Mojtaba Ahmadi-Baloutaki

Straight-bladed vertical axis wind turbine rotor design guide based on aerodynamic performance and loading analysis

Vertical axis wind turbines with straight blades are attractive for their relatively simple structure and aerodynamic performance. An efficient design methodology is required to enhance this resurging renewable energy technology. This paper aims to provide a robust design procedure built on an existing analytical approach to determine the optimum range of the design parameters for prototype construction. Identifying the proper range of design parameters can save significant time and resources in the initial turbine development stages. Here the double-multiple streamtube method has been utilized to analyze turbine aerodynamic performance. A parametric optimization has been performed for several design factors to maximize the turbine power coefficient and its operational range. The results show that the optimum value of the rotor solidity factor, blade aspect ratio, and rotor aspect ratio are in the range of 0.2 < σ < 0.6, 10 < μ < 20, and 0.5 < H/D < 2, respectively. Aerodynamic loading analysis has also been carried out, and the most severe stresses acting on the blades and supporting arms were determined. The most favorable bending stress distribution along the blade occurred when two supporting arms per blade were used at intermediate locations of 21% and 79% along the blade length. A comparative study of different supporting arm shapes demonstrated that utilizing aerodynamic profiles for turbine arms created the most acceptable aerodynamic response. A summary of design aspects addressed in this paper is presented in a useful summary flowchart.

A computational study on robust prediction of transition point over NACA0012 aerofoil surfaces from laminar to turbulent flows

Flow transition from laminar to turbulent is prerequisite to decide whereabouts to apply surface ow control techniques. This appears missing in a number of works in which the control eects were merely investigated without getting insight into alteration of transition position. The aim of this study is to capture the correct position of transition over NACA0012 aerofoil at dierent angles of attack. Firstly, an implicit, time marching, high resolution total variation diminishing (TVD) scheme was developed to solve the governing Navier{Stokes equations for compressible uid ows around aerofoil sections to obtain velocity proles around the aerofoil surfaces. Secondly, the linear instability solver based on the Orr{Sommerfeld equations and the e N methods were developed to calculate the onset of transition over the aerofoil surfaces. For the low subsonic Mach number of 0.16, the accuracy of the compressible solutions was assessed by some available experimental results of low speed incompressible ows. In all cases, transition positions were accurately predicted which shows applicability and superiority of the present work to be extended for higher Mach number compressible ows. Here, transition prediction methodology is described and the results of this analysis without active ow control or separation are presented. c

Frequency Analysis of a Trailing Vortex Flow Subjected to External Turbulence

The frequency response of a trailing vortex downstream the free end of a NACA0015 wing section has been studied in a closed loop wind tunnel. The wing spanning approximately half height of the wind tunnel section was fixed to a dynamic load cell at the base. The flow cases studied have constant angle of attack of 10 degrees and constant Reynolds number of 160,000 based on the wing chord length while two levels of 0.5 and 4.6% free-stream turbulence were introduced to the flow. Lift and drag forces acting on the wing section were quantified using a load cell while an X-probe hot-wire was used to measure the turbulence parameters in the near-field wake region. The tip vortex was captured with sufficient accuracy. The effect of free-stream turbulence on the vortex structure has been discussed in detail by characterizing several turbulence parameters via time-averaging and frequency analysis of the turbulence signal.Copyright

Design Criteria on Sizing and Material Selection of SB-VAWTS

A design methodology has been presented on the sizing and material selection of straight-bladed vertical axis wind turbines. Several design parameters such as turbine power coefficient, blade tip speed ratio, rotor solidity factor, blade aspect ratio and rotor moment of inertia have been analyzed. Material selection and its relevant design criteria have also been discussed for different parts of a straight-bladed vertical axis wind turbines with three blades and two supporting arms per blade. The number of the supporting arms and their optimum locations have been determined via minimizing the bending moments on the blade. A comparative study has also been performed to examine the effect of blade density and turbine H/D ratio on the rotor moment of inertia. It was found that the turbine rotational speed increases as blade density decreases and this increase is larger at higher turbine H/D ratio.Copyright