A Numerical Investigation of High Lift Coefficient Airfoils Near Regions of Stall

2013 ◽  
Author(s):  
Ravon Venters ◽  
Brian Helenbrook
Keyword(s):  
Experimental Data ◽  
Free Stream ◽  
Numerical Models ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Optimal Placement ◽  
Navier Stokes ◽  
Cross Sectional ◽  
High Lift ◽  
Optimal Angle

The cross-sectional geometry of a diffuser-augmented wind turbine (DAWT) is often that of a cambered airfoil oriented at an angle of attack such that the lift coefficient of the airfoil is maximal. Beyond this angle separation occurs, and the performance decreases. Thus, predicting this transition is important for creating an optimally designed diffuser. The focus of this work is to validate two numerical methods for predicting the onset of separation for highly cambered airfoils. The numerical models investigated are a Reynolds-averaged-Navier-Stokes (RANS) k–ε model and XFOIL. The results were compared to each other and to experimental data. Overall the most accurate model was the k–ε model. Using this model, an optimization of a 2D DAWT was performed which determined the optimal placement of the diffuser. This optimization showed that the optimal angle of attack for the diffuser is much greater than what one would expect based on the maximum lift angle of an airfoil in a free-stream.

Ducted Wind Turbine Optimization

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Ravon Venters ◽  
Brian T. Helenbrook ◽  
Kenneth D. Visser
Keyword(s):  
Wind Turbine ◽  
Power Output ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Optimal Placement ◽  
Cross Sectional ◽  
Local Flow ◽  
Open Rotor ◽  
Rotor Disk ◽  
Optimal Coefficient

This study presents a numerical optimization of a ducted wind turbine (DWT) to maximize power output. The cross section of the duct was an Eppler 423 airfoil, which is a cambered airfoil with a high lift coefficient (CL). The rotor was modeled as an actuator disk, and the Reynolds-averaged Navier–Stokes (RANS) k–ε model was used to simulate the flow. The optimization determined the optimal placement and angle for the duct relative to the rotor disk, as well as the optimal coefficient of thrust for the rotor. It was determined that the optimal coefficient of thrust is similar to an open rotor in spite of the fact that the local flow velocity is modified by the duct. The optimal angle of attack of the duct was much larger than the separation angle of attack of the airfoil in a freestream. Large angles of attack did not induce separation on the duct because the expansion caused by the rotor disk helped keep the flow attached. For the same rotor area, the power output of the largest DWT was 66% greater than an open rotor. For the same total cross-sectional area of the entire device, the DWT also outperformed an open rotor, exceeding Betz's limit by a small margin.

Partially Cavitating Hydrofoils: Experimental and Numerical Analysis*

2000 ◽  
Vol 44 (01) ◽  
pp. 40-58
Author(s):  
Christian Pellone ◽  
Thierry Maître ◽  
Laurence Briançon-Marjollet
Keyword(s):  
Numerical Models ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Local Pressure ◽  
Two Phase ◽  
Complete Study ◽  
Flow Configurations ◽  
Potential Methods

The numerical modeling of partially cavitating foils under a confined flow configuration is described. A complete study of previous numerical models highlights that the presence of a turbulent and two-phase wake, at the rear of the cavity, has a nonnegligible effect on the local pressure coefficient, the cavitation number, the cavity length and the lift coefficient; hence viscous effects must be included. Two potential methods are used, each being coupled with a calculation of the boundary layer developed downstream of the cavity. So, an "open cavity" numerical model, as it is called, was developed and tested with two types of foil: a NACA classic foil and a foil of which the profile is obtained performing an inverse calculation on a propeller blade test section. On the other hand, under noncavitating conditions, for each method, the results are compared with the results obtained by the Navier-Stokes solver "FLUENT." The cavitating flow configurations presented herein were carried out using the small hydrodynamic tunnel at Bassin d'Essais des Carènes [Val de Reuil, France]. The results obtained by the two methods are compared with experimental measurements.

A 3-D Thin Layer Navier-Stokes Code for Supersonic Laminar and Turbulent Flows

2002 ◽  
Author(s):  
Omid Abouali ◽  
Mohammad M. Alishahi ◽  
Homayoon Emdad ◽  
Goodarz Ahmadi
Keyword(s):  
Experimental Data ◽  
Shock Wave ◽  
Mach Number ◽  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Cross Flow ◽  
Navier Stokes ◽  
Cross Sectional ◽  
Laminar And Turbulent Flows ◽  
Circumferential Pressure

