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COB77 DYNAMIC STALL MODELING TECHNIQUES IN WIND TURBINES
Jorge Antonio Villar Alé
Pontificia Universidade Católica do Rio Grande do Sul - PUCRS
Departamento de Engenharia Mecânica - Eólus - Grupo de Energia Eólica
Av Ipiranga 6681, Porto Alegre, RS, CEP 90.619-900 - E-mail: villar@music.pucrs.br
Techniques for modeling dynamic stall in Vertical Axis Wind Turbines (VAWT) are analyzed using semi-empirical models. Some existing models, the Boeing-Vertol, MIT and Indicial are reviewed. Is proposed the utilization of a modified ONERA model with improved performance. The model is based on a set of differential equations. The resulting aerodynamic forces are presented with the proposed model, after including modifications that extend the model to operation at low tip speed ratio where the amplitude oscillation of the attack angle is high. The results are compared with experiment showing good agreement.
Keywords: Dynamic stall, wind turbines, unsteady aerodynamics.
COB238 OTIMIZAÇÃO DE INJETORES DE AR EM TÚNEIS DE VENTO/ INJECTOR OPTIMIZATION FOR WIND TUNNEL
Sidney Lage Nogueira
Instituto de Aeronáutica e Espaço- CTA/IAE, CEP 12228-904São José dos Campos, S.P., Brasil - E-mail, tts@iconet.com.br
This paper presents the theory of injectors as applied to Wind Tunnels, and the optimization process used to improve the performance characteristics of the Brazilian Transonic Wind Tunnel Project-TTS. The mathematical model includes the utilization of diffuser, blow off, and pressures losses of the configuration, as well as the principles of using the injectors on a different design point. A Pilot Tunnel using injectors device has been installed in the Brazilian Aerospace Technical Center, and the results obtained are also included.
Keywords: Wind Tunnel , Injectors, Design, Pressure Loss, Testing.
COB258 estudo numérico e experimental do escoamento ao redor de um perfil aerodinâmico naca 0012 / NUMERICAL AND EXPERIMENTAL STUDY OF THE FLOW AROUND A NACA 0012 AIRFOIL
Cláudio Lindquist, Edson D.R. Vieira, Ricardo Alan V. Ramos & Sérgio S. Mansur
Departamento de Engenharia Mecânica, Faculdade de Engenharia - UNESP - Ilha Solteira
CEP 15.385-000 Ilha Solteira - SP, Brasil, E-mail: mansur@feis.unesp.br
Velocity measurements in the wake of a NACA 0012 airfoil have been made with hot wire anemometer in a vertical low turbulence water tunnel, which has a test section of 146 ´ 146 ´ 500 mm. The drag coefficient of the airfoil have been determined, employing the momentum equation on a control volume that encloses the airfoil. The same problem has been numerically studied using the finite control volumes method. In this study, a structured non-uniform grid has been used, with a more refined mesh near the airfoil, where pressure and velocity gradients are more pronounced. Navier-Stokes equations solution has been obtained with the SIMPLE method, considering the flow as laminar, two-dimensional and steady. The experimental and numerical results have been compared, showing a good agreement between them. Flow visualization has also been performed, using the liquid dye injection technique.
Keywords: NACA 0012 airfoil; drag coefficient; water tunnel; flow visualization; numerical simulation; aerofólio NACA 0012; coeficiente de arrasto; túnel hidrodinâmico; visualização de escoamento; simulação numérica.
COB290 VEHICLE AERODYNAMICAL SIMULATIONS BASED ON RUNGE-KUTTA TIME-STEPPING SCHEMES
Álvaro Luiz de Bortoli
Department of Pure and Applied Mathematics, Federal University of Rio Grande do Sul - Bento Gonçalves 9500 - 90501-900
Porto Alegre - RS - Brazil - E-mail: dbortoli@mat.ufrgs.br
Simulation is an important tool in the development of today’s automobile. This technology allows to reduce the time and the cost to complete the design, development and manufacture of vehicles. However, there are no general methods for all situations. This work employs a method to solve compressible and almost incompressible fluid flows using a finite volume explicit Runge-Kutta multistage scheme, with central spatial discretization. The discretization used follows the cell-centered arrangement of the control volume for the flow variables. Numerical tests are carried out for vehicle configurations and airfoils for Mach-numbers ranging from 0.002 to 0.63.
