جستجوی مقالات مرتبط با کلیدواژه « Airfoil » در نشریات گروه « مکانیک »

Freezing is a common issue in blowers, wind turbines and flying vehicles. This phenomenon has a great impact on reducing aerodynamic performance, increasing noise pollution and imposing extra load on the structure. In this article, the effect of freezing on the aerodynamic and aeroacoustic performance of the Naka-0012 airfoil has been studied. Transient and three-dimensional Navier-Stokes equations have been used for aerodynamic prediction. Sound wave is calculated using Fox-Williams and Hawkins equations. Simulation of eddies has been done using LES method and WALE subgrid scale model. First, all calculation methods have been validated using experimental data. Then the effect of freezing on airfoil performance has been studied. Flow vortices have been studied and sound production mechanisms corresponding to these vortices have been identified. The results show that freezing reduces the lift force by 9.7% and increases the drag force by 3.8 times. In the range of maximum human hearing sensitivity (one to five kHz), the average amount of sound increase is around 9 dB, which is a significant amount in terms of noise pollution. The increase in sound caused by freezing can be used to identify and deal with this phenomenon faster and reduce its risks.

In this article, a numerical investigation of the effect of simultaneous suction and blowing on an airfoil is studied to reduce the separation bubble. This investigation was done at Re=8.5×106 and the simulations are done by commercial Fluent software. First, the suction and blowing systems are used at different blowing and suction angles (30, 45 and 90 degrees) along with their location (distance ratio 0, 0.1, 0.2, 0.3, 0.6, 0.7 and 0.8) were investigated. In this study, the ratio of lift to drag, pressure coefficient, velocity and pressure contours were compared in different cases compared to the one with no slot, and finally the best state was determined. The results of this study showed that the suction on the leading edge and blowing on the tailing edge can improve the aerodynamic performance of the airfoil at an angle of attack of 17 degree. The best performance was the blowing at a distance ratio of 0.6C and suction at 0.1C, which increased the lift-to-drag ratio by 55%. Compared to the one without any slot.

This study is conducted on the effects of leading-edge slat and longitudinal slots in delaying the flow separation. The case study is a conventional wind turbine airfoil and four different types of slots have been investigated. The aerodynamic simulation is performed on the basis of a steady state air flow over the NREL S809 airfoil and the solution is obtained numerically using the structured grids. The results show that at Reynolds number of 1e+6 and an angle of attack equal to 16.22o, with the addition of leading-edge slat, the separation is delayed from x / c = 0.47 to x / c = 0.67 and the lift coefficient is increased by 64% (from 1.17 to 1.92). So, by adding several types of longitudinal slots, it is observed that a sinusoidal slot with 45o of phase lead, has the best performance.Through studying the values of the aperture, depth and location of the sinusoidal slot, the best values of these parameters were obtained as follows: 3% of the chord for the aperture value, 0.5% of the chord for the depth value and 0.85 for the x/c ratio. By completely removing the flow separation, at the mentioned Reynolds number with the same angle of attack, the lift coefficient has 117% increase, reaching the value of 2.54.

In the present study, an efficient numerical algorithm based on theoretical methods is developed for the prediction of the noise of aerodynamic flows around two-dimensional geometries. The theoretical formulation for calculating different types of noise is proofed and a solver with a negligible computational cost is developed accordingly. By using the present noise solver, the aeroacoustic characteristics around two test cases are predicted and the obtained results are presented in comparison with the available numerical and experimental data. The present results for noise around NACA0012 and S822 are in excellent agreement with those reported in the literature which shows the accuracy and performance of the present solver based on the theoretical formulation. Employing this quick solver is very crucial to save costs in the preliminary design process of low noise geometries in aerospace engineering. The extension of the present two-dimensional noise solver for the prediction of noise properties around three-dimensional geometries is undergoing.