Turbulence behaviour investigation in transient flows

ABSTRACT

Two-dimensional numerical simulations are conducted using a k-ϵ turbulence model and results are compared with experimental data. First, the parameters affecting the process of production and dissipation of turbulent kinetic energy during different cycles of water hammer, including the effects of increasing Reynolds number, are investigated. Second, turbulence intensity in accelerated and decelerated periods of water hammer is analysed. The results show that the process of turbulent kinetic energy production, dissipation and eddy viscosity diffusion occur more vigorously in flows with higher Reynolds numbers. During decelerated periods turbulence intensity increases, and conversely it decreases during accelerated periods; the decreasing process happens with a higher rate. During accelerated periods, turbulence intensity in regions close to the wall increases more than its steady flow values, but after some cycles it decreases to values less than those for steady flow. In the central regions, turbulence intensity remains less than steady flow values.

Keywords:

• Acceleration
• deceleration
• turbulence intensity
• viscosity diffusion
• water hammer

Subscripts

rms	=	=root mean square
0	=	=steady state
w	=	=wall