Predictions of the performance of operating wind turbines are challenging for many reasons including the unsteadiness of the wind and uncertainties in blade aerodynamic behaviour. In the current study an extended blade element momentum (BEM) program was developed to compute the rotor power of an existing 4.3 m diameter turbine and compare predictions with reported controlled experimental measurements. Beginning with basic blade geometry and the iterative computation of aerodynamic properties, the method integrated the BEM analysis into the program workflow ensuring that the power production by a blade element agreed with its lift and drag data at the same Reynolds number. The parametric study using the extended BEM algorithm revealed the close association of the power curve behaviour with the aerodynamic characteristics of the blade elements, the discretization of the aerodynamic span, and the dependence on Reynolds number when the blades were stalled. Transition prediction also affected overall performance, albeit to a lesser degree. Finally, to capture blade finite area effects, the tip loss model was adjusted depending on stall conditions. The experimental power curve for the HAWT of the current study was closely matched by the extended BEM simulation.
Wind turbines operate within an environment of varying wind direction and magnitude leading to misalignment or yaw between the wind and the turbine rotor. Many control techniques have been applied to small horizontal axis wind turbines (HAWTs) to prevent significant yaw loads, but in reality, most of the time the rotor is under some yaw load which may be significant. A blade element of a HAWT rotor under yaw loading is similar to a sinusoidally pitching airfoil. Here a miniaturized pitching S822 airfoil with a reduced frequency k of 0.025 at a Reynolds number ( Re = 105) is considered where the maximum dynamic angle of attack is equal to the static angle where the maximum lift to drag ratio occurs. These dynamic results obtained with laser Doppler anemometry (LDA), particle image velocimetry (PIV) and a numerical simulation with the Transition SST method are compared to a constant wind-loaded blade element. Since direct load measurement for dynamic miniaturized models in wind tunnels is very challenging, the non-intrusive PIV control volume analysis approach has been applied for load determination. Unlike the rotor in an ideal unidirectional freestream flow, a rotor under yaw loads, as presented here, experiences significant unbalanced loading in one cycle and a non-uniform wake. Results may be used to predict the cyclical range of loads a blade element experiences in yaw conditions and effects on the downstream rotor wake.
In this paper, we discuss the impact of a wavy-walled pipe cross-section on steady flow in a curved tube at moderate Dean numbers and small tube radius-to-radius-of-curvature ratios. Parameters investigated include the protrusion height, the number of protrusions around the tube circumference, and the pipe curvature. This work extends a previous analytical investigation that employed a double perturbation expansion to elucidate the flow field as a function of these parameters. Due to the rapid growth in the solution complexity as the number of terms in each expansion increases, the analytical work is relegated to small wall perturbations and low Dean numbers. These barriers are removed in the present study by numerically solving the Navier–Stokes equations at Dean numbers up to 2500. The impact on the axial and secondary flow structures are emphasized, along with the resulting wall shear stress distributions.
As a simplified stent model, fully-developed flow of an incompressible, Newtonian fluid through a curved tube with axially aligned wall protuberances is investigated to define the impact of stent implantation on hemodynamic behavior in curved vessels. According to previous research local hemodynamics tends to trigger biochemical pathways that result in the inception and progression of in-stent restenosis (ISR) and ultimately lead to stent failure. In this manuscript, we focus on hemodynamic changes due to stent strut protrusion into the vessel lumen as a facilitator of ISR. We investigate a range of physiologically relevant stent strut heights and flow parameters using computational fluid dynamics (CFD).
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