Twenty-Second Symposium on Naval Hydrodynamics (1999) / Chapter Skim
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15 CFD Validation
15 CFD Validation
Pages 920-1014
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From page 920... ...
Thi.; is not intended as a survey of thefield in general; rather, it is a summary of the ongoing research and development of computational tools in the Computational Fluid Dynamics Lab at Mississippi State University. A discussion is given of the enabling technologies on which most of the computational tools are based.
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From page 921... ...
2.1 Grid Generation Structured multiblock grids have been used for some time for the computation of steady and unsteady Naval hydrodynamic problems. However, unstructured grid technology has been an active area of research, and the fruits of this effort are now beginning to be used for these same hydrodynamic problems.
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From page 922... ...
An algebraic turbulence model [191, a k-e model, and a nonlinear k-e model [20] have been implemented within the code and used for the turbulent flow computations.
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one-equation turbulence model is used to model turbulence. The discretized scheme uses a node-based finite-volume upwind approximation.
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From page 924... ...
2.6 CFS System Computing a computational field simulation (CFS) solution involves a number of steps, including components of geometry, grid generation, field simulation solvers, and visualization.
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Numerous solutions at several angles of drift were computed and compared to experimental data in [52] [331 using the Baldwin-Lomax turbulence model.
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The stern region of the unstructured grid is shown in Figure 2. A more compelete configuration was constructed by adding a sail plane and rotating propeller to the basic SUBOFF geometry.
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From page 927... ...
Numerous grid sizes were investigated in these computations that included structured multiblock grid densities of 300,000 to 1,500,000 points. Also various turbulence models were investigated that included algebraic, two~quation linear models, and tw~equation non-linear models.
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From page 928... ...
how well do the various turbulence models approximate the physics of flows, and for what type of flows of interest are the various turbulence models applicable, (3) how does grid selection influence the solution, (4)
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From page 929... ...
4.2 Implications for Flow Solvers, Equation Sets and Turbulence Modeling To summarize some of these comments, although turbulence plays an important role in establishing the (averaged) flow structure to be resolved, much of the flow resolution requirements and computational cost for practical flow simulations can come from complex inviscid flow structures induced by geometry and wall layers.
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From page 930... ...
There is also a need for improvements in structured and unstructured grid generation capabilities. Although much progress has been made in this area, it is only recently that the speed at which unstructured viscous grids can be built has improved to the point that one might consider a complete regridding for a moving body, rather than a partial regrinding in order to save time.
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From page 931... ...
Verification and Validation Experiments 4.6 New Computational Tools Computational design optimization is receiving considerable attention in the aircraft community as a means of aircraft component and full configuration design, and it seems that more attention should be devoted to this topic in the Naval hydrodynamic community. Although computational design, as opposed to to design by analysis, is an area of research that is not routinely used at present, even in the aerospace field, this approach may have tremendous pay-off, and it is believed that this should be an active research area in the ship design community as well.
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From page 932... ...
[2] Gaither, A., "A Topology Model for Numerical Grid Generation," in Proceedings of the 4th International Conference on Numerical Grid Generation in Computational Fluid Dynamics and Related Fields, Swansea, UK, pp.
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From page 933... ...
[381 Marcum, D.L., "Advancing-Front/Local-Reconnection (AFLR) Unstructured Grid Generation." Computational Fluid Dynamics Review 1997, edited by M.M.
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From page 934... ...
[58] Beddhu, M., Jiang, M-Y., Taylor, L.K., and Whitfield, D.L., "Computation of Steady and Unsteady Flows with a Free Surface Around the Wigley Hull," Mississippi State Annual Cor7ference on Differential Equations and Computational S`mulations, Mississippi State, MS, April 1995.
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From page 935... ...
INTRODUCTION The increasing availability of low costs hardware computational resources has lead Computational Fluid Dynamics to undergo a thorough development in the last years. The benefits are felt both in the research field and in practical engineering problems like fluid-structure interaction calculations.
