Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
43
3
2016
Study of Vortex Breakdown in a Cylindrical Cavity with a Rotating Endwall
189-205
Akash
Yalagach
Vikram Sarabhai Space Centre, Indian Space Research Organisation Thiruvananthpuram, India
Abdusamad
Salih
Department of Aerospace Engineering
Indian Institute of Space Science and Technology
Thiruvananthapuram - 695547, India
Flow in a cylindrical cavity with a rotating endwall is studied here. The flow structure is governed by two dimensionless parameters: Reynolds number and aspect ratio of the cavity. For certain combinations of Reynolds numbers and aspect ratios, vortex breakdown occurs and one or more recirculating regions are observed along the axis of rotation. Three-dimensional Navier−Stokes equations are solved for three aspect ratios (AR = 1.5, 2, and 2, 5) and for various Reynolds numbers, where steady solution exists. Results are compared with axisymmetric solutions. It was observed that, at higher Reynolds numbers the flow transforms from axisymmetric to three-dimensional and at very high Reynolds number, spiral counter-rotating vortices are formed due to centrifugal instabilities in the Stewartson layer.
Secondary Flow Behaviour in Various Rounded-Edge Bifurcation T-Junctions and Its Relation to Head Loss
206-217
YB.
Lukiyanto
Sanata Dharma University
I. N. G.
Wardana
Mechanical Engineering Department, Brawijaya University Jln. MT. Haryono 167, Malang 65145, Indonesia
Widya
Wijayanti
Mechanical Engineering Department, Brawijaya University Jln. MT. Haryono 167, Malang 65145, Indonesia
M. Agus
Choiron
Mechanical Engineering Department, Brawijaya University Jln. MT. Haryono 167, Malang 65145, Indonesia
Visualization of secondary flow behavior were carried out for the laminar flow (Re = 81) in a sharp-edged and rounded-edged 90° T-junction with an inlet flow perpendicular to both inline outlet flows orientation with a bifurcation ratio of 0.5. Particles were added to the fluid. The fluid was salt solution for density similarity with the particles, leading to eliminate the bouyance effect. Static pressures were measured at the inlet and one of the outlet channels by a U-manometer. The result shows that the rounded edge affected the recirculation secondary flow area and position leading to the reduction of the head loss. The image of the secondary flow demonstrates that a T-junction with the rounded edge with a rounded-edge radius ratio of 0.5 had a broader bifurcation area and a smaller secondary flow occupation area in the outlet channel, as compared to the sharp edge. The decreasing head loss ratio was 51 %. At rounded-edge radius ratio of 0 up to 1.5 part of secondary flow was located in the bifurcation area and the outlet area, whereas at rounded-edge radius ratio of 2 and of 2.5 it was located completely within the bifurcation area. Changing rounded-edge radius ratio from 1.5 to 2 reduced the head loss ratio up to 49.72 %.
Numerical Simulation of Heat Transfer on Simultaneously Developing Flow in Microchannel under Inlet Pulsation
218-233
Tapas K.
Nandi
Department of Mechanical Engineering, Techno India College of Technology
Kolkata, 700156, India
Himadri
Chattopadhyay
Department of Mechanical Engineering, Jadavpur
University, Kolkata − 700032, West Bengal, India
The present work investigates the effect of inlet pulsation on the transport process in two types of microchannel as circular and wavy microchannel. The flow was both thermally and hydrodynamically developing while the channel walls were kept at a uniform temperature. The inlet velocity varies sinusoidally in time for a range of dimensionless frequencies (St = 1, 5, 10) up to an amplitude of 0.8. The transient solution of two-dimensional Navier−Stokes equation was obtained using the SIMPLE algorithm with the momentum interpolation technique of Rhie and Chow. The simulations were performed in the laminar regime within the Reynolds number range between Re = 0.1 to 100 and Prandtl number 0.7 for both circular and wavy channels. The results of pulsating flow simulation have been analysed and compared with steady flow simulations. It is observed that the effect of pulsation in circular channel is significant only at low Reynolds number (Re ≤ 10) beyond which pulsation has little effect. On the contrary, wavy passage does not provide any significant heat transfer enhancement when the flow is steady, particularly at very low Reynolds number. Significant increase in heat transfer is observed when the flow is made unsteady. Further, non-dimensional pressure difference, friction factor and performance are analysed in this study.
Experimental Study of Turbulent Offset Jets
234-250
Martin
Agelin-Chaab
Automotive, Mechanical and Manufacturing Engineering Department, University of Ontario Institute of Technology Oshawa, ON, L1H 7K4, Canada
Proper orthogonal decomposition and swirl strength analyses were applied to turbulent offset jets at a Reynolds number based on a maximum mean jet exit velocity and nozzle diameter of 10000. The offset jets are water jets flowing into quiescent water media and have offset heights (h) based on nozzle diameter (d) of h/d = 2 and 4. The data were obtained using a particle image velocimetry (PIV) technique. The results indicate that the reconstruction of the turbulent quantities is so effective that the reconstructed profiles collapsed on the ensemble PIV data using only the first 25 POD modes. The offset height did not have any effect on the convergence of the reconstructed profiles. The mean swirl strength is non-zero at any location about 35 % of the time. The higher offset height has a lower percentage of non-zero swirl in the inner shear layer.
Natural Convection Heat Transfer Inside a Square Enclosure with Partial Heating
251-270
Ramin
Rabani
Department of Mechanical Engineering, Yazd University,Yazd, Iran
Mehrdad
Rabani
Department of Mechanical Engineering, Yazd University,Yazd, Iran
In this paper, the natural convection heat transfer inside a square enclosure with partial heating has been studied in the unsteady and steady state. In order to implement the partial boundary condition, a part of the left wall was maintained at high temperature and the rest of it was considered to be insulated. The Rayleigh numbers were 104, 105 and 106. The critical Rayleigh number which is defined as the transition of flow stream from pure conduction to natural convection was also investigated. The results indicated that in the unsteady state, with an increase in the heating region and decrease in the Rayleigh number, the time to reach the steady state of the solution decreases. Furthermore, heating from the middle of the left wall requires shorter time to reach the steady state. In the steady state, at Rayleigh numbers 104 and 105, heating from the middle part of the left wall results in higher Nusselt number for S/L < 0.6 compared to the heating from the bottom, while in the Rayleigh number 106 this phenomenon occurs for S/L < 0.4. It was also observed that the increase in the Rayleigh number causes the flow pattern to be changed and the vortices to be multiple.
An Estimation of Turbulent Vector Fields, Spectral and Correlation Functions Depending on Initial Turbulence Based on Stochastic Equations. The Landau Fractal Equation
271-280
Artur V.
Dmitrenko
Department of Thermal Physics, National Research Nuclear University "MEPhI", 31 Kashirskoe Shosse, Moscow, 115409, Russia; Department of Power Engineering, Moscow State University of Railway Engineering (MIIT),
9 Obraztsov St., Moscow, 127994, Russia
Analytical expressions for estimation of turbulent vector fields, spectral and correlation functions depending on the initial turbulence based on stochastic equations are presented. Calculated values of exponent of the velocity profile and the second-order correlation are in satisfactory agreement with the data for classical turbulent flows. Also, with the use of stochastic equations, the two new fractal equations for generation and diffusion of turbulence are obtained. In special case, the second fractal equation takes the form of the Landau equation. As the result, the second-order correlations and turbulent Prandtl number are presented as the functions of the initial turbulence.