Keywords: Vehicle, aerodynamics, numerical simulation, finite volume, Runge-Kutta / Veículo, aerodinâmica, simulação numérica, volumes finitos, Runge-Kutta
COB746 ANALYSIS OF A JET FLOW LEAVING A TUBE INTERACTING WITH THE WAKE OF A NORMAL FLAT PLATE
Roberto M. Girardi
Instituto Tecnológico de Aeronáutica (ITA) 12.228-900-São José dos Campos, SP, Brasil - E-mail: girardi@aer.ita.cta.br
The configuration analyzed in the present paper is constituted by a tube connected with a flat plate normal to the tube axis. Such model is placed inside a wind tunnel and the undisturbed flow is aligned to the tube axis. The main objective of this work is to study the interaction occurring between the flow leaving the tube and the external flow over the flat plate, which is dominated by the wake flow. Pressure distributions on the flat plate surface and along the tube axis were measured, as well as the velocity of the tube internal flow. Using screens with different meshes, the internal flow velocity was varied and a relation between base pressure and tube flow velocity was obtained. Finally, application of this kind of configuration to wind turbine improvement is discussed at the end of this paper.
Keywords: Internal pipe flow; Aerodynamics; Experimental procedure; Wind energy; Bluff body / Escoamento em tubo; Aerodinâmica: Procedimento experimental; Energia Eólica; Corpos rombudos.
COB747 AVALIAÇÃO DA INTERFERÊNCIA DAS PAREDES DE UM TÚNEL DE VENTO SOBRE RESULTADOS EXPERIMENTAIS / EVALUATION OF WIND TUNNEL WALL INTERFERENCE ON EXPERIMENTAL RESULTS
Roberto da Mota Girardi & Breno Moura Castro
CTA - ITA - Divisão de Engenharia Aeronáutica - Praça Mal. Eduardo Gomes, 50
CEP 12.228-900 - São José dos Campos - SP - Brasil - E-mail: girardi@aer.ita.cta.br
A method for correction of the blockage effect of the wind tunnel walls on the experimental results, based on the panel technique, is presented. The method is valid only for subsonic flows (Mach£ 0,3). Some comparisons with the worldwide adopted method proposed in Rae & Pope (1984) are made and some contributions of the present work are discussed.
Keywords: Wind tunnel, blockage corrections, panel method, tridimensional flow, complex geometries.
COB785 UNSTEADY AIRFOIL INVISCID FLOW SIMULATIONS USING UNSTRUCTURED DYNAMIC MESHES
Carlos Frederico Castro Simões
EMBRAER - Empresa Brasileira de Aeronáutica, Av. Brigadeiro Faria Lima, 2170
12227-901 - São José dos Campos - SP - BRAZIL - E-mail: fred@aer.ita.cta.br
João Luiz Filgueiras Azevedo
Instituto de Aeronáutica e Espaço, CTA/IAE/ASE-N
12228-904 - São José dos Campos - SP - BRAZIL - E-mail: joaoaze@darwin.cesup.ufrgs.br
The efforts for the simulation of unsteady airfoil flows using an unstructured finite volume algorithm are described. The flowfield is modeled using the inviscid equations of gasdynamics, i.e., the Euler equations, which are discretized in a cell centered unstructured grid made up of triangles. Time integration uses an explicit, second-order accurate, hybrid scheme which evolved from the consideration of Runge-Kutta time stepping schemes. Steady state and unsteady calculations for NACA 0012 and NACA 64A010 airfoils at transonic flow conditions are presented. The results obtained are discussed and the implications of using the present time stepping scheme for unsteady calculations are highlighted.