A 3-D Thin Layer Navier-Stokes (TLNS) code for solving viscous supersonic flows is developed. The new code uses several numerical algorithms for space and time discretization together with appropriate turbulence modeling. Roe’s method is used for discretizing the convective terms and the central differencing scheme is employed for the viscous terms. An explicit time marching technique and a finite volume space discretization are used. The developed computational model can handle both laminar and turbulent flows. The Baldwin-Lomax model and Degani-Schiff modifications are used for turbulence modeling. The computational model is applied to a hypersonic laminar flow at Mach 7.95 around a cone at different incidence angles. The circumferential pressure distribution is compared with the experimental data. The cross-sectional Mach number contours are also presented. It is shown that in addition to the outer shock, a cross-flow shock wave is also present in the flow field. The cases of supersonic turbulent flows with Mach number 3 around a tangent-ogive with incidence angles of 6° and a secant-ogive with incidence angles of 10° are also studied. The circumferential pressure distributions are compared with the experimental data and the Euler code results and good agreement is obtained. The cross-sectional Mach number contours are also presented. It is shown that in this case also in addition to the outer shock, a cross-flow shock wave is also present at the incidence angle of 10°.

scholarly journals Numerical investigation of the low-frequency flow oscillation over a NACA-0012 aerofoil at the inception of stall

2019 ◽  
Vol 11 ◽  
pp. 175682931983368 ◽  
Author(s):  
Yasir A ElAwad ◽  
Eltayeb M ElJack
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Separation Bubble ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Low Frequency ◽  
Laminar Separation Bubble ◽  
Flow Oscillation ◽  
Laminar Separation ◽  
Naca 0012

High-fidelity large eddy simulation is carried out for the flow field around a NACA-0012 aerofoil at Reynolds number of [Formula: see text], Mach number of 0.4, and various angles of attack around the onset of stall. The laminar separation bubble is formed on the suction surface of the aerofoil and is constituted by the reattached shear layer. At these conditions, the laminar separation bubble is unstable and switches between a short bubble and an open bubble. The instability of the laminar separation bubble triggers a low-frequency flow oscillation. The aerodynamic coefficients oscillate accordingly at a low frequency. The lift and the drag coefficients compare very well to recent high-accuracy experimental data, and the lift leads the drag by a phase shift of [Formula: see text]. The mean lift coefficient peaks at the angle of attack of [Formula: see text], in total agreement with the experimental data. The spectra of the lift coefficient does not show a significant low-frequency peak at angles of attack lower than or equal the stall angle of attack ([Formula: see text]). At higher angles of attack, the spectra show two low-frequency peaks and the low-frequency flow oscillation is fully developed at the angle of attack of [Formula: see text]. The behaviour of the flow-field and changes in the turbulent kinetic energy over one low-frequency flow oscillation cycle are described qualitatively.

Stability Analysis of a Light Aircraft Configuration Using Computational Fluid Dynamics

2012 ◽  
Vol 225 ◽  
pp. 391-396 ◽  
Author(s):  
Mohammed Mahdi ◽  
Yasser A. Elhassan
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Rate Of Change ◽  
Navier Stokes ◽  
Rolling Moment ◽  
Moment Coefficient ◽  
Stability Derivatives ◽  
Lift And Drag

This work aims to simulate and study the flow field around SAFAT-01 aircraft using numerical solution based on solving Reynolds Averaged Navier-Stokes equations coupled with K-ω SST turbulent model. The aerodynamics behavior of SAFAT-01 aircraft developed at SAFAT aviation complex were calculated at different angles of attack and side slip angles. The x,y and z forces and moments were calculated at flight speed 50m/s and at sea level condition. Lift and drag curves for different angles of attack were plotted. The maximum lift coefficient for SAFAT-01 was 1.67 which occurred at angle of attack 16° and Maximum lift to drag ratio (L/D) was 14 which occurred at α=3°, and the zero lift drag coefficient was 0.0342. Also the yawing moment coefficient was plotted for different side slip angles as well as rolling moment. The longitudinal stability derivatives with respect to angle of attack, speed variation (u), rate of pitch (q) and time rate of change of angle of attack were calculated using obtained CFD results. Concerning lateral stability only side slips derivatives were calculated. To validate this numerical simulation USAF Digital DATCOM is used to analyze this aircraft; a comparison between predicted results for this aircraft and Digital DATCOM indicated that this numerical simulation has high ability for predicting the aerodynamics characteristics.

scholarly journals Active Control of a Stalled Airfoil Through Steady or Unsteady Actuation Jets

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
V. G. Chapin ◽  
E. Benard
Keyword(s):  
Active Control ◽  
Computational Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Position Angle ◽  
Navier Stokes ◽  
Suction Surface ◽  
Parametric Studies ◽  
Naca 0012

