Advanced Fan modelling and analysis in ANSYS Icepak

1. Introduction

An Icepak 3D fan object may sometimes behave differently from real fan behavior. Typically this is due to flow features like swirl and centrifugal spread resultant from the spinning fan rotor as well as the rotor blade geometry. In an Icepak fan based setup, this swirl is estimated and calculated off a 2D annular flow face rather than off the physical surfaces of the blade.

The MRF approach allows for a more accurate representation of the internal geometry of the fan and therefore results in a better modeling of the flow features. In Icepak MRF simulations, the actual blade geometry is modeled as a CAD block object and a fluid cylinder rotates into contact with the surfaces to create a spinning flow.

In this project, An Imported icepak fan blades model is used which rotates in a modelled MRF fluid blocks to create flow in the model. Then, through the analysis, the flow pattern of the 3D fan and its cooling effectiveness on PCBs and power modules are detailly analysed.

2. Geometry description

The Geometry of the Electronic compartment includes two power modules, a master PCB, fours sub-pcb assemblies, two 3D fan assemblies and supporting elements like beams and corners.

A Reference image has been attached below to understand the compartment more effectively.

The Assemblies are named in order (From the left) below:

1. Power modules - This Module supplies the power to the unit and those are controlled separately by a PCB which is controlled by the Master PCB.

2. Sub-PCB assemblies - This Assembly has four PCB assemblies assembled vertically and each assembly is individually connected the Master PCB placed in the rear side through connectors.

3. Fan assembly - This Assembly has two fans, fan cases, cylindrical fluid blocks to provide the flow in the cabinet.

2. Meshing the model:

2.1. General mesh settings:

The General mesh settings used for the model is shown below. The Model has been meshed with the Mesher HD type.

2.2. Individual mesh settings for Fan assembly:

2.3. Multi level mesh settings:

The Meshed model's minimum quality is satisfactory and described below.

Volume: 1.3e-12 m3

Face allignment: 0.1031

Skewness: 0.004352

2.4. Mesh visualisation:

A. Along YZ plane:

B. Mesh on Fan assembly:

C. Along XZ plane:

3. Setting up the case and Solving the simulation:

3.1. Rotating fluid block:

A Cylindrical fluid block around the fan casing has been created and activated for Moving reference frame approach with 6000 rpm.

3.2. Power sources: The Power sources are assigned to the components respectively as per the configuration.

3.3. Problem setup:

A. Basic parameters:

B. Ambient conditions and defaults materials:

C. Basic settings:

D. Discretisation schemes:

E. Under relaxing values:

4. Solution description:

The Simulation has ran and got converged at 800 iterations with respect to the residuals and its monitor points of temperature and velocity.

A. Residual plot:

B. Monitor points for temperature:

C. Monitor points for Velocity:

4.1. Object face contour:

The Object face contour is created to understand the temperature distribution over the domain.

4.2. Plane cut analysis:

Temperature and Velocity distribution oon Z normal plane in Fan B assembly is shown below.

4.3. Particle traces:

The Particle traces has been created with respect to the Fan blades to understand the flow pattern.

This shows us how the swirl is captured by implementing MRF approach.

5. Conclusion:

An Imported 3D icepak fan blades model is imported and analysed its flow pattern through MRF approach. On Analysis, its clear that the maximum temperature in the compartments is 70 degC which states its cooling effectiveness on PCBs and power modules.