Study of flow instability in a centrifugal fan based on energy gradient theory

2016 ◽  
Vol 30 (2) ◽  
pp. 507-517 ◽  
Author(s):  
Meina Xiao ◽  
Qing Xiao ◽  
Hua-Shu Dou ◽  
Xiaoyang Ma ◽  
Yongning Chen ◽  
...  
Keyword(s):  
Flow Instability ◽  
Gradient Theory ◽  
Centrifugal Fan ◽  
Energy Gradient Theory ◽  
Energy Gradient

ENERGY SPECTRUM OF DISTURBANCE AT TURBULENT TRANSITION VIA ENERGY GRADIENT METHOD

2012 ◽  
Vol 19 ◽  
pp. 293-303 ◽  
Author(s):  
HUA-SHU DOU ◽  
BOO CHEONG KHOO
Keyword(s):  
Energy Spectrum ◽  
Flow Instability ◽  
Three Dimensional ◽  
Wave Number ◽  
Gradient Theory ◽  
Turbulent Transition ◽  
Energy Gradient Theory ◽  
Energy Gradient ◽  
The Difference ◽  
2D And 3D

The energy gradient theory for flow instability and turbulent transition was proposed in our previous work. The theoretical result obtained accords well with some experimental data for pipe and channel flows in the literature. In the present study, the energy gradient theory is extended to examine the effect of disturbance frequency on turbulent transition. Then, the energy spectrum of disturbance at the turbulent transition is obtained, which scales with the wave number by an exponent of –2. This scaling is near to the K41 law of –5/3 for the full developed isentropic homogenous turbulence. The difference for the two energy spectra may be due to the intermittency of turbulence at the transition state. The intermittence causes the distribution of the energy spectrum to take on a steeper gradient (tending to –2 from –5/3). Finally, the flow instability leading to turbulent transition can be classified as two-dimensional (2D) or three-dimensional (3D) in terms of the wave number and the Re. It is found that there is an optimum wave number which separates the 2D and 3D transitions and at which the disturbance energy at transition is minimum.

Numerical Investigation of Flow Instability in Centrifugal Pump Based on Energy Gradient Method

2016 ◽  
Author(s):  
Lulu Zheng ◽  
Hua-Shu Dou ◽  
Xiaoping Chen ◽  
Zuchao Zhu ◽  
Baoling Cui
Keyword(s):  
Flow Rate ◽  
Flow Instability ◽  
Flow Stability ◽  
Gradient Theory ◽  
Small Flow Rate ◽  
Energy Gradient Theory ◽  
Energy Gradient ◽  
Centre Region ◽  
Small Flow ◽  
Gradient Function

Simulation of turbulent flow in a pump is carried out with the RANS equations and the RNG k-epsilon turbulence model. Numerical simulation has been compared with the experimental data. The results show that separating vortex is firstly produced at the pressure side of the impeller passage near the tongue. Then it spreads to the inlet and outlet of the impeller passages and moved to the centre region of impeller passages from the boundaries. Finally, it almost occupies all the impeller passages and multiple vortices exist in impeller passages at small flow rate. It is found that the tongue has large effect on the flow in the impeller passage approaching to it. The impeller passage near the tongue is easily tending to be unstable comparing with others passages. The energy gradient theory is used to analyze the flow stability in the impeller. The region with larger value of energy gradient function K means the bigger turbulence intensity and poor flow stability. At small flow rate the regions with large value of K are enlarged and are mainly located at both sides of blade pressure and suction surfaces where the flow is easily tending to be unstable.

scholarly journals Stability of boundary layer flow based on energy gradient theory

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840003
Author(s):  
Hua-Shu Dou ◽  
Wenqian Xu ◽  
Boo Cheong Khoo
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Flow Instability ◽  
Mechanical Energy ◽  
Navier Stokes ◽  
Gradient Theory ◽  
External Edge ◽  
Energy Gradient Theory ◽  
Energy Gradient ◽  
Gradient Function

The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier–Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

scholarly journals A Numerical Study of Natural Convection Heat Transfer in Fin Ribbed Radiator

