Experimental study of stall control over an airfoil with dual excitation of separated shear layers

, Article Aerospace Science and Technology ; Volume 82-83 , 2018 , Pages 402-411 ; 12709638 (ISSN) Ebrahimi, A ; Hajipour, M ; Ghamkhar, K ; Sharif University of Technology

2018

Abstract

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...

Wavelet analysis of the flow field around an oscillating airfoil undergoing pure pitching motion at low Reynolds number

, Article Physics of Fluids ; Volume 35, Issue 6 , 2023 ; 10706631 (ISSN) Ghamkhar, K ; Ebrahimi, A ; Shariloo, K ; Sharif University of Technology

American Institute of Physics Inc 2023

Abstract

This paper investigates the flow field around a NACA (National Advisory Committee for Aeronautics) 0012 airfoil undergoing pure pitching motion using continuous wavelet transform. Wind tunnel experiments were performed with a test-stand that provides a wide range of oscillation frequencies (f = 0-10 Hz). Sinusoidal pure pitching motion was considered with respect to the quarter chord for five reduced frequencies (K = 0.05, 0.1, 0.15, 0.2, and 0.3) at a Reynolds number of Re = 6 × 104. Mean angle of attack and pitch amplitude for all the cases were considered 0° and 6°, respectively. Unsteady surface pressure measurement was conducted, and the lift coefficient was calculated based on the...

Aerodynamic Performance Investigation of a Tandem Airfoil Configuration at Low Reynolds Numbers

, Ph.D. Dissertation Sharif University of Technology Ghamkhar Pishkhani, Kamran (Author) ; Ebrahimi, Abbas (Supervisor)

Abstract

The main goal of this research is to study the flow field around an airfoil undergoing pure pitching motion in single and tandem configurations. Despite numerous experimental and numerical studies on flow structures at low Reynolds numbers, less attention has been given to the frequency analysis of flow structures in pitching airfoils. Additionally, the effect of reduced frequency on lift coefficient behavior, surface pressure, and wake pressure for a pitching airfoil at low Reynolds numbers is not well understood. Specifically, the unsteady aerodynamics of tandem pitching foils with independent reduced frequencies has been remained less assessed. In this dissertation the physics of the flow...

Effect of Corona Virus Outbreak on Different Industries in Iran stock Exchange

, M.Sc. Thesis Sharif University of Technology Ghamkhar, Dorsa (Author) ; Zamani, Shiva (Supervisor) ; Talebiyan, Masoud (Supervisor)

Abstract

This research is an event study about the effects of the Corona Virus Outbreak on different industries in the Iran Stock Exchange. This study examines which industries had been affected more negatively or positively by the COVID-19 pandemic outbreak. In the first step, we calculate Alphas, Betas, and expected returns of stocks in an estimation window before the event using the market model. Then, we group all stocks in 17 different industries and calculate average cumulative abnormal returns in the event period as good measures for examining defects of this outbreak. Our results show that transportation, chemical products, processed products, real estate, and automobile manufacturing were...

Numerical Study and Sensitivity Analysis of a Flowmeter Based on a Fluidic Oscillator

, M.Sc. Thesis Sharif University of Technology Shahidi, Hassan (Author) ; Ebrahimi, Abbas (Supervisor) ; Ghamkhar, Kamran (Co-Supervisor)

Abstract

In this thesis, the flow behavior in a fluidic oscillator-based flowmeter is investigated using two-dimensional numerical simulations and experimental tests. The primary objective of this study is to analyze the effect of geometrical parameters and flow conditions on the performance of the fluidic oscillator and to determine the relationships between key parameters such as oscillation frequency, oscillation amplitude, pressure drop, and the standard deviation of the Strouhal number. The numerical simulations are conducted using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) model and the finite volume method, with the k−ω SST turbulence model applied for flow modeling. The computations...

Experimental Study of a DBD Plasma Actuators Location and Actuation Frequency on Flow Separation Control

, M.Sc. Thesis Sharif University of Technology Ghamkhar Pishkhani, Kamran (Author) ; Ebrahimi, Abbas (Supervisor) ; Puoryousefi, Gholamhossein (Co-Supervisor)

Abstract

This thesis investigates the stall control over an airfoil employing dual excitation of separated shear layers with DBD plasma actuators. This research is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 300000, respectively. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the trailing edge, are exploited to control the baseline flow. Surface pressure distribution, as well as the dominant natural frequency associated with flow structures in the wake, are evaluated. Based on the active actuators, three controlled cases are considered in the present study. In the first...