Sharif Digital Repository

Extensive low speed wind-tunnel tests were conducted to study the unsteady aerodynamic behaviour of an airfoil sinusoidally oscillating in plunge. The experiments involved measuring the surface pressure distribution over a range of amplitudes, H = ±5 to ±15cm. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with a constant reduced frequency, k = 0.058, at three mean angles of attack of 0°, 10° and 18°. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. The plunging displacements were... 

Unsteady aerodynamic experiments were conducted on an oscillating airfoil in a subsonic wind tunnel. The model was oscillated in two types of motion, pitch and plunge, at a range of reduced frequencies, k=0.029-0.1. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The unsteady surface pressure is measured along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different types of motion on the unsteady pressure distribution of the airfoil at pre-stall, near stall, and post stall conditions. It was found that the variations of the pressure distribution with angle of attack have... 

Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools, etc. However their favorable thermal performance has allowed them to be employed in other buildings like bazaars, or market places in Iran. In this investigation, wind pressure coefficients were determined experimentally for a domed roof model in a boundary layer wind tunnel. The model was a 1/10 scale model of the dome of an old school in the city of Yazd, in the central desert region of Iran. The model included a number of windows at the collar of the dome, and a hole on its apex. A total of 48 pressure tabs were employed to measure the air pressure at various... 

In this work, a new method based on the modified Enskog theory (MET) is presented for calculation of transport properties at high densities (ρ > ρc). The main limitation of using the MET is lack of experimental data for co-volume, b0. We have substituted b0 from hard sphere (HS) theory and zero density transport properties from the kinetic theory of gases for HS in the MET expression, because of the fact that dense fluids behave more and less like a HS fluid. As a result, a simple linear expression for the self diffusion (D) and quadratic expressions for viscosity (η) and thermal conductivity (λ) coefficients have been obtained in terms of Y at high densities (ρ > ρc), where Y = (T (∂ p / ∂... 

A series of experiments was performed to investigate the interaction of an under-expanded axisymmetric supersonic jet exhausted from a flat plate with a high subsonic crossflow. The goal was to study the effect of boundary layer thickness (δ) and jet to freestream dynamic pressure ratio (J) on flow field pressure distributions. The resulting measurements upstream of the jet showed that with increasing boundary layer thickness, the magnitude of the pressure coefficient decreases, whereas downstream of the jet, the recovery of the back-pressure moved closer to the nozzle exit. Flow field measurements indicated that with increasing boundary layer thickness, the jet plume dissipation rate... 

This paper investigates the stall control over an airfoil employing dual excitation of separated shear layers with dielectric barrier discharge plasma actuators. This novel approach is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 0.3×106, respectively. To analyze the baseline flow, Time-averaged pressure distributions on the airfoil surfaces are evaluated with 40 pressure taps. Further, the dominant natural frequencies associated with flow structures in the airfoil wake are examined utilizing a hot-wire anemometer. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the... 

Aerodynamic coefficients on a two dimensional plunging airfoil, in a low-speed wind tunnel are presented. Dynamic motion was produced by plunging the model over a range of reduced frequencies, and mean angles of attack. The Reynolds number in the present test was held fixed (Re = 1.5×10 5), and the reduced frequency was varied in an almost wide range. Surface static pressure distribution was measured on the upper and lower sides of the model, during the oscillating motion. It was found that reduced frequency had strong effects on the pressure distribution, near the leading edge of the airfoil. For mean equivalent angles of attack of 0, 5 degrees, hysteresis loops on the upper surface of the... 

A series of experiments were carried out to investigate unsteady behavior of the flow field as well as the boundary layer of an airfoil oscillating in plunging-type motion in a subsonic wind tunnel. The measurements involved surface-mounted hot films complimented with surface pressure. In addition, wind tunnel wall pressure distribution was acquired to furnish a baseline for the wall interference corrections. The airfoil is the section of a 660-kW wind turbine blade. The experiments were conducted at a Reynolds number of 0.42 million, and over two reduced frequencies of k = 0.06 and 0.085, at prestall, nearstall, and poststall regions. The unsteady aerodynamic loads were calculated from the... 

As balance is the foundation for all voluntary motor skills, considerable research has been conducted to evaluate postural control in patients with low back pain (LBP). Although reliability is a population-specific property, to the authors' knowledge, there has been no study to determine the test-retest reliability of the center of pressure (COP) measures in the general population of LBP patients. As many as 11 patients with a history of nonspecific LBP randomly completed postural measurements with three levels of difficulty (rigid surface-eyes open, rigid surface-eyes closed, and foam surface-eyes closed) in two sessions. The COP data were used to calculate standard deviation of amplitude,... 

A series of low speed wind tunnel tests were conducted to study the unsteady aerodynamic behavior of an airfoil sinusoidally oscillating in plunge. The experiments included measuring the surface pressure distribution over a range of reduced frequencies, k = 0.03 - 0.06. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with amplitude of ±15 cm and at three different mean angles of attack of 0, 10° and 18°. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces. The plunging displacements were transformed into... 

Numerous experiments were conducted on an oscillating airfoil in a subsonic wind tunnel. The experiments involved measuring the surface pressure distribution when the model oscillated in two types of motion, pitch and plunge, at three different Reynolds numbers, 0.42, 0.63 and 0.84 million, and over a range of reduced frequencies, k = 0.03 0.09. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphasis was placed on the effects of different types of motion on the unsteady pressure distribution of the airfoil at pre-stall, near-stall and post-stall conditions. It was...