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From page 936... ...
So a large set of experiments has been planned and performed at the Towing Tank of DINMA concerning the local behaviour of the fluidbody interaction. Here steady state wall pressure and free surface elevation around the cylinder in different wave conditions have been measured.
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From page 937... ...
Since most of the important features of the wave pattern were expected to be distinguishible in the near field, namely within a few radii from the cylinder wall, the maximum nondimensional distance r/a of the wave gauges from the cylinder axis has been set to 3 (D=0.305 m)
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From page 938... ...
Ad. NON-LINEAR NUMERICAL SIMULATION In the following, the wavy flow of an inviscid incompressible fluid generated by the interaction of a regular wave train with a vertical cylinder piercing the free surface ]
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From page 939... ...
The latter is the only portion of the boundary domain that remains unchanged during the evolution, while the free surface and the wetted surface of the body change in time. In the numerical solution the surface ~ of (3)
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From page 940... ...
and about 6000 source points on the free surface.
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, no value of the dynamic pressure has been assigned to the numerical results therefore these values are not shown in the figures. For all other cases, the agreement with the experiments is quite good, strictly following bumps and other nonlinear features.
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From page 942... ...
15. Di Mascio, A., Landrini, M., Lalli, F., Bulgarelli, U., "Three dimensional Nonlinear Diffractrion Around a Fixed Structure", Proceedings of the 20th Symposium of Naval Hydrodynamics 1994, Santa Barbara (California)
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From page 943... ...
and nonlinear numerical results ( C3 )
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with 1 st ~) , 2nd ~- - - ~ and 3rd ~- ~ harmonic component, linear prediction ~ and nonlinear numerical results ~O ~ - Test I
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with 1 st ~) , 2nd ~- - - ~ and 3rd ~- ~ harmonic component, linear prediction ~- ~ and nonlinear numerical results ~O ~ - Test H
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, 2nd (~ - - ~ and 3rd ~~ ~ harmonic component, linear prediction ~ ~ and nonlinear numerical results ~O ~ - Test G
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From page 947... ...
, second and third order terms in the total force appear in the free surface zone due to the first order and nonlinear potential. There, the contributions connected with different wavebody interaction effects have been derived separately.
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From page 948... ...
The numerical solutions successfully cam tured many important features of transient flow around a berthing ship including the underkeel flow acceleration, wake flow separation, water cushion between the ship and harbor quay wall, and the complex interactions between the bow, shoulder, and stern waves. A direct validation of the accuracy of these simulation results, however, was not possible due to the lack of experimental data.
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From page 949... ...
The subscripts,,jand,jk,representthecovariantderivatives. In the present study, the two~layer turbulence model of Chen and Patel t11]
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From page 950... ...
(12) Using this relationship, the turbulent kinetic energy can be determined from equation (8)
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From page 951... ...
More detailed description of the chimera R~ANS/free surface method and the associated data management system are given in Hubbard and Chen [13i, t144. For unsteady problems involving relative motions between different grid blocks, the solu tion procedure can be summarized as follows: 1.
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From page 952... ...
Current meters are placed at ten different locations along the ship path as also shown in Figure 4. In the present chimera domain decomposition approach, a 61 x 31 x 51 body-fitted numerical grid was constructed for accurate resolution of the turbulent boundary layer flow around the ship hull.
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From page 953... ...
and inline (in the direction of ship motion) velocity contours at several different time instants of t = 255.8s, 305.2s, 354.6s, and 453.4s to illustrate the general characteristics of the transient flow field induced by the ship berthing operation.
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From page 954... ...
The method solves the unsteady Reynolds-Averaged Navier-Stokes equations in conjunction with a chimera domain decomposition technique for detailed assessment of the hydrodynamic coupling between the ship, the harbor floor, and the harbor quay wall. The numerical solutions successfully captured many important features of the transient flow around the berthing ship including the underkeel flow acceleration, separation in the wake region behind the ship path, and water cushion between the ship and the harbor quay wall.
