6 Time-accurate techniques for turbulent heat transfer analysis in complex geometries

Tafti, Danesh K.

doi:10.2495/978-1-84564-144-3/06

Cited by 16 publications

(9 citation statements)

References 83 publications

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“…The computer program used for these computations has been extensively tested for various applications [24][25][26][27][28]. Detailed information can be found in Tafti et al [25,29,30].…”

Section: P +1^\7<2mentioning

confidence: 99%

Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

Selvarasu

Tafti

2012

Journal of Biomechanical Engineering

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Cardiovascular diseases are the number one cause of death in the world, making the understanding of hemodynamics and the development of treatment options imperative. The effect of motion of the coronary artery due to the motion of the myocardium is not extensively studied. In this work, we focus our investigation on the localized hemodynamic effects of dynamic changes in curvature and torsion. It is our objective to understand and reveal the mechanism by which changes in curvature and torsion contribute towards the observed wall shear stress distribution. Such adverse hemodynamic conditions could have an effect on circumferential intimal thickening. Three-dimensional spatiotemporally resolved computational fluid dynamics (CFD) simulations of pulsatile flow with moving wall boundaries were carried out for a simplified coronary artery with physiologically relevant flow parameters. A model with stationary walls is used as the baseline control case. In order to study the effect of curvature and torsion variation on local hemodynamics, this baseline model is compared to models where the curvature, torsion, and both curvature and torsion change. The simulations provided detailed information regarding the secondary flow dynamics. The results suggest that changes in curvature and torsion cause critical changes in local hemodynamics, namely, altering the local pressure and velocity gradients and secondary flow patterns. The wall shear stress (WSS) varies by a maximum of 22% when the curvature changes, by 3% when the torsion changes, and by 26% when both the curvature and torsion change. The oscillatory shear stress (OSI) varies by a maximum of 24% when the curvature changes, by 4% when the torsion changes, and by 28% when both the curvature and torsion change. We demonstrate that these changes are attributed to the physical mechanism associating the secondary flow patterns to the production of vorticity (vorticity flux) due to the wall movement. The secondary flow patterns and augmented vorticity flux affect the wall shear stresses. As a result, this work reveals how changes in curvature and torsion act to modify the near wall hemodynamics of arteries.

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“…The computer program used for these computations has been extensively tested for various applications [24][25][26][27][28]. Detailed information can be found in Tafti et al [25,29,30].…”

Section: P +1^\7<2mentioning

confidence: 99%

Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

Selvarasu

Tafti

2012

Journal of Biomechanical Engineering

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“…The Reynolds and Prandtl numbers are defined by Re = ρ in U in D h /µ in and Pr = µ in C p in /k in with assumed values of 100,000 and 0.7, respectively. For application in generalized coordinates, Equations (7)-(9) are mapped from physical coordinates ( x ) to logical/computational coordinates ( ξ ) by a boundary conforming transformation x = x ( ξ ) [101].…”

Section: Continuitymentioning

confidence: 99%

“…The momentum, energy, and pressure equations are converged to a residual L 1 norm below 1 × 10 −7 at each time step. More details on the software GenIDLEST used in this study can be found in [42,101,105].…”

Section: Continuitymentioning

confidence: 99%

High Reynold Number LES of a Rotating Two-Pass Ribbed Duct

2018

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Cooling of gas turbine blades is critical to long term durability. Accurate prediction of blade metal temperature is a key component in the design of the cooling system. In this design space, spatial distribution of heat transfer coefficients plays a significant role. Large-Eddy Simulation (LES) has been shown to be a robust method for predicting heat transfer. Because of the high computational cost of LES as Reynolds number (Re) increases, most investigations have been performed at low Re of O(104). In this paper, a two-pass duct with a 180° turn is simulated at Re = 100,000 for a stationary and a rotating duct at Ro = 0.2 and Bo = 0.5. The predicted mean and turbulent statistics compare well with experiments in the highly turbulent flow. Rotation-induced secondary flows have a large effect on heat transfer in the first pass. In the second pass, high turbulence intensities exiting the bend dominate heat transfer. Turbulent intensities are highest with the inclusion of centrifugal buoyancy and increase heat transfer. Centrifugal buoyancy increases the duct averaged heat transfer by 10% over a stationary duct while also reducing friction by 10% due to centrifugal pumping.

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“…The corrector step solves a pressure Poisson equation to satisfy mass continuity [18]. The non-dimensional pressure Poisson equation in generalized coordinates has the following form in GenIDLEST [18],…”

Section: Genidlestmentioning

confidence: 99%

Recycling Krylov subspaces for CFD applications and a new hybrid recycling solver

Amritkar

Sturler

Swirydowicz

et al. 2015

Journal of Computational Physics

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Please cite this article in press as: A. Amritkar et al., Recycling Krylov subspaces for CFD applications and a new hybrid recycling solver, J. Comput. Phys. (2015), http://dx. AbstractWe focus on robust and efficient iterative solvers for the pressure Poisson equation in incompressible Navier-Stokes problems. Preconditioned Krylov subspace methods are popular for these problems, with BiCGStab and GMRES(m) most frequently used for nonsymmetric systems. BiCGStab is popular because it has cheap iterations, but it may fail for stiff problems, especially early on as the initial guess is far from the solution. Restarted GMRES is better, more robust, in this phase, but restarting may lead to very slow convergence. Therefore, we evaluate the rGCROT method for these systems. This method recycles a selected subspace of the search space (called recycle space) after a restart. This generally improves the convergence drastically compared with GMRES(m). Recycling subspaces is also advantageous for subsequent linear systems, if the matrix changes slowly or is constant. However, rGCROT iterations are still expensive in memory and computation time compared with those of BiCGStab. Hence, we propose a new, hybrid approach that combines the cheap iterations of BiCGStab with the robustness of rGCROT. For the first few time steps the algorithm uses rGCROT and builds an effective recycle space, and then it recycles that space in the rBiCGStab solver.We evaluate rGCROT on a turbulent channel flow problem, and we evaluate both rGCROT and the new, hybrid combination of rGCROT and rBiCGStab on a porous medium flow problem. We see substantial performance gains on both problems.

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6 Time-accurate techniques for turbulent heat transfer analysis in complex geometries

Cited by 16 publications

References 83 publications

Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

Investigation of the Effects of Dynamic Change in Curvature and Torsion on Pulsatile Flow in a Helical Tube

High Reynold Number LES of a Rotating Two-Pass Ribbed Duct

Recycling Krylov subspaces for CFD applications and a new hybrid recycling solver

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