CFD (computational fluid dynamics) is used to better understand flow characteristics in pumps and compressors. The solid modeling task is to develop or extract the passages within the housings which contain the flow. These passages which must be a 'water tight volume' are meshed by the CFD software for use in the simulation constrained by the boundary conditions at the inlet and outlet. If part of the equipment is rotating such as in a pump that flow volume is designated a Moving Reference Frame. The CFD simulation then represents an instantaneous picture or 'freeze frame' of the flow conditions at one particular angular orientation during rotation.
The following screw centrifugal pump is a project for a client in which FreeCAD played a critical role. STEP models of the pump components were supplied by the client from their in-house high end CAD system.
FreeCAD was used to extract the flow passages as shown in the following figure. Generally this involves subtracting a component from the boundaries of the flow passages. The impeller was a straight forward boolean cut, but the volute housing was a bit of a challenge. The figure shows the sequence required to obtain a clean flow passage. Several steps were required. The first was to make cuts on the housing essentially half way through the wall thickness. That left the internal passage and bits and pieces of the housing. The pieces go away when a pad or pocket is made on the part you want to keep.
The solid components are exported as STEP files and imported into the CAD system for meshing as shown in the following figure.
Sample results from the simulation can include pressures, flow velocity magnitude and direction, hydraulic forces, and fluid drag or torque.
OS: Windows 8.1
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.15.4671 (Git)
Python version: 2.7.8
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17
CFD software: Symscape Caedium 5.2.0 (opensource OpenFoam)