NUMERICAL STUDY OF EFFECTS OF PULSATILE AMPLITUDE ON UNSTEADY LAMINAR FLOWS IN RIGID PIPE WITH RING-TYPE CONSTRICTIONS

1997 ◽  
Vol 24 (3) ◽  
pp. 275-290 ◽  
Author(s):  
T. S. Lee ◽  
T. W. Ng ◽  
Z. D. Shi
Keyword(s):  
Numerical Study ◽  
Laminar Flows ◽  
Ring Type

Numerical study of a turbulent separation bubble with sweep

2019 ◽  
Vol 880 ◽  
pp. 684-706
Author(s):  
G. N. Coleman ◽  
C. L. Rumsey ◽  
P. R. Spalart
Keyword(s):  
Pressure Gradient ◽  
Numerical Study ◽  
Separation Bubble ◽  
Laminar Flows ◽  
Swept Wing ◽  
Mean Velocity ◽  
Independence Principle ◽  
Velocity Magnitude ◽  
Turbulent Separation ◽  
Swept Wings

Direct numerical simulation (DNS) is used to study a separated and rapidly reattached turbulent boundary layer over an idealized $35^{\circ }$ infinite swept wing. The separation and reattachment are induced by a transpiration profile at fixed distance above the layer, with the pressure gradient applied to a well-defined, fully developed, zero-pressure-gradient (ZPG) collateral state. To isolate the influence of the sweep, results are compared with one of our earlier DNS of an unswept flow, with the same chordwise transpiration distribution and appropriate upstream momentum thickness. The independence principle (IP) traditionally proposed for swept wings, which is exact for laminar flows, is found to be close to valid in some regions (bridging the separation/reattachment zone) and to fail in others (in the ZPG layers upstream and downstream of the separation). This is assessed primarily through the skin friction and integral thicknesses. The regions in which the IP is approximately valid correspond to regions of diminished Reynolds-stress divergence, compared to the pressure-gradient magnitude. The mean-velocity profiles exhibit significant skewing as the flow develops, while the velocity magnitude departs only slightly from the ZPG logarithmic profile, even above the separation zone. Implications for Reynolds-averaged turbulence modelling are discussed.

Heat Transfer in Fully-Developed, Laminar Flows of Dissipative Pseudoplastic and Dilatant Fluids in Circular Conduits

2020 ◽  
Author(s):  
Massimo Capobianchi ◽  
Richard Cangelosi ◽  
Patrick McGah
Keyword(s):  
Shear Rate ◽  
Flow Curve ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Laminar Flows ◽  
Rate Parameter ◽  
Constant Heat ◽  
Shear Rates ◽  
Nusselt Numbers ◽  
Entire Flow

Abstract This paper reports the results of a numerical study that determined the Nusselt number for hydrodynamically and thermally fully-developed, laminar, dissipative flows of pseudoplastic and dilatant fluids through circular conduits. Two boundary conditions were considered, constant heat flux and constant temperature. Constitutive equations were used that describe the entire flow curve, from the zero-shear rate through the infinite-shear rate Newtonian regions, so that computed Nusselt numbers are valid for whatever shear rates may exist in the flow field. Nusselt numbers are reported as a function of a dimensionless shear rate parameter that establishes the region of the flow curve where the system is operating, and are shown to be bound by the Newtonian and power law values. The conditions required for the system to perform at these asymptotic limits are quantified.

Effect of Periodic Pulsations on Heat Transfer in Simultaneously Developing Laminar Flows: A Numerical Study

2010 ◽  
Author(s):  
Balkrishna Mehta ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Amplitude Ratio ◽  
Numerical Study ◽  
Transport Coefficients ◽  
Internal Flow ◽  
Laminar Flows ◽  
Operating Conditions ◽  
Parallel Plates ◽  
Species Transport ◽  
Unidirectional Flow

