Hybrid RANS-LES for Turbomachinery

Eddy Simulation ◽

Turbulent Statistics ◽

Wide Range ◽

Original Definition ◽

Two Dimensional Flow ◽

Sas Model

A range of popular hybrid Reynolds averaged Navier-Stokes - large eddy simulation (RANS-LES) methods are tested for cavity and labyrinth seal flows using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the Spalart-Allmaras (SA) and Menter SST variants of delayed detached eddy simulation (DDES), the Menter scale adaptive simulation (SAS) model, and a new enhanced variant of SA-DDES recently presented in the literature. The latter modifies the original definition of the subgrid length-scale used in DDES based on local vorticity and strain. For both geometries, the meshes are hybrid RANS-LES adequate. Very low levels of resolved turbulent content are observed for both the cavity and labyrinth seal flows for all models apart from the enhanced version of DDES. Similar findings are observed for both the commercial and in-house CFD codes. For both cases most models essentially produce a quasi-two-dimensional flow field with minimal resolved content. For the cavity simulations there is a significant under prediction of turbulent statistics. The enhanced version of SA-DDES shows a significant improvement and resolves turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed. It is recommended that extreme care should be taken where hybrid RANS-LES simulations are essentially steady but have lower than RANS levels of eddy viscosity.

Enhanced Delayed Detached Eddy Simulation for Cavities and Labyrinth Seals

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4045484 ◽

2019 ◽

Vol 142 (1) ◽

Author(s):

Richard J. Jefferson-Loveday

Keyword(s):

Labyrinth Seal ◽

High Order ◽

Experimental Measurements ◽

Specific Flow ◽

Eddy Simulation ◽

New Variant ◽

Wide Range ◽

Original Definition

Abstract A range of popular hybrid Reynolds-averaged Navier–Stokes -large eddy simulation (RANS-LES) methods are tested for a cavity and two labyrinth seal geometries using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the standard Spalart–Allmaras (SA) and Menter shear stress transport (SST) versions of delayed detached eddy simulation (DDES) and the Menter scale adaptive simulation (SAS) model. A recently formulated, enhanced, variant of SA-DDES presented in the literature and a new variant using the Menter SST model are also investigated. The latter modify the original definition of the subgrid length scale used in standard DDES based on local vorticity and strain. For all geometries, the meshes are considered to be hybrid RANS-LES adequate. Very low levels of resolved turbulence and quasi-two-dimensional flow fields are observed for the standard DDES and SAS models even for the test cases here that contain obstacles, sharp edges, and swirling flow. Similar findings are observed for both the commercial and in-house high-order CFD codes. For the cavity simulations, when using standard DDES and SAS, there is a significant under prediction of turbulent statistics compared with experimental measurements. The enhanced versions of DDES, on the other hand, show a significant improvement and resolve turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed for profiles of the vertical velocity component. For the first labyrinth seal geometry swirl velocities are more accurately captured by the enhanced DDES versions. For the second labyrinth seal geometry, the mass flow coefficient prediction using the enhanced models is significantly improved (up to 30%). Standard, industrially available hybrid RANS-LES models, when applied to the present canonical cases can produce little to no resolved turbulent content. The standard SA- and Menter-based DDES models can yield lower levels of eddy viscosity when compared to equivilent steady RANS simulations which means that they are not operating as RANS or LES. It is recommended that hybrid RANS-LES models should be extensively tested for specific flow configurations and that special care is exercised by CFD practitioners when using many of the popular hybrid RANS-LES models that are currently available in commercial CFD packages.

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

Numerical study of the flow over the modified simple frigate shape

10.1177/0954410020977752 ◽

2020 ◽

pp. 095441002097775

Author(s):

Tong Li ◽

Yibin Wang ◽

Ning Zhao

Keyword(s):

Bluff Body ◽

Recirculation Zone ◽

Numerical Study ◽

Reference Value ◽

Flow Fields ◽

Navier Stokes ◽

Eddy Simulation ◽

Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

On LES Methods Applied to Seal Geometries

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-68840 ◽

2012 ◽

Cited By ~ 2

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.

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 6 ◽

Calculation of Manoeuvring Forces on Submarines Using Two Viscous-Flow Solvers

10.1115/omae2010-20373 ◽

2010 ◽

Cited By ~ 10

Author(s):

Guilherme Vaz ◽

Serge Toxopeus ◽

Samuel Holmes

Keyword(s):

