The flow through rotating orifices is of interest to the designer of machines incorporating such features. The designer often requires a set of correlations which can be used to check out preliminary designs and converge on a solution prior to attempting detailed and expansive analysis. The correlations given in this paper are based on the incidence angle, i, of the flow into the orifice and they allow the discharge coefficient for rotating orifices to be estimated for as many conditions and geometries as possible. The approach adopted is to group the parameters that affect the discharge coefficient to i = 0° (Reynolds number, orifice chamfer and radius, L/d ratio, pressure ratio, and pumping effect) and i ≠ 0° (rotation of the disc, preswirl, cross-flow, and the angle of inclination of the orifice). The effect of each parameter on the discharge coefficient can easily be observed when using this method. Furthermore, the method can predict the discharge coefficient for systems that have various parameters that are combined together. There is a good agreement between the correlations and the experimental results and the available data on rotating orifices in the open literature. The correlations also agree with various combinations run in computational fluid dynamics (CFD). The approach adopted in this paper, which is based on the incidence angle, can assist designers to find the combination of geometric and flow parameters that gives the best discharge coefficient for rotating orifices.
This paper describes an extensive experimental and computational investigation of the fluid flow in radial and radially inclined oriented rotating orifices. Such geometries frequently occur as part of the internal cooling system within gas turbine engines and can also be found in many classes of high speed machinery such as industrial compressors and high speed electrical machinery. The objective of the work was to enhance the understanding of the flows in such geometries and reliably establish discharge coefficients which can be used for air system design purposes. Publications in the area of rotating orifices are still sparse in comparison with other subjects although some important work has very recently been published for rotating orifices with axial orientation [1]. However, for radially or radially inclined orifices, there is close to nothing in the public domain. Although much of the understanding derived from the study of axially orientated orifices is relevant, the effect of change in radius is much more substantial, as significant Euler work transfer occurs. In many cases, there is a rise in static pressure as opposed to a reduction, normally associated with the flow through orifices. A rig was designed and built to perform the experiments and the results were compared with the numerical analysis performed using the proprietary software STAR-CD. The results indicate that the discharge coefficient is affected by the presence of the pumping effect from rotation of the orifice. This effect is more visible when the orifices are inclined towards the direction of rotation of the disc since the flow enters the orifice with reduced entry losses. To describe this phenomenon, the usual approach used in orifice flow theory is merged with the turbomachinery concepts, particularly through the Euler Turbomachine equation. A new theory for maximizing discharge coefficient based on the evaluation of the incidence angle has been developed and found to be successful. Most of the studies in the past used the ratio of tangential velocity and axial velocity as a parameter to represent the discharge coefficient, but it has been observed that using the incidence angle is more helpful in formulating discharge coefficient in rotating systems, especially when orifices with angle of inclination are to be treated. The results show that by having incidence angle at around zero degrees, the discharge coefficient for any combinations of flow and geometric parameters can be optimized.
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