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Hua-Shu Dou ◽  
Gang Jiang ◽  
Lite Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Instability ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Gradient Theory ◽  
Computational Domain ◽  
Energy Gradient ◽  
Gradient Function ◽  
Fin Shape

This paper numerically investigates the thermal flow and heat transfer by natural convection in a cavity fixed with a fin array. The computational domain consists of both solid (copper) and fluid (air) areas. The finite volume method and the SIMPLE scheme are used to simulate the steady flow in the domain. Based on the numerical results, the energy gradient functionKof the energy gradient theory is calculated. It is observed from contours of the temperature and energy gradient function that the position where thermal instability takes place correlates well with the region of largeKvalues, which demonstrates that the energy gradient method reveals the physical mechanism of the flow instability. Furthermore, the effects of the fin height, the fin number, and the fin shape on the heat transfer rate are also investigated. It is found that the thermal performance of the fin array is determined by the combined effect of the fin space and fin height. It is also observed that the effect of fin shape on heat transfer is insignificant.

scholarly journals Analysis of vortex breakdown in an enclosed cylinder based on the energy gradient theory

2018 ◽  
Vol 71 ◽  
pp. 66-76
Author(s):  
Meina Xiao ◽  
Hua-Shu Dou ◽  
Chuanyu Wu ◽  
Zuchao Zhu ◽  
Xifeng Zhao ◽  
...  
Keyword(s):  
Vortex Breakdown ◽  
Gradient Theory ◽  
Energy Gradient Theory ◽  
Energy Gradient

On the Instability of Plane Poiseuille Flow of Two Immiscible Fluids Using the Energy Gradient Theory

2014 ◽  
Vol 30 (3) ◽  
pp. 299-305 ◽  
Author(s):  
I. Farahbakhsh ◽  
S. S. Nourazar ◽  
H. Ghassemi ◽  
H.-S. Dou ◽  
A. Nazari-Golshan
Keyword(s):  
Experimental Data ◽  
Viscosity Ratio ◽  
Reynolds Numbers ◽  
Immiscible Fluids ◽  
Gradient Theory ◽  
Energy Gradient Theory ◽  
Energy Gradient ◽  
Lower Viscosity ◽  
High Reynolds ◽  
Comparison Of The Results

ABSTRACTIn the present study, the instability of laminar flow of two immiscible fluids is investigated. The theory of energy gradient is employed for the analysis. The distributions of energy gradient for various viscosity ratios, i.e., ratios of lower viscosity to higher one, are obtained and the results for the onset of instability are compared with the available experimental data. The comparison of the results shows excellent agreement with the existing experimental data. It will be also demonstrated that as the viscosity ratio decreases the flow becomes more stable even at high Reynolds numbers.

Prediction of Laminar to Turbulent Transition in 90° Curved Duct Based on Energy Gradient Theory

2014 ◽  
Author(s):  
Xuekuan Fu ◽  
Hongsheng Yuan ◽  
Chong Chen ◽  
Hanying Chen ◽  
Yulin Song ◽  
...  
Keyword(s):  
Dimensionless Parameter ◽  
Three Dimensional ◽  
Gradient Theory ◽  
Three Dimensional Flow ◽  
Geometry Model ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Curved Duct ◽  
Energy Gradient Theory ◽  
Energy Gradient

Study on laminar to turbulent transition in a 90° curved duct is carried out. Professional mesh generation tool ICEM is used to create geometry model and generate mesh, then the mesh is imported to the fluid dynamics software CFX to simulate three-dimensional flow. The dimensionless parameter K is calculated in the duct with velocity and pressure distribution obtained by numerical simulation. According to energy gradient theory, K is the ratio of energy gradient in the transverse direction to that in the streamwise direction, which can be used to measure stability of the flow field. It is found that fluid is most likely to lose its stability where the maximum K is, and laminar to turbulent transition occurs when K reaches a certain value, corresponding to the critical Reynolds number. The instability and transition characteristics predicted by energy gradient method agree well with former researchers’ results.

Sign in / Sign up

Export Citation Format

Share Document