Assessment of Cavitation Erosion With a URANS Method

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Zi-ru Li ◽  
Mathieu Pourquie ◽  
Tom van Terwisga
Keyword(s):  
Large Scale ◽  
Cavitation Erosion ◽  
Time Derivative ◽  
Mean Value ◽  
Navier Stokes ◽  
Local Pressure ◽  
Erosion Risk ◽  
Damage Area ◽  
Large Scale Structures ◽  
Unsteady Rans

An assessment of the cavitation erosion risk by using a contemporary unsteady Reynolds-averaged Navier–Stokes (URANS) method in conjunction with a newly developed postprocessing procedure is made for an NACA0015 hydrofoil and an NACA0018-45 hydrofoil, without the necessity to compute the details of the actual collapses. This procedure is developed from detailed investigations on the flow over a hydrofoil. It is observed that the large-scale structures and typical unsteady dynamics predicted by the URANS method with the modified shear stress transport (SST) k-ω turbulence model are in fair agreement with the experimental observations. An erosion intensity function for the assessment of the risk of cavitation erosion on the surface of hydrofoils by using unsteady RANS simulations as input is proposed, based on the mean value of the time derivative of the local pressure that exceeds a certain threshold. A good correlation is found between the locations with a computed high erosion risk and the damage area observed from paint tests.

Unsteady RANS Simulation of Turbulent Flow and Heat Transfer in Ribbed Coolant Passages of Different Aspect Ratios

2004 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Rotation Number ◽  
Large Scale ◽  
Density Ratio ◽  
Navier Stokes ◽  
Flow Structures ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Unsteady Rans

The flow and heat transfer in ribbed coolant passages of aspect ratios (AR) of 1:1, 4:1, and 1:4 are numerically studied through the solution of the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The URANS procedure can resolve large-scale bulk unsteadiness, and utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The computations are carried out for a fixed Reynolds number of 25000 and density ratio of 0.13 while the Rotation number has been varied between 0.12–0.50. The average duct heat transfer is the highest for the 4:1 AR case. For this case, the secondary flow structures consist of multiple roll cells that direct flow both to the trailing and leading surfaces. The 1:4 AR duct shows flow reversal along the leading surface at high rotation numbers with multiple rolls in the secondary flow structures near the leading wall. For this AR, the potential for conduction-limited heat transfer along the leading surface is identified. At high rotation number, both the 1:1 and 4:1 AR cases exhibit loss of axial periodicity over one inter-rib module. The friction factor reveals an increase with the rotation number for all aspect ratio ducts, and shows a sudden jump in its value at a critical rotation number because of either loss of spatial periodicity or the onset of backflow.

scholarly journals Coherent large-scale structures from the linearized Navier–Stokes equations

2019 ◽  
Vol 873 ◽  
pp. 89-109 ◽  
Author(s):  
Anagha Madhusudanan ◽  
Simon. J. Illingworth ◽  
Ivan Marusic
Keyword(s):  
Large Scale ◽  
Eddy Viscosity ◽  
Stokes Equations ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Large Scale Structures ◽  
Viscosity Profile ◽  
Wide Range ◽  
Scale Structures

The wall-normal extent of the large-scale structures modelled by the linearized Navier–Stokes equations subject to stochastic forcing is directly compared to direct numerical simulation (DNS) data. A turbulent channel flow at a friction Reynolds number of $Re_{\unicode[STIX]{x1D70F}}=2000$ is considered. We use the two-dimensional (2-D) linear coherence spectrum (LCS) to perform the comparison over a wide range of energy-carrying streamwise and spanwise length scales. The study of the 2-D LCS from DNS indicates the presence of large-scale structures that are coherent over large wall-normal distances and that are self-similar. We find that, with the addition of an eddy viscosity profile, these features of the large-scale structures are captured by the linearized equations, except in the region close to the wall. To further study this coherence, a coherence-based estimation technique, spectral linear stochastic estimation, is used to build linear estimators from the linearized Navier–Stokes equations. The estimator uses the instantaneous streamwise velocity field or the 2-D streamwise energy spectrum at one wall-normal location (obtained from DNS) to predict the same quantity at a different wall-normal location. We find that the addition of an eddy viscosity profile significantly improves the estimation.

