NUMERICAL STUDY OF A SWIRLING TURBULENT FLOW THROUGH A CHANNEL WITH AN ABRUBT EXPANSION

2021 ◽  
pp. 93-101
Author(s):  
Z.M. Malikov ◽  
◽  
M.E. Madaliev ◽  
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Swirling Flow ◽  
Numerical Study ◽  
Turbulence Models ◽  
Sudden Expansion ◽  
Stagnation Region ◽  
Spiral Vortex ◽  
Flow Through ◽  
Draft Tubes

A strongly swirling turbulent flow through an abrupt expansion is studied using the highly resolved DNS, LES, and SAS to shed more light on a stagnation region and spiral vortex destruction, though these methods require high computational expenses. The vortex fracture induced by a sudden expansion resembles the so-called vortex rope that occurs in hydropower draft tubes. It is known that large-scale spiral vortex structures can be captured by regular RANS turbulence models. In this paper, a numerical study of a strongly swirling flow, which abruptly expands, is carried out using the Reynolds stress models SSG / LRR-RSM and EARSM with experimental measurements implemented by Dellenback et al. (1988). Calculations are carried out using the finite volume method. The flow dynamics is studied at the Reynolds number of 3.0 × 104 at almost constant large swirl numbers of 0.6. The time-averaged velocity and pressure fields, as well as the root-mean-square values of the velocity fluctuations are recorded and studied qualitatively. The obtained results are compared with known experimental data. The aim of this work is to test the ability of the models to describe anisotropic turbulence. It is shown that the SSG / LRRRSM model is more appropriate for studying such flows.

Assessment of Predictive Capability of Hybrid RANS/LES Turbulence Models for Thermofluid Applications

2021 ◽  
Author(s):  
Anup Zope ◽  
Avery Schemmel ◽  
Xiao Wang ◽  
Shanti Bhushan ◽  
Prashant Singh ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Flow Separation ◽  
Large Scale ◽  
Swirling Flow ◽  
Turbulence Models ◽  
Sudden Expansion ◽  
Oblique Shock Wave ◽  
Detached Eddy Simulation ◽  
Boundary Layer Interaction

Abstract In this study, we have assessed performance of URANS model, various hybrid RANS/LES turbulence models such as detached eddy simulation, Nichols-Nelson HRLES model, dynamic HRLES (DHRL) model, as well as LES for two classes of problems: (a) heat transfer due to subsonic swirling flow subjected to a sudden expansion leading to cylindrical chamber, and (b) flow separation due to oblique shock wave-turbulent boundary layer interaction (STBLI). The results are assessed using the heat transfer characteristics, separation and reattachment characteristics, and capability to predict flow unsteadiness. The study indicates that URANS can predict large scale flow features reasonably well. However, it fails to resolve turbulence. PANS improves TKE prediction, hence, improves heat transfer prediction. Among the hybrid RANS/LES models, DHRL coupled with ILES is capable of providing accurate prediction of flow separation/reattachment characteristics for boundary layer flows. For free-shear dominated flows, implicit LES performs better compared to the explicit LES models.

scholarly journals Effect of Prandtl number on heat transfer characteristics in an axisymmetric sudden expansion: A numerical study

2007 ◽  
Vol 11 (4) ◽  
pp. 171-178
Author(s):  
Khalid Alammar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Numerical Study ◽  
Sudden Expansion ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Simulated Effect

Using the standard k-e turbulence model, an incompressible, axisymmetric turbulent flow with a sudden expansion was simulated. Effect of Prandtl number on heat transfer characteristics downstream of the expansion was investigated. The simulation revealed circulation downstream of the expansion. A secondary circulation (corner eddy) was also predicted. Reattachment was predicted at approximately 10 step heights. Corresponding to Prandtl number of 7.0, a peak Nusselt number 13 times the fully-developed value was predicted. The ratio of peak to fully-developed Nusselt number was shown to decrease with decreasing Prandtl number. Location of maximum Nusselt number was insensitive to Prandtl number.

