Introduction

Once a new case is created in ColdStream, the next step is to upload the geometric entities. This article explains how to properly upload and populate your CAD models within the platform. It assumes that all necessary CAD preparations have already been completed. For detailed instructions on geometry preparation, refer to the CAD Preparation Guide.

CAD file format

All geometric models must be uploaded using the STEP file format. Ensure your export settings meet the following strict requirements:

• Protocol: Export using Application Protocol (AP) 214. While this is the default for most mechanical CAD packages, always verify your export settings.
• File Structure: The file must be exported as a single Part file, not an Assembly file. An assembly file merely references external parts without containing the geometry itself. If you are working with an assembly, consolidate it into a single multi-body part before exporting, or contact support for assistance.

Uploading a geometry

ColdStream offers two distinct methods for populating your case with the necessary regions, subregions, and boundaries.

Method 1: Single File Upload

This method allows you to upload a single, comprehensive STEP file containing all regions, subregions, and boundaries simultaneously. This is the recommended approach for the initial geometry setup.

• Click Upload STEP and select your prepared CAD file.
• Click Populate case.

The platform will automatically parse the file, translating individual 3D bodies into regions and subregions, and assigning 2D surfaces as boundaries to their respective parent regions. The geometry undergoes strict validation checks during this process; any bodies or surfaces violating geometric guidelines will generate an error and will not be created.

Method 2: Individual Entity Upload

Alternatively, you can construct your case piecemeal by uploading individual STEP files for each specific region, subregion, or boundary.

1. Click the + (plus) icon next to the Regions header to upload a new region.
2. Once a region is created and its type is defined, specific buttons will appear within its settings panel allowing you to upload and assign individual subregions and boundaries directly to that parent region.

Naming Conventions

Upon the initial CAD upload, ColdStream automatically attempts to read and assign the entity names defined within your original CAD software.

Because STEP export definitions vary across CAD packages, some names may fail to parse. In these instances, ColdStream applies a default naming convention structured as [type] [number] (e.g., Region 0, Boundary 1). The numbering begins at 0 and resets for the subregions and boundaries within each specific parent region.

Geometry guidelines

A successful simulation requires a strategic balance of geometric detail. Excessive detail increases computational overhead and complicates meshing, while insufficient detail compromises the accuracy of the predictive simulation. Follow these best practices:

• Curate Small Features: Only retain micro-features if they critically impact fluid flow or thermal transfer. Remove purely aesthetic or non-functional details.
• Remove Decorative Realism: Strip out embossed or engraved text, logos, individual fasteners, threads, and disconnected screws.
• Eliminate Degeneracies: Avoid non-manufacturable CAD artifacts that cause meshing errors, such as zero-thickness sliver surfaces, cusps, or knife-edges.
• Simplify Thin Walls: Consider removing extremely thin solid geometric regions and replacing their physical effect by applying a Thermal Interface boundary condition within the platform.
• Clear Nomenclature: Assign distinct, descriptive names to all regions, subregions, and boundaries in your CAD tree before exporting to STEP.
• Global Orientation: Align the primary geometric axes strictly with the global X, Y, and Z coordinate axes. This improves meshing quality and overall solver performance.