Evaluation of PANS Methodology With Nonlinear Eddy Viscosity Closure: Flow Past a Heated Sphere

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Sagar Saroha ◽  
Krishnendu Chakraborty ◽  
Sawan S. Sinha ◽  
Sunil Lakshmipathy
Keyword(s):  
Eddy Viscosity ◽  
Thermal Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow Past ◽  
Large Eddy ◽  
Reynolds Averaging ◽  
Better Than ◽  
Flow Past A Sphere

Abstract The partially averaged Navier–Stokes (PANS) approach has emerged as a viable scale-resolving bridging method over the last decade. Conventional PANS method, based on the linear eddy viscosity closure, overcomes the scale-resolving inadequacies of Reynolds-averaging but still suffers from limitations arising from linear constitutive modeling of turbulent stresses. Linear PANS has been evaluated in a variety of complex flow fields, including the benchmark case of flow around a sphere. In this work, the authors assess the potential of nonlinear eddy viscosity closure and further extend the evaluation of nonlinear closure in predicting thermal characteristics (besides hydrodynamics) of flow past a sphere. The presented evaluation has been performed on the basis of various surface-related and wake-related quantities. Our results are compared against available experimental and direct numerical simulation (DNS)/large eddy simulation studies. Our study shows that for the same value of the filter-control parameters, nonlinear PANS performs significantly better than linear PANS.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Current Capabilities of DES and LES for Submarines at Straight Course

2010 ◽  
Vol 54 (03) ◽  
pp. 184-196 ◽  
Author(s):  
N. Alin ◽  
R.E. Bensow ◽  
C. Fureby ◽  
T. Huuva ◽  
U. Svennberg
Keyword(s):  
Statistical Moments ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
First Order ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Actuator Disc ◽  
Rans Models ◽  
Coarse Grids

The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both "towed" and "self-propelled" conditions, where as for the bare hull, only a "towed" condition is considered. For the AFF1 and the "towed" AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.

Numerical study of transonic cavity flows using large-eddy and detached-eddy simulation

2007 ◽  
Vol 111 (1117) ◽  
pp. 153-164 ◽  
Author(s):  
P. Nayyar ◽  
G. N. Barakos ◽  
K. J. Badcock
Keyword(s):  
Energy Content ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Promising Alternative ◽  
Eddy Simulation ◽  
Massively Separated Flows ◽  
Large Eddy

Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0·85 and 6·783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.

scholarly journals Assessments ofk-kLTurbulence Model Based on Menter’s Modification to Rotta’s Two-Equation Model

2015 ◽  
Vol 2015 ◽  
pp. 1-18 ◽  
Author(s):  
Khaled S. Abdol-Hamid
Keyword(s):  
Turbulence Model ◽  
Equation Model ◽  
Navier Stokes ◽  
Length Scale ◽  
Turbulent Length Scale ◽  
Eddy Simulation ◽  
Grid Convergence ◽  
Large Eddy ◽  
Natural Inclusion ◽  
Better Than

The main objective of this paper is to construct a turbulence model with a more reliable second equation simulating length scale. In the present paper, we assess the length scale equation based on Menter’s modification to Rotta’s two-equation model. Rotta shows that a reliable second equation can be formed in an exact transport equation from the turbulent length scale and kinetic energy. Rotta’s equation is well suited for a term-by-term modeling and shows some interesting features compared to other approaches. The most important difference is that the formulation leads to a natural inclusion of higher order velocity derivatives into the source terms of the scale equation, which has the potential to enhance the capability of Reynolds-averaged Navier-Stokes to simulate unsteady flows. The model is implemented in the CFD solver with complete formulation, usage methodology, and validation examples to demonstrate its capabilities. The detailed studies include grid convergence. Near-wall and shear flows cases are documented and compared with experimental and large eddy simulation data. The results from this formulation are as good or better than the well-known shear stress turbulence model and much better thank-εresults. Overall, the study provides useful insights into the model capability in predicting attached and separated flows.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Siniša Krajnović ◽  
Per Ringqvist ◽  
Branislav Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Better Than ◽  
Good Agreement ◽  
Near Wall

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Tom Hickling ◽  
Li He
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Systematic Investigation ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Detached Eddy Simulation ◽  
Bulk Fluid ◽  
Eddy Simulation ◽  
Rotating Cavity ◽  
Large Eddy