Flow Patterns Downstream of a Mechanical Heart Valve During Systole

2007 ◽  
Author(s):  
P. Oshkai ◽  
F. Haji-Esmaeili
Keyword(s):  
Turbulent Flow ◽  
Heart Valve ◽  
Large Scale ◽  
Cardiac Cycle ◽  
Mechanical Heart Valve ◽  
Opening Angle ◽  
Image Velocimetry ◽  
Imaging Approach ◽  
Systolic Phase ◽  
Flow Through

Digital particle image velocimetry is employed to study turbulent flow through a bileaflet mechanical heart valve during systolic phase of a cardiac cycle. Unsteady vortex shedding from the valve’s leaflets displays distinct characteristic frequencies, depending on the opening angle of each leaflet. Small- and large-scale transverse oscillations of the separated shear layers are studied using global quantitative flow imaging approach. Turbulent flow structures including jet-like regions and shed vortices are characterized in terms of patterns of instantaneous and time-averaged velocity, vorticity, and turbulence statistics.

Numerical study of turbulent flow over an S-shaped hydrofoil

2008 ◽  
Vol 222 (9) ◽  
pp. 1717-1734 ◽  
Author(s):  
T Micha Prem Kumar ◽  
Dhiman Chatterjee
Keyword(s):  
Shear Stress ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Turbulence Models ◽  
Pressure Gradients ◽  
Convex Surfaces ◽  
Shear Stress Transport ◽  
Formidable Challenge

In this paper, a numerical study of turbulent flow over the S-shaped hydrofoil at 0° angle of attack has been reported. Here, the flow takes place over concave and convex surfaces and is accompanied by the favourable and adverse pressure gradients and flow separation. Modelling such a flow poses a formidable challenge. In the present work four turbulence models, namely, k–∊ realizable, k–ω shear stress transport

Investigation of Inverse-Turbulent-Prandtl Number with Four RNG k-ε Turbulence Models on Compressor Discharge Pipe of Bioenergy Micro Gas Turbine

2016 ◽  
Vol 819 ◽  
pp. 392-400 ◽  
Author(s):  
Ahmad Indra Siswantara ◽  
Budiarso ◽  
Steven Darmawan
Keyword(s):  
Prandtl Number ◽  
Turbulence Model ◽  
Large Scale ◽  
Swirling Flow ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Small Scale ◽  
Turbulent Prandtl Number ◽  
Curved Pipe ◽  
Molecular Viscosity

Inverse-Turbulent Prandtl number (α) is an important parameter in RNG k-ε turbulence models since it affects the ratio of molecular viscosity and turbulent viscosity. In curved pipe, this highly affects the model prediction to a large range eddy-scale flow. According to Yakhot & Orzag, the α range from 1-1.3929 has not been investigated in detail in curved pipe flow (Yakhot & Orszag, 1986) and specific Re. This paper varied inverse-turbulent Prandtl number α to 1-1.3 in RNG k-ε turbulence model on cylindrical curved pipe in order to obtain the optimum value of α to predict unfully-developed flow in the curve with curve ratio R/D of 1.607. Analysis was conducted numericaly with inlet specified Re of 40900 which was generated from the experiment at α 1, 1.1, 1.2, 1.3. Wall surface roughness is not considered in this paper. With assumption that thermal diffusivity is always dominant to turbulent viscosity, higher Inverse-turbulent Prandtl number represent domination of turbulent viscosity to molecular viscosity of the flow and predict to have more interaction between large scale eddy to small scale eddy as well. The results show the use of α = 1.3 has increased the turbulent kinetic energy by 7% and the turbulent dissipation by 5% compared to general inverse-turbulent Prandtl number of 1. The value difference shows that the use of higher α on RNG turbulence model described more interaction between eddies in secondary and swirling flow at pipe curve at Re = 40900.

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