JOURNAL OF AERONAUTICAL ENGINEERING (JOAE)
Year:2010 | Volume:12 | Issue:1|Papers Count:12

Experimental investigations of pressure distribution and aerodynamic forces coefficients of a cascade of stator blades in airplane engine compressor were conducted in this research. The blades are of the 67A blade type which relate to the controlled diffusion blades family and are applied in the first stage of the compressor of the turbofan engines. In this regards, three parallel blades were built from Plexiglas, using the Laser cutting method, which two flat plates are attached to both sides of them. Pressure distribution measurement over the blade surface and coefficients of lift, drag and moment at five different angles of attacks ranging between 20 and 45o at Reynolds numbers of 400,000 through 600,000 are obtained. Flow separation effects, especially near the blades leading edges, and their effects on the pressure distribution and aerodynamic coefficients and stall phenomenon are investigated. Angle of attack variations highly affects the flow structure and aerodynamic coefficients of the blades cascade. Furthermore, increasing the angle of attack increases the flow interactions between the blades. The flow separation point over the suction side of the blade moves towards the leading edge due to increasing the angle of attack and it has negligible effects on the separation on the pressure side of the blade.

In this research, low speed wind tunnel tests have been carried out to investigate the canard configuration and location on the pressure distribution over a maneuverable aircraft model. The applied wing and canard are delta shape with a sharp leading-edge. The investigations have been performed at free stream velocity of 18 m/sec, angles of attack of 14 and 18 degree, and different canard angles respect to the main wing. The main wing sweep angle is 60 degree and the canards have the sweep angles of 60 and 70 degrees with different thicknesses. The velocity distribution over the main wing was measured at three canard positions, including low, mid and up respect to the main wing, and the pressure distribution was measured only at mid and up canard positions. The results showed that the vortex which is generated over the wing having a sharp leading edge canard is stronger and bigger than the vortex of the delta wing having a rounded leading edge. Also, at the up position of the canard, maximum pressure reduction over the wing surface is observed. Furthermore, by increasing the wing sweep angle and decreasing the canard thickness, higher pressure reduction would be obtained.

Downburst has been a potential threat for flight safety, especially during takeoff and landing, and has been identified as one of the most important causes of aviation accidents during these phases. Aircraft performance degradation in this phenomenon gives pilot a very little opportunity to control the aircraft correctly. Determination and evaluation of downburst destructive effects need a precise model of wind field in it. In this paper, flight data analysis and reconstruction has been presented when the aircraft was traversing through the downburst. In the first step, wind components and their gradients were determined using FDR outputs. Then aircraft performance degradation was computed quantitatively with a factor called F-Factor. In both accidents which were investigated in this research, F-Factor had values eventually resulted in accidents. Finally with modeling equations of motion and aerodynamic parameters, while using derived wind components, it was tried to find a suitable landing abort strategy. The results showed that best landing abort strategy during downburst encounter was to hold constant pitch attitude while using maximum engine thrust. This method was exactly applied on received data from NTSB and final results, in comparison with previous researches, completely verified the method. So, the required ability has been obtained for the analysis of FDR data.

In high speed milling, prediction of cutting forces is of prime importance for optimum selection of end mill and machine tools. Since, machining of short blades can be performed only using a roughing and a finishing operation, increasing the machining efficiency during roughing and semi finishing is significant. In roughing process, removing the chips is an important factor, in which, by simulating the milling process, suitable cutting condition before performing the machining process. In this research, at first, Instantaneous chip geometry was estimated using a 3D simulation software. Then, the cutting force coefficients were determined using the full immersion milling tests and the mass, stiffness and damping matrices are obtained using the finite element analysis. Finally, modeling and dynamic simulation of the cutting forces are performed and the effect of the depth of cut is determined and cutting conditions are predicted before doing the machining process. The simulation results are investigated and validated using the experimental results.

The aerodynamic plasma actuators have shown their capability as a flow control device in different applications. This study presents an inventory design in which a power supply is used to generate a high voltage (up to 8kV) at high frequency (up to 10 kHz) output. The High voltage generator is applied to ionize ambient air at atmospheric pressure at the surface of a plasma actuator. The configuration of the plasma actuator is simple. It consists of two electrodes arranged asymmetrically. One of the electrodes was exposed to the surrounding air, and the other was on the other side of the dielectric material.. When a high AC voltage was applied, a plasma discharge appeared on the insulator surface above the insulated electrode, and directed momentum was coupled into the surrounding air. The amount of the coupling momentum was effective in substantially altering airflow over the actuator surface. The coupling momentum induced an air flow that expanded over both sides of dielectric layer. Such a coupling can increase air velocity in boundary layer from zero modifying air flow. However in this study the induced air flow was measured in the absence of external airflow using a pilot tube. The effect of frequency and dielectric material on induced air velocity was also studied. The results showed that there is an optimal frequency (7.5 kHz in this study) at which the induced air flow reaches its maximum velocity. The results revealed that the induced air velocity at the top of dielectric up to 0.5 mm reaches to 5m/s for Plexiglas dielectric and to 6m/s for Teflon. Hence, the dielectric constant plays a significant role in inducing air velocity. The advantages of the plasma actuator flow control device over traditional flow control devices are: smaller in size and weight, absence of moving parts, higher reliability, inexpensiveness, broader bandwidth (quick response), reduced drag and increased aerodynamic agility.

An analytical study is conducted in this paper to determine the characteristics of sound transmission through laminated composite double-walled thin cylindrical shells with infinite length. It is assumed that the external and internal fluid media surrounded the shells, and there is fluid existence in the annular space between them. A uniform flow exists with a constant velocity in the external medium. An exact solution is obtained by solving the classical shell equations and acoustic wave equations simultaneously. Transmission losses obtained from the numerical solution in this paper are compared with the results of other investigators for composite single-walled cylindrical shell. Comparison revealed good agreement. Finally, the effects of different source conditions, structural, fluid and gap properties as well as flight conditions on TL have been studied for a range of values, specifically; incident angle of the plane wave, Mach number and flight altitude of aircraft, thickness and curvature of shells lay-up stacking sequence and damping.