Viscous Flow ◽

Accurate Determination ◽

Turbulence Models ◽

Navier Stokes ◽

Empirical Methods ◽

Eddy Simulation ◽

Commercial Solver

Submersibles used for exploration, maintenance and naval warfare have to be both manoeuvrable and easy to control. Simulation of the trajectory for these vessels requires the accurate determination of the hydrodynamic forces and moments which are determined by model-testing, empirical methods or a combination of both. CFD can play a role here by permitting an easier and more accurate determination of these loads. In this paper we focus on the accurate prediction of the manoeuvring forces of free swimming streamlined submersibles (submarines) using CFD. We compare simulations of a standardised well-known submarine shape (DARPA SUBOFF) for two configurations, one bare hull (AFF-1) and one fully-appended hull (AFF-8), under different inflow angles. The viscous-flow solvers used are the finite volume solver ReFRESCO developed by MARIN, and the finite element commercial solver AcuSolve. Verification studies are performed and the numerical results are validated with the experimental data available in the literature. The influence of different turbulence models is investigated and results obtained with a RANS (Reynolds-Averaged-Navier-Stokes) approach are compared with the theoretically more realistic DDES (Delayed-Detached-Eddy-Simulation) results. The influence of the appendages on the forces and flow fields is also investigated and analysed. As a last example, results of a forced pitch motion including dynamic effects are presented.

CFD Investigation on Hydrodynamic Resistance of a Novel Subsea Shuttle Tanker

Journal of Marine Science and Engineering ◽

10.3390/jmse9121411 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1411

Author(s):

Yihan Xing ◽

Marek Jan Janocha ◽

Guang Yin ◽

Muk Chen Ong

Keyword(s):

High Efficiency ◽

Navier Stokes ◽

Hydrodynamic Resistance ◽

Eddy Simulation ◽

Large Eddy ◽

Computational Fluid Dynamics Cfd ◽

Carbon Dioxide Co2 ◽

Subsea Pipelines

The Subsea Shuttle Tanker (SST) was proposed by Equinor as an alternative to subsea pipelines and surface tankers for the transportation of liquid carbon dioxide (CO2) from existing offshore/land facilities to marginal subsea fields. In contrast to highly weather-dependent surface tanker operations, the SST can operate in any condition underwater. Low resistance is paramount to achieving maximum range. In this paper, the resistance of the SST at an operating forward speed of 6 knots (3.09 m/s) and subject to an incoming current velocity of 1 m/s is computed using Computational Fluid Dynamics (CFD). The Delayed Detached Eddy Simulation (DDES) method is used. This method combines features of Reynolds-Averaged Navier–Stokes Simulation (RANS) in the attached boundary layer parts at the near-wall regions, and Large Eddy Simulation (LES) at the unsteady, separated regions near to the propeller. The force required to overcome forward resistance is calculated to be 222 kN and agrees well with experimental measurements available in the open literature. The corresponding power consumption is calculated to be 927 kW, highlighting the high efficiency of the SST. The method presented in this paper is general and can be used for resistance optimization studies of any underwater vessel.

Assessment of improved delayed detached eddy simulation in predicting unsteady flows and sound around a circular cylinder

Modern Physics Letters B ◽

10.1142/s021798492150384x ◽

2021 ◽

pp. 2150384

Author(s):

Bo Luo ◽

Wuli Chu ◽

Song Yan ◽

Zhengjing Shen ◽

Haoguang Zhang

Keyword(s):

Circular Cylinder ◽

Unsteady Flows ◽

Navier Stokes ◽

Numerical Resolution ◽

Eddy Simulation ◽

Unsteady Wake ◽

Large Eddy ◽

Computational Resources

Unsteady flows in the field of engineering are usually calculated by the Unsteady Reynolds-Averaged Navier–Stokes (URANS) owing to the low requirements for computational efforts. However, the numerical resolution of URANS, especially in predicting the unsteady wake flows and sound, is still questionable. In this work, unsteady flow and sound calculations of a circular cylinder are carried out using Improved Delayed Detached Eddy Simulation (IDDES) and the Ffowcs Williams–Hawkings (FW-H) analogy. The predicted results of this calculation are compared with those from the previous studies in the literature in terms of the mean and RMS of the velocity components as well as the sound pressure. The results show that IDDES retains much of the numerical accuracy of the Large Eddy Simulation (LES) approach in predicting unsteady flows and noise while requiring a reduced computational resources in comparison to LES. It is believed that the IDDES can be applied to calculate the complex unsteady flows and flow generated sound with reasonable accuracy in engineering field, which can be used as a promising method for scale-resolving simulations to avoid the expensive computational requirements of LES.

