Lecture 5 Multiple-Rotating Reference Frame Modeling (MRF) 14.5 Relea
Advanced Rotating Machinery
© 2012 ANSYS, Inc. June 18, 2013 1 Relea 14.5
Outline
• • • • • • • Introduction to MRF Modeling What is the MRF Model? Interfaces MRF Problem Setup Troubleshooting MRF Problems Summary Appendix
© 2012 ANSYS, Inc.
June 18, 2013
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Introduction to MRF Modeling退休生活
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• Many rotating machinery problems involve stationary components which cannot be described by surfaces of revolution – SRF is not valid! – You must create interfaces between stationary and rotating regions Systems like the which involve stationary and rotating components parated by interfaces can be addresd with FLUENT using three different approaches: – Multiple reference frame model (MRF) – Mixing plane model (MPM) – Sliding mesh model (SMM) The MRF model, the simplest and most approximate of the three approaches, will be discusd in detail in this lecture
June 18, 2013 3 Relea 14.5
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© 2012 ANSYS, Inc.
What is the MRF Model?
• Computational domain is divided into multiple stationary and moving fluid zones – Interfaces placed between zones Steady-state solution is calculated At the interfaces, appropriate transformations of the velocity vectors and velocity gradients are performed, and local fluxes of mass, momentum, ener
效率低下gy, and other scalars are determined No account is taken for the relative motion of one domain with respect to the other!
– Meshes do not move with time – For this reason MRF is often referred to as the “frozen rotor” approach – You can also think of the MRF solution as an approximation of the instantaneous (unsteady) flow solution when the rotor is in the position defined by the (fixed) mesh • Reasonable for incompressible flows as flow field responds instantly to changes in rotor position
© 2012 ANSYS, Inc. June 18, 2013 4 Relea 14.5
绸字组词• •
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MRF Illustration
送元二使Flow pass locally through the interface红地球葡萄
interface
stationary zone
rotating zone
© 2012 ANSYS, Inc.
June 18, 2013
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Characteristics of MRF Models
• • • Steady-state flow field with constant speed moving reference frames in lected cells zones Boundaries which are contained within the moving zone interfaces must follow the geometry rules for SRF models For rotating zones, the interfaces must be a surfaces of revolution with respect to the axes of rotation of the rotating zones Can employ rotationally periodic boundaries, but the periodic angles of all zones must be equal*
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* There exists a beta feature in FLUENT 14.5 which permits nonequal periodic periodic angles. This feature, known as the Pitch Scale Model, is documented in the Appendix.
© 2012 ANSYS, Inc.
June 18, 2013
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