LES and DES of strongly swirling turbulent flow through a suddenly expanding circular pipe

Javadi, Ardalan; Nilsson, Håkan

doi:10.1016/j.compfluid.2014.11.014

Cited by 31 publications

(19 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…They may thus also produce significant electrical power swings. Under circumstances leading to the surge, the swirling flow tends to separate into two concentric flow regions [1]. The axial flow basically occurs in the outer region, while the inner region may contain an on-axis recirculation region, also called stagnation region [2].…”

Section: Introductionmentioning

confidence: 99%

“…The goal has been to understand and control the naturally occurring phenomena. The knowledge can be applied to increase the turbulent convection in heat and mass transfer applications [1], or to reduce unwanted pressure pulsations in e.g. hydro power [2].…”

Section: Introductionmentioning

confidence: 99%

“…If these prerequisites are not fulfilled, IDDES acts like a regular DDES. Javadi and Nilsson [1] reported that the IDDES does not act like DDES in highly swirling flows even if the inflow does not contain any turbulence. Since there is a remarkable level of turbulence production in highly swirling flows, the simulation is independent of applying turbulence fluctuations at the inlet boundary.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

Javadi

Nilsson

2015

Flow Turbulence Combust

Self Cite

View full text Add to dashboard Cite

A series of numerical simulations is undertaken to study a highly swirling turbulent flow generated by rotor-stator interaction in a swirl generator. The purpose is to assess the applicability of different turbulence models in swirling flow with a high level of unsteadiness and a significant production and dissipation of turbulence in the flow away from the wall. Nine turbulence models are compared: four high-Reynolds URANS, two low-Reynolds URANS and three hybrid URANS-LES. These are the standard k − , SST k − ω, realizable k − , RNG k − , Launder-Sharma k − , Lien-Cubic k − , delayed DES Spalart-Allmaras, DDES SST k − ω and improved DDES-SA. The URANS models are capable of capturing the main unsteady feature of this flow, the so-called helical vortex rope, which is formed by the strong centrifugal force and an on-axis recirculation region. However, the size of the on-axis recirculation region is overestimated by the URANS models. Although the low-Reynolds URANS formulations resolve the boundary layers in the runner and the draft tube more accurately, they still encounter difficulties in predicting the main flow features in the adverse pressure gradient in the draft tube. It is shown that a more detailed resolution, which is provided by the hybrid URANS-LES methods, is necessary to capture the turbulence and the coherent structures. The flow contains a strong disintegration of the vortex rope which is predicted well by the hybrid RANS-LES models. The hybrid methods also capture the blade wakes better than the other models, elucidating the wake interaction with the vortex rope. The frequency of the vortex rope is predicted well and the total turbulence (resolved and modeled), suggested by DDES-SA, corresponds reasonably well to the experimental results.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

Javadi

Nilsson

2015

Flow Turbulence Combust

Self Cite

View full text Add to dashboard Cite

show abstract

“…The precession happens far from the wall effects, and thus the DDES method is an applicable approach for highly swirling flows (Javadi & Nilsson, 2015a). Javadi and Nilsson (2015b) showed that the DDES method is still sensitive to wall-parallel grid spacing and, in the case of coarse spacing, the method does not switch to the LES mode at all. Wunderer and Schilling (2008) used DES to study active flow control in hydro turbines.…”

Section: Introductionmentioning

confidence: 99%

“…Javadi and Nilsson (2014a) studied the Scale-Adaptive Simulation (SAS) (Menter & Egorov, 2010) approach in highly swirling flows and reported that the approach predicts the massively separated swirling flows very well. Detached-Eddy Simulation (DES) (Spalart, Jou, Strelets, & Allmaras, 1997) is another promising hybrid URANS-LES strategy which is studied for application to swirling flows (Javadi & Nilsson, 2015a, 2015bJavadi et al, 2016). The Delayed DES (DDES) methodology was proposed by Spalart et al (2006) to identify the boundary layer thickness and to extend the URANS mode compared to that of the initially proposed DES methodology.…”

Section: Introductionmentioning

confidence: 99%

Active flow control of the vortex rope and pressure pulsations in a swirl generator

Javadi

Nilsson

2016

Engineering Applications of Computational Fluid Mechanics

Self Cite

View full text Add to dashboard Cite

The vortex rope and pressure pulsations caused by a radial pressure gradient in the conical diffuser of a swirl generator is controlled using continuous slot jets with different momentum fluxes and angles injected from the runner crown. The swirl apparatus is designed to generate flows similar to those in the different operating conditions of a Francis turbine. The study is done with numerical modelling using the hybrid URANS-LES (Unsteady Reynolds-Averaged Navier-Stokes-Large Eddy Simulation) method with the rotor-stator interaction. The comprehensive studies of Javadi and Nilsson [Time-accurate numerical simulations of swirling flow with rotor-stator interaction. Flow, Turbulence and Combustion, Vol. 95,, and Javadi, Bosioc, Nilsson, Muntean and Susan-Resiga [Experimental and numerical investigation of the precessing helical vortex in a conical diffuser, with rotor-stator interaction. ASME Journal of Fluids Engineering, doi:10.1115/1.4033416] are considered as the bench mark, and the capabilities of the technique is studied in the present work with the validated numerical results presented in those studies. The pressure pulsations caused by the pressure gradient generated by the swirl, present at off-design conditions, are cumbersome for hydropower structures. The investigation shows that the pressure pulsation, velocity fluctuations and the size of the vortex rope decrease when the jet is injected from the runner crown. The flow rate of the jet is less than 3% of the flow rate of the swirl generator. The momentum flux, angle of injection of the jet and the position of the slot are important factors for the effectiveness of the flow control technique. ARTICLE HISTORY

show abstract

Numerical study of an impinging jet in cross-flow within and without influence of vortex generator structures on heat transfer

Javadi

2019

Heat Mass Transfer

View full text Add to dashboard Cite

LES and DES of strongly swirling turbulent flow through a suddenly expanding circular pipe

Cited by 31 publications

References 33 publications

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

Time-accurate Numerical Simulations of Swirling Flow with Rotor-stator Interaction

Active flow control of the vortex rope and pressure pulsations in a swirl generator

Numerical study of an impinging jet in cross-flow within and without influence of vortex generator structures on heat transfer

Contact Info

Product

Resources

About