokes Equations ◽

Three Dimensional ◽

Reynolds Numbers ◽

Navier Stokes ◽

Navier Stokes Equations ◽

Developed Turbulence ◽

Advection Term ◽

Nonlinear Amplification

Using direct numerical simulations performed on periodic cubes of various sizes, the largest being $8192^3$ , we examine the nonlinear advection term in the Navier–Stokes equations generating fully developed turbulence. We find significant dissipation even in flow regions where nonlinearity is locally absent. With increasing Reynolds number, the Navier–Stokes dynamics amplifies the nonlinearity in a global sense. This nonlinear amplification with increasing Reynolds number renders the vortex stretching mechanism more intermittent, with the global suppression of nonlinearity, reported previously, restricted to low Reynolds numbers. In regions where vortex stretching is absent, the angle and the ratio between the convective vorticity and solenoidal advection in three-dimensional isotropic turbulence are statistically similar to those in the two-dimensional case, despite the fundamental differences between them.

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