Sharif Digital Repository

A new technique for the laminar-turbulent intermittency measurement based on the surface hot-film data is presented. The existing techniques require data acquired from the calibrated hot-films which leads to the real wall shear stress values. However, calibration of the hot-films is usually very complex. In the proposed method, a technique based on the probability distribution function (PDF) of the acquired data using the uncalibrated hot-film sensors is presented and evaluated. The PDF is prepared for a reduced form of the quasi-wall shear stress value instead of the real shear stress value one. This leads to a standard normal distribution curve for the PDF in the turbulent flow region and... 

Transitional boundary layer over an airfoil in the combined pitch-plunge oscillating motions at low Reynolds number is experimentally investigated. The study is based on the data obtained from both surface hot-film and surface static pressure. Different oscillation zones prior to, within, and beyond the static stall angle of attack of the airfoil are considered. The hysteresis loops for the laminar separation bubble, transition, relaminarization points, as well as the airfoil lift coefficient are investigated and are compared for different types of dynamic motions. Two different types of combined pitch-plunge motions, constructive and destructive, are considered. In the constructive motion,... 

In this study, we performed experiments to investigate the effect of sweep angle on the transition location of laminar flow to turbulent flow. Three half wing models were used, each having a different sweep angle but with the same aspect ratio in various angles of attack. Two flat plates were used at the ends of the swept wing models to prevent the flow from rolling up over the wing. By simulating flow over infinity swept wing by eliminating tip vertices, the effect of sweep angle on flow transition phenomenon was investigated. The experiments included the study of transition flow via hot-film sensors, which were glued on the wing surface. We found that the small leading-edge radius and low... 

Extensive experimental investigation was conducted to study the effect of leading-edge roughness on the state of the boundary layer of a wind turbine blade section. The application of surface grit roughness simulates surface irregularities that occur on the wind turbine blades. The measurements were done using multiple hot-film sensors and surface pressure transducers in both static and plunging oscillation of the airfoil. Frequency domain analysis was used to determine the state of the unsteady boundary layer