Study On The Characteristics Of Residence Time Distribution In Laminar Cavity Flow

Cavity flow is a typical phenomenon.When the fluid flows through a cavity,due to the separation of the boundary layer,some of the fluid will enter the cavity and drive the liquid in it to flow together.In order to master the hydrodynamic laws,Understanding the residence time distribution of the liquid entering the cavity is important.In this paper,experimental and numerical simulation methods are used to study the effects of various parameters of laminar cavity flow,such as liquid flow rate,viscosity,and cavity aspect ratio(L/H),on the liquid residence time distribution(RTD)in the square cavity,and to find the correlation between RTD and various parameters.Firstly,ink as tracer was used to qualitatively characterize the flow field in the cavity,providing a basis for judging the flow characteristics from the residence time distribution density function(E(t))curve.Then,using conductivity as a quantitative characterization parameter for residence time distribution.By detecting the conductivity of liquid at the outlet of the cavity,and using observation and model methods to get information in the cavity from the global residence time distribution information,the effects of liquid flow rate and L/H on RTD were obtained.In addition,numerical simulation method is also used to calculate the residence time distribution of the liquid in the cavity,and the effects of flow rate,L/H,and liquid viscosity on the residence time distribution are analyzed.Finally,a suitable flow model is established based on the non-ideal flow of the liquid to describe the RTD in the cavity.The results indicate that a large amount of liquid flows past cavity and a small amount enters in cavity.In laminar flow,increasing flow rates will move the center of the vortex in the cavity to downstream,also result in a decrease of liquid residence time in the cavity,and the outflow is more uniform.The increase in liquid viscosity will turn the rotational motion of the liquid in the cavity to downstream,while the change in RTD is not obvious.As L/H decreases,the dead zone in the cavity has increased.The established flow model based on the non-ideal flow describes the experimental results well.According to this model,a cavity can be designed or selected to keep the liquid in the cavity for a specific time.