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From page 955... ...
J and Chen, H.C., "A Chimera Scheme for Incompressible Viscous Flows with Applications to Submarine Hydrodynamics," AIAA Paper 9~2210, 25th AIAA Fluid Dynamics Conference, Colorado Spring, CO, June 20-23, 1994.
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From page 956... ...
b - eaz" 1C.7 e" ' 1~nrillg Reese: ~ c~Jsec, 10 em~'sec (1) ,29 c~nfsec war depth: 21 cm, 26.?
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From page 959... ...
. ~ M/V Independece: X650D .
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From page 960... ...
velocity Contours IC~ (d) t = 453.4 see Figure 9: Free surface velocity vectors at t = 329.9 see 960
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From page 961... ...
Figure 10: Velocity vector plots at X/L = 0.42 961 (a)
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:::: Figure 11: \hloc1ty vector Ilotsat Jr/[ = 0.92 962 (a)
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From page 963... ...
· ' ' 100 150 200 (d) t 404.0 see Figure 12: Free surface pressure Contours 10 5 'I O it' - 5 ~0 - 10 _ ~ ~ 10 5 ·s ~ O TIC ~5 - 10 250 300 350 40C t (see)
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From page 964... ...
The Office of Naval Research (OUR) has cently undertaken a Computational Fluid Dynamics (CFD)
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From page 965... ...
SLAW SLAW is a Ship Lift and Wave free surface potential flow panel code, developed at SA1C, Annapm lis (6~. Either a Dawson-lype or Rankine singularity model is employed to distribute source panels over a portion of the flee surface, and a double-body lineanzation is applied at each panel.
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From page 966... ...
Model 5415 Body Plane and Profile View Validation data was obtained at the David Taylor Model Basin, Naval Surface Warfare Center, Carderock Division for two Froude numbers, Fn=0.28 and Fn=0.41. This validation study concentrated on the Fn=0.28 case and focused on the comparisons of wave profiles along the hull, longitudinal wave cuts obtained at a fixed distance from the hull, stern wave height topography, and velocity field measurements obtained in propeller plane (13,14~.
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From page 967... ...
The longitudinal location of the stern separation, the angle of the divergent stern wave with the hull, and the stern wave heights are well modeled in the RANS codes and in the potential flow codes with the exception of SWAN-1. The predictions obtained with SWAN-I indicates that the code does not compute the angle of the divergent wave nor the wave elevations in the stern region correctly.
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From page 968... ...
K., and Arabshahi, A., "CFD Validation of the Free Surface Flow Around DTMB Model 5415 Using Rey nolds Averaged Navier-Stokes Equations," Third Osaka Colloquium on Advanced CFD Applications to Ship Flow and Hull Form Design, Osaka, Japan, May 2527, 1998.
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From page 969... ...
and Treakle, T., "Steady and Unsteady Ship Waves Predicted by Large-Amplitude Motion Program," 1st Symposium on Marine Applications of Computational Fluid Dynam ics, McLean, Virginia, USA, 1998.
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From page 970... ...
0~02 0.016 0.01 ~_ ~C 0 _# ~S 5oe - 6 ._ _, cn ~o o Ct "C ~.00B C~ ._ I ~.01 SERIES 60 COI1JIPARISON OF MEASURED AND PREDICTED LONGITUDINAL WAVECUT AT Y/L=0.1 08 M5S.TATE - UNCL£.0MAS ' ~SAlC-~W SAlC - ~MP ~UMICH - UMOELTA !
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From page 971... ...
~ ~ ona _1 0.08 0.04 0.02 sly D.06 1 1.06 1.1 AIL SERIES 60 - WAVE HEIGHT TOPOGRAPHY EXPERIMENTAL 0.96 1 1.06 1.1 1.15 1.2 X/L SERIES 60 - WAVE HEIGHT TOPOGRAPHY UMICH - UMDELTA SERIES 60 - WAVE HEIGHT TOPOGRAPHY SAIC - AMP Zig it..
