Loss Characteristics of Orifices and Nozzles

1978 ◽  
Vol 100 (3) ◽  
pp. 299-307 ◽  
Author(s):  
S. H. Alvi ◽  
K. Sridharan ◽  
N. S. Lakshmana Rao
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Discharge Coefficient ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Center Line ◽  
Laminar Regime ◽  
Variation Of Parameters ◽  
Turbulent Flow Regime

Loss characteristics of sharp-edged orifices, quadrant-edged orifices for varying edge radii, and nozzles are studied for Reynolds numbers less than 10,000 for β ratios from 0.2 to 0.8. The results may be reliably extrapolated to higher Reynolds numbers. Presentation of losses as a percentage of meter pressure differential shows that the flow can be identified into fully laminar regime, critical Reynolds number regime, relaminarization regime, and turbulent flow regime. An integrated picture of variation of parameters such as discharge coefficient, loss coefficient, settling length, pressure recovery length, and center line velocity confirms this classification.

Effects of the Divergence Angle on the Onset of Asymmetric Flow Through a Planar Diffuser

2009 ◽  
Author(s):  
Majid Nabavi ◽  
Luc Mongeau
Keyword(s):  
Reynolds Number ◽  
Flow Regime ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Asymmetric Flow ◽  
Symmetric Flow ◽  
Turbulent Flow Regime ◽  
Flow Through ◽  
Gradual Expansion

In this study, two-dimensional laminar incompressible and turbulent compressible flow through the planar diffuser (gradual expansion) for different divergence half angles of the diffuser (θ), and different Reynolds numbers (Re) was numerically studied. The effects of θ on the critical Reynolds number at which the onset of asymmetric flow is observed, were investigated. In the laminar flow regime, it was observed that for every values of θ, there is a critical Re beyond which the flow is asymmetric. However, in the turbulent flow regime, for θ ≥ 20°, even at low Reynolds number the flow is asymmetric. Only for θ ≤ 10°, symmetric flow was observed below a critical Re.

Computerized Model of Transition in Circular Pipe Flows: Part 1 — Experimental Definition of the Problem

1999 ◽  
Author(s):  
Hidesada Kanda
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Critical Reynolds Number ◽  
Natural Disturbance ◽  
Reynolds Numbers ◽  
Entrance Region ◽  
Circular Pipe ◽  
Experimental Investigations ◽  
Circular Pipes ◽  
Definition Of

Abstract A conceptual model was constructed for the problem of determining in circular pipes the conditions under which the transition from laminar to turbulent flow occurs, so that it becomes possible to calculate the minimum critical Reynolds number. Up until now this problem has been investigated by stability theory with disturbances at the pipe inlet. However, the minimum critical Reynolds number has not yet been obtained theoretically. Hence, the author took up the problem directly from many previous experimental investigations and found that (i) plots of the transition length versus the Reynolds number show that the transition occurs in the entrance region under the condition of a natural disturbance, and (ii) plots of the critical Reynolds number versus the ratio of bellmouth diameter to the pipe diamter show that with larger shapes of bellmouths, laminar flow will persist to higher Reynolds numbers. The problem is thus defined clearly as: Under the condition of an ordinary disturbance, the transition from laminar to turbulent flow occurs in the entrance region of a straight circular pipe, then the Reynolds number takes a minimum value of about 2000.

scholarly journals Numerical analysis of a leading edge tubercle hydrofoil in turbulent regime

2019 ◽  
Vol 878 ◽  
pp. 292-305 ◽  
Author(s):  
Blanca Pena ◽  
Ema Muk-Pavic ◽  
Giles Thomas ◽  
Patrick Fitzsimmons
Keyword(s):  
Numerical Analysis ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Main Flow ◽  
Hydrodynamic Performance ◽  
Turbulent Regime ◽  
Transitional Regime ◽  
Turbulent Flow Regime

This paper presents a numerical performance evaluation of the leading edge tubercles hydrofoil with particular focus on a fully turbulent flow regime. Efforts were focused on the setting up of an appropriate numerical approach required for an in-depth analysis of this phenomenon, being able to predict the main flow features and the hydrodynamic performance of the foil when operating at high Reynolds numbers. The numerical analysis was conducted using an improved delayed detached eddy simulation for Reynolds numbers corresponding to the transitional and fully turbulent flow regimes at different angles of attack for the pre-stall and post-stall regimes. The results show that tubercles operating in turbulent flow improve the hydrodynamic performance of the foil when compared to a transitional flow regime. Flow separation was identified behind the tubercle troughs, but was significantly reduced when operating in a turbulent regime and for which we have identified the main flow mechanisms. This finding confirms that the tubercle effect identified in a transitional regime is not lost in a turbulent flow. Furthermore, when the hydrofoil operates in the turbulent flow regime, the transition to a turbulent regime takes place further upstream. This phenomenon suppresses a formation of a laminar separation bubble and therefore the hydrofoil exhibits a superior hydrodynamic performance when compared to the same foil in the transitional regime.