Keywords: Unsteady flow, unstructured mesh, finite volume method, aerodynamic hysteresis.
COB789 SIMULAção NUMÉRICA de Problemas Aeroespaciais no Contexto de Malhas Estruturadas e Não Estruturadas / NUMERICAL SIMULATIONS OF aerOSPACE PROBLEMS ON STRUCTURED AND UNSTRUCTURED MESHES
João L. F. Azevedo(1) & Edisson S. G. Maciel(2)
(1) Instituto de Aeronáutica e Espaço, Centro Técnico Aerospacial - CTA/IAE - azevedo@ase2.iae.cta.br
(2) Instituto Tecnológico de Aeronáutica, Centro Técnico Aerospacial - CTA/ITA - mesg@aer.ita.cta.br
12228-904 - São José dos Campos - SP - Brasil
The paper presents comparisons between different algorithms used for the solution of the Euler equations for typical aerospace applications. The schemes considered include a cell centered, unstructured, explicit method and an implicit, unfactored algorithm constructed on structured grids. The unstructured method is based on Jameson and Mavriplis’ work and it yelds a centered, spatially 2nd-order accurate scheme. The structured algorithm is based on MacCormack’s flux vector splitting scheme, but it is only 1st-order accurate in space. The particular applications considered were transonic nozzle flows and supersonic blunt body flows. The aspects emphasized in the present comparison were the final solution quality for steady state applications, the overall easiness of code implementation, and the method’s computational efficiency.
Keywords: Equações de Euler, Esquemas Explícito e Implícito, Comparação de Eficiência Computacional / Euler Equations, Implicit and Explicit Schemes, Computational Efficiency Comparison.
COB790 SLOTTED TRANSONIC WIND TUNNEL FLOW SIMULATIONS USING THE EULER EQUATIONS
Renato Vieira(1), João L.F. Azevedo(2) & Nide G.C.R. Fico, Jr.(3)
(1) Faculdade de Engenharia de Guaratinguetá, FEG/UNESP - mec94125@lccp1.feg.unesp.br
(2) Instituto de Aeronáutica e Espaço, Centro Técnico Aerospacial - IAE/CTA - azevedo@ase2.iae.cta.br
(3) Instituto Tecnológico de Aeronáutica, Centro Técnico Aerospacial - ITA/CTA - nide@aer.ita.cta.br
12228-904 - São José dos Campos - SP - Brasil
The paper presents flow simulations relevant to transonic wind tunnel design and operation. A three-dimensional, finite difference, computational code which solves the Euler equations in a general, body conforming, curvilinear grid has been developed and used for these simulations. This code incorporates the capability of including test section wall slots for realistic simulation of a transonic wind tunnel facility. Test cases considered include a tunnel contraction alone and a complete high speed tunnel segment. Both cases with closed and open slots were considered. The results obtained adequately reproduced the expected flow features for the conditions analyzed and indicated that the particular configuration studied holds promise of providing very good test section flow quality.
Keywords: Transonic Wind Tunnel, TTS Project, Slotted Walls, Inviscid Flow Simulation, Finite Difference Method.
