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ANALYSIS OF WIND TURBINE WAKES

Objective

THIS PROJECT CONSISTS IN THE DEVELOPMENT OF TWO TYPES OF CODES : THE FIRST ONE TO MODEL INDIVIDUAL WAKES AND THE OTHER ONE TO MODEL WIND FARMS. THE OUTPUT OF THE WAKE CODE IS USED AS AN INPUT FOR THE WIND FARM MODEL. AS A RESULT, THE CHARACTERISTICS OF THE INCIDENT WIND IN EACH MACHINE CAN BE PREDICTED, IN PARTICULAR THE VELOCITY AND TURBULENCE LEVEL WHICH MAY AFFECT ITS POWER PRODUCTION AND STRUCTURAL BEHAVIOUR. THE WAKE CODE IS BASED ON THE K-E MODEL FOR THE CLOSURE OF THE TURBULENT FLOW EQUATIONS, AND THE WAKE OF THE WIND TURBINE IS SUPPOSED TO BE IMMERSED IN A NON-UNIFORM AIR STREAM CORRESPONDING TO THE ATMOSPHERIC BOUNDARY LAYER. RELEVANT PARAMETERS DESCRIBING THE PROCESS ARE WIND VELOCITY AT TURBINE HEIGHT, GROUND ROUGHNESS, ATMOSPHERIC STABILITY, TURBINE DIMENSIONS AND INITIAL MOMENTUM DEFICIT.
THIS WAKE CODE HAS BEEN VALIDATED BY APPLYING IT TO TEST CASES, BOTH IN WIND TUNNEL (TNO) AND IN FIELD EXPERIMENTS (NIBE) WITH FULL SCALE MACHINES; ALSO, A NUMERICAL VALIDATION OF THIS CODE HAS BEEN CARRIED OUT BY SOLVING SIMILAR CASES USING THE PHOENICS CODE. THE WAKE MODEL HAS BEEN INTEGRATED IN ALREADY EXISTING WIND FARM CODES WHICH HAVE BEEN USING SIMPLER KINEMATIC MODELS FOR WAKE DESCRIPTION. THE RESULTING WIND FARM CODE IS VALIDATED BY COMPARISON WITH MEASUREMENTS FROM EXPERIMENTAL INSTALLATIONS, IN PARTICULAR FROM THE ZEEBRUGGE WIND FARM.
2 types of computer code were developed. The first one to model individual wakes and the other one to model wind farms. The output of the wake code is used as an input for the wind farm model. As a result, the characteristics of the incident wind in each machine can be predicted, in particular regarding the velocity and turbulence level which may affect its power production and structural behaviour. The developed code, which is termed UPMWAKE, is based on the resolution of the turbulent flow equations. It has to be incorporated into already existing wind farm codes in order to predict the individual and overall behaviour of all the machines in the wind farm.
TWO WAKE CODES HAVE BEEN DEVELOPED; ONE OF THEM IS BASED ON THE K-EPSILON MODEL FOR THE CLOSURE OF THE TURBULENT FLOW EQUATIONS (UPM), AND THE OTHER ONE USES AN EDDY-VISCOSITY APPROACH (TNO), BASED ON AN ANALYTIC EXPRESSION FOR THIS VARIABLE. THE UPM COMPUTER CODE TO MODEL THE WAKE HAS BEEN VALIDATED BY APPLYING IT TO TEST CASES, BOTH IN WIND TUNNEL AND IN FIELD EXPERIMENTS WITH FULL SCALE MACHINES. IN THE UPM MODEL, THE WAKE OF THE WIND TURBINE IS SUPPOSED TO BE IMMERSED IN A NON-UNIFORM AIR STREAM CORRESPONDING TO THE ATMOSPHERIC BOUNDARY LAYER. RELEVANT PARAMETERS DESCRIBING THE PROCESS ARE WIND VELOCITY AT TURBINE HEIGHT, GROUND ROUGHNESS, ATMOSPHERIC STABILITY, TURBINE DIMENSIONS AND INITIAL MOMENTUM DEFICIT. THE WIND TUNNEL MEASUREMENTS CORRESPOND TO EXPERIMENTS CARRIED OUT AT TNO. THE FULL SCALE EXPERIMENTS CHOSEN FOR COMPARISON ARE THOSE FROM NIBE WIND TURBINES IN DENMARK, ALTHOUGH SOME OF THESE EXPERIMENTS ARE NOT YET COMPLETED. THE RESULTS OF THE UPM CODE ARE ALSO COMPARED WITH THOSE OBTAINED WITH KINEMATIC MODELS AND WITH THE EDDY-VISCOSITY MODEL. A NUMERICAL VALIDATION OF THE UPM CODE HAS ALSO BEEN CARRIED OUT BY SOLVING SIMILAR CASES USING THE PHOENICS CODE.
THE PARAMETERS CHARACTERIZING THE WAKE DEVELOPMENT, WHICH HAVE TO BE INCORPORATED TO WIND FARM COMPUTER CODES, HAVE BEEN DEFINED. THE ADVANCED WAKE MODELS PREVIOUSLY MENTIONED HAVE BEEN INTEGRATED IN ALREADY EXISTING WIND FARM CODES WHICH NOW USE SIMPLER KINEMATIC MODELS FOR WAKE DESCRIPTION. THE RESULTING CODES HAVE TO BE VALIDATED BY COMPARISON WITH MEASUREMENTS FROM THE EXPERIMENTAL INSTALLATIONS BELONGING TO THE CONCERTED ACTION "WAKE EFFECTS", WHICH CORRESPOND TO THE GLOBAL BEHAVIOUR OF THE FARM. IN PARTICULAR THE DATA CORRESPONDING TO THE ZEEBRUGGE WIND FARM HAS BEEN INTRODUCED IN THIS CODE FOR ITS VALIDATION WHEN EXPERIMENTAL RESULTS ARE AVAILABLE.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSIDAD POLITECNICA DE MADRID
Address
Av. Ramiro De Maeztu 7 S/n
28040 Madrid
Spain

Participants (1)

NETHERLANDS ORGANISATION FOR APPLIED SCIENTIST RESEARCH (TNO)
Netherlands
Address

Dept. Fluid Dynamics