Flow Around the Revolving Propeller Blades in Low Reynolds Number Field

2007 ◽  
Author(s):  
Nobuyuki Arai ◽  
Hironori Yoshida ◽  
Katsumi Hiraoka
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Number Field ◽  
Wind Tunnel Testing ◽  
Edge Region ◽  
Blade Surface ◽  
Propeller Blade ◽  
Trailing Edge ◽  
Propulsion Efficiency ◽  
Propeller Blades

By studying the flow around the revolving propeller blades, an improvement of the propulsion efficiency can be found. We made the propeller blade optimized to get good propulsion efficiency by the Adkins & Liebeck’s propeller theory in low Reynolds number field. We call this blade “Prop00”. In order to investigate the flow around the propeller blades, distributions of pressure on the surface of the revolving propeller blade in some pitch angles were measured by wind tunnel testing. For Prop00, it was observed that the contour lines of Cp are dense near the trailing edge of blade’s tip. And it is thought that the separation may exist around the tip of blade. In order to compare the flow characteristics and to get the hint of improvement of the shape of the propeller blades, three different shape types of propeller blades, rectangle, trapezoid, and inverted trapezoid, were made. We call these blades “Prop01”, “Prop02”, and “Prop03”, respectively. According to the pressure distribution, it’s necessary to improve the shape of the propeller which suppresses the effect by a separation to improve the propulsion efficiency more. We took some photographs of tufts on the revolving blades with stroboscope to investigate vectors of the flow on the blade surface. These photographs are taken under identical conditions of the direct pressure measurement. It was observed that tufts tend to bent to the outer side direction by centrifugal force. However, differences on tufts bending were observed in the regions of the leading and the trailing edges at same radius. The tufts at the trailing edge region more bent to the tip of blade than that at leading edge region. Then, it is thought that separation and crossflow on the blade surface exist. We thought that the stability of the flow around the trailing edge is lost by the separation and the boundary layer transition. Furthermore, universal CFD software is used to study the improvement of the propeller performance. By using FLUENT 6 as universal CFD software, the result of CFD was compared with the result of wind tunnel testing.

Engineering Extrapolation to Flight Reynolds Number for Supercritical Airfoil Pressure Distribution Based on CFD Results

2013 ◽  
Vol 444-445 ◽  
pp. 517-523
Author(s):  
Da Wei Liu ◽  
Xin Xu ◽  
Zhi Wei ◽  
De Hua Chen
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Pressure Distribution ◽  
Low Reynolds Number ◽  
Trailing Edge ◽  
Supercritical Airfoil ◽  
Short Period ◽  
Wind Tunnel Data ◽  
Mach Numbers ◽  
Low Reynolds

Pressure distribution of supercritical airfoil at flight Reynolds number could not be fully simulated except in cryogenic wind tunnel such as NTF (National Transonic Facility) and ETW (European Transonic Wind tunnel), which is costly and time resuming. This paper aimed to explore an engineering extrapolation to flight Reynolds number from low Reynolds number wind tunnel data for supercritical airfoil pressure distribution. However, the extrapolation method requiring plenty of data was investigated based on the CFD results for the reason of low cost and short period. Flows over a typical supercritical airfoil were numerically simulated by solving the two dimensional Navier-Stokes equations, with applications of ROE scheme spatial discretization and LU-SGS time march. Influence of computational grids convergence and turbulent models were investigated during the process of simulation. The supercritical airfoil pressure distribution were obtained with Reynolds numbers varied from 3.0×106to 30×106per airfoil chord, angles of attack from 0 degree to 6 degree and Mach numbers from 0.74 to 0.8. Simulated results indicated that weak shock existed on the upper surface of supercritical airfoil at cruise condition, that the shock location, shock strength and trailing edge pressure were dependent of Reynolds number, attack angles and Mach numbers. A similar parameter describing the Reynolds number effects factors was obtained by analyzing the relationship of shock wave location, shock front pressure and trailing edge pressure. Based on the similar parameter, airfoil pressure distribution at Reynolds number 30×106was obtained by extrapolation. It was shown that extrapolated result compared well with simulated result at Reynolds number 30×106, implying that the engineering method was at least promising applying to the extrapolation of low Reynolds number wind tunnel data.