COB876 Simulation of Unsteady Transonic Flow over a Fighter Wing Using a Zonal Navier-Stokes/Full-Potential Method
Olympio Achilles de Faria Mello†
Instituto de Aeronáutica e Espaço, Centro Técnico Aeroespacial
12228-904 - São José dos Campos - SP, Brazil - e-mail: oamello@iconet.com.br
Lakshmi N. Sankar
School of Aerospace Engineering, Georgia Institute of Technology
Atlanta, Georgia 30332, U.S.A. - e-mail:lakshmi.sankar@ae.gatech.edu
An improved hybrid method for computing unsteady compressible viscous flows is presented. This method divides the computational domain into two zones. In the inner zone, the Navier-Stokes equations are solved using a diagonal form of an alternating-direction implicit (ADI) approximate factorization procedure. In the outer zone, the unsteady full-potential equation (FPE) is solved. The two zones are tightly coupled so that steady and unsteady flows may be efficiently solved. Characteristic-based viscous/inviscid interface boundary conditions are employed to avoid spurious reflections at that interface. The resulting CPU times are about 60% of the full Navier-Stokes CPU times for unsteady flows in non-vector processing machines. Applications of the method are presented for a F-5 wing in steady and unsteady transonic flows. Steady surface pressures are in very good agreement with experimental data and are essentially identical to the full Navier-Stokes predictions. Density contours show that shocks cross the viscous/inviscid interface smoothly, so that the accuracy of full Navier-Stokes equations can be retained with a significant savings in computational time.
Keywords: Transonic flow, zonal methods, viscous/inviscid interaction, unsteady flow, finite-difference methods.
COB908 - TRANSONIC TURBULENT FLOW CALCULATIONS OVER THE VLS FOREBODY
Cesar A. Buonomo & João L. F. Azevedo
Instituto de Aeron'autica e Espa¸co, Centro T'ecnico Aeroespacial - CTA/IAE/ASE-N CEP 12228-904 - S~ao Jos'e dos Campos - SP - Brasil - E-mail: azevedo@ase2.iae.cta.br
Abstract
A detailed study of transonic, turbulent flow conditions over the first Brazilian satellite launcher, the VLS, is described. The emphasis of the work is in developing the capability of accurately simulating realistic rocket flowfields and in understanding the behavior of two turbulence models in such conditions. The flowfields over the VLS at zero angle of attack are modeled by the axisymmetric, thin layer Navier-Stokes equations, and turbulence closure is obtained with the implementation of two different eddy viscosity models. A comparison of the characteristics of these two models is performed. Accurate solutions for the transonic flight regime are obtained. Non-reflective boundary conditions are also implemented, improving the representation of far field boundaries and the code's convergence characteristics in most cases.
Keywords
Transonic Flow, VLS, Turbulence Modeling, Finite Difference Method, Improved Boundary Conditions.
COB909 MULTIBLOCK SIMULATIONS OF TURBULENT VISCOUS FLOWS OVER THE VLS AFTERBODY REGION
Daniel Strauss(1) & João L. F. Azevedo(2)
(1)Instituto Tecnológico de Aeronáutica, Centro Técnico Aeroespacial -CTA/ITA/IEAA - daniels@aer.ita.cta.br
(2)Instituto de Aeronáutica e Espaço, Centro Técnico Aeroespacial - CTA/IAE/ASE-N - azevedo@ase2.iae.cta.br
12228-904 - São José dos Campos - SP - Brasil
Axisymmetric, turbulent, viscous flow simulations over the first Brazilian satellite launcher, the VLS, are presented. The emphasis of the work is on multiblock calculations for afterbody flows. The details of the multiblock implementation are presented together with a brief description of the numerical method. The implementation is validated against previous solutions for forebody flows over the same vehicle and through comparisons with experimental data for afterbody flows. The increased resolution of the multiblock calculations for the afterbody region is evidenced through comparisons with previous single block grid solutions.
Keywords: Axisymmetric Formulation, Multiblock Methods, Viscous Flow, Turbulent Flow.