Heat transfer in the channels and ducts are well understood in the steady laminar flows for engineering applications. In contrast, unsteady flows have potential for research as many aspects of such flows are still unclear. Periodic pulsating flow in a channel is a kind of unsteady flow which requires further investigation because (i) many upcoming applications, especially in mini-micro scale engineering domain e.g. enhanced mixing, MEMS applications, bio-fluidic devices and thermal management of electronics etc. (ii) critical review of literature reveals that there is prevailing confusion related to the species transport coefficients. Thus, need for a systematic parametric study, both numerical and experimental, cannot be overemphasized. In this paper, two different configurations of laminar pulsatile internal flow, i.e. Case (i): unidirectional flow with axial superimposed pulsations (flow in circular axisymmetric tube) and, Case (ii) unidirectional flow with superimposed transverse pulsations (parallel plates) have been numerically scrutinized. Effect of frequency (Womersley number, Wo), Prandtl number (Pr), Reynolds number (Re) and amplitude ratio, on the instantaneous and time averaged heat transfer and friction factor (Poiseuille number) is studied. It is found that the change in species transport is either marginal or highly limited and is primarily occurring in the developing length of the channel/ plate. Nusselt number under pulsating conditions in the fully developed flow regime is not very different from its steady counterpart. Enhancement of species transport due to such periodic pulsatile internal flows, over and above the non-pulsatile regular flow conditions, is questionable, and at best, rather limited. Enhancement in heat transfer is seen in Case (ii) under certain operating conditions. This latter configuration is more attractive than the former and further optimization studies are required to improve understanding.

Numerical study of natural convection in an enclosure with localized heating from below—creeping flow to the onset of laminar instability

1969 ◽  
Vol 36 (1) ◽  
pp. 33-54 ◽  
Author(s):  
K. E. Torrance ◽  
J. A. Rockett
Keyword(s):  
Natural Convection ◽  
Numerical Study ◽  
Theoretical Calculations ◽  
Hot Spot ◽  
Boussinesq Approximation ◽  
Companion Paper ◽  
Laminar Flows ◽  
Creeping Flow ◽  
Initial Flow ◽  
Transfer Rates

An analytical study was made of the natural convection induced in an enclosure by a small hot spot centrally located on the floor. The enclosure was a circular cylinder, vertically oriented, with height equal to radius. A Prandtl number of 0.7 (air) was assumed; the Grashof number (Gr) was based on cylinder height and hot spot temperature. The equations of fluid flow in axisymmetric cylindrical co-ordinates were simplified with the Boussinesq approximation. The equations were solved numerically with a computationally stable, explicit method. The computation, starting from quiescent conditions, proceeded through the initial transient to the fully developed flow. Solutions were obtained for Gr from 4 × 104 to 4 × 1010. The theoretical flows are in excellent agreement with experimentally observed laminar flows (Gr [lsim ] 1.2 × 109) which are discussed in a companion paper, Torrance, Orloff & Rockett (1969). Turbulence was observed experimentally for Gr [gsim ] 1.2 × 109. When the theoretical calculations were extended to Gr = 4 × 1010, a periodic vortex shedding developed, suggestive of the onset of laminar instability. The theoretical results reveal a √Gr scaling for the initial flow transients and, at large Gr, the velocities and heat transfer rates.

A numerical study of fully developed laminar flows in pipes with two planar curvatures

2006 ◽  
Vol 51 (8) ◽  
pp. 849-879 ◽  
Author(s):  
C. Niewiadomski ◽  
M. Paraschivoiu ◽  
P. Sullivan
Keyword(s):  
Numerical Study ◽  
Laminar Flows

scholarly journals Geometrical investigation of microchannel with two trapezoidal blocks subjected to laminar convective flows with and without boiling

2022 ◽  
Vol 3 (1) ◽  
pp. 20-36
Author(s):  
Bruno Costa Feijó ◽  
◽  
Ana Pavlovic ◽  
Luiz Alberto Oliveira Rocha ◽  
Liércio André Isoldi ◽  
...  
Keyword(s):  
Numerical Study ◽  
Thermal Conditions ◽  
Reynolds Numbers ◽  
Laminar Flows ◽  
Cooling Power ◽  
Constructal Design ◽  
Boiling Process ◽  
Multi Phase ◽  
Power Generation Systems ◽  
Optimal Configurations

Microchannels are important devices to improve the heat exchange in several engineering applications as heat, ventilation and air conditioning, microelectronic cooling, power generation systems and others. The present work performs a numerical study of a microchannel with two trapezoidal blocks subjected to laminar flows, aiming to analyze the influence of the boiling process on the geometric configuration of the microchannel. Constructal Design and Exhaustive Search are used for the geometrical evaluation of the blocks. The Mixture multi-phase model and the Lee phase change model were both employed for the numerical simulation of the boiling process. In this study, the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate and pressure drop for different magnitudes of the ratio between the lower width and higher width (L12/L11) was investigated. It is considered water in monophase cases and water/vapor mixture for multiphase flow. Two different Reynolds numbers (ReH = 0.1 and 10.0) were investigated. Results indicated that, for the present thermal conditions, the consideration of boiling flows were not significant for prediction of optimal configurations. Results also showed that in the cases where the boiling process was enabled, the multi-objective performance was higher than in the cases without boiling, especially for ReH = 0.1.

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