Enhanced Heat Transfer Through the Use of Nanofluids in Forced Convection

2004 ◽  
Author(s):  
Daniel J. Faulkner ◽  
David R. Rector ◽  
Justin J. Davidson ◽  
Reza Shekarriz
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Forced Convection ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Enhanced Heat Transfer ◽  
Low Reynolds Numbers ◽  
Turbulent Flow Regime

Much attention has been paid in recent years to the use of nanoparticle suspensions for enhanced heat transfer. The majority of this work has focused on the thermal conductivity of these nanofluids, which can be as much as 2.5 times higher than that of the plain base fluid. The present work moves beyond measurements of non-flowing liquids, to explore the role that nanofluids can play in enhancing convective heat transfer within microscale channels. A unique pseudo-turbulent flow regime is postulated, which simulates turbulent behavior at very low Reynolds numbers, in what are nominally laminar flows. The resulting fluid mixing has the potential to raise the average convective heat transfer coefficient within the channel. Numerical modeling, using the lattice Boltzmann method, confirms the existence of the pseudo-turbulent flow regime. Finally, experimental results are presented which demonstrate a significant heat transfer enhancement when using nanofluids in forced convection. The current results are especially relevant to microchannel heatsinks, where the low Reynolds numbers impose limitations on the maximum Nusselt number achievable.

Analysis of Aerothermal Characteristics of Surface Micro-Structures

2017 ◽  
Author(s):  
M. Kapsis ◽  
L. He
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Computational Study ◽  
Number Range ◽  
High Loss ◽  
Turbulent Flow Regime ◽  
Roughness Elements ◽  
Element Pattern ◽  
Micro Structures

Recent advances in manufacturing technologies, such as additive manufacturing, have raised the potential of choosing surface finish pattern as a design parameter. Hence, understanding and prediction of aerothermal effects of machined micro-structures (‘machined roughness’) would be of great interest. So far, however, roughness has been largely considered as a stochastic attribute and empirically modelled. A relevant question is: if and how would shape of the machined roughness elements matter at such fine scales? In this paper, a systematic computational study has been carried out on the aerothermal behaviour and impact of some discrete micro-structures. Two shapes of micro-structure configurations are considered: hemispherical and rectangular elements for a Reynolds number range typical for those roughness elements (Re<5000). Several validation cases are studied as well as the turbulence modelling and grid sensitivities are examined to ensure the consistence of the numerical results. Furthermore, LES analyses are performed to contrast the behaviour in a well-established turbulent flow regime to a transitional one. The present results reveal a distinctive common flow pattern change (from an ‘open separation’ to a ‘reattached separation’) associated with a drastic change of drag/loss correlation from a low to a high loss regime. The results also indicate a clear dependence of drag and heat transfer characteristics on the element pattern and orientation relative to the flow. The distinctive performance correlations with Reynolds number can be affected considerably by the element shape, for both a transitional and a turbulent flow regime. The results also consistently illustrate that conventional empirical stochastic roughness parameters would be unable to predict these trends.

Flow Through a Finite Packed Bed of Spheres: A Note on the Limit of Applicability of the Forchheimer-Type Equation

2004 ◽  
Vol 126 (1) ◽  
pp. 139-143 ◽  
Author(s):  
Agne`s Montillet
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Fluid Velocity ◽  
Type Equation ◽  
Packed Bed ◽  
Turbulent Flow Regime ◽  
Fully Developed Turbulent Flow ◽  
Flow Through

The variation of the pressure drop measured as a function of the fluid velocity through a packed bed of spheres is presented and discussed in the range of particle Reynolds number 30–1500. Based on previous studies, the observed limit of validity of the so-called Forchheimer law may be attributed to the concomitant effects of the finite character of the tested bed and of the transition of flow regime which is marking the beginning of the fully developed turbulent flow regime. The limit of validity of the Forchheimer-type law was formerly noticed by several authors.

Thermal performance analysis of plate fin arrays with hexagonal perforations under turbulent flow regime

2019 ◽  
Author(s):  
Imtiaz Taimoor ◽  
Md Lutfor Rahman ◽  
Nazneen Sultana Aankhy ◽  
Muzahid Bin Khalid
Keyword(s):  
Performance Analysis ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Thermal Performance ◽  
Turbulent Flow Regime

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

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