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1、15-1ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.April 28, 2009 Inventory #002598Chapter 15Review and TipsIntroduction to CFX Review and Tips15-2ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.April 28, 2009 Inventory #002598Training ManualDomain Interfaces Domain Interf
2、aces can be used as part of a meshing strategy as well as for connecting different domains or reference frames together Boundary conditions are created in each domain when a Domain Interface is created; generally you should not edit these directly When the mesh is different on each side of the inter
3、face a GGI (General Grid Interface) is used This will use more memory in the Solver than a continuous mesh Accuracy across a GGI interface is usually not a concern as long as the mesh length scales on each side are similar Automatic Domain Interfaces are created by CFX-Pre in some cases Always check
4、 these and dont assume that all the required Domain Interfaces have been createdReview and Tips15-3ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.April 28, 2009 Inventory #002598Training ManualSources Sources are used to account for physics or processes that have not been directly reso
5、lved in the simulation Momentum sources can be used to create a pressure drop (e.g. a screen, a porous material) or a pressure rise (e.g. a fan) Energy sources can account for heat added/removed from the simulation When sources are functions of the solved variable (e.g. momentum sources that are fun
6、ctions of velocity, energy sources that are functions of temperature) the Source Coefficient should be set The Source Coefficient must be negative otherwise the solver will diverge May need to re-write the Source so that is has a negative derivativeReview and Tips15-4ANSYS, Inc. Proprietary 2009 ANS
7、YS, Inc. All rights reserved.April 28, 2009 Inventory #002598Training ManualTransient Simulations In a transient analysis the timestep should be small enough to capture the transient behaviour of interest Boundary conditions can be functions of time Convergence should be monitored so that each times
8、tep is converged It is generally better to reduce the overall timestep size to improve convergence rather than increasing the number of coefficient loops Remember to create the Transient Results object before runningReview and Tips15-5ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.Apri
9、l 28, 2009 Inventory #002598Training ManualTurbulence Estimate the flow Reynolds Number to determine if the flow is laminar or turbulent Check y+ values to make sure the near-wall mesh is suitable y+ 0.2) should use the Total Energy model The double precision setting for the Solver is recommended fo
10、r CHT simulations (i.e. when a solid domain is included) Always make sure energy imbalances have reached acceptable levels in CHT cases Enable Viscous Work or Viscous Dissipation if heating due to viscous effects is important If thermal radiation is modeled choose an appropriate model depending on t
11、he optical thickness Thin Wall modeling and thermal contact resistances can be set at domain interfacesReview and Tips15-7ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.April 28, 2009 Inventory #002598Training ManualMoving Zones Moving boundaries can be simulated in several different w
12、ays For rotating walls, a wall velocity can simply be imposed if the motion is purely tangential (e.g. a rotating hub or a solid brake disk) When the rotating walls have a normal component of velocity they must be placed inside a rotating domain (e.g. blades, vented brake disk) Stationary walls then
13、 become counter-rotating in the rotating domain and must form surfaces of revolution (i.e. no normal component of velocity) Although a Mesh Motion approach is possible, it is much more computationally expensive Mesh motion is usually used to simulate deforming boundaries or linear / cyclic motionRev
14、iew and Tips15-8ANSYS, Inc. Proprietary 2009 ANSYS, Inc. All rights reserved.April 28, 2009 Inventory #002598Training ManualMoving Zones At a change in reference frame a frame change model is used From low fidelity/cost to high fidelity/cost the choices are Frozen Rotor, Stage or Transient Rotor Sta
15、tor Other approaches for moving regions are: Rigid Body Motion A 6-DOF solves calculates the solid body motion Used in conjunction with Mesh Motion Immersed Solid Used to simulate moving solids that cannot be accommodated with Mesh MotionReview and Tips15-9ANSYS, Inc. Proprietary 2009 ANSYS, Inc. Al
16、l rights reserved.April 28, 2009 Inventory #002598Training ManualWhy Does My Case Fail in the Solver? First carefully read the error message The error message may recommend setting an Expert Parameter This may be an appropriate fix, or it may mask an underlying problem Example: +-+ | Checking for Isol
