Numerical Study On The Effect Of Orifice Shape On The Flow Field Of Plane Jet Flow Via Multi-Relaxation-Time Lattice Boltzmann Method

Jet flow is an important topic in the field of fluid mechanics owing to its widely applications in many industries such as water conservancy and hydropower, aerospace engineering, water supply and sewerage engineering, etc. It is indicated that the change of orifice shape has a significant effect on the flow characteristics of jet flows. However, the influence has not been well-studied up to now to our knowledge. In this paper, a two-dimensional (2-D) incompressible plane jet flow is simulated using the Multi-Relaxation-Time lattice Boltzmann method. Jet flow with three types of orifices, the expanded, flat-plate and contracted ones is investigated under some typical Reynolds numbers (Re=50,100,300 and 700). Numerical results show that the flow field of jet flow is greatly influenced by the orifice shape. In this paper, the inclination degree at the jet exit, namely the slope orifice, is changed to investigate the influence of the shape. Under the condition of turbulent flow, we couple the Large-Eddy-Simulation to the Multi-Relaxation-Time lattice Boltzmann method to simulate the plane free jet flow with the high Reynolds number, and calculate three types of orifice shape, namely the expanded, flat-plate and contracted ones to research the channel orifice shape effect on the jet flow characteristics. The main results are summarized as follows:within the laminar flow condition, (1)with the orifice shape changes from the contracted ones to expanded ones, the maximum center-line stream-wise velocity decreases, in the meantime, the half-width, which is defined as the distance from the center-line to the point where half of the center-line stream-wise velocity locates spreads larger; (2)the 3 power of reciprocal of center-line stream-wise velocity is proved to be in a linear relationship with jet axis distance from original point, while an in-depth research proves that the linear parameter is in a exponential function with respect to the orifice slope; (3)the 3/2 power of half-width of stream-wise velocity profile is proved to be in a linear relationship with jet axis distance. However, the linear parameters here can be found to change with the orifice slope; and under the condition of turbulent flow,(1)the change of Reynolds number does not have an significant impact on the jet flow characteristics, including the center-line stream-wise velocity, the stream-wise velocity profile at each x-coordinate station;(2) the contracted orifice shape makes the stream-wise velocity profile longer and narrower compared with the flat-plate orifice; while the expanded case has the opposite effects.