Blade element theory

About: Blade element theory is a research topic. Over the lifetime, 1537 publications have been published within this topic receiving 22517 citations.

Flight Mechanics of a Dragonfly

Abstract: SUMMARY The steady slow climbing flight of a dragonfly, Sympetrum frequens, was filmed and analysed. By using the observed data, the mechanical characteristics of the beating wings were carefully analysed by a simple method based on the momentum theory and the blade element theory, and with a numerical method modified from the local circulation method (LCM), which has been developed for analysing the aerodynamic characteristics of rotary wings. The results of calculations based on the observed data show that the dragonfly performs low speed flight with ordinary airfoil characteristics, instead of adopting an abnormally large lift coefficient. The observed phase advance of the hindwing, Adi — 80° can be fully explained by the present theoretical calculation. Similarly, the spanwise variation of the airloading and the time variations of the horizontal force, vertical force, pitching moment and torque or power can be definitely estimated within a reasonable range of accuracy in comparison with the flight data. The distribution of loading between the fore and hind pairs of wings is also clarified by the calculations.

Optimal design of horizontal-axis wind turbines using blade-element theory and evolutionary computation

Abstract: This paper describes a multi-objective optimization method for the design of stall-regulated horizontal-axis wind turbines. Two modules are used for this purpose: an aerodynamic model implementing the blade-element theory and a multi-objective evolutionary algorithm. The former provides a sufficiently accurate solution of the flow field around the rotor disc; the latter handles the decision variables of the optimization problem, i.e., the main geometrical parameters of the rotor configuration, and promotes function optimization. The scope of the method is to achieve the best trade-off performance between two objectives: annual energy production per square meter of wind park (to be maximized) and cost of energy (to be minimized). Examples of the best solutions found by the method are described and their performance compared with those of commercial wind turbines.

Interaction between soil and a wide cutting blade using the discrete element method

Abstract: Modeling soil-tillage interaction is a complex process due to dynamic soil-implement interaction which includes a high rate of plastic deformation and soil failure, characterized by the flow of soil particles. The need for a sound modeling technique for soil-implement interaction is the motivation for the present work. The discrete element method (DEM) seems to be a promising approach for constructing a high-fidelity model to describe the soil-implement interaction and can serve as a predicting simulation tool in the process of designing the implement shape. The wide cutting-blade interaction was modeled using a 2D discrete element code-PFC2D and the soil particles by clumps of two disks with a cohesion force contact model between the particles. Four different blade shapes were analyzed by the discrete element model and experimentally by a soil box filled with sand. A very good correlation was obtained between the discrete element simulation and the experimental results. The simulations indicate an increasing horizontal force applied on the blades during motion, as a result of the piling effect of the soil in front of the blade. It was found that the soil flow beneath the blade tip can affect the vertical force applied on the blade. The simulation results were also compared with classical soil mechanics theories for straight blades (the McKyes approach). A good correlation was obtained between the simulation results and McKyes approach for the horizontal force applied on the blade. Weaker correlations were obtained in the vertical direction. This finding can be explained by the soil particle flow beneath the blade tip, which the McKyes approach, does not take into consideration. Observation of the simulation revealed that the failure curve could be reasonably described by a straight line, as assumed in the classical theories.

The interaction of entropy fluctuations with turbine blade rows; a mechanism of turbojet engine noise

Abstract: The theory relating to the interaction of entropy fluctuations ('hot spots'), as well as vorticity and pressure, with blade rows is described. A basic feature of the model is that the blade rows have blades of sufficiently short chord that this is negligible in comparison with the wavelength of the disturbances. For the interaction of entropy with a blade row to be important, it is essential that the steady pressure change across the blade row should be large, although all unsteady perturbations are assumed small. A number of idealized examples have been calculated, beginning with isolated blade rows, progressing to single and then to several turbine stages. Finally, the model has been used to predict the low-frequency rearward-radiated acoustic power from a commercial turbojet engine. Following several assumptions, together with considerable empirical data, the correct trend and level are predicted, suggesting the mechanism to be important at low jet velocities.

Computational investigation of micro-scale coaxial rotor aerodynamics in hover

Abstract: In this work, a compressible Reynolds-averaged Navier-Stokes solver is used to investigate the aerodynamics of a microscale coaxial-rotor configuration in hover, to evaluate the predictive capability of the computational approach and to characterize the unsteadiness in the aerodynamic flowfield of the microscale coaxial systems. The overall performance is well-predicted for a range of rpm and rotor spacing. As the rotor spacing increases, the top-rotor thrust increases and the bottom-rotor thrust decreases, while the total thrust remains fairly constant. The thrusts approach a constant value at very large rotor spacing. Top rotor contributes about 55 % of the total thrust at smaller rotor spacing, which increases to about 58% at the largest rotor separation. The interaction between the rotor systems is seen to generate significant impulses in the instantaneous thrust and power. Unsteadiness is mainly caused due to blade loading and wake effect. Additional high-frequency unsteadiness was also seen due to shedding near the trailing edge. The phasing of the top vortex impingement upon the bottom rotor plays a significant role in the amount of unsteadiness for the bottom rotor. Interaction of the top-rotor tip vortex and inboard sheet with the bottom rotor results in a highly three-dimensional shedding on the upper surface of the blade in the outboard region and a two-dimensional shedding on the lower surface at the inboard portion of the blade. The wake of the top rotor contracts faster compared with that of the bottom rotor because of the vortex-vortex interaction. Further, the top-rotor wake convects vertically down at a faster rate due to increased inflow.