Experimental Investigation of the Steady and Unsteady Relative Flow in a Model Centrifugal Impeller Passage

Abstract

The behaviour of the relative flow in centrifugal turbomachines is extremely complex due to the existence of various fluid dynamic phenomena and their interaction. At design and off-design operating conditions, the relative flow is subject to stationary unsteadiness which includes flow separation and wakes associated with passage pressure gradients, secondary flows, and boundary layer stability. It may also be subject to periodic unsteadiness such as is the rotating stall and cyclic flow phenomena induced by the casing. This paper describes detailed measurements of the relative velocity field in a very low specific speed centrifugal pump impeller (Ns=515). Measurements were conducted by means of a recently developed rotating laser-Doppler anemometry system. Detailed quantitative description of the mean and fluctuating components of the primary and secondary velocity fields are presented for an impeller without volute at design, 50% design and shut-off conditions. The flow pattern in this low specific speed impeller with high blade loading is dominated by the relative eddy (a phenomenon also present in potential flow) which has suppressed suction side separation. When the impeller was fitted with a volute, the cyclic variation of the impeller exit flow, induced by the volute at low flow rates, is also presented.

Effect of Rotation Speed and Flow Rate on Slip Factor in a Centrifugal Pump

“…At an overload flow rate of 1.2 Q BEP , the streamlines follow the blade curvature without flow separation, and a low-velocity region develops at the blade outlet. is occurrence has been previously reported [32,33]. e distribution of velocity is uniform at the outlet of the impeller and has minimal effects on the slip factor.…”

Unsteady Analysis of Impeller-Volute Interaction in Centrifugal Pump

“…The smooth and blade curvature congruent flow within the blade passages can changed to a stalled flow as reported by Pedersen et al [8] or becomes a significant flow separation as experimentally observed by Liu et al [9] and Abramian and Howard [10]. Other measurements done by Wuibaut et al [11], Westra et al [12], Visser [13], Choi et al [14] further demonstrated that flow field within impeller passages is highly complex and depends on flow rate, number of blades, blade curvature and specific speed as well.…”

Numerical Study of Inlet and Impeller Flow Structures in Centrifugal Pump at Design and Off-design Points

“…Due to decrease of flow rate, radial flow decelerated on shroud/suction surface, the secondary flow and vorticity increases in the passage. Further investigation by Abramian and Howard [10] using laser Doppler anemometer measurement showed that pressure side mean flow separation under low flow condition within the impeller passage is affected by a combined effect between a secondary vorticity initiated at the inlet and a potential vortex which dominates the flow at impeller exit. The flow within the passage of the highly backward swept blades also dominated by the rotational effect because of the changing Rossby number along the curvature of the blade from the leading edge to trailing edge.…”