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Evaluation of RANS models in predicting low reynolds, free, turbulent round jet
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Department of Management and Engineering, Linköping University.ORCID iD: 0000-0003-3472-4210
2014 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, Vol. 136, no 1, 011201Article in journal (Refereed) Published
##### Abstract [en]

In order to study the flow behavior of multiple jets, numerical prediction of the three-dimensional domain of round jets from the nozzle edge up to the turbulent region is essential. The previous numerical studies on the round jet are limited to either two-dimensional investigation with Reynolds-averaged Navier-Stokes (RANS) models or three-dimensional prediction with higher turbulence models such as large eddy simulation (LES) or direct numerical simulation (DNS). The present study tries to evaluate different RANS turbulence models in the three-dimensional simulation of the whole domain of an isothermal, low Re (Re = 2125, 3461, and 4555), free, turbulent round jet. For this evaluation the simulation results from two two-equation (low Re k-ε and low Re shear stress transport (SST) k-ω), a transition three-equation (k-kl-ω), and a transition four-equation (SST) eddy-viscosity turbulence models are compared with hot-wire anemometry measurements. Due to the importance of providing correct inlet boundary conditions, the inlet velocity profile, the turbulent kinetic energy (k), and its specific dissipation rate (ω) at the nozzle exit have been employed from an earlier verified numerical simulation. Two-equation RANS models with low Reynolds correction can predict the whole domain (initial, transition, and fully developed regions) of the round jet with prescribed inlet boundary conditions. The transition models could only reach to a good agreement with the measured mean axial velocities and its rms in the initial region. It worth mentioning that the round jet anomaly is still present in the turbulent region of the round jet predicted by the low Re k-ε. By comparing the k and the ω predicted by different turbulence models, the blending functions in the cross-diffusion term is found one of the reasons behind the more consistent prediction by the low Re SST k-ω.

##### Place, publisher, year, edition, pages
2014. Vol. 136, no 1, 011201
##### Keyword [en]
Hot-wire anemometry, Low Reynolds, RANS models, Round jet, SST k-ω, Reynolds-Averaged Navier-Stokes, Round jets, Specific dissipation rate, Three dimensional simulations, Three-dimensional predictions, Anemometers, Blending, Boundary conditions, Computational fluid dynamics, Forecasting, Kinetics, Large eddy simulation, Nozzles, Three dimensional, Turbulence models, Wakes, Wire, Navier Stokes equations
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
ISI: 000327511000009ScopusID: 2-s2.0-84888105847OAI: oai:DiVA.org:hig-18462DiVA: diva2:770211
Available from: 2014-12-10 Created: 2014-12-10 Last updated: 2017-01-03Bibliographically approved
##### In thesis
1. Near-Field Study of Multiple Interacting Jets: Confluent Jets
Open this publication in new window or tab >>Near-Field Study of Multiple Interacting Jets: Confluent Jets
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
##### Abstract [en]

This thesis deals with the near-field of confluent jets, which can be of interest in many engineering applications such as design of a ventilation supply device. The physical effect of interaction between multiple closely spaced jets is studied using experimental and numerical methods. The primary aim of this study is to explore a better understanding of flow and turbulence behavior of multiple interacting jets. The main goal is to gain an insight into the confluence of jets occurring in the near-field of multiple interacting jets.

The array of multiple interacting jets is studied when they are placed on a flat and a curved surface. To obtain the boundary conditions at the nozzle exits of the confluent jets on a curved surface, the results of numerical prediction of a cylindrical air supply device using two turbulence models (realizable $\kappa$$\epsilon$ and Reynolds stress model) are validated with hot-wire anemometry (HWA) near different nozzles discharge in the array. A single round jet is then studied to find the appropriate turbulence models for the prediction of the three-dimensional flow field and to gain an understanding of the effect of the boundary conditions predicted at the nozzle inlet. In comparison with HWA measurements, the turbulence models with low Reynolds correction ($\kappa$ − $\epsilon$ and shear stress transport [SST] $\kappa$ − $\omega$) give reasonable flow predictions for the single round jet with the prescribed inlet boundary conditions, while the transition models ($\kappa$$\kappa$$\iota$ − $\omega$ and transition SST $\kappa$$\omega$) are unable to predict the flow in the turbulent region. The results of numerical prediction (low Reynolds SST $\kappa$$\omega$model) using the prescribed inlet boundary conditions agree well with the HWA measurement in the nearfield of confluent jets on a curved surface, except in the merging region.

Instantaneous velocity measurements are performed by laser Doppler anemometry (LDA) and particle image velocimetry (PIV) in two different configurations, a single row of parallel coplanar jets and an inline array of jets on a flat surface. The results of LDA and PIV are compared, which exhibit good agreement except near the nozzle exits.

The streamwise velocity profile of the jets in the initial region shows a saddle back shape with attenuated turbulence in the core region and two off-centered narrow peaks. When confluent jets issue from an array of closely spaced nozzles, they may converge, merge, and combine after a certain distance downstream of the nozzle edge. The deflection plays a salient role for the multiple interacting jets (except in the single row configuration), where all the jets are converged towards the center of the array. The jet position, such as central, side and corner jets, significantly influences the development features of the jets, such as velocity decay and lateral displacement. The flow field of confluent jets exhibits asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. The velocity decays slower in the combined regio  of confluent jets than a single jet. Using the response surface methodology, the correlations between characteristic points (merging and combined points) and the statistically significant terms of the three design factors (inlet velocity, spacing between the nozzles and diameter of the nozzles) are determined for the single row of coplanar parallel jets. The computational parametric study of the single row configuration shows that spacing has the greatest impact on the near-field characteristics.

##### Series
, Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1639
##### Keyword
Multiple interacting jets, confluent jets, axisymmetric/round jet, Low Reynolds number jet, Particle Image Velocimetry (PIV), Laser Doppler Anemometry (LDA), Hot-Wire anemometry (HWA), RANS turbulence models, SST −, Low Reynolds −, Response Surface Method
##### National Category
Fluid Mechanics and Acoustics
##### Identifiers
urn:nbn:se:hig:diva-18837 (URN)978-91-7519-161-4 (print) (ISBN)
##### Public defence
2015-02-06, C3, C-huset, Campus Valla, Linköping, 10:15 (English)
##### Supervisors
Available from: 2015-01-23 Created: 2015-01-23 Last updated: 2017-01-03Bibliographically approved

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Ghahremanian, ShahriarMoshfegh, Bahram
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