Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
37
6
2010
Numerical Investigation of aWinglet Nozzle Configuration Suitable for a Supersonic COIL Medium
491-505
10.1615/InterJFluidMechRes.v37.i6.10
Gaurav
Singhal
Laser Science and Technology Center, India
P. M. V.
Subbarao
Department of Mechanical Engg., Indian Institute of Technology, New Delhi, 110016, INDIA
Mainuddin
Laser Science and Technology Center, India
A. L.
Dawar
Laser Science and Technology Center, India
Chemical oxygen iodine laser (COIL) is amongst the most potential high power laser capable of being utilized extensively in both industrial as well as defense scenarios. Typically, lasers are low efficiency devices requiring much higher pumping power as compared to the laser power output and conventional supersonic COIL systems employing slit nozzle configurations are no exception. The power extraction efficiencies can be improved by producing better mixing of the secondary lasing media (I2) with the primary pumping medium (O21Δg) in a cross flow injection of the former in supersonically flowing pumping medium. This is due to reduced singlet oxygen losses found to occur in conventional systems using subsonic injection schemes. However, supersonic injection schemes have an inherent problem in terms of achieving homogenously mixed lasing media due to reduced mixing through pure diffusion. The present study, therefore, focuses on the possibility of utilizing scalloped lobed mixer geometry produced by employing delta wings placed in an X-configuration. In order to predict the cavity flow conditions employing this new nozzle configuration a detailed numerical study was undertaken to evaluate the various fluid dynamic parameters prior to initiating the prototype fabrication. The numerical studies carried out for a 10° lobe angle reveal that the winglet nozzle geometry not only produces a strong field of stream-wise vortices due to variation in aerodynamic loading along the winglets, capable of producing distinctly better mixing, but also serves as a supersonic nozzle for producing a Mach number of nearly 1:75 at the exit of the winglets. The numerically predicted circulation at the exit of the winglets is nearly 1.57 m2/s. The region of maximum turbulence and fully developed streamwise vortices is observed to occur close to the exit, at x/λ of 0.5, of the winglets making it the most suitable region for secondary flow injection for achieving efficient mixing. The predicted length scale of the streamwise vortices formed by the winglet nozzle is 4λ.
Numerical Study of Steady Thermocapillary Convection in a Cylindrical Half-Floating-Zone
506-529
10.1615/InterJFluidMechRes.v37.i6.20
Shaligram
Tiwari
Department of Mechanical Engineering, Indian Institute of Technology Madras,
Chennai, 600036, India
Koichi
Nishino
Department of Mechanical Engineering and Materials Science, Yokohama National University, Yokohama 240, Japan
Numerical investigations are carried out to study the steady thermocapillary flow in a half-floating-zone, suspended vertically between two differentially heated disks of circular cross-section. The surface tension driven flow inside the floating zone gets strongly influenced by the flow conditions of the surrounding gas. Computations are carried out over a wide range of Marangoni numbers (Ma) to investigate the flow behavior in the floating zone and surrounding gas and heat transfer at the liquid-gas interface. A comparison of flow and temperature fields within the liquid bridge and the surrounding air under normal and microgravity conditions has been presented. Heating of the confined and unconfined ambient gas is observed to influence the radial and axial temperature gradients at the liquid-gas interface and within the liquid bridge which in turn affects the nature of thermocapillary flow.
Variation of Wall Shear Stress and Flow Characteristics Across Cosine Shaped Stenotic Model with Flow Reynolds Number and Degree of Stenosis
530-552
10.1615/InterJFluidMechRes.v37.i6.30
Moloy Kumar
Banerjee
Department of Mechanical Engineering, Future Institute of Engineering and Management Kolkata, India
Ranjan
Ganguly
Department of Power Engineering, Jadavpur University Kolkata 700098, India
Amitava
Datta
Power Engineering Department, Jadavpur University, Salt Lake Campus, Kolkata 700098, India
A numerical analysis has been carried out to investigate the hemodynamic flow through stenosed arteries having mild (S = 25 %) to severe (S = 65 %) occlusions and under different regimes of flow Reynolds numbers ranging from 50 to 400, considering laminar flow and modeling blood as both Newtonian and non-Newtonian fluid. Reattachment point, wall shear stress, and it's physiological aspects have been studied in detail. From the study, it is revealed that for all the cases a sharp variation in dimensionless wall shear stress (WSS) is observed near the zone of restriction. The maximum value of this peak WSS in the stenosed region is more sensitive to a change in the degree of occlusion rather than change in the flow Re. Atherosclerotic plaque formation tends to start from very low flow Reynolds number of 50 with 50 % restriction. For Reynolds numbers of 200 and above, it starts at 25 % stenosed condition.
Flow and Performance Characteristics of S-Shaped Diffusers
553-566
10.1615/InterJFluidMechRes.v37.i6.40
Mukka
Govardhan
Thermal Turbomachines Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras Chennai, India
Prasad Vijay
Padwad
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India
The present investigation aims to computationally analyse the effect of various geometric parameters on the flow and performance characteristics of S-shaped diffusers. S-shaped diffusers are encountered in various engineering applications such as aircraft intakes, turbomachinary passages, diffusing bends of piping systems. The geometric parameters namely; aspect ratio, area ratio, centerline length and shape of the diffusers are varied in the present computational investigation. Varying centerline length of the diffuser increased the total pressure loss coefficient. Rectangular diffuser with area ratio of four performs better with higher static pressure rise and lower total pressure loss.
Radiation Effects on MHD Combined Convective Flow and Heat Transfer Past a Porous Stretching Surface
567-581
10.1615/InterJFluidMechRes.v37.i6.50
Swati
Mukhopadhyay
Department of Mathematics, The University of Burdwan, India
Gorachand C.
Layek
Department of Mathematics, University of Burdwan Burdwan, West Bengal, India
R.S.R.
Gorla
Department of Mechanical Engineering, Cleveland State University, Cleveland, OH, 44115 USA; Department of Mechanical Engineering, University of Akron, Akron, Ohio 44325, USA; Department of Mechanical & Civil Engineering, Purdue University Northwest, Westville, IN 46391, USA
Heat transfer analysis has been presented for the boundary layer combined convective flow of an electrically conducting liquid due to a porous vertical stretching plate with a power-law stretching velocity in presence of a transverse magnetic field. In the flow region, heat balance is maintained with thermal radiation. The similarity solutions for this problem are obtained by using a special form of Lie group transformations viz. scaling group of transformations. The equations are then solved numerically. With increasing values of the radiation parameter, the streamwise velocity as well as temperature decreases. At a particular point of the porous stretching sheet, the streamwise velocity decreases with the increasing suction parameter. The dimensionless temperature at a point of the sheet decreases due to suction but increases due to injection. With the increase of magnetic field intensity, the fluid velocity decreases but the temperature increases in both cases of suction and blowing. In the absence of magnetic field intensity and suction/ injection, the streamwise velocity displays a velocity maximum within the boundary layer when the stretching velocity power law exponent is negative. The findings of this study reveal that radiation and suction can be used as means of cooling the boundary layer flow region.