بررسي تجربي پارامترهاي هندسي رزوناتور هلمهولتز بر روي ساختارهاي جريان آن با استفاده از تكنيك PIV

چكيده انگليسي :

Experimental investigation of Helmholtz resonator geometrical parameters on its flow structures using PIV technique Javad Mohammadpour j mohammadpour@me iut ac ir May 20 2020 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree Master of Science Language FarsiSupervisor Mehdi Nili Ahmadabadi Assoc Prof m nili@cc iut ac ir AbstractThe Helmholtz resonator is a cavity in which an acoustic wave is created by a vortex shedding at its edge The specifications of this wave depend on various parameters such as cavity geometry and main flow velocity In the present study in order to maximize pressure fluctuations the pressure fluctuations were measured anddiscussed at different velocities by changing the geometry of the cavity These studies include the effect ofopening width and depth of cavity on the vortex shedding acoustic wave intensification frequencies and theamplitude of pressure fluctuations In the following two auxiliary cavities were used to strengthen the pres sure fluctuations in the cavity and the pressure fluctuations were received in the two conditions with small andlarge distances After examining the parameters of the cavity and using the auxiliary cavities the appropriatewidth of the opening was designed and created for two specific velocities and the pressure fluctuations weremeasured A number of rectangular cavities with different dimensions were designed made and connected tothe wall of the wind tunnel to measure the pressure fluctuations The pressure fluctuations were measured at theend of the cavity using the pressure sensors for a period of time Eventually the results were transferred to thefrequency field using a Matlab code and Fast Fourier Transform to obtain the dominant frequencies of the cavityand the amplitude of the corresponding oscillations The results showed that as the vortex shedding frequencyreaches different acoustic frequency modes an intensification happens and the amplitude of the oscillationssuddenly increases The amplitude of the oscillations decreases in the intensified state as the depth of the cav ity increases and it occurs at the lower frequencies due to acoustic attenuation In addition placing auxiliarycavities close to the main cavities strengthens the pressure fluctuations in both auxiliary and main cavities Inthe following with the aim of improving the flow structure and intensifying the fluctuations frequency at lowvelocities a plannar time resolved PIV measurement was used to investigate the effect of edge creation in threedifferent modes In order to use the PIV technique a seeding mechanism was designed and made and olive oilwas injected into the main stream of a suction wind tunnel as the tracer particles In the following the vortexshedding into the cavity was captured in different modes and the required results were extracted using imageprocessing The results demonstrated that by placing the edge in the opening of the cavity and shrinking it theirregular flow in the opening of the cavity changes to a harmonic structure and a regular vortex shedding fellout Also the vortex shedding frequency and the power of the incoming vortex will increase by reducing thewidth of the opening of the cavity The infiltration of the vortex into the cavity will increase and will occupymore space in the throat KeywordsHelholtz Resonator Deep Cavity Pressure Fluctuations Hydrodynamic Modes Acoustic Modes PIV Tech nique

محمدپور، جواد

بررسي تجربي پارامترهاي هندسي رزوناتور هلمهولتز بر روي ساختارهاي جريان آن با استفاده از تكنيك PIV

رزوناتور هلمهولتز , حفره عميق , نوسانات فشار , مود هيدروديناميكي , مود آكوستيك , حفره آكوستيك , تكنيك PIV