Using URANS to Predict Turbulent Flow Features in a Channel with Lateral Slot

2013 ◽  
Vol 394 ◽  
pp. 101-107 ◽  
Author(s):  
Tiago de Melo ◽  
Jhon Goulart ◽  
Sandi Souza
Keyword(s):  
Large Scale ◽  
Rectangular Channel ◽  
Lateral Wall ◽  
Navier Stokes ◽  
Large Scale Structures ◽  
Commercial Code ◽  
Flow Features ◽  
The Mean ◽  
Gap Width ◽  
Reynolds Average

Employing a commercial code an unsteady Reynolds Average Navier-Stokes (URANS) with Spalart-Allmaras as turbulence model numerical calculations were performed in order to predict the mean and velocity fluctuations fields in a rectangular channel with a lateral slot. The slot is attached to a lateral wall channel, being characterized by its deepness p and the gap width d. Simulations were performed keeping constant the slot deepness p and the length L while the gap width d was increased from 2 up to 6 mm. Three test sections involving p/d ratios12.50, 6.25 and 4.17were studied. Main results revealed that turbulence production increases with gap dimension decreasing. Large scale structures appearance were also the target of this paper. The study showed gap width plays an important role on this issue. As the gap width was increased large scales structures could be observed farther from channels entrance. Moreover, a kind of viscous effect in the gap was observed. As gap become very tight the frequency of coherent motions is reduced.

A Comparison of Unsteady RANS and DES for Simulating an Axial Compressor Stage

2020 ◽  
Author(s):  
Edward A. Miller ◽  
Michael J. Cave ◽  
David M. Williams ◽  
Khandan Thayalakhandan
Keyword(s):  
Large Scale ◽  
Axial Compressor ◽  
Industrial Scale ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Sliding Mesh ◽  
Eddy Simulation ◽  
Massively Parallel Computing ◽  
Unsteady Rans ◽  
Computing Platforms

Abstract Computational fluid dynamics (CFD) of industrial-scale, axial compressor geometries has traditionally been performed using steady state methods such as the mixing plane approach. With the surge in the development of large-scale, massively-parallel computing platforms, fully 3D unsteady approaches are rapidly growing in popularity. The fully 3D, unsteady approach involves building a full 3D domain for each blade row, and then coupling the stationary and rotating domains using a sliding interface. In the literature, there are various methods for solving this 3D unsteady problem, such as the Unsteady Reynolds Averaged Navier-Stokes (URANS) and the Detached Eddy Simulation (DES) methods. While these methods are well documented for a variety of real-world problems, there have been limited efforts to compare the effectiveness of these methods for fully 3D, unsteady turbomachinery problems. In this study, the first stage of an industrial-scale axial compressor was simulated using: i) the URANS approach, and ii) the DES approach. The compressor geometry consisted of an inlet housing, inlet guide vanes (IGV), a rotor, and a stator. The RANS model for both simulations was the k-epsilon model. For both of these cases, sliding mesh interfaces were located between the IGV and rotor, and between the rotor and stator. The results of the URANS and DES approaches were time-averaged and their predictions were compared. Throughout the study, our goal was to provide important insights into the performance of the URANS and DES approaches, and to highlight the essential differences.

scholarly journals Consistency relations for large-scale structures: Applications for the integrated Sachs-Wolfe effect and the kinematic Sunyaev-Zeldovich effect

2017 ◽  
Vol 606 ◽  
pp. A128 ◽  
Author(s):  
Luca Alberto Rizzo ◽  
David F. Mota ◽  
Patrick Valageas
Keyword(s):  
Power Spectrum ◽  
Equivalence Principle ◽  
Large Scale ◽  
Initial Conditions ◽  
Time Derivative ◽  
Matter Density ◽  
Microwave Background ◽  
Large Scale Structures ◽  
Cross Correlations ◽  
Scale Structures

