STAR-CCM+ and SPEED for electric machines cooling analysis

STAR-CCM+ and SPEED for electricmachines cooling analysisStefan Holst

OverviewSPEED’s own thermal capability consists of simplified circuit models– Good for a first shot– Circuit model allows for quick analysis of duty cycle simulationsEfficiency requirements, space and weight restrictions lead to morecomplex machine and machine enclosure designs– Identifying hot spots becomes tricky– STAR-CCM+ can show its strength in these modelsUser should benefit as much as possible from the work done in SPEED– Import geometry– Import distribution of heat loads electromagnetic losses– Future: coupled EMAG and thermal analysis in a single tool

Loss mechanisms and distributionOhmic heating in all conducting parts– Windings, laminated rotor and stator core and magnets– Winding/copper losses are usually the largest contributorHysteresis effects mostly in steel partsSimulation these effects directlyrequires coupled transient EMAG run– Very costly for a design calculationNote: Losses occur locally

Steinmetz Loss calculationAlternative to coupled simulation– Hysteresis and eddy currents are mostlydriven by changes in the magnetic field– Get magnetic field for various rotorpositions and attribute losses to size offield changes– Strong variation in the teethMagnets shield the rotor core

Workflow diagramInitial 2D Machine Layout•Perform EMAG layout•Perform thermal circuitsimulation of duty cycles 10-16nodesGeometry Import•Meshing automatically specified•Physical setup•Either CHT•Or EMAG•Or even coupledHeat Loads from SPEED•Import via STAR-CCM+ fileformat *.sbd•Surface data needs to bemapped to volume

Geometry importxGDF & xDEF files contain the completeEMAG setup in XML• Currently only Geometry import• Future versions include physics andmodels for end-windings, skew

Cooling mechanismAir cooled– Exterior and interiorSpray cooling of the end windingsWater cooling around the stator– More on that now

Results for a cooling jacket around the statorHeat conduction, convection and radiation in the interior air1l/min water pumped throughHow to keep the rotor cool?

Introduce holes into the rotorFour CAD features later we’ve got holes in the rotorRemesh and further iterating gives

Data MapperLosses are given in 2D but the thermal simulation is in 3DData Mapper functionality extension to facilitate precise mapping evenfor skewed machines will come with 7.04– Improved mapping quality comparedto current nearest neighbourinterpolationThree mappings are defined here:– Rotor– Stator– WindingsSPEED only provides total losses inmagnets

Support for end windingsExamples so far have been hand made 3D CAD constructions

Glimpse on the EMAG solverMagnetostatic runs for different rotor positions

Glimpse on the EMAG solverLow frequency electro-magnetic solver– Frequency/domain size determines applicability‣ An e-machines frequency range might not be allowed in areas like minedetection with far larger length scalesCoupled transient and magnetostatic mode– Magnetostatic can be coupled with motion to cater for loss calculationsNon-linear material support– SPEED model import brings in BH-curves– Tabular data or functional description– Isotropic electric conductivity and permeability

EMAG solver outlookCircuit– Transient 3D requires feedback from the circuit• Extend circuit capability in BSM for general use– Flux linkage report for electromagnetic circuit elementsField simulation– Hysteresis modeling• Residual magnetism– Force/Torque calculation– Anisotropy• Electric conductivity andpermeability• Infrastructure

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