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Series 60 Comparison of Measurements and Potential Flow Predictions of Sterna Wave Height Topography 972 ZL Boos o.
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From page 973... ...
o. 1 407 ~ "0 B02 -'' Y/1~ 0.06 0 SERIES 60 - AXIAL VELOCITY FIELD AT XJL=1~0 IASSTATE- UNCLE.OMAS Figure 6.
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From page 974... ...
Ref=1.0 en no -0.02 in no ~ is." in no -0.06 -0.07 ~.08r ~ ~ ~ ~ 1 , , , , 1 , , , , ^ 0.02 0.04 Y/L I , , , , I 0.06 0.08 SERIES 60 - CROSSPLANE VELOCITY FIELD AT X/L=1.0 EXPERIMENTAL o mn1 ~.02t -0.03 is." .05 ~ns -0.07 Ref=1.0 ~ ~'.~'''"~','' "n n, I ~\ 4 08 r~ ,~ I I , ~ I , . , · I , ~I ~ ~ ~I -o os 0 0.02 0.04 0.06 0.08 · 0 0~02 0.04 Y/L SERIES 60 - CROSSPLANE VELOCITY FIELD AT X/L=1~0 CFDSHIP - IOWA , ,\ , , Ref=1.0 NN"'' N' I ,` , , , I 0.06 ~08 SERIES 60 - CROSSPLANE VELOCITY FIELD AT X/L=1.0 MSSTATE - UNCLE.OMAS Figure 7.
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From page 976... ...
Model 5415 Comparison of Measurements and R~! IS Predictions of Stern Wave Height Topography 976 a..
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From page 977... ...
Model 5415 Comparison of Measurements and Potential Flow Predictions of Stern Wave Height Topography 977 ZtL O.005 O.004 0.003 0.002 ~ 0.001 1 o.ooo .001 -0.002 .003 ~ -to 1 0.005
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From page 978... ...
Mlodel 5415 Comparison of Measured and Predicted Axial Velocity at x/L~.93 978 v o." o" Q.71 a.' a." o." 4146 Em Olga 020 As
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From page 979... ...
Ref=1 .0 -0.05 .noR _ . .nn7 _ 2 1 ~ ~ ~ \ ~ \ 1 _ 1 ~ ~ ~ \ 1 1 1 1 _ ~ -odor , ~, , , ~, 1 · 4 1 ~ 0 0.02 0.04 o.os 0.08 YtL MODEL 5415 -CROSSPLANE VELOCITY FIELD AT )
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From page 980... ...
This is a simpler flow, with dry transom, treated compu-tationally with promising results at David Taylor Model Basin [1~. Application of the RANS codes to this less challenging problem might help sort out remaining unknowns affecting stern wave predictions.
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From page 981... ...
The numerical method solves the unsteady r Reynolds-averaged Navier-Stokes and continuity equations with the Baldwin-Lomax turbulence model, exact nonlinear kinematic and approximate dynamic fi~sur~e boundary conditions, and a body/~surface conforming grid. The experimental and computational conditions, i.e., Froude number 0.16 and 0.316 for the experiments arid 0 and 0.316 for the computations, allow comparisons of low and high Froude number results, respectively, which enables evaluation of Froude number effects and validation of the computational fluid dynamics at both low and high Froude number.
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From page 982... ...
case, wave-induced effects on the boundary layer and wake are significant due to the larger wave amplitudes especially on the windward side than for the zero-yaw case. Recent advancements in computational fluid dynamics (CFD)
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From page 983... ...
and (q, Hi. Spacings are specified in the Indirection at the Ace of the hull, which for the Baldwin-Lomax turbulence model should be at a Y+~l, and in the (-direction at both the centerplane and free surface.
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From page 984... ...
