A CFD study of the losses in sharp and radiused orifices with and without inlet cross-flow

• Main Author: Nguyen, Tien
• Format: Others
• Language: English
• Published: KTH, Mekanik 2015
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170038

Increasing efficiency demands on modern gas turbines require higher operating temperatures which increase the thermal load on the materials. The secondary air system transfers heat away from the components to ensure that the operating conditions are under the components’ critical values. In the secondary air system, orifices are an essential component, thus a thorough understanding of the flow behaviour, more specifically the mass flow and pressure loss, is crucial. Siemens Industrial Turbomachinery initiated an experimental study regarding the discharge coefficient for sharp and chamfered orifices (Binder, 2013). This work seeks out to enhance the previous study with radiused orifices through the use of Computational Fluid Dynamics (CFD). Additionally, inlet cross-flow was studied for radiused orifices. A literature study was conducted to provide a deeper understanding of the flow behaviour and to provide a basis for comparison. A mesh verification study was performed to ensure that the meshes used were adequate, this was done only for flow cases without inlet cross-flow. A validation study was conducted with the data from Binder (2013) and Hüning (2012) for two representative cases without inlet cross-flow and one case with inlet cross-flow. The CFD calculations showed in general a good agreement with the previous work. Furthermore, a small turbulence model study was conducted and validated with the work of Binder (2013). 85 cases with different orifice length to diameter ratios, radius to diameter ratios and pressure ratios were run and 34 cases with inlet cross-flow were calculated with varying length to diameter ratio, radius to diameter ratio and cross-flow ratio. A comprehensive study of the results was done with comparison with previous articles and correlations, and the obtained result showed good agreement regarding the flow behaviour and discharge coefficient. Furthermore, the CFD approach offered more insight into the flow behaviour since the field variables can be visualized more easily as compared with experimental studies. Finally, all the discharge coefficients were collected into three correlations, one for the cases without inlet cross-flow and two for the cases with inlet cross-flow. The correlations have excellent performance in their defined range but should not be used outside the range and a number of suggestions are presented for the use of the correlations outside the range.