Turbulence modelling techniques for aeroelastic problems: results and comments from the Second AIAA Aeroelastic Prediction Workshop

Aircraft Engineering and Aerospace Technology ◽

10.1108/aeat-01-2017-0051 ◽

2017 ◽

Vol 89 (5) ◽

pp. 683-691 ◽

Cited By ~ 2

Author(s):

Marcello Righi

Keyword(s):

Navier Stokes ◽

Test Case ◽

Special Flow ◽

Content Type ◽

Eddy Simulation ◽

Large Eddy ◽

Modelling Techniques

Purpose The quality of aeroelastic predictions strongly depends on the quality of aerodynamic predictions. At the boundary of a typical flight envelope, special flow conditions may arise, which challenge the conventional Reynolds-averaged Navier–Stokes (RANS) approach beyond reasonable limits. Design/methodology/approach Test Case 3 of the Second AIAA Aeroelastic Prediction Workshop is a representative test case, where the flow over a supercritical wing separates downstream of the shock waves and generates large turbulent lengthscales. Findings In this study, RANS predictions are compared to those obtained in this particular test case with the more sophisticated hybrid RANS–large eddy simulation (LES) approach, in particular with the Spalart–Allmaras–delayed detached eddy simulation model. Results are indeed closer to experimental data. Originality/value However, the costs associated with this approach are much higher. It is argued that adopting hybrid RANS–LES modelling is not a simple model switch.

RANS and Hybrid RANS-LES Simulations of an H-Type Darrieus Vertical Axis Water Turbine

Energies ◽

10.3390/en11092348 ◽

2018 ◽

Vol 11 (9) ◽

pp. 2348 ◽

Cited By ~ 3

Author(s):

Omar Mejia ◽

Jhon Quiñones ◽

Santiago Laín

Keyword(s):

Turbulence Models ◽

Vertical Axis ◽

Navier Stokes ◽

Speed Ratio ◽

Small Scale ◽

Eddy Simulation ◽

Flow Phenomena ◽

Water Turbine

Nowadays, the global energy crisis has encouraged the use of alternative sources like the energy available in the water currents of seas and rivers. The vertical axis water turbine (VAWT) is an interesting option to harness this energy due to its advantages of facile installation, maintenance and operation. However, it is known that its efficiency is lower than that of other types of turbines due to the unsteady effects present in its flow physics. This work aims to analyse through Computational Fluid Dynamics (CFD) the turbulent flow dynamics around a small scale VAWT confined in a hydrodynamic tunnel. The simulations were developed using the Unsteady Reynolds Averaged Navier Stokes (URANS), Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) turbulence models, all of them based on k-ω Shear Stress Transport (SST). The results and analysis of the simulations are presented, illustrating the influence of the tip speed ratio. The numerical results of the URANS model show a similar behaviour with respect to the experimental power curve of the turbine using a lower number of elements than those used in the DES and DDES models. Finally, with the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the DES and DDES models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine.

Delayed Detached Eddy Simulation of Rotating Stall for a Full Annulus Transonic Axial Compressor Stage

Volume 2A: Turbomachinery ◽

10.1115/gt2016-57985 ◽

2016 ◽

Cited By ~ 1

Author(s):

Jiaye Gan ◽

Hong-Sik Im ◽

Ge-Cheng Zha

Keyword(s):

Stokes Equations ◽

Axial Compressor ◽

Rotating Stall ◽

Tip Clearance ◽

Navier Stokes ◽

Stall Inception ◽

Eddy Simulation ◽

Stall Cells

This paper solves the filtered Navier-Stokes equations to simulate stall inception of NASA compressor transonic Stage 35 with delayed detached eddy simulation (DDES). A low diffusion E-CUSP Riemann solver with a 3rd order MUSCL scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. A full annulus of the rotor-stator stage is simulated with an interpolation sliding boundary condition (BC) to resolve the rotor-stator interaction. The tip clearance is fully gridded to accurately resolve tip vortices and their effect on stall inception. The DDES results show that the stall inception of Stage 35 is initialized by a weak harmonic disturbance with the length scales of the full annulus and grows rapidly with two emerging spike like disturbance. The two spike disturbances propagate in counter rotational direction with about 42% of rotor speed. The spike stall cells cover about 6 blades. They lead to two stall cells grown circumferentially and inwardly.

Assessment of DES Models for Separated Flow From a Hump in a Turbulent Boundary Layer

Journal of Fluids Engineering ◽

10.1115/1.4000376 ◽

2009 ◽

Vol 131 (11) ◽

Cited By ~ 15

Author(s):

Daniel C. Lyons ◽

Leonard J. Peltier ◽

Frank J. Zajaczkowski ◽

Eric G. Paterson

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Mean Field ◽

Separated Flow ◽

Separation Point ◽

Navier Stokes ◽

Flow Solver ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation

Separated flow past a hump in a turbulent boundary layer is studied numerically using detached-eddy simulation (DES), zonal detached-eddy simulation (ZDES), delayed detached-eddy simulation (DDES), and Reynolds-averaged Navier–Stokes (RANS) modeling. The geometry is smooth so the separation point is a function of the flow solution. Comparisons to experimental data show that RANS with the Spalart–Allmaras turbulence model predicts the mean-field statistics well. The ZDES and DDES methods perform better than the DES formulation and are comparable to RANS in most statistics. Analyses motivate that modeled-stress depletion near the separation point contributes to differences observed in the DES variants. The order of accuracy of the flow solver ACUSOLVE is also documented.