Energy conversion characteristics of gas-liquid two-phase flow inside a drainage self-priming pump under different rotational speeds during self-priming

• The self-priming time is significantly influenced by the rotational speed, showing an inverse relationship with it. • At rated and high rotational speeds, the self-priming time is shortened primarily during the rapid exhaust stage, while the effects on the rapid suction and oscillatory exhaust stages are relatively minor. • At low rotational speed, the duration of the oscillatory exhaust stage is considerably prolonged. A self-priming pump is a type of centrifugal pump that can automatically draw and transport water without the need to fill the pump and suction pipeline with water prior to startup. As a result, it is widely used in applications such as agricultural irrigation and municipal flood drainage. The self-priming performance is one of the core indicators for evaluating the quality of a self-priming pump. In addition to the internal geometric structure of the pump, external operating conditions, such as variations in rotational speed, also significantly influence the self-priming performance. Therefore, understanding the specific impact of rotational speed changes on self-priming performance is essential. In this study, using computational fluid dynamics (CFD) methods, three constant rotational speed schemes were designed to numerically simulate the self-priming process in a recirculating pipeline system that includes a self-priming pump. The influence of constant rotational speed on the self-priming performance was thoroughly investigated, highlighting the hydraulic performance, self-priming performance, and internal flow characteristics under different rotational speeds. The results show that the self-priming time is significantly affected by rotational speed and is inversely proportional to it, with a maximum reduction of up to 36.69%. At rated and high rotational speeds, the speed mainly affects the duration of the accelerated exhaust stage, which can be shortened by up to 37.5%. At low rotational speeds, the duration of the oscillatory exhaust stage is significantly extended, approximately twice as long as that at medium and high rotational speeds.