Modelling of a Centrifugal Impeller in KOMPAS-3D from Cloud Point Data
In turbomachinery, impellers are critical components responsible for transferring energy from a motor to a fluid by accelerating it outwards from the center of rotation. Designing high-efficiency closed centrifugal impellers presents severe geometric challenges: the blades must follow highly optimized, three-dimensional curved paths to minimize aerodynamic losses, prevent cavitation, and maximize pressure recovery. “By implementing a hybrid modeling workflow in KOMPAS-3D—where high-precision coordinates are automatically translated into 3D curves, surface patches, and seamless solid bodies—designers can construct production-ready turbomachinery with mathematical precision.” Core Technical Concepts in Impeller Design Before reviewing the CAD steps, it is essential to understand the aerodynamic and structural logic incorporated in this impeller: Backward-Curved Blades: Bending the blades opposite to the direction of rotation ensures higher operational efficiency, stable head-capacity behavior, and lower surge susceptibility. Splitter Blades: Shorter, intermediate blades sit at the outer diameter of the impeller. They provide optimal fluid guidance at the outlet, preventing jet-wake flow separation while maintaining a large throat area at the inlet to avoid choking. Closed Impeller Structure: The blades are fully enclosed between the backplate (hub) and the front cover plate (shroud). This watertight sealing prevents fluid recirculation losses, drastically increasing volumetric efficiency compared to open impellers. Step-by-Step CAD Modeling Timeline The following sequential timeline documents the exact, step-by-step CAD workflow recorded in our high-resolution design video, illustrating the automated B-spline reconstruction, hybrid surfacing, direct modeling calibration, circular array patterning, and stress-concentration filleting. 1 Launch KOMPAS-3D Macro Manager The modeling workflow begins by launching the native KOMPAS-Macro utility within the Part workbench. This interface serves as the entry point for selecting and running custom automation scripts. Active Tasks Launch Macro selection dialog Initialize Part (.m3d) environment Prepare script execution path Engineering Insight Executing automation directly through the native Macro Manager ensures a clean workflow execution integrated into the CAD tree. 2 Select TurboGrid Curve Files Rather than using a generic turbomachinery importer utility, the custom Python script is loaded. The designer selects the generated coordinate files in the TurboGrid .curve format, which contain coordinates for the impeller hub and shroud flow paths. Active Tasks Select impeller-stage1_hub.curve file Select impeller-stage1_shroud.curve file Configure coordinates for script input Engineering Insight Using .curve data generated by fluid dynamics programs directly connects the hydrodynamic design coordinates to the CAD environment. 3 Automated Spline Drawing The custom Python script parses the coordinate data from the TurboGrid curve files and directly draws/constructs the 3D spline curves in the KOMPAS-3D viewport, establishing the precise blade paths in the tree. Active Tasks Script reads 322 points for the hub curve Script reads 242 points for the shroud curve Directly draws 3D spline curves in viewport Engineering Insight Because the script itself draws the spline curves, manual sketching is completely bypassed, eliminating transcription errors and guaranteeing absolute curve accuracy. 4 Blade Surface Creation Using the Surface by grid of curves feature in KOMPAS-3D, the designer selects the generated splines to loft and construct the complex three-dimensional suction and pressure surfaces of the impeller blade. Active Tasks Select Surface by Grid of Curves feature Map Direction U and V curves from splines Loft aerodynamic blade surfaces Engineering Insight The Surface by Grid of Curves feature allows for perfect geometric control of the three-dimensional blade profiles across varying span-wise layers. 5 Surface Boundary Capping To transition from open surface grids to a sealed watertight shell, the designer executes the Patch tool, selecting the edge boundaries of the leading and trailing edges to form clean end-cap surfaces. Active Tasks Capping boundary edge loops Prepare surface sheet assemblies for stitching Create watertight zero-thickness boundaries Engineering Insight Applying exact surface boundaries at the leading and trailing edges establishes the sharp, aerodynamically optimized stagnation boundaries required for fluid entry. 6 Solid Blade Generation The individual surface grids and cap patches are knitted together. The resulting watertight envelopes are solidified into dense 3D volumes. This yields two separate solids in the tree: the Main Blade and the Splitter Blade. Active Tasks Stitch surfaces into a solid envelope Generate distinct ‘Main Blade’ and ‘Splitter Blade’ solids Organize part hierarchy under Part (Solids-2) Engineering Insight Converting surfaces to solid structures is mandatory to perform downstream physical calculations such as material mass, structural integrity (FEA), and Boolean merges. 7 Joining the Faces Instead of direct modeling face deletions, this step is simply joining the faces (stitching surfaces). The individual surface sheets are stitched together to ensure a watertight sheet assembly before converting them into solid volumes. Active Tasks Select adjoining blade boundary faces Stitch and join surfaces into unified sheet Ensure airtight boundary geometry Engineering Insight Joining and sewing the individual surface boundaries is a critical prerequisite to ensure that the sheet can be successfully thickened or solidified without geometric gaps. 8 Align Blade to Hub & Shroud The selected blade faces are moved/offset specifically to align and match perfectly with the hub and shroud surfaces. This alignment is critical to prevent gaps and geometric mismatch errors, ensuring a flawless Boolean union later. Active Tasks Select blade boundary faces Move selected faces to overlap hub/shroud Eliminate gaps to prevent Boolean errors Engineering Insight Moving faces to achieve a perfect physical overlap with the hub and shroud prevents mesh self-intersections and zero-thickness geometry errors during Boolean operations. 9 Concentric Array Launch The revolved solid hub is generated. The designer initiates the Array by concentric grid command, selecting the thickened main and splitter blade solids to pattern around the central Z-axis. Active Tasks Define rotation axis: Central Z-Axis Select Main & Splitter solids as patterned inputs Configure array parameters and concentric grid Engineering Insight Circular patterning ensures absolute geometrical symmetry, which is vital for preventing rotor imbalance and mechanical vibration. 10 Concentric Blade Copying The pattern generates an alternating array of blades. The designer runs a Boolean operation (Merging) to fuse the patterned blades and the revolved hub backplate solid into a single, seamless monolithic solid. Active Tasks Concentric array patterns 7 main and 7 splitter blades Perform Boolean Merging (Union) of all blade solids Preview single contiguous impeller
