Entropy production analysis of hysteresis characteristic of a pump-turbine model

In the present paper, epsilon (e) in the Omega vortex identification criterion (Ω method) is defined as an explicit function in order to apply the Ω method to different cases and even different time steps for the unsteady cases. In our method, e is defined as a function relating with the flow without any subjective adjustment on its coefficient. The newly proposed criteria for the determination of e is tested in several typical flow cases and is proved to be effective in the current work. The test cases given in the present paper include boundary layer transition, shock wave and boundary layer interaction, and channel flow with different Reynolds numbers.

Determination of epsilon for Omega vortex identification method

The diffusion of dust in a fully-mechanized mining face with a mining height of 7 m and the application of wet dust-collecting nets

Cavitation is a challenging flow abnormality that leads to undesirable effects on the hydraulic behaviour of centrifugal pumps. This study analyses the cavitating flow at a normal flow rate using t...

Entropy generation analysis for the cavitating head-drop characteristic of a centrifugal pump:

Effects of flow pattern on hydraulic performance and energy conversion characterisation in a centrifugal pump

Unstable or flat head-flow curves can cause problems in parallel operations or in flat systems. Despite the considerable efforts that have been devoted to the study of head-flow curve instability in single-stage centrifugal pumps with volute casing, the cause of such phenomenon is not sufficiently understood. In this study, we investigated the variation of hydraulic losses based on the relationship between velocity distribution and entropy generation fields. Steady-state and unsteady simulations were obtained for a pump with an impeller outlet diameter of 174 mm, and the unsteady results are more coincided with the experiments. Results showed that the losses mainly focused on the blade suction surface and volute tongue, as well as in the region of the volute discharge at high flow rates. The entropy generation rate of the pump casing at partial flow rates changed slightly with a decrease in flow rate, whereas the energy losses in the impeller increased steeply when the flow rate dropped to 35 m3/h (the de...

Experimental and numerical investigations of head-flow curve instability of a single-stage centrifugal pump with volute casing

The effect of the blade loading distribution on head, radial force and pressure pulsation of a low specific-speed centrifugal pump with cylindrical impeller blades were investigated in the present study. Blade shapes were obtained by adopting the 1D inverse design method, impellers with different blade loading curves were obtained while the distribution of the blade loading was carefully tailored. Threedimensional URANS simulation method based on the Shear stress transport (SST) k-ω turbulence model was employed for the analyzation of flow patterns. Numerical results including the pressure distribution and velocity profile were validated by comparing with the available experimental data, and an acceptable agreement was obtained. Three typical parameters of the blade loading curve, including the location of the fore-loading point (mpre), location of the aft-loading point (mpost) and slope of the rectilinear segment (K), were analyzed. Results showed that the well-designed blade loading curve, such as the fore-loading impeller, can effectively reduce the pressure pulsation amplitude and the radial force. The significant effect of the variation of the aft-loading point on pump hydrodynamic performance was also investigated. Meanwhile, pressure and velocity distributions at different slopes of the blade loading curves show that the fore-loading impeller produces more uniform flow issuing from the impeller than that of the pump with aft-loading impeller, thus reduces the radial force and pressure pulsation of the pump.

Effect of the blade loading distribution on hydrodynamic performance of a centrifugal pump with cylindrical blades

Cavitation is a challenging flow abnormality that leads to undesirable effects on the energy performance of the centrifugal pump and the reliable operation of the pump system. The onset and mechanism of a phenomenon that results in unsteady cavitation must be realised to ensure a reliable operation of pumps under the cavitation state. This study focuses on cavitation instability at normal flow rate, at which point the unsteady cavitation occurs as the available net positive suction head (NPSHa) falls below 5.61 m for the researched pump. An ameliorative algorithm–united algorithm for cavitation vibration analysis is proposed on the basis of short time Fourier transform (STFT) and Wigner–Ville distribution (WVD). The STFT–WVD method is then tested using vibration data measured from the centrifugal pump. The relationship between vibration and suction performance indicates that the inception and development of cavitation can be effectively detected by the distribution and intensity of the united algorithm at the testing points. Intermediate frequency components at approximately 6 kHz fluctuate initially with the development of cavitation. A time–frequency characteristic is found to be conducive to monitoring the cavitation performance of centrifugal pumps.

Yi Li

Papers

Entropy generation analysis for the cavitating head-drop characteristic of a centrifugal pump:

Experimental and numerical investigations of head-flow curve instability of a single-stage centrifugal pump with volute casing

Effect of the blade loading distribution on hydrodynamic performance of a centrifugal pump with cylindrical blades

An experimental study on the cavitation vibration characteristics of a centrifugal pump at normal flow rate

Application of enstrophy dissipation to analyze energy loss in a centrifugal pump as turbine