The centrifugal compressor is a central part of the turbocharger on a truck. It compresses the air which allows for a larger intake of gas into the cylinders. This raises the amount of oxygen available for combustion which increases the efficiency of the engine. However, the operating range of a compressor is limited. If the mass flow through the compressor gets too low, it can start to surge. The surging phenomenon for centrifugal compressors is characterized by axial oscillations in the mass flow which can cause a backflow of air through the compressor. This can result in structural damage on the compressor. It is therefore important to understand under which conditions surge occurs. When it comes to the development and design of compressors, Computational Fluid Dynamics (CFD) is a valuable tool. It enables us to simulate the performance of compressors without the costly process of building a prototype and testing it. Even simpler steady-state simulations can give valuable insight on the performance. However, since surge is a dynamic phenomenon, it is not readily accessible through one of these steady-state simulations, where the sought solution is a flow field constant in time. The aim of this thesis is to capture the surge phenomenon in a steady-state simulation and develop a method for predicting when the compressor surges. This is done by looking at oscillations in the solver for the total pressure at a cross-sectional plane upstream of the compressor wheel. We find that the amplitude of these oscillations increases when the compressor is approaching surge. From this we define a surge criterion and fit the model parameters to an experimentally determined surge line. We then predict the location of the surge line for the same compressor, now equipped with a ported shroud (a geometry feature with the intention of mitigating surge). With this ported shroud, we expect the compressor’s operating range to be widened, which is also what the model predicts. However, this prediction needs to be compared with real data in order to see if the method accurately captures the location of the surge line.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-531518 |
| Date | January 2024 |
| Creators | Malmsten, Jakob |
| Publisher | Uppsala universitet, Elektricitetslära |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | UPTEC F, 1401-5757 ; 24032 |
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