A/R Effects on Asymmetric Twin-Entry Radial Turbine Performances Under Steady and Pulsatil Flow Conditions

The design for better performances of the twin-entry spiral housing volute flow turbines is of prime importance as it affects the stage turbine performance at both design and off design conditions. Thus, attentions have to be paid to both inlet domain and spiral domain since the main roles of the spiral domain are to collect gases to distribute it properly all around the periphery of the rotor in the case of vaneless volute and around the stator in the case of vaned volute. The gases have to be delivering in an appropriate flow direction dictated by optimum turbine efficiency. This paper investigates numerically the effect of A/R ration on the flow characteristic in a twin-entry turbine. The flow in the spiral part of volute is characterized by the secondary flows in the form of counter-rotating vortices and the Dean vortices formed practically within the hub side of the volute. The swirling flow is convected to the rotor entry from the outer wall and leaves the volute before an azimuthal position of 180 deg from the tongue. For a turbine in which the global ratio A/R was keep similar to reference one, whereas the ratio A/R related to hub-entry side is chosen greater than the shroud side. The flow structure within this turbine highlights that the secondary flow disappears. In pulsating flow condition and at the rotor entry there is a typical dissymmetrical behavior characterized by high non-uniformities in the spanwise and circumferential directions. Also, at a position around 180° from tongue, the relative flow angle is highly influenced by the migration of the two vortices from the hub side of volute to the interspaces. The finding of this paper could lead to improvement of such volute type.