Hydrodynamic Design of a Submersible Multi-Stage Pump

Introduction

The customer, one of the world’s leading manufacturers of ESP pumps, asked ADT to carry out the detailed hydrodynamic design of a multistage submersible mixed-flow pump, including a detailed analysis about the axial thrust acting on the impeller and a multi-phase flow analysis of the gas handling capability of the machine.

The customer set requirements at design point in terms of Head and Power, along with a maximum target axial thrust at shut-off conditions. No gas lock with 60% (GVF) was also required.

Preliminary and Meanline Stage Design

During the initial preliminary design phase, TURBOdesign Pre was used to estimate the pump stage overall sizing and hydraulic performance; TURBOdesign Pre is a 1D sizing and preliminary design code which only requires basic duty point requirements such as Head, speed and Flow-rate to provide the meridional shape of each component and estimates efficiency and power. The quick iterative process allowed ADT designers to quickly evaluate geometrical sizing and hydraulic performances for given design point requirements and obtain suitable preliminary stage design data. TURBOdesign Pre directly exports the meridional shape and all the required data for the detailed 3D blade design of both pump and turbine impellers into TURBOdesign1.

TURBOdesign1 is unique blade design software that uses the 3D Inverse Design approach to compute the blade shape for a given blade loading distribution

3D Pump Impeller Design

The meridional shape, number of blades and component specific work rVt (ie. impeller head) were loaded from TURBOdesign Pre into TURBOdesign1 for the detailed 3D design of the pump impeller and diffuser. TURBOdesign1 is unique blade design software that uses the 3D Inverse Design approach to compute the blade shape for a given blade loading distribution.

A number of design iterations were performed directly in TURBOdesign1 with the help of the 3D inviscid flow solution and performance data provided by the code to fine tune the meridional shape and blade loading, before assessing the impeller performance via 3D CFD. The initial design loop in TURBOdesign1 taking less than 30 seconds per design iteration, it ensures large areas of the design space are covered with minimal number of CFD iterations, making it possible to achieve breakthrough designs without increasing product development costs.

Leakage Gaps and Balancing Holes Design

The design of the leakage gaps and the balancing holes was performed looking for a trade –off between reduced axial thrust, below the limit requested by the customer, and low leakage and disk friction loss. Leakage flow carries the angular momentum into the impeller sidewall gaps and thus enhances fluid rotation which causes disk friction, on the other hand pressure losses along the sidewall gaps helps to reduce the amount of fluid leaked through the gaps. The sidewall gaps were then shaped based on these considerations, looking for the right compromise between disk friction losses and leakage losses.

Balancing holes diameter were designed as result of an iterative approach looking for a configuration which can guarantee axial thrust below the requested value while ensuring low losses due to the flow disturbance caused by the presence of the holes.

The initial design loop in TURBOdesign1 takes less than 30 seconds per design iteration, it ensures large areas of the design space are covered with minimal number of CFD iterations

Gas Handling Capabilities

The gas handling capabilities of the pump was also analysed using multi-phase flow simulations. Results demonstrate good gas handling capabilities of the pump and no gas lock was experienced up to 60% GFV. Results highlight the formation of a gas pocket, yet no segregated flow was individuated.

Gas volume fractions at different spanwise locations (hub, midpoint and shroud)