Prediction of Viscous Ship Roll Damping by Unsteady Navier-Stokes Techniques

1997 ◽  
Vol 119 (2) ◽  
pp. 108-113 ◽  
Author(s):  
R. A. Korpus ◽  
J. M. Falzarano
Keyword(s):  
Potential Flow ◽  
Turbulence Modeling ◽  
Numerical Technique ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Ship Motions ◽  
Ship Hulls ◽  
Unsteady Rans ◽  
Flow Effects ◽  
Real Flow

This paper describes a numerical technique for analyzing the viscous unsteady flow around oscillating ship hulls. The technique is based on a general Reynolds-averaged Navier-Stokes (RANS) capability, and is intended to generate viscous roll moment data for the incorporation of real-flow effects into potential flow ship motions programs. The approach utilizes the finite analytic technique for discretizing the unsteady RANS equations, and a variety of advanced turbulence models for closure. The calculations presented herein focus on viscous and vortical effects without free-surface, and utilize k-epsilon turbulence modeling. Series variations are presented to study the effects of frequency, amplitude, Reynolds number, and the presence of bilge keels. Moment component breakdown studies are performed in each case to isolate the effects of viscosity, vorticity, and potential flow pressures.

Study of Tip Vortex Cavitation Inception Using Navier-Stokes Computation and Bubble Dynamics Model

1999 ◽  
Vol 121 (1) ◽  
pp. 198-204 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Laura L. Pauley
Keyword(s):  
Vortex Core ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
Window Size ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Cavitation Inception ◽  
Flow Effects ◽  
Bubble Sizes ◽  
Real Flow

The Rayleigh-Plesset bubble dynamics equation coupled with the bubble motion equation developed by Johnson and Hsieh was applied to study the real flow effects on the prediction of cavitation inception in tip vortex flows. A three-dimensional steady-state tip vortex flow obtained from a Reynolds-Averaged Navier-Stokes computation was used as a prescribed flow field through which the bubble was passively convected. A “window of opportunity” through which a candidate bubble must pass in order to be drawn into the tip-vortex core and cavitate was determined for different initial bubble sizes. It was found that bubbles with larger initial size can be entrained into the tip-vortex core from a larger window size and also had a higher cavitation inception number.

scholarly journals Numerical and Experimental Investigation of the Wake Flow Downstream of a Linear Turbine Cascade

1998 ◽  
Author(s):  
Wolfgang Sanz ◽  
Arno Gehrer ◽  
Jakob Woisetschläger ◽  
Martin Forstner ◽  
Wolfgang Artner ◽  
...  
Keyword(s):  
Turbulence Modeling ◽  
Turbulence Models ◽  
Wake Flow ◽  
Navier Stokes ◽  
Laser Doppler Velocimeter ◽  
Turbine Cascade ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
And Performance ◽  
Transonic Cascade

In turbomachinery the wake flow together with the inherent unsteadiness caused by interaction between stator and rotor has a significant impact on efficiency and performance. The prediction of the wake flow depends largely on the turbulence modeling. Therefore in this study the evolution of a viscous wake downstream of a linear turbine cascade is experimentally and computationally investigated. In a transonic cascade test stand Laser Doppler Velocimeter (LDV) measurements of velocity and turbulent kinetic energy are done in several axial planes downstream of the blade trailing edge. Two different turbulence models are then incorporated into a two-dimensional Navier-Stokes solver to calculate the turbulent wake flow and the results are compared with the experimental data to test the quality of the turbulence models. The large discrepancies between measurement and Calculation are assumed to be caused by the periodic vortex shedding from the blunt trailing edge which is not taken into account by the turbulence models. But further research is needed to resolve this issue.

scholarly journals Turbulence Modeling a Review for Different Used Methods

2021 ◽  
Vol 39 (1) ◽  
pp. 227-234
Author(s):  
Khelifa Hami
Keyword(s):  
Turbulence Modeling ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Simulation Models ◽  
Navier Stokes ◽  
Future Research ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Eddy Simulation ◽  
Complicated Geometries

