Simulation of Entropy Generation under Stall Conditions in a Centrifugal Fan

Zheng

Advances in Mechanical Engineering

et al. 2019

Self Cite

Rotating stall is a common instability phenomenon that occurs in turbomachinery. Rotating stall 3D instability can be characterized as one or more stall cells rotating at a fraction of rotor velocity. In this article, the ANSYS Fluent software was used to numerically simulate entropy generation. The relative velocity of the monitoring points in the rotor is discussed, and the type of stall inception is a spike. In addition, five typical conditions that affect the evolution of rotating stalls are presented and discussed with respect to characterizing entropy generation in a two-stage variable-pitch axial fan. The results reveal that entropy generation significantly improves after the stall phenomenon appears. Because rotating stall first occurs in the second rotor, its entropy production is higher than that of the first rotor over the entire evolution period. The high entropy generation region moves in the circumferential and radial directions of the first and second rotors during the evolution of rotating stall.

Section: Grid Divisionmentioning

confidence: 88%

Simulation of entropy generation during the evolution of rotating stall in a two-stage variable-pitch axial fan

Zheng

Advances in Mechanical Engineering

et al. 2019

Self Cite

Proceedings of the Institution of Mechanical Engineers, Part C:

“…Zhang et al. 13 studied KED in a centrifugal fan under rotating stall conditions and showed that energy dissipation increases after stall inception. High energy dissipation moves along the circumferential and axial directions and combines into one stall cell.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of energy loss in a centrifugal pump through kinetic energy dissipation theory

Lai

Zhu

2020

In this study, energy loss within a centrifugal pump is investigated by post-processing three-dimensional unsteady flow field through kinetic energy dissipation theory. The three-dimensional unsteady flow field is predicted by solving unsteady Reynolds-averaged Navier–Stokes equations. The kinetic energy dissipation consists of three parts: averaged kinetic energy dissipation, turbulent kinetic energy dissipation, and near-wall revised kinetic energy dissipation. The total value variations of three kinetic energy dissipations in the centrifugal pump with flowrate are investigated and compared. Results show that with the increase in flowrate, the total near-wall revised kinetic energy dissipation gradually increases, the total turbulent kinetic energy dissipation first gradually decreases and then gradually increases, and reaches the minimum value at the design flowrate. The total averaged kinetic energy dissipation is less than the total turbulent and the total near-wall revised kinetic energy dissipations, and the total near-wall revised kinetic energy dissipation is larger than the total turbulent kinetic energy dissipation when the flowrate is larger than 0.75 Qdes. The space variation of the near-wall revised kinetic energy dissipation with flowrate shows that large near-wall revised kinetic energy dissipation mainly occurs at the volute and transfers from the small cross-section casing to large cross-section casing and discharge pipe with the increase in flowrate. The space variations of the turbulent kinetic energy dissipation with time for three flowrates are also discussed. Results indicate that large turbulent kinetic energy dissipation near the volute tongue evidently changes with the rotation of the impeller, particularly in 0.5 Qdes. The large turbulent kinetic energy dissipation gradually expands to the pressure side of the blade when the volute tongue gradually approaches the middle of the impeller blade passage. The large turbulent kinetic energy dissipation transfers from the impeller inlet and outlet to the volute tongue and discharge pipe with the increase in flowrate. The findings of this study can serve as guide to improve the design of centrifugal pumps.

“…Dalir (2014) studied the non-Newtonian fluids, such as Jeffrey's flow on the tensile plates, and used computational fluid dynamic methods to analyze the generation of entropy. Zhang et al (2014) simulate the entropy generation of centrifugal fans under stall conditions. Nouwrozi (2012) analyzed the combined flow in a vertical channel under constant flux and concluded that under optimal conditions, the contribution of thermal entropy generation is about four to five times the frictional entropy generation.…”

Section: Introductionmentioning

confidence: 99%

Investigating the entropy generation around an airfoil in turbulent flow

Saffarian

Jamaati

Mohammadi

et al. 2020

AEAT

Purpose This study aims to evaluate the amount of entropy generation around the NACA 0012 airfoil. This study takes place in four angles of attack of 0°, 5°, 10° and 16° and turbulent regime. Also, the variation in the amount of generated entropy by the changes in temperature and Mach number is investigated. Design/methodology/approach The governing equations are solved using computational fluid dynamics techniques. The continuity, momentum and energy equations and the equations of the SST k-ω turbulence model are solved. The entropy generation at different angles of attack is calculated and compared. The effect of various parameters in the generation of entropy is presented. Findings Results show that the major part of the entropy generation is at the tip of the airfoil. Also, increasing the angle of attack will increase the entropy generation. Also, results show that with increasing the temperature of air colliding with the airfoil, the production of entropy decreases. Originality/value Entropy generation is investigated in the NACA 0012 airfoil at various angles of attack and turbulent flow using the SST turbulence model. Also, the effects of temperature and Mach number on the entropy generation are investigated.