Study on the impact of blades wrap angle on the performance of pumps as turbines used in water supply system of high-rise buildings
International Journal of Low-Carbon Technologies
The use of pumps as turbines (PATs) in different applications has attracted increasing attention in recent years. Based on our previous research, the PAT could be used in water supply system of high-rise buildings for water head reduction and hydropower generation, but the efficiency is relatively low. Due to the high water head and low flow rate, PATs used in water pipelines are usually low specific speed turbines. According to the impeller inlet and outlet velocity triangles, the blades wrap angle of a centrifugal pump is not optimal for low specific speed turbines, so the impact of blades wrap angle on the PAT performance should be studied. In this paper, the impact is investigated by numerical and experimental methods. Firstly, a 3D model of an original PAT was built in CAD software, then the model was imported into the ICEM to generate grids and then imported into Ansys CFX for simulation. After simulation, a PAT prototype was tested in the lab test rig to validate the simulation results. The comparison between simulation and experimental results indicates that although some deviations exist, the simulation could provide an acceptable prediction of the PAT's performance. Finally, four PAT models with different blades wrap angles were developed to compare their performance in terms of both power output and water head reduction. The results show that the blades wrap angle does have effects on the PAT's efficiency and hydraulic loss, to achieve a good balance between water head reduction and power output. The model with −60° wrap angle has the best performance.
pump as turbines; blades wrap angle; water supply system; high-rise buildings
1 INTRODUCTION
In recent decades, the pump as turbine (PAT) has attracted
increasing attention in remote micro hydropower generation
and industry hydropower recovery due to its low cost, easy
maintenance and easy access in the market [
1, 2
]. In our former
research, the feasibility of micro hydropower generation in the
water supply system of high-rise buildings using the PAT has
been studied by both numerical and experimental methods.
The results showed that the PAT has a good performance in
electricity generation as well as water head reduction. However,
the results also indicated that efficiency of the PAT used in the
water supply pipeline, which is characterized by high water
head and low flow rate, is relatively low [3]. Therefore, it is an
important topic in PAT investigation to improve the PAT’s
efficiency.
Many researchers have attempted different techniques to
improve the PAT efficiency. Among them, some investigators put
their attention on the PAT geometry modification or optimization
for performance improvement. Yang [
4
] proposed a PAT’s volute
design method to optimize the volute shape for PAT performance
enhancement. In the study of D.R. Giosio [
1
], the volute of one
commercially available pump is modified for incorporation of inlet
flow control, experimental results showed that the customized
PAT has a wider range of high efficiency operation than the
parent pump. Baoshan Zhu [
5
] conducted optimization design on the
PAT blades based on 3D inverse design, computational fluid
mechanics (CFD) and lab tests, this study proved that the blades
shape optimization could improve the PAT performance with
high efficiency and operation stability. The research of several
investigators paid the focus on the effect of blades, hub and shroud
rounding on PAT efficiency, the results showed that the rounding
of blades, hub and shroud could lead to 1–3% efficiency increase
[
6–8
]. Besides, impeller trimming can lead to efficiency
improvement at part load operating conditions [
8
].
According to the design principle of turbomachine blades,
the original blades shape of the pump is designed to provide
sufficient power to the water. But when a pump operates in
reverse as a turbine in a working condition of high water head
[
9
]. Yang [
10
] investigated the influence of blades wrap angle
on the PAT performance by numerical and experimental
methods, but this research only focused on the back curved blades,
the effects of forward curved with different wrap angles on the
PAT performance still lacks.
In the present paper, the effects of different wrap angles on the
PAT performance was studied by numerical and experimental
methods. Firstly, the CAD model of the original PAT was built
and imported into ICEM for meshing, then CFD simulation was
conducted in Fluent. Thereafter, the prototype of the PAT was
tested in the hydraulic test rig to validate the simulated results.
After that, another three PAT models with different blades curving
degree were built and simulated to compare the performance in
output power, efficiency and water head reduction.
2 METHODOLOGY
In recent years, CFD technology has been a successful and mature
way in aspects of PAT inner flow analysis, performance
prediction and optimization (...truncated)