Consistency relations of large-scale structures provide exact nonperturbative results for cross-correlations of cosmic fields in the squeezed limit. They only depend on the equivalence principle and the assumption of Gaussian initial conditions, and remain nonzero at equal times for cross-correlations of density fields with velocity or momentum fields, or with the time derivative of density fields. We show how to apply these relations to observational probes that involve the integrated Sachs-Wolfe effect or the kinematic Sunyaev-Zeldovich effect. In the squeezed limit, this allows us to express the three-point cross-correlations, or bispectra, of two galaxy or matter density fields, or weak lensing convergence fields, with the secondary cosmic microwave background distortion in terms of products of a linear and a nonlinear power spectrum. In particular, we find that cross-correlations with the integrated Sachs-Wolfe effect show a specific angular dependence. These results could be used to test the equivalence principle and the primordial Gaussianity, or to check the modeling of large-scale structures.

On the Applicability of Cavitation Erosion Risk Models With a URANS Solver

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Themistoklis Melissaris ◽  
Norbert Bulten ◽  
Tom J. C. van Terwisga
Keyword(s):  
Cavitation Erosion ◽  
Navier Stokes ◽  
Maritime Industry ◽  
Risk Models ◽  
Erosion Risk ◽  
Erosion Prediction ◽  
Computational Fluid Dynamics Cfd ◽  
Propeller Blades ◽  
Energy Balance Approach ◽  
Scale Data

In the maritime industry, cavitation erosion prediction becomes more and more critical, as the requirements for more efficient propellers increase. Model testing is yet the most typical way a propeller designer can, nowadays, get an estimation of the erosion risk on the propeller blades. However, cavitation erosion prediction using computational fluid dynamics (CFD) can possibly provide more information than a model test. In the present work, we review erosion risk models that can be used in conjunction with a multiphase unsteady Reynolds‐averaged Navier–Stokes (URANS) solver. Three different approaches have been evaluated, and we conclude that the energy balance approach, where it is assumed that the potential energy contained in a vapor structure is proportional to the volume of the structure, and the pressure difference between the surrounding pressure and the pressure within the structure, provides the best framework for erosion risk assessment. Based on this framework, the model used in this study is tested on the Delft Twist 11 hydrofoil, using a URANS method, and is validated against experimental observations. The predicted impact distribution agrees well with the damage pattern obtained from paint test. The model shows great potential for future use. Nevertheless, it should further be validated against full scale data, followed by an extended investigation on the effect of the driving pressure that leads to the collapse.

Partially Averaged Navier-Stokes Method for Turbulence: Fixed Point Analysis and Comparison With Unsteady Partially Averaged Navier-Stokes

2005 ◽  
Vol 73 (3) ◽  
pp. 422-429 ◽  
Author(s):  
Sharath S. Girimaji ◽  
Eunhwan Jeong ◽  
Ravi Srinivasan
Keyword(s):  
Fixed Point ◽  
Turbulent Flows ◽  
Large Scale ◽  
Navier Stokes ◽  
Control Parameters ◽  
Point Analysis ◽  
Large Eddy ◽  
Reasonable Cost ◽  
Unsteady Rans ◽  
The Right

Hybrid/bridging models that combine the advantages of Reynolds averaged Navier Stokes (RANS) method and large-eddy simulations are being increasingly used for simulating turbulent flows with large-scale unsteadiness. The objective is to obtain accurate estimates of important large-scale fluctuations at a reasonable cost. In order to be effective, these bridging methods must posses the correct “energetics”: that is, the right balance between production (P) and dissipation (ε). If the model production-to-dissipation ratio (P∕ε) is inconsistent with turbulence physics at that cutoff, the computations will be unsuccessful. In this paper, we perform fixed-point analyses of two bridging models—partially-averaged Navier Stokes (PANS) and unsteady RANS (URANS)—to examine the behavior of production-to-dissipation ratio. It is shown that the URANS-(P∕ε) ratio is too high rendering it incapable of resolving much of the fluctuations. On the other hand, the PANS-(P∕ε) ratio allows the model to vary smoothly from RANS to DNS depending upon the values of its resolution control parameters.

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

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