The oscillation of the solutions is considered in the analysis of iteration uncertainty described in the following section. UNCERTAINTY ANALYSIS In the following, more detailed characteristics of the present computational grids are discussed in conjunction with uncertainty analysis.
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From page 985... ...
The differences between the present and experimental data can likely be attributed to the above-mentioned differences in the fix/free condition. In addition, some shortcomings of the present method in resolving complicated features in flow field may be related to the differences, e.g., underpredicted magnitude of axial vortices as well as absence d: wave-breaking and bubble-entrainment effects.
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From page 986... ...
For both the present and experimental results, the overall trends are similar between the Fr=0 and 0.316 flow fields, in which significant free-surface effects are also exhibited for the latter. Most of the flow features in the yawed condition are significantly different from those for zero-yaw case.
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From page 987... ...
. In the present results, the forebody-bilge vortex weakens faster than that for measurements, which is likely due to the inadequate accuracy in turbulence model and longitudinal grid resolution.
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From page 988... ...
Discussion of the results are focused on important flow features of yaw- and wave-induced effects in comparison with experiments. Satisfactory agreement is demonstrated between the calculations and the experimental data, i.e., the asymmetric wave field close to the hull, and meanflow fields dominated by strong crossflow effects that drive the flow from the port to the starboard side and asymmetric vorticity development at the forebody bilge, forebody keel, afterbody bilge, and aderbo~y keel are correctly simulated.
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From page 989... ...
(1995) , "CFDSHIP-IOWA: Computational Fluid Dynamics Method for Surface-Ship Boundary Layers, Wakes, and Wave Fields," IIHR Report, No.
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From page 990... ...
Table 1. Lift, drag, and moment Fr=,0=10° Fm0~31 B,,=10° Conditions ~ Ro=4xtO.
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From page 991... ...
1, Fr=0.3 16) Fig.2 Computational grid
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From page 992... ...
- - ~002 Pr~'lre S:i~ CPX Z .
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From page 993... ...
Fr=0 0.020 , Ft~o 0.010 Pr~ure Side 0.000 .010 .020 .030 4.040 .050 0 .o 0.020 0.010 0.000 -0.010 .OQ'O .030 -0.040 -0.050 0.020 0.01~)
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From page 995... ...
· 20.00 18." 1~ coo 4.m X~1., 1 o.oo ~ 1 4.00 i -12.00 1 -16.00 1 -20.00 1.02 0.96 o.so 0.84 X=1.1 X=1]
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From page 996... ...
(c) pressure Fig.8 Mean-flow measurements for ,B-10° and F - 0.16.
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From page 998... ...
~ .~ ~ .~ ._ I' (a) pressure Fig.10 Mean-flow measurements for ,B=10° and Fm0.316.
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From page 999... ...
We compared six components of Reynolds stress distributions win several turbulence models. In Hat case, even if the velocity distributions have good agreement between CFD and EFD, the Reynolds stress distributions do not agree so much.
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From page 1000... ...
Computational Fluid Dynamics (CFD) has been shown to be capable of predicting the fluid velocity distributions at model scale to accuracies of around 5% of measured values, but many of these predictions have failed to capture accurately details of the flow features, for example, Me wake harmonics [1~.
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From page 1001... ...
This paper describes some preliminary CFD results of the Reynolds' scaling of the RNG k-£ and the standard Wilcox and the Menter k- ~ turbulence models in the presence of an adverse pressure gradient and with embedded vortices in the boundary layer. The incompressible RANS equations for momentum and continuity are: (0UiBUi)
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From page 1002... ...
The coefficients for the two cases are given Table 1 Coefficients for Wilcox and Menter turbulence models 0.0750 ~1 _ - as I 1~ Initial and Boundary Conditions | Wilcox (id)
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From page 1003... ...
These requirements mean that additional care must be taken within the grid generation process to ensure that accurate, high quality grids are produced within the boundary layers. The total number of cells required to ensure this quality increases for the advanced turbulence models.