Design Considerations, Performance Enhancing Techniques, and Wind Tunnel Testing for Small-Scale, Low Reynolds Number Wind Turbines

2011 ◽  
Author(s):  
Jason R. Gregg ◽  
Timothy A. Burdett ◽  
Kenneth W. Van Treuren ◽  
Stephen T. McClain
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Power Output ◽  
Low Reynolds Number ◽  
Small Scale ◽  
Wind Tunnel Testing ◽  
Low Reynolds ◽  
Lift And Drag

Wind turbines have become a significant part of the world’s energy equation and are expected to become even more important in the years to come. A much-neglected area within wind turbine research is small-scale, fixed-pitch wind turbines with typical power outputs in the 1–10 kW range. This size wind system would be ideal for residential and small commercial applications. The adoption of these systems could reduce dependence on the aging U.S. power grid. It is possible to optimize a small-scale system to operate more efficiently at lower wind speeds, which will make wind generation possible in areas where current wind technology is not feasible. This investigation examines the use of the S818 airfoil, a typical blade root airfoil designed by the National Renewable Energy Laboratory (NREL), as a basis for the design of low Reynolds number (less than 200,000) systems. The literature shows that many of the airfoils proposed for wind turbine applications, including the S818, only have lift and drag data generated by numerical simulations. In previous research at Baylor, 2-D simulations published by NREL have been shown to predict an optimal design angle of attack (which is the angle at which L/D is maximized) up to 2.25° different from actual wind tunnel data. In this study, the lift and drag generated by the S818 airfoil has been measured experimentally at a Reynolds number of approximately 150,000 and compared with NREL simulation data, showing a discrepancy of 1.0°. Using the S818 airfoil, a set of wind turbine blades has been designed to collect wind turbine power data in wind tunnel testing. Design parameters investigated include the effect of design tip speed ratios (TSR) (1, 3, and 7) and the influence of the number of blades (2, 3 and 4) on power generated. At the low Reynolds numbers tested (ranging from 14,000–43,200 along the blade for a design TSR of 3 and a wind speed of 10 mph), the effect of roughness was explored as a performance enhancing technique and was seen to increase power output by delaying separation. Under these low Reynolds number conditions, separation typically occurs on smooth blades. However, the roughness acted as a passive flow control, keeping the flow attached and increasing power output. Preliminary data suggest that as much as a 50% improvement can be realized with the addition of roughness elements for a TSR of 3. Additionally, the increase in power output due to roughness is comparable with the increase in power due to adding another smooth blade.

Blade Curve Influences on Performance of Savonius Rotors: Experimental and Numerical

2010 ◽  
Author(s):  
Ali Kianifar ◽  
Morteza Anbarsooz ◽  
Mohammad Javadi
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
Pressure Distribution ◽  
Power Coefficient ◽  
Blade Surface ◽  
Wind Tunnel Tests ◽  
Savonius Rotor ◽  
Circular Curves

In this study, the effect of blade curve on the power coefficient of a Savonius rotor is investigated by means of numerical simulation and wind tunnel tests. The tests were conducted on six rotors with identical dimensions but different blade curves, and the influences of blade curve and Reynolds number were studied. Followed by a simulation of the flow field around rotors with identical semi-circular curves and different overlaps, torque was calculated using pressure distribution on the blade surface, and the effect of Reynolds number and blade curve were studied on torque as well. Results indicate that changing the blade curve affects the power coefficient and torque by causing different drag coefficients. Also the rotor that yields the highest power coefficient and torque in one revolution compared with other rotors is highlighted.

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