Toward non-swirling uniform inflow and stabilized flow in a centrifugal turbomachine model with an intake elbow using rotational guide vanes

The centrifugal turbomachines deployed in pipeline systems are usually subject to inflow from a curved intake pipe designed to satisfy the space limitation. The separated and swirling flow form in the curved pipe, imposing a swirling non-uniform inflow for the impeller, which destabilizes the flow at the inlet and in the blade passages, deteriorating the operation safety of the turbomachine. This work numerically studies the effectiveness of a stationary rotational guide vanes (RGVs) in reducing the separation and swirling and improving the uniformity of flow at the impeller's inlet under the 25% design flow rate condition. The motivation and objective are to identify the appropriate geometric parameters of the RGV and reveal the flow physics in the intake pipe and the centrifugal turbomachine. The transient simulation was performed for three models of the intake pipe, i.e., the straight pipe and the curved pipe without and with a RGV. Numerical results reveal that the RGV with long vanes inclined in the clockwise direction at an appropriate angle effectively suppresses the separation and swirling inflow at the impeller's inlet. The flow in the curved intake pipe well reproduces the mean pressure and velocity fields of the straight-pipe model. The RGV significantly suppresses the velocity and pressure fluctuations for flow in the blade passages of the impeller; the fluctuating amplitude is roughly the same as the straight-pipe model but is considerably lower than the RGV-free model. The fluctuation of static pressure on the blade's surfaces could be reduced by over 50% at the inlet of the non-stalled passages and is also significant in the stalled passages. The RGV does not directly impact the flow at the impeller's outlet and in the radial vaneless region, which is primarily dependent on the rotor–stator interaction and the development of large-scale vortices.