Fluent-Intro_15.0_L09_MovingZones.pdf

1 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential 15.0 Release Lecture 9: Non-Conformal Interfaces & Moving Zones Introduction to ANSYS Fluent 2 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Lecture Theme: Many CFD applications across industries involve systems or devices with moving parts. Fluent offers many different models for rotating machinery, for arbitrary prescribed motion and for objects whose path is determined by the flow. Learning Aims: You will learn: •How to define non-conformal interfaces and periodic boundary conditions •The models available for rotating machinery such as the multiple reference frame and sliding mesh models •The different dynamic meshing methods for arbitrary motion, including the coupled 6- DOF solver Learning Objectives: You will be able to use non-conformal meshes and will become familiar with Fluent’s models for systems with moving parts and when a particular model is applicable. Introduction Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 3 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Across an interface between two cell zones, the nodes may or may not exactly align •If the nodes match perfectly, this is a ‘Conformal’ mesh – If using DesignModeler, combining bodies into a single part will give a conformal mesh •If the nodes do not match up, this is a ‘Non Conformal’ mesh – Fluent can interpolate across the interface, but this must be defined in the GUI. – If not, Fluent will treat the interface as a wall, and no fluid can flow through. Overview Conformal Non-Conformal Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 4 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Non-conformal Interfaces can be used for: •Connection of mismatched meshes (hex to tet for example) – a single mesh file may contain non-matching mesh regions and require non-conformal interfaces •Changes in reference frames between cell zones – even if the mesh matches •Connect different types of cell zones together (e.g. Fluid and Solid) •Create periodic regions within a domain Overview Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 5 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Inserting Non-conformal Interfaces • To create a non-conformal interface: – Step 1: Define/Boundary Conditions •Change the type of each pair of zones that comprises the non-conformal boundary to interface – Step 2: Define/Mesh Interfaces •Enter a name for the interface in the Mesh Interface text-entry box •Specify the zones comprising the interface by selecting one or more zones below Interface Zone 1 and one or more below Interface Zone 2 –If one interface zone is much smaller than the other, specify the smaller zone as Interface Zone 1 to improve the accuracy of the intersection calculation •Enable the desired interface options if appropriate Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 6 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential • To create a Periodic boundary condition – Enable the Periodic Boundary Condition option in the Mesh interfaces panel – Select either Translational or Rotational as the periodic boundary condition Type • Retain the enabled default setting of Auto Compute Offset if you want ANSYS Fluent to automatically compute the offset – Mesh can be conformal or non-conformal Periodic Boundary Condition •Translational Periodicity – Simulates geometries that have translational periodicity – Allows for either the mass flow rate or the pressure change across the interface to be specified – The quantity not specified will be part of the solution •Rotational Periodicity – Simulates rotationally periodic geometries – Before proceeding, you have to correctly enter the rotational axis for the corresponding cell zone in the BC panel Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 7 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Introduction to Moving Zones • Many flow problems involve domains which contain translating or rotating components • Two types of motion are possible: translational and rotational • There are two basic modeling approaches for moving domains: – Moving Reference Frames •Frame of reference is attached to the moving domain •Governing equations are modified to account for moving frame – Moving / Deforming Domains •Domain position and shape are tracked with respect to a stationary reference frame •Solutions are inherently unsteady Introduction Non-Conformal Interfaces Rotating Zones Dynamic Mesh Summary 8 © 2013 ANSYS, Inc. February 28, 2014 ANSYS Confidential Moving Reference Frames vs. Mesh Motion • Moving Reference Frame • Domain moves with coordinate system • To follow the motion of the body, topology of the mesh does not need to be updated  Rotation / Translation of the Moving domain • Mesh Motion • Domain changes shape as a function of time • To follow the motion of the body, topology of the mesh n。