This contribution represents a critical view of the advantages and limits of the set of mathematical models of the physical phenomena of turbulence. Turbulence models can be grouped into two categories, depending on how turbulent quantities are calculated: direct numerical simulations (DNS) and RANS (Reynolds Averaged Navier-Stokes Equations) models. The disadvantage of these models is that they require enormous computing power, inaccessible, especially for large and complicated geometries. For this reason, hybrid models (combinations between DNS and RANS methods) have been developed, for example, the LES (“Large Eddy Simulation”) or DES (“Detached Eddy Simulation”) models. They represent a compromise - are less precise than DNS, but more precise than RANS models. The results presented in this contribution will allow and facilitate future research in the field the choice of the model approach necessary for the case studies whatever their difficulty factor.

scholarly journals COMPARISON OF NUMERICAL WAVE TANKS WITH VARIOUS TURBULENCE MODELS IN APPLICATION TO LONG WAVE MOTION AND ITS INTERACTION WITH A VERTICAL WALL

2018 ◽  
pp. 29
Author(s):  
Gizem Ezgi Cinar ◽  
Hasan Gokhan Guler ◽  
Taro Arikawa ◽  
Cuneyt Baykal ◽  
Ahmet Cevdet Yalciner
Keyword(s):  
Wave Motion ◽  
Turbulence Modeling ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Time ◽  
Long Wave ◽  
Large Eddy ◽  
Numerical Wave

In this study, performances of interFoam solver of OpenFOAM and CADMAS-SURF computational tools with several turbulence modelling approaches on the numerical modelling of long wave motion and its interaction with a vertical wall based on the physical model experiments presented by Arikawa (2015) are investigated and compared. IHFOAM is used as wave generation and absorption boundary condition (Higuera et al., 2013). Three-dimensional simulations are carried out solving Reynolds Averaged Navier Stokes (RANS) with no-turbulence model and with k-ε and k-ω SST (Shear Stress Transport) turbulence models in addition to Large Eddy Simulations (LES). The aim of this study is to understand the contribution from turbulence modeling and compare the numerical wave tanks in long wave motion and their interaction with a vertical wall. The results are further discussed in scope of required accuracy in such engineering applications focusing on computational time.

A Methodology for Simulating Compressible Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 405-412 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Bluff Body ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Fine Grid ◽  
Local Flow

A flow simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modeling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for Reynolds averaged Navier-Stokes (RANS)) and scaling of the model terms with a “contribution function.” The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that it approaches direct numerical simulations (DNS) in the fine-grid limit and such that it provides modeling of all scales in the coarse-grid limit and thus approaches a RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in large eddy simulation (LES). However, FSM is distinctly different from LES in that it allows for a consistent transition between RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step and a plane wake behind a bluff body, both at low Mach number, and supersonic axisymmetric wakes. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for simulations of turbulent compressible flows for complex geometries.

Numerical Investigation of Turbulence Modelling on Condensing Steam Flows in Turbine Cascade

2014 ◽  
Author(s):  
Yogini Patel ◽  
Teemu Turunen-Saaresti ◽  
Giteshkumar Patel ◽  
Aki Grönman
Keyword(s):  
Turbulence Modeling ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Turbulence Modelling ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Navier Stokes ◽  
Condensation Process ◽  
Turbine Cascade ◽  
Lp Turbine

Understanding the condensation process at the low-pressure (LP) turbine is important because condensation introduces extra losses, and erosion caused by the droplets wear turbine blades. The paper presents an investigation of the turbulence modelling on the non-equilibrium homogeneous condensing steam flow in a stationary turbine cascade employing 2D compressible Navier-Stokes (NS) equations. The classical nucleation theory is utilized to model the condensation phenomena. The performance of various turbulence models (i.e., the Spalart-Allmaras, the k-ω, the k-ε, the RNG k-ε, the Realizable k-ε, and the SST k-ω) in condensing steam flows is discussed. The SST k-ω model is modified and implemented into a commercial computational fluid dynamics (CFD) code. Substantial improvements in the prediction accuracy are observed when compared with the original SST k-ω model. Overall, the modified model is in excellent agreement with the measurements in all studied test cases of the turbine cascade. The qualitative and quantitative analysis illustrates the importance of turbulence modeling in wet-steam flows.

