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Browsing by Author "Iowa State University. Department of Aerospace Engineering"

Now showing 1 - 3 of 3
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    An Analytical Procedure for Evaluating Aerodynamics of Wind Turbines in Yawed Flow
    Rajagopalan, R. Ganesh; Guntupalli, Kanchan; Fischels, Mathew V.; Novak, Luke A. (Virginia Tech, 2015-06)
    A new analytical method for evaluating the performance of wind turbines in yawed flow is presented. The method, based on momentum theory, relates the yaw angle to the tip-path-plane orientation of the turbine rotor and the non-dimensional deficit velocity. The analytical calculations are compared with results from Rot3DC, a kernel within the RotCFD software package, an integrated environment for rotors. Rot3DC, a 3-D Navier-Stokes based module, can simulate one or more Horizontal Axis Wind Turbines (HAWT) and uses the concept of momentum sources to compute the turbine performance and flowfield in a self contained manner. Rot3DC simulations are validated against NREL Phase-II experiments. Analytical results for yawed turbines correlate well with Rot3DC and are found to be within 10% error margin for the extreme yaws considered. The developed analytical formulation provides a simple model for quantification of turbine performance in yawed flow and can be used as an input to onboard feedback systems for yaw control.
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    A Prescribed-Wake Vortex Line Method for Aerodynamic Analysis and Optimization of Multi-Rotor Wind Turbines
    Rosenberg, Aaron; Sharma, Anupam (Virginia Tech, 2015-06)
    The objective of this paper is to extend the xed wake vortex lattice method (VLM), used to evaluate the performance of single-rotor wind turbines (SRWT), for use in analyzing dual-rotor wind turbines (DRWT). VLM models wind turbine blades as bound vortex laments with helical trailing vortices. Using the Biot-Savart law, it is possible to calculate the induction in the plane of rotation allowing for a computationally inexpensive, yet accurate, prediction of blade loading and power performance. This paper presents a method for modeling the additional vortex system introduced by a second rotor while taking into account the singularities that occur when the trailing vortices from the upstream turbine interact with the bound vortices of the downstream turbine. Time averaging is done to account for the rotors operating at di different rotational velocities. This method will be used to predict the performance of the DRWT introduced in Rosenberg et al. (2014). This turbine consists of a large, primary rotor behind and a smaller, auxiliary rotor. Blade loading and power performance obtained with VLM will be compared to the LES results of the same con configuration presented in Moghadassian et al. (2015).
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    A Wind Tunnel Study on the Aeromechanics of Dual-Rotor Wind Turbines
    Wang, Zhenyu; Tian, Wei; Sharma, Anupam; Hu, Hui (Virginia Tech, 2015-06)
    In the present study, we report our recent efforts to develop a novel dual-rotor wind turbine (DRWT) concept to improve aerodynamic efficiency of isolated turbines as well as wind farms. The DRWT concept employs a secondary, smaller, co-axial rotor with two objectives: (1) mitigate losses incurred in the root region of the main rotor by using an aerodynamically optimized secondary rotor, and (2) mitigate wake losses in DRWT wind farms through rapid mixing of turbine wake. Mixing rate of DRWT wake will be enhanced by (a) increasing radial shear in wind velocity in wakes, and (b) using dynamic interaction between primary and secondary rotor tip vortices. Velocity shear in turbine wake are tailored (by varying secondary rotor loading) to amplify mixing during conditions when wake/array losses are dominant. The increased power capacity due to the secondary rotor can also be availed to extract energy at wind speeds below the current cut-in speeds, in comparison to conventional single-rotor wind turbine (SRWT) design. For a DRWT system, the two rotors sited on the same turbine tower can be set to rotate either in the same direction (i.e., co-rotation DRWT design) or at opposite directions (i.e., counter-rotating DRWT design). It should be noted that a counter-rotating rotor concept (i.e., the rotors rotate at opposite directions) has been widely used in marine (e.g., counter-rotating propellers used by Mark 46 torpedo) and aerospace (e.g., Soviet Ka-32 helicopter with coaxial counter-rotating rotors) applications to increase aerodynamic efficiency of the systems. The recent work Ozbay et al. (2015) reveal that, with the two rotors in counter-rotating configuration (i.e., counter-rotating DRWT design), the downwind rotor could benefit from the disturbed wake flow of the upwind rotor (i.e., with significant tangential velocity component or swirling velocity component in the upwind rotor wake). As a result, the downwind rotor could harvest the additional kinetic energy associated with the swirling velocity of the wake flow. With this in mind, the effects of relative rotation direction of the two rotors on the aeromechanics performances of DRWTs (i.e., co-rotation DRWT design vs. counter-rotating DRWT design) and the turbulent mixing process in the DRWT wakes are also evaluated in the present study. The experimental study was performed in a large-scale Aerodynamics/Atmospheric Boundary Layer (AABL) Wind Tunnel located at the Aerospace Engineering Department of Iowa State University. Scaled DRWT and SRWT models were placed in a typical Atmospheric Boundary Layer (ABL) wind under neutral stability conditions. In addition to measuring the power outputs of the DRWT and SRWT systems, static and dynamic wind loads acting on the test models were also investigated to assess the effects of the secondary, smaller, co-axial rotor in either counter-rotating (rotors rotate at opposite directions) or co-rotating (rotors rotate at same direction) configuration on the power production performance and the resultant dynamic wind loads (both aerodynamic forces and bending moments) acting on the DRWT models. Furthermore, a high-resolution stereoscopic Particle Image Velocimetry (Stereo-PIV) system was also used to make both "free-run" and "phase-locked" measurements to quantify the transient behavior (i.e., formation, shedding and breakdown) of unsteady wake vortices and the flow characteristics behind the DRWT and SRWT models. The detailed flow field measurements were correlated with the power output data and dynamic wind loading measurements to elucidate underlying physics for higher total power yield and better durability of wind turbines operating in turbulent non-homogenous atmospheric boundary layer (ABL) winds.