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From page 1004... ...
Flow predictions were carried out for Reynolds' number of I .2x107, 3x107, 6x107, 1 .2x108, 3x108, 6x108 and I .2x109 for each of the turbulence models. Comparison of the boundary layer profiles of the axial velocity component and the turbulent kinetic energy respectively are given in figure 2 and 3 for the axial stations x/L = 0.978 and 1.040.
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From page 1005... ...
Expenmcnt ~ "` Figure 3 Turbulent kinetic energy at x =0.978 and x = 1.040 1005 Comparisons of the profiles for the axial velocity component and turbulent kinetic energy for the boundary layer at x = 0.978 and for the wake along the axis are given in figures 5 to 7. Comparison between each of the turbulence models for three Reynolds' numbers of 1.2x107, 1.2xlOg and 1 .2xlO9 are shown in figures 5, 6 and 7 for the boundary layer and wake profiles.
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From page 1006... ...
RNG -- - Menta ...... Wllcox Figure 6 Boundary layer and wake profiles at Re = I .2x 1 o8
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From page 1007... ...
Therefore, for underlying grid resolutions of 200,000 and 400,000 cells for the pressure field, approximately 250,000 and 500,000 cells were used for the 'wall fimction' grid with 500,000 and 1,000,000 cells used for the equivalent 'down-to-thewall' grids. The same number of cells and first cell spacing in the innermost layers as described for the AFF1 configuration was used for each turbulence model and Reynolds' number.
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From page 1008... ...
The size and strength of the embedded vortices increased as the Reynolds' number increased and the position of the stagnation point forward of the appendages moved upstream. Overall, the Menter turbulence model showed considerably more activity than the RNG model, especially in the boundary layer, which increased as the Reynolds' number increased.
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From page 1009... ...
+_. ~_ _ + , ~ 0 1 5 30 45 60 75 Figure 10 Wake profiles for RNG at x = 0.978 and Re = 1 .2x 107 ~.
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From page 1010... ...
.~ O - -- 1 1 ~+ 1 5 30 45 .... ~ -- - - t 60 75 90 Figure 12 Wake profiles for RNG at x = 0.978 and Re = 1 .2x 1 o8
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From page 1011... ...
.; 1~/~ '; `' \< 0.00005 0.0001 V 0.00005 o r/R = 0.25 -- - rtR = 0.30 ....- r/R = 0.40 -- r/R=0.50 0.00015 V 0.0001 ''`\ ~ ~;~ _' , ~- - ~. ,_' O - - 1 1 - 1 ~1 ~1 0 15 30 45 60 75 90 r/R= 0.25 -- - r/R = 0.30 - r/R = 0.40 -- r/R=0.50 -___ ~ -__ ~ -- O - ~- ~ -- ~- 1 -- ~ ~1 1 5 30 45 60 75 9001 5 30 45 60 75 90 Figure 13 Wake profiles for Menter at x = 0.978 and Re = 1.2xlO9 Figure 14 Wake profiles for RNG at x = 0.978 and Re = 1 .2x 109 1011
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From page 1012... ...
Menter at Re = I .2x107 Menter at Re=l .2xlO~ RNG at Re = 1 .2x107 RNG at Re = 1.2xlO~ Menter at Re = 1 .2xlO9 Figure 15 RNG at Re = I .2x109 Figure 16 1012
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From page 1013... ...
However, for this exercise, it was necessary to maintain a consistent specification of the initial condition which encompassed a range of Reynolds' numbers. Examination of the wake profiles for AFF4 shows that the Menter turbulence model is predicting larger variations in the velocity and turbulence parameters than the RNG model at model scale.
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From page 1014... ...
This also extends to the critical assessment of the predicted flow field, and its level of convergence. The RAG turbulence model in conjunction with wall functions and the Menter turbulence model can make predictions from model to full scale for appended and unappended bodies.
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