Development and exploitation of a multipurpose CFD tool for optimisation of microbial reaction and sludge flow

2006 ◽  
Vol 53 (3) ◽  
pp. 101-110 ◽  
Author(s):  
T. Oda ◽  
T. Yano ◽  
Y. Niboshi
Keyword(s):  
Wastewater Treatment ◽  
Wastewater Treatment Plants ◽  
Numerical Models ◽  
Numerical Technique ◽  
Turbulence Models ◽  
Reaction Model ◽  
Experimental Results ◽  
Navier Stokes ◽  
Transfer Model ◽  
The Right

A numerical analysis technique for optimisation of microbial reaction and sludge flow has been developed in this study. The technique is based on the 3D multiphase Navier–Stokes solver with turbulence models. In order to make numerical analyses of the total processes in wastewater treatment plants possible, four numerical models, the microbial reaction model, a sludge settling model, oxygen mass transfer model from coarse bubbles, and a model from fine bubbles, are added to the solver. All parameters included in those models are calibrated in accordance with experimental results, and good agreements between calculated results and experimental results are found. Finally, this study shows that the numerical technique can be used to optimise wastewater treatment plants with an example of the operational optimisation of an intermittent agitation in anoxic reactors by coarse bubbles. With a proper appreciation of its limit and advantages, the exploitation of the CFD efficiently leads us to the right direction even though it is not quantitatively perfect.

Effect of Turbulence Modeling on VIV Numerical Simulation

2005 ◽  
Author(s):  
Juan B. V. Wanderley ◽  
Gisele H. B. Souza ◽  
Carlos Levi
Keyword(s):  
Numerical Method ◽  
Compressible Flows ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Reynolds Average

Author’s previous work Wanderley [1] presented an efficient numerical method to investigate VIV phenomenon on circular cylinders. The numerical model solves the unsteady Reynolds Average Navier–Stokes equations for slightly compressible flows using the Beam–Warming implicit factored scheme. In the present work, the effect of the turbulence model on the results is evaluated for both Baldwin Lomax and k-ε models. To demonstrate the quality of the numerical method, results for the transversal oscillation of a cylinder laterally supported by spring and damper are compared with experimental data. The application of the turbulence models showed the much better agreement of the k-ε model with the experimental results.

A Method for Conjugate Heat Transfer With Unsteady RANS Simulation

2014 ◽  
Author(s):  
Takashi Yamane ◽  
Yuhi Tanaka
Keyword(s):  
Heat Transfer ◽  
Time Scale ◽  
Thermal Conduction ◽  
Conjugate Heat Transfer ◽  
Turbulence Modeling ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Solid Materials ◽  
Rans Simulation ◽  
Unsteady Rans

The conjugate heat transfer simulation is expected to simulate precise temperature distributions of turbine cooling structures and contribute to the reduction of cooling air usage. This method has mainly been used to predict steady state temperature because of the large difference of time scale between RANS flow simulation and thermal conduction in solid materials, thus the accuracy of temperature estimation depends on the modeling of the turbulence. Despite many efforts to improve turbulence models, an inherent limitation of RANS and turbulence modeling and the necessity of unsteady simulation for better accuracy in heat transfer simulations have been pointed out. The aim of this study is to combine the unsteady RANS simulation with the steady thermal conduction of solid materials. The “Time Smoothing” method was introduced to compensate the large time scale difference between fluid and solid, then the effectiveness of the method was confirmed through conjugate heat transfer simulations around a pipe shape object where strong flow unsteadiness prevails.

scholarly journals A comparative study of URANS, DDES and DES simulations of Jetstream 31 aircraft near the compressibility limit

2021 ◽  
Vol 16 (2) ◽  
pp. 159-172
Author(s):  
Hrishabh Chaudhary ◽  
Nicolas Ledos ◽  
László Könözsy
Keyword(s):  
Comparative Study ◽  
Turbulence Modeling ◽  
Pressure Coefficient ◽  
Turbulence Models ◽  
Flight Test ◽  
Scale Model ◽  
Navier Stokes ◽  
Ansys Fluent ◽  
Fluent Software ◽  
Lift And Drag

This work presents a comparative study of Unsteady Reynolds–Averaged Navier–Stokes (URANS), Detached Eddy Simulations (DES) and Delayed Detached Eddy Simulations (DDES) turbulence modeling approaches by performing numerical investigation with the ANSYS-FLUENT software package on a full-scale model of the Jetstream 31 aircraft. The lift and drag coefficients obtained from different models are compared with flight test data, wind tunnel data and theoretical estimates. The different turbulence models are also compared with each other on the basis of pressure coefficient distributions and velocity fluctuations along various lines and sections of the aircraft. For the mesh and the conditions presented in this study, the DDES Spalart–Allmaras model gives the best overall results.

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