Problem Solving For High-Energy Pumps

Today’s research and development efforts to improve high-energy centrifugal pumps concentrate on abnormal flows. The normal flow conditions found in the common centrifugal pump have been optimized over the past century. These industrial pumps run at low power and low head-per-stage. Now, the next step is to make centrifugal pumps that are durable and reliable at higher energy-density levels.

These are needed for such applications as rocket engines, large-capacity pipelines in mountainous terrain, and supercritical boiler-feed applications. This article addresses the problems of reaching high energy and running into abnormal flow phenomena.

The very simplicity of a centrifugal pump is the source of difficulty. The impeller blades have a fixed geometry. The user demands that the pump operate over a wide range of flows. The basic geometry can be calculated by Euler’s one-dimensional equation.* In the 3-D world of high-energy pumps, separated, reversed, and unsteady flows crop up and make the pump fail. Understanding and combating pump cavitation, recirculation and other multiphase flows is the challenge for both researchers and designers.

Early work started with model tests to discover the off-design characteristics of large pumps, such as those used in the Grand Coulee irrigation project [1]. Pressure pulsations, arising from diffuser vanes, were computed by Iino [10]. A model of the interior of an operating pump impeller was used to figure out how to reduce inception-NPSH in the face of a simultaneously recirculating and cavitating off-design flow field [19]. Boiler pumps were studied in England [11]. Early successes were achieved with rocket-engine propulsion pumps for liquid fuel because they always operated at approximately the design flowrate and because the operating time (life) of the pump was very short [13, 14].

The pump industry is being driven to develop pumps of higher energydensity levels, adapting the technology explored in rocket pumps and high-energy, utility boiler-feed pumps. Problems include:

• The pump structures lack durability and fail to withstand the stronger pressure pulsations and unsteady fluid dynamic forces that arise from impeller blade interaction with diffuser vanes and casing-volute cutwaters
• Unsteady reversed flows from diffusers and impellers, often complicated by the presence of gas and, sometimes, solid particles
• The erosion of surfaces due to the collapse of cavitation bubbles

Today’s research and development efforts to improve high-energy centrifugal pumps concentrate on abnormal flows. The normal flow conditions found in the common centrifugal pump have been optimized over the past century. These industrial pumps run at low power and low head-per-stage. Now, the next step is to make centrifugal pumps that are durable and reliable at higher energy-density levels.

These are needed for such applications as rocket engines, large-capacity pipelines in mountainous terrain, and supercritical boiler-feed applications. This article addresses the problems of reaching high energy and running into abnormal flow phenomena.

The very simplicity of a centrifugal pump is the source of difficulty. The impeller blades have a fixed geometry. The user demands that the pump operate over a wide range of flows. The basic geometry can be calculated by Euler’s one-dimensional equation.* In the 3-D world of high-energy pumps, separated, reversed, and unsteady flows crop up and make the pump fail. Understanding and combating pump cavitation, recirculation and other multiphase flows is the challenge for ...