Experimental Analysis of an Actuator Disk under cyclic unsteady loading

Abstract

Experimental Analysis of an Actuator Disk under cyclic unsteady loading.
Wind Energy is one of the cleanest forms of energy. It does not contribute to the greenhouse gases and is also one of the least expensive forms of renewable energy. Due to this, number of wind turbines are increasing annually. Therefore, it is crucial to understand the physics behind a wind turbine wake and how to optimize its power production. One of the most common tools used in designing a wind turbine is Blade Element Momentum theory (BEM), which is based on the classic momentum theory (or Actuator disk theory). In momentum theory, flow is assumed to be steady, stationary, in-compressible and in-viscid. But in reality, wind turbines operate in very unsteady conditions such as gust, pitching, yawing, turbulence, etc. So, it is important to study an actuator disk wake under unsteady loading.
In this project, cyclic unsteady loading on an actuator disk is studied. The main research objective is to study the behaviour of wake behind an actuator disk under cyclic unsteady loading. As learnt during the literature review, only a small number of studies have been dedicated to this research topic. In order to fulfil the objective, an experimental approach is taken. Particle Image Velocimetry (PIV) is used to acquire data in order to study the flow field behind the disk. Actuator disk is modelled using a porous disk. The porosity of the disk is used change the rate of change unsteadiness. This disk's porosity ranged between 14%-65%. The disk porosity was modified sinusoidally to simulate the effect of cyclic loading. The wake for steady loading was captured up to 1 rotor diameter downstream and 0.8 rotor diameters in radial direction. For unsteady load cases, data was collected up to 2 rotor diameters. For unsteady loading, three different reduced frequencies (k) were tested. The load on the disk was estimated using momentum integration of the flow field. Finally, the results from the experiment were compared to the velocity fields estimated using Vortex Ring (VR) method.