Influence of corner radius on the near wake structure of a transversely oscillating square cylinder

R. Ajith Kumar,손창현,B. H. Lakshmana Gowda 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.9

The near wake flow field features of transversely oscillating square section cylinders with different corner radii were studied in an attempt to assess the influence of corner radius. The investigation was performed by using particle image velocimetry (PIV) technique in a water channel with a turbulence intensity of 6.5%. Five models were studied with r/B=0, 0.1, 0.2, 0.3 and 0.5 (r is the corner radius and B is the characteristic dimension of the body), and the body oscillation was limited to lock-in condition (at fe/fo=1.0; fe is the excitation frequency and fo is the vortex shedding frequency from a stationary cylinder at the same Re). The corner radius was found to significantly influence the flow features around the bodies. Except for r/B=0.5, for all the other cases of r/B ratios, cycle-to cycle variation in the mode of vortex shedding was observed in the case of oscillating cylinders inducing highly non-linear wake characteristics. Apart from variation in the shedding mode, changes in shedding cycle timing were also observed for sharp and rounded square cylinders. The hgher the r/B ratio, shedding in the near wake was found to be more uniform (lesser variation in shedding cycle timings). Another admissible shedding mechanism is newly identified to operate in the near wake of oscillating cylinders now being called as the ‘passive shedding’ mechanism. Results indicate that increasing the corner radius suppresses the possible instabilities of the cylinder.

A PIV study of the near wake flow features of a square cylinder: influence of corner radius

R. Ajith Kumar,손창현,B. H. Lakshmana Gowda 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

In this study, the near wake characteristics of transversely oscillating square-section cylinders with different corner radii were investigatedusing the particle image velocimetry (PIV) technique in a water channel with turbulence intensity of 6.5%. Five models with r/B =0, 0.1, 0.2, 0.3, and 0.5, respectively (where r and B represent the corner radius and the characteristic dimension of the body, respectively),were studied, with the body oscillation limited to that under the lock-in condition. Corner radius was found to significantly influence thecharacteristics of the flow around the bodies, both under stationary and oscillating conditions. The results indicate that the Strouhal numberand vortex strength of the flow increase and decrease, respectively, with an increase in the r/B ratio. The spacing between two rows ofvortices (b) as well as that between consecutive vortices in a row (a) was also found to decrease with the increase in the corner radius. The b/a ratio was found to be nearly independent of the r/B ratio and body oscillation.

Interference excitation of a square section cylinder

R. Ajith Kumar,B. H. L.Gowda,손창현 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.3

Wind tunnel experiments were conducted to study the interference excitation of a square section cylinder (test cylinder) and the results are reported in this paper. The study was carried out at some specific relative positions identified between the test cylinder (side dimension B) and the interfering cylinder (side dimension b) so that the latter is never upstream of the former. Experiments were carried out for the b/B ratios of 0.5, 1.0, 1.5 & 2.0. In this paper, emphasis is laid on bringing out the influence of b/B ratio on the vibratory response of the test cylinder, considering a few interference positions. The results show that at a particular relative position, the magnitude of vibrations and the response trend of the test cylinder are markedly influenced by the b/B ratio. Under certain combinations of b/B ratio, relative position and reduced velocity, test cylinder vibrations are considerably magnified and in certain other combinations they are suppressed. Flow visualization results are provided in an attempt to bring out the influence of b/B ratio and also to explain the observed vibratory features of the test cylinder.

진동하는 물체 주위의 유동특성 해석

주명근,R. Ajith Kumar,손창현,B.H.L. Gowda 한국유체기계학회 2007 유체기계 연구개발 발표회 논문집 Vol.- No.-

An experimental investigation on upward solar air heater with impinging air jets

M. Harikrishnan,R. Ajith Kumar,S. Ajithkumar,Rajesh Baby 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.1

This study presents and discuss the results of an experimental investigation conducted to understand and quantify the impact of air mass flow rate(m) over the heat transfer attributes of an upward solar air heater (SAHRR) utilizing impinging air jets. Experimental investigation was carried out for various mass flow rates ranging from 0.008 to 0.024 kg/s for various impinging air jet diameters (4, 6 and 8 mm). The thermal performance was evaluated based on the average value of Nusselt number, first law thermal efficiency, thermohydraulic efficiency and exergy efficiency. The lowest and the highest first law efficiency for an upward SAHRR employing 6 mm diameter jet is between 44 % and 88 %, respectively, when the solar radiation maintained is 1000 W/m 2 . Moreover, the final outcomes are compared with the base model (SAHRR without jet impingement) in order to highlight the positive impact of jet impingement on the performance of SAHRR.

NUMERICAL FLOW VISUALIZATION ANALYSIS AROUND AN OSCILLATING SQUARE CYLINDER

M.K. Ju(주명근),R. Ajith Kumar,C.H. Sohn(손창현),R.H.L. Gowda 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

In this paper, a flow visualization analysis has been carried out on an oscillating square section cylinder, numerically, using a commercially available code CFD-ACE. In this study, the square cylinder is forced to oscillate at different frequencies of excitation, viz., fe/fo=0.5, 1.0 and 2.0 (where, fe is the excitation frequency provided to the cylinder and fo is the natural vortex shedding frequency from the stationary cylinder at a particular Reynolds number (=5200). In all the cases, the peak-to-peak amplitude of oscillation is kept at 32% of the side dimension of the square cylinder. These studies are conducted to understand the influence of frequency of oscillation on the flow field features around the cylinder, particularly the mode of vortex shedding. Results indicate that, the flow field around a square cylinder is very much influenced by the excitation frequency, in particular the vortex shedding mode. It is also found that, the vortex street parameters are significantly influence by the oscillation frequency. Comparison with earlier reported experimental studies has also been attempted in this paper. In appears that, such a numerical exercise (as performed in this paper) is first of its kind. It is believed that, these studies would enable one to understand the mechanisms underlying the flow-induced vibrations of a square section cylinder.

Drag reduction for flow past a square cylinder through corner chamfering

Muhammad Ahsan Nawaz,Muhammad Abubaker,R. Ajith Kumar,Chang Hyun Sohn 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.11

This study investigates the unsteady incompressible flow around a square cylinder with different chamfer ratios (CRs) using a commercial finite volume code, ANSYS Fluent. CR ranges from 0.0 (sharp square cylinder) to 0.5 (diamond cylinder) with variable increments. Detailed analysis of flow characteristics is conducted at Reynolds number (Re) = 2100. Additionally, simulation is extended to cover Re, i.e., Re = 100, 500, and 10000. The simulation results show that cylinder with CR = 0.1 outperforms all other cases by enabling a drag reduction of about 60 % at Re = 10 4 . Drag has an inverse relationship with the wake closure length. Time-averaged coefficient of pressure, streamlines, and vorticity contours are also discussed to better understand near-wake features and the physics of drag reduction.