COB1379 CARGAS AERODINÂMICAS SOBRE UM CILINDRO DE SEÇÃO RETANGULAR / aerodynamic loads acting on a cylinder with a rectangular shape
Miguel Hiroo Hirata & Vanessa Gonçalves Guedes
Programa de Engenharia Mecânica - COPPE/UFRJ
CEP 21945 - Rio de Janeiro, Brasil - E.mail: hirata@serv.com.ufrj.br
The flow around a body with a complex shape possesses much scientific interest, since it presents phenomena that are not fully understood, such as the shadow effect and the blockage effect. In particular, the calculation of the aerodynamic loads on the body is of great technological importance in the analysis and design of vehicles, offshore structures, etc. In a previous work it has been shown that the estimate of the drag coefficient of such bodies is viable when it is assumed that the body is formed of a combination of simpler bodies. The motivation to this work is to find alternative and efficient methods to estimate the aerodynamic loads that act on a cylinder with a rectangular shape and different aspect ratios, for any value of the Reynolds number. The approach adopted here uses fuzzy logic to estimate the loads, as well as genetic algorithms to improve the accuracy of the calculation.
Keywords: Drag coeficient, bluff body, fuzzy logic, genetic algorithm, interference
COB1380 ANÁLISE DO ESCOAMENTO AO REDOR DE UM CILINDRO DE SEÇÃO CIRCULAR / ANALYSIS OF THE FLOW AROUND A CIRCULAR CYLINDER
Angelo A Mustto, Miguel H. Hirata & Gustavo C. R. Bodstein
Programa de Engenharia Mecânica, COPPE/UFRJ - Caixa Postal 68503
CEP 21945-970 Rio de Janeiro, RJ, Brasil - E-mails: mustto@serv.com.ufrj.br; gustavo@serv.com.ufrj.br
Flows around bluff bodies have always attracted scientific interest due to the complex phenomena that occur, such as separation and the resulting wake formation downstream of the body. In this paper we use the discrete vortex method to study the unsteady, incompressible and two-dimensional flow around a circular cylinder immersed in a uniform flow. With the aid of the circle theorem to impose the flow-tangency condition, vortices with a Lamb core are generated along the cylinder surface whose strengths are determined so that the no-slip condition is satisfied. The dynamics of the body wake is computed using the convection-diffusion splitting algorithm, where the convection process is carried out with a lagrangian time-marching scheme, and the diffusion process is simulated using the random walk method. The aerodynamic forces are calculated from the unsteady Blasius equation. Results are presented for a high Reynolds number flow, showing good agreement with experiments.
Keywords: Método de Vórtices, Teorema do Círculo, Corpo Rombudo, Esteira, Separação / Vortex Method, Circle Theorem, Bluff Body, Wake, Separation.
COB1441 A NUMERICAL SIMULATION OF TRANSONIC AERODYNAMIC FLOW, USING THE BALDWIN-LOMAX MODEL, LARGE SCALE FIELD AND EULER SIMULATIONS / SIMULAÇÃO DE UM ESCOAMENTO AERODINÂMICO TRANSÔNICO, USANDO OS MODELOS DE BALDWIN-LOMAX, DE GRANDES ESCALAS E DE EULER
Biage, M. & Lopes, M. A.
Mechanical Department, Federal University of Uberlândia
phone: (55)(34)239-4192, fax: (55)(34)239-4106 and e-mail: mbiage@ufu.br, 34.800-902, Uberlândia-MG, Brazil
This work presents a numerical simulation study to compute a turbulent compressible aerodynamic flows. The numerical algorithm used is the finite volume formulation for spatial discretization and a stepping time procedure with multi-stages for time discretiztion. Also, a multigrid procedure is used with aim for speeding up the steady state convergence. The aerodynamic flows solutions around airfoils in transonic state were performed using Euler equations (Euler model), large scale field simulation (LES) and Baldwin-Lomax model. The results achieved are compared with experimental data available for two kinds of airfoils (NACA0012 and RAE2822), in the transonic range for Reynolds number equal to 9,0x106 and for large variation of attack angles. Some supersonic results were also obtained and compared with analytical evaluations. All computations were made for the three models, aiming to estimate of accuracy of the solutions and how expensive they are.
Keywords: Numerical Simulation (Simulação numérica), Turbulence Model (Modelo Turbulento), Compressible Flows (Escoamento Compressível), Airfoils (Aerofólios), Finite Volume Formulation (Formulação de Volumes Finitos).