Investigation of turbulent mixing layer flow in a vertical water channel by particle image velocimetry (PIV)

Heat transfer is considerably influenced by flow stagnation, separation and reattachment regions due to the ribbed plates. Placing the ribs such as fins, turbulators that trigger the flow separation, enhances the heat transfer inside the channel by increasing the turbulence intensity. The flow separation is caused by disturbing the thermal and hydrodynamic development lengths. Moreover, these ribs also make an impact that increases the heat transfer by enlarging the heat transfer area. However, the ribs lead to the increment of the required pumping power in the meantime due to the increasing pressure loss in such systems. This aforementioned method is used for the heat exchangers, the solar collectors, the cooling of electronic devices. The investigation of the flow characteristics is very crucial to understand the heat transfer mechanism in the ducts for this reason. In the present paper, the flow characteristics between the plates have been experimentally researched. Particle Image Velocimetry system in the open water channel of Selcuk University Advanced Technology Research and Application Center has been used. The smooth plates have been taken as the reference model and used for the comparison with the plates having the rectangular cross-sectional ribs. The ribs with various heights of 0.1 ? h' = h/H ? 0.3 have been symmetrically placed on the internal surfaces of the plates via several spacing values of 0.5 ? S' = S/H ? 1 for varying Reynolds numbers as 10000 ? Re ? 20000. As a result, the flow characteristics have been given in terms of the contour graphics for velocity vector field, velocity components and vorticity.

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Energy Concentration by Bluff Bodies—A Particle Image Velocimetry Investigation

Journal of Fluids Engineering ◽

10.1115/1.4041886 ◽

2018 ◽

Vol 141 (6) ◽

Author(s):

Eshodarar Manickam Sureshkumar ◽

Maziar Arjomandi ◽

Bassam B. Dally ◽

Benjamin S. Cazzolato ◽

Mergen H. Ghayesh

Keyword(s):

Particle Image Velocimetry ◽

Circular Cylinder ◽

Bluff Body ◽

Particle Image ◽

Transverse Velocity ◽

Water Channel ◽

Energy Concentration ◽

Backward Facing Step ◽

Flow Energy ◽

Image Velocimetry

Particle image velocimetry (PIV) of four cylinders with different cross sections were performed in a recirculating water channel at Reynolds numbers of 5000 and 10,000. The cylinders were split into two distinct categories; semicircular and convex-edged triangular (c-triangular) prisms which have a smooth diverging fore-face and a flat, backward facing step aft-face, and a trapezoid which has a flat fore face and a backward-facing step aft-face. The resulting streamwise and transverse velocity vectors (u and v, respectively) were analyzed to provide a qualitative comparison of the bluff body wakes to the circular cylinder, which is the standard upstream stationary body in wake-induced vibration (WIV) energy technology. The Reynolds stresses, turbulent kinetic energy (TKE), mean spanwise vorticity, and the energy in the fluctuating component of the wake were compared. The main findings are: (i) a convex fore-face and a backward-facing step aft face are more effective at converting the flow energy to temporal wake energy (+20%) compared to a circular cylinder, (ii) a trapezoid type shape is less effective at converting flow energy to temporal wake energy (−40%) compared to a circular cylinder, (iii) increasing Reynolds number reduces the efficiency of conversion of upstream flow energy to downstream transverse temporal energy. Utilizing stationary upstream bodies such as the semicircle and the c-triangle can result in concentrating more energy in the fluctuating components for the downstream transversely vibrating bluff body in a WIV system, and hence can realize in more efficient WIV technology.

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