Exploiting DNS in 3D Design

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Research AimsCurrently, unsteady numerical studies with DNS still rely on time averaged quantities. This means that, even today, unsteady flows are still viewed from a fundamentally steady point of view with no existing framework to switch to a truly unsteady perspective. Establishing a truly unsteady framework with which to characterise flows is the first aim of this project.Following on from this, the unsteady framework developed will be applied to a radial impeller to predict the unsteady losses, especially from the gap between the blade tip and the wall (tip gap). This serves to fill two gaps in knowledge: firstly, it is currently known that reducing the tip gap in radial impellers reduces the loss, but it is still unknown how the loss can be reduced for a fixed tip gap e.g. if it minimum tip gap is limited by manufacturing constraints. Secondly, the ability to predict radial impeller performance lags behind that for axial compressors. Achieving this aim will provide a step forward in reducing this discrepancy.Finally, from the DNS data and unsteady framework, develop a reduced order model for radial impeller loss that is fast enough to be used in the 3D design stage.Research ApproachTo achieve the first aim, DNS will be performed on a cascade version of the radial impeller (this is a simpler version of the geometry) in order to test different unsteady frameworks.Once a framework has been selected, the second aim will be achieved by performing DNS of the full radial impeller geometry with tip gaps under full operating conditions. Using the unsteady framework, unsteady flow behaviour can be linked to loss which will allow prediction of radial impeller performance.Methodology for achieving the third aim will likely involve the identification of the flow features within a radial impeller which dominates loss, with others being stripped from the loss prediction model.Novel Engineering/Physical SciencesTruly unsteady framework for characterising unsteady and turbulent flowsDevelopment of loss reduction methods in radial impellers with a fixed tip gapHigher accuracy radial impeller performance prediction