LES and Hybrid RANS-LES Simulation of a Pulsating Channel Flow

Abstract

Simulation of turbulent boundary layers for flows characterized by unsteady driving conditions is important for solving complicated engineering problems such as combustion, blood flow in stenosed arteries, and flow over immersed structures. These flows are often dominated by complex vortical structures, regions of varying turbulence intensities, and fluctuating pressure fields. Pulsating channel flow is one such case that presents a unique set of challenges for newly developed and existing turbulence models used in computational fluid dynamics (CFD) solvers. In the present study, performance of the dynamic hybrid RANS-LES model (DHRL) with exponential time averaging (ETA) is evaluated against Monotonically Integrated Large Eddy Simulation (MILES) and a previously documented LES study for a fully developed channel flow with a time-periodic driving pressure gradient. Results indicate that MILES over predicts mean streamwise velocity for all forcing frequencies while the DHRL model with ETA provides a method for improved results, especially for the lower frequencies. It is concluded that a hybrid RANS-LES model with ETA is a useful alternative to simulate unsteady non-stationary flows but further work is needed to determine the appropriate filter width for ETA to significantly improve the predictive capabilities of the DHRL model.

Pulsatile Flow Interaction between Aorta and Pulmonary Artery

“…The design of the PDA stent that persuades turbulence is to be important in stent development. The previous study had only carried out steady flow analysis, revealing velocity contours in the PDA system (9,(14)(15)(16). This study had analyzed the transient flow characteristics and vortices formation and dissipation characteristics in the aorta-pulmonary artery system.…”

Improving flow efficiency in curved pipes during multi-phase, immiscible fluid flow using edge-tailored guide vanes

“…The improved delayed detached-eddy simulation (IDDES) method is implemented to resolve turbulence closure. The model solves the conservation equation for each phase, independently making it suitable for most Newtonian flows (Jamal et al, 2018). The momentum equation which describes the transport behavior of a fluid (crude oil or water) is shown in Eq.…”

“…This term is given the name eddy viscosity. Theoretically, this term obtains a numerical value appropriate for a modeled Reynolds stress at the RANS near the wall region and does the same for a modeled subgrid stress far from the wall (Jamal et al, 2018). Moreover, studies have proven that combining the effect of spatially filtered and ensemble-averaged velocity fields with the aid of a single scalar variable introduces major discrepancy into the modeling process.…”

“…( 5), both the first and second terms at the right can be linearized as functions of the subgrid stress (SGS) and ensembled-averaged in that order. These stress terms are derivable from SGS and RANS models, respectively (Jamal et al, 2018). The terms α and β represent proportionality constant, which may be constant or vary.…”

“…Regions with no resolved fluctuations have a value of 1, which is a steady-state condition. Here, pure RANS modeling is achieved (Jamal et al, 2018). However, in areas at which the velocity fluctuations are resolved, α value is increased to 1.…”