Centrifugal Fan Design and Simulation
This report presents a comprehensive centrifugal fan analysis using TCAE simulation software.
Introduction
This study shows a complex step-by-step analysis of a centrifugal fan from its design to an advanced CFD & FEA simulation, including FSI and modal analysis. The simulation software used for this analysis is TCAE – a comprehensive simulation environment based on open-source. This particular centrifugal fan which is used in this example is completely artificial, however, it was derived from a real existing fan, for which the comparison of the CFD and FEA results with measurement has been made. The goal of this study is to show in detail how to make a comprehensive analysis of the basic centrifugal fan characteristics: efficiency, phi-psi, torque, power, pressure, stress, displacement, modal analysis, and many more.
Centrifugal Fan Design
A typical input for a detailed simulation analysis is a watertight (wet) surface model in form of STL surface. For CFD simulation, it is needed to have a closed watertight model (sometimes called waterproof, or model negative, or wet surface) of the fan inner parts where the air flows. For FEA simulation, it is needed to have a closed surface model of solid of the impeller in form of a single one STL surface.
In general, there are multiple ways how the centrifugal fan model can be created. The CAD model of the centrifugal fan can be generally created in any CAD software manually or in an automated way via parametric model. Or, engineers can use a special dedicated software for turbomachinery design like for example CFturbo, Concepts NREC, or TURBOdesign Suite and create the CAD model and export STL surface. Alternatively, the surface model of a centrifugal fan can be created in an open-source software like for example Salome, FreeCAD, or Open Cascade. In any case, a centrifugal fan can be described with the help of a set of parameters that describe all the important shapes and measures of a fan.
CFDSUPPORT has developed a special geometry builder for centrifugal fans, based on Salome, inside TCAE software module TCAD. This centrifugal fan TCAD geometry builder reads the set of parameters and creates the CAD geometry in the STEP format, and extracts the STL surface out of it. STL surface is needed for the CFD & FEA simulation. For example, consider the following centrifugal fan parameters:
D1 = 0.6
blade_angle = math.radians(29.0)
spiral = True
cross_1 = 0.732
k2_radius = 0.802
inlet_length_2 = 0.100
D2 = 1.100
b2 = 0.3
BS = 0.5
cross_2 = 0.863
k3_radius = 0.946
inlet_fillet_radius = 0.077
blade_radius = 0.5
b1 = 0.3
TR = 0.05
cross_3 = 1.018
k4_radius = 1.116
inlet_angle = math.radians(32)
blade_thickness = 0.01
shaft_length = 0.04
HV = 0.9
cross_4 = 1.201
out_length = 1.2
opennes_angle = math.radians(55)
number_of_blades = 10
impeller_solid_thickness = 0.010
delta_rz = 0.138
k1_radius = 0.680
inlet_length_1 = 0.743/2
lock_length = 0.010
Such combination of parameters leads to the following centrifugal fan geometry:
Centrifugal Fan - CFD Preprocessing
For CFD simulation it is best to split the centrifugal fan into several waterproof components because of rotation (some parts are rotating and some parts are not). Each component consists of a few or multiple STL surfaces. It is smart to split the surface model into multiple surfaces because it opens a wider range of simulation methods (mesh refinements, manipulation, boundary conditions, evaluation of results on model parts, …). This particular centrifugal fan seems reasonable to be split into three components: Spiral, Impeller, and Suction.
The model topology is always up to the user, there are no limitations on the number of components or individual surfaces. In any case, the final model for CFD simulation needs to be split into closed waterproof components. This centrifugal fan is split into three components. First one is called suction. The second one is called impeller (this component is rotating). The third component is called spiral. The following image shows the meridional view of the centrifugal fan split into three components:
Each component consists of individual STL files. Typically, they are the inlet, the outlet, and the wall. For example, within a simplest possible approach, the impeller component can consist just out of three STL surfaces called, for instance:
impeller-inlet.stl impeller-outlet.stl impeller-wall.stl
Or, within a detailed approach, the impeller component can consist out of the following parts:
impeller-inlet.stl impeller-outlet.stl impeller-wall.stl