Abstract Across the open literature, there is no clear consensus on what the most suitable modeling fidelity is for rotating cavity flows. Although it is a widely held opinion that unsteady Reynolds-averaged-Navier–Stokes (URANS) approaches are unsuitable, many authors have succeeded in getting reasonable heat transfer results with them. There is also a lack of research into the validity of hybrid URANS/large eddy simulation (LES) type approaches such as detached eddy simulation (DES). This paper addresses these research challenges with a systematic investigation of a rotating cavity with axial throughflow at Grashof numbers of 3.03×109 and 3.03×1011. The disk near-wall layers remained laminar at both conditions, meaning that a turbulence model should not be active in these regions. The disk heat transfer was observed to affect the near-disk aerodynamics, which in turn affect the disk heat transfer: this feedback loop implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, additional eddy viscosity in URANS and DES was found to interfere with the formation of heat transfer enhancing streaks, whilst these were always captured by LES. DES exhibited a concerning behavior at the higher Grashof number. Locally generated eddy viscosity from the shroud was injected into the bulk fluid by the radial inflow. This contaminated the entire cavity with nonphysical modeled turbulence. As the radial inflow is a characteristic feature of rotating cavity flows, these results show that caution is necessary when applying hybrid URANS/LES approaches to this type of flow.

Propulsive jets and their acoustics

2007 ◽  
Vol 365 (1859) ◽  
pp. 2443-2467 ◽  
Author(s):  
Alexander N Secundov ◽  
Stanley F Birch ◽  
Paul G Tucker
Keyword(s):  
Navier Stokes ◽  
Jet Flows ◽  
Complex Flow ◽  
Flow Physics ◽  
Eddy Simulation ◽  
Daunting Task ◽  
Wide Range ◽  
Large Eddy ◽  
Computational Resources ◽  
Hybrid Forms

The complex flow physics challenges and asks questions regarding these challenges a wide range of jet flows found in aerospace engineering. Hence, the daunting task facing Reynolds-averaged Navier–Stokes (RANS) technology, for which the time average of the turbulent flow field is solved, is set out. Despite the clear potential of large eddy simulation (LES)-related methods and hybrid forms involving some RANS modelling, numerous current deficiencies, mostly related to the limitations of computational resources, are identified. It is concluded that currently, these limitations make LES and hybrids most useful for understanding flow physics and refining RANS technology. The use of LES in conjunction with a ray-tracing model to elucidate the physics of acoustic wave transmission in jets and thus improved RANS technology is described. It is argued that, as a stopgap measure, pure RANS simulations can be a valuable part of the design process and can now predict acoustics spectra and directivity diagrams with useful accuracy. Ultimately, hybrid RANS–LES-type methods, and then pure LES, will dominate, but the time-scales for this transition suggests that improvements to RANS technology should not be ignored.

A Hybrid-LES-RANS Transported PDF Combustion Model for Non-Premixed Flames

2012 ◽  
Author(s):  
Alexander Brandl ◽  
Michael Pfitzner
Keyword(s):  
Density Function ◽  
Mixture Fraction ◽  
Premixed Flames ◽  
Navier Stokes ◽  
Combustion Model ◽  
Complex Flow ◽  
Filtered Density Function ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

The intention of this work is to combine Large-Eddy-Simulation (LES) for the prediction of flow and mixture fraction fields with a Reynolds-Averaged-Navier-Stokes (RANS) transported probability density function (TPDF) method for the prediction of turbulent non-premixed flames. The motivation for this work is based upon the property of LES to provide a better description of complex flow fields than most current RANS methods can offer, while TPDF-methods excel in predicting the reacting species fields. However, using the straight forward extension of PDF methods for LES, the filtered density function (FDF) approach requires a large number of PDF particles in each LES cell and is thus computationally expensive. Therefore, a method is proposed to use the time-averaged LES flow field, mixture fraction field and mixture fraction PDF as a turbulence model for a RANS TPDF method operating on a much coarser grid. A projection of the mixture fraction conditioned PDF to evaluate the instantaneous LES density field is proposed as coupling device. The reconstruction of mixture fraction PDF from a LES simulation and the coupling to the TPDF method in postprocessing mode is validated using the TNF Sandia D flame, showing good agreement with experiment.

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