The active control of the leading-edge (LE) separation on the suction surface of a stalled airfoil (NACA 0012) at a Reynolds number of 106 based on the chord length is investigated through a computational study. The actuator is a steady or unsteady jet located on the suction surface of the airfoil. Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations are solved on hybrid meshes with the Spalart–Allmaras turbulence model. Simulations are used to characterize the effects of the steady and unsteady actuation on the separated flows for a large range of angle of attack (0 < α < 28 deg). Parametric studies are carried out in the actuator design-space to investigate the control effectiveness and robustness. An optimal actuator position, angle, and frequency for the stalled angle of attack α = 19 deg are found. A significant increase of the lift coefficient is obtained (+ 84% with respect to the uncontrolled reference flow), and the stall is delayed from angle of attack of 18 deg to more than 25 deg. The physical nonlinear coupling between the actuator position, velocity angle, and frequency is investigated. The critical influence of the actuator location relative to the separation location is emphasized.

Comparison of Experimental Data of a Moored Multibody Wave Energy Device With a Hybrid CFD and BIEM Numerical Analysis Framework

2015 ◽  
Author(s):  
Ali Nematbakhsh ◽  
Constantine Michailides ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Wave Energy ◽  
Stokes Equations ◽  
Numerical Models ◽  
Integral Equation Method ◽  
Boundary Integral ◽  
Navier Stokes ◽  
Analysis Framework ◽  
Energy Device

In the present paper, a hybrid Computational Fluid Dynamics (CFD) and Boundary Integral Element Method (BIEM) framework is developed in order to study the response of a moored Multibody wave Energy Device (MED) to a panchromatic sea state. The relevant results are the surge and heave responses of the MED. The Numerical Analysis Framework (NAF) includes two different models; the first model uses Navier-Stokes equations to describe the flow field and is solved with an in-house CFD code to quantify the viscous damping effect, while the second model uses boundary-integral equation method and is solved with the tool WAMIT\SIMO\RIFLEX. By studying the free decay tests with the Navier-Stokes based model, the uncoupled linear and quadratic damping coefficients of the MED in surge and heave directions are calculated. These coefficients are given as input to the WAMIT\SIMO\RIFLEX model and the responses of the MED to different wave conditions are determined. These responses are compared with the experimental data and very good agreement is obtained. The MED responses calculated by the presented NAF have been obtained in connection with a hydrodynamic modeling competition and selected as one of the numerical models, which well predict the blind experimental data that were unknown to the authors.

Unsteady RANS Simulation of Flow Around a 5:1 Rectangular Cylinder at High Reynolds Numbers

2012 ◽  
Author(s):  
Muk Chen Ong
Keyword(s):  
Free Stream ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Stream Velocity ◽  
High Reynolds Numbers ◽  
Rectangular Cylinder ◽  
Mean Pressure ◽  
Unsteady Rans ◽  
High Reynolds

The unsteady flows around a stationary two dimensional rectangular cylinder with chord-to-thickness ratio B/D = 5.0 at high Reynolds numbers, ReB = 5×105, 1×106, 1.5×106 and 2×106 (based on the free stream velocity and the chord length), are investigated numerically by solving the Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with a standard high Reynolds number k-ε turbulence model. The objective of the present study is to evaluate whether the model is applicable for engineering design within this flow regime. Hydrodynamic results (such as time-averaged drag coefficient, root-mean-square of fluctuating lift coefficient, Strouhal number and mean pressure distribution around the rectangular cylinder) are compared with published experimental data. The mechanism of vortex shedding is also discussed.

scholarly journals Computational analysis of high-lift-generating airfoils for diffuser-augmented wind turbines

2021 ◽  
Vol 6 (1) ◽  
pp. 149-157
Author(s):  
Aniruddha Deepak Paranjape ◽  
Anhad Singh Bajaj ◽  
Shaheen Thimmaiah Palanganda ◽  
Radha Parikh ◽  
Raahil Nayak ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Computational Analysis ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Two Dimensions ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Energy Access ◽  
Cross Sectional ◽  
High Lift

Abstract. The impetus towards sustainable energy production and energy access has led to considerable research and development on decentralized generators, in particular diffuser-augmented wind turbines. This paper aims to characterize the performance of diffuser-augmented wind turbines (DAWTs) using high-lift airfoils employing a three-step computational analysis. The study is based on computational fluid dynamics, and the analysis is carried out by solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equations in two dimensions. The rotor blades are modeled as an actuator disk, across which a pressure drop is imposed analogous to a three-dimensional rotor. We study the change in performance of the enclosed turbine with varying diffuser cross-sectional geometry. In particular, this paper characterizes the effect of a flange on the flow augmentation provided by the diffuser. We conclude that at the end of the three-step analysis, Eppler 423 showed the maximum velocity augmentation.

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