Aerodynamic Design of Centrifugal Compressor for Heavy Duty Truck Applications

Sammanfattning: The transport sector is one of many markets facing new challenges in the pursuit of reduced greenhouse gas emissions. The people at Volvo Powertrain in Malmö are continuously working to develop new and improved techniques that are able to live up to the ever-increasing legislations. A well performing turbocharger is an essential part of the combustion engine in order to reduce the fuel consumption and CO2- emissions. The engineers of today have powerful tools at their disposal that help them with the task of designing, developing and analysing these kinds of components. Advanced calculations such as CFD can be performed thanks to the great computational power of computers, a task that would seem impossible by hand. These tools have been used to create a new design for one of Volvo’s in-house turbo compressors for heavy duty vehicle application, with the purpose of improving the performance. The parts of the compressor that were subject to the design update are the impeller and diffuser. The in-house-compressor was first analysed in three operating points in the CFD- simulation program Star-CCM+. These results would constitute the benchmark for the new design. Using the in-house-compressor design as a starting point, new designs for the impeller and diffuser were made using the software package TURBOdesign Suite. The new impeller design was then put through iterations of optimizations in TURBOdesign and CFD-simulations in Star-CCM+ in the same three operating points as the in-house-compressor. The new diffuser design didn’t go through any optimizations. The results from the CFD-simulations of the final new impeller and diffuser designs were finally compared to those of the in-house-compressor to discern the differences in performance between the two designs. The new design displays higher efficiencies in all three operating points, with the biggest improvement in the design point where the efficiency is 1.8%-points higher. The flow analysis shows that the new design has more even flows; it however doesn’t achieve as high flows as the in-house-compressor. One explanation for this may be the more tangential diffuser vanes of the new diffuser design. Consequently, the diffuser of the in-house-compressor performs better than the new one in the high operating point (high mass flow). The leading edge of the impeller blades were found to be a bit too thin in the stress and vibration analyses in order to pass the criterion that Volvo has on the strength of the blade with regards to the eigenfrequency. Future studies may want to look into further designs of the diffuser vane since only one new diffuser design was tested together with the new impeller. This could lead to achieving higher flow rates. Furthermore, the leading edge of the impeller blade should be made thicker in order to pass the strength criteria. Since this can lead to a slightly smaller throat area in the impeller this alteration should be accompanied by adjustments to counteract this, for example a reduction of the blade and meridional hub angle at the inlet.