Experimental investigation of the turbulent near wake flow field of multiscale/fractal grids

Download
2018
Amiri Hazaveh, Hooman
Turbulent near-field flow of three different fractal grids, as well as conventional square grid, is investigated using two-dimensional particle image velocimetry. All grids are designed to maintain similar solidity, effective mesh size, and the smallest thickness for comparison. Experiments are conducted at a Reynolds number of 12000 based on effective mesh size. The instantaneous velocity field is realized on four sets of 35 equally spaced horizontal planes downstream of turbulence-generating-grids. Threedimensional mean flow is reconstructed by stitching aforementioned horizontal planes, extending to 22 effective mesh size downstream of each grid. Additional mean flow variables are then obtained by rotating horizontal planes to the corresponding vertical ones in grids comprising geometrical symmetry. Turbulent mixing characteristics in the near-wake region are assessed and turbulent kinetic energy production, decay, and dissipation rate as well as estimation of length scales downstream of turbulence-generating-grids are carried out. It has been shown that grids with different fractal patterns can be used as a passive devices to custom tailor turbulence even in the non-homogeneous anisotropic near grid region. Dissipation rate coefficient is also shown to be not constant in the near-wake region.

Suggestions

Thermal Sensitivity of the Fundamental Natural Frequency of a Resonant MEMS IR Detector Pixel
Pala, Sedat; Azgın, Kıvanç (2017-08-10)
This paper presents the effect of temperature on the natural frequency of (1,1) mode shape of a Resonant MEMS IR bolometer pixel in the range of 295-340 K. The detector pixel has a square plate geometry having side length of 1400 mu m and thickness of 35 mu m. The resonating plate is supported at its geometric center, enabling more robust pixels with fill factor greater than 90% and less complicated fabrication process. The sensor is fabricated using a Silicon-On-Glass (SOG) process. For the first time in t...
Efficient algorithms for convolutional inverse problems in multidimensional imaging
Doğan, Didem; Öktem, Figen S.; Department of Electrical and Electronics Engineering (2020)
Computational imaging is the process of indirectly forming images from measurements using image reconstruction algorithms that solve inverse problems. In many inverse problems in multidimensional imaging such as spectral and depth imaging, the measurements are in the form of superimposed convolutions related to the unknown image. In this thesis, we first provide a general formulation for these problems named as convolutional inverse problems, and then develop fast and efficient image reconstruction algorith...
Experimental investigation of waveform tip injection on the characteristics of the tip vortex
Ostovan, Yashar; Uzol, Oğuz; Department of Aerospace Engineering (2011)
This study investigates the effect of chordwisely modulated tip injection on the flow and turbulence characteristics of the tip vortex through experimental measurements downstream of a rectangular half-wing that has an aspect ratio of three. This injection technique involves spanwise jets at the tip that are issued from a series of holes along the chord line normal to the freestream flow direction. The injection mass flow rate from each hole is individually controlled using computer driven solenoid valves a...
Investigation of effect of design and operating parameters on acoustophoretic particle separation via 3D device-level simulations
Sahin, Mehmet Akif; ÇETİN, BARBAROS; Özer, Mehmet Bülent (Springer Science and Business Media LLC, 2019-12-16)
In the present study, a 3D device-level numerical model is implemented via finite element method to assess the effects of design and operating parameters on the separation performance of a microscale acoustofluidic device. Elastodynamic equations together with electromechanical coupling at the piezoelectric actuators for the stress field within the solid parts, Helmholtz equation for the acoustic field within fluid, and Navier-Stokes equations for the fluid flow are coupled for the simulations. Once the zer...
Numerical Modeling of Electromagnetic Scattering from Periodic Structures by Transformation Electromagnetics
ÖZGÜN, ÖZLEM; Kuzuoğlu, Mustafa (2016-09-22)
The transformation electromagnetics is applied to the modeling of electromagnetic scattering from periodic structures in conjunction with the finite element method with periodic boundary conditions. In a unit cell of periodic structure, a uniform mesh is used over a flat surface and the arbitrary periodic surface is modeled by a coordinate transformation. The major advantage of this approach is that arbitrary geometries can be handled by using a single and simple mesh. Therefore, repeated computations (such...
Citation Formats
H. Amiri Hazaveh, “Experimental investigation of the turbulent near wake flow field of multiscale/fractal grids,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.