Modelling and simulation of flow through a flowbench

Project Objective:- To create a 3D model of a flow bench and run a CFD flow analysis and obtain a plot of lift vs mass flow rate. A grid dependency test was done to show the effect of valve lift on mass flow rate. 

Introduction:-  Computational Fluid Dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems that involve turbulent fluid flows. It is widely accepted that the Navier–Stokes equations (or simplified Reynolds-averaged Navier–Stokes equations) are capable of exhibiting turbulent solutions, and these equations are the basis for essentially all CFD codes. 

The Reynolds number is the ratio of inertial forces to viscous forces and is a convenient parameter for predicting if a flow condition will be laminar or turbulent. It can be interpreted that when the viscous forces are dominant (slow flow, low Re) they are sufficient to keep all the fluid particles in line, then the flow is laminar. Even exceptionally low Re indicates viscous creeping motion, where inertia effects are negligible. When the inertial forces dominate over the viscous forces (when the fluid is flowing faster and Re is larger) then the flow is turbulent.

An air flow bench is a device that measures the volume or mass of air that will pass through a bounded path or conduit in relation to an applied pressure differential. The pressure differential is usually relative to ambient air pressure and is often produced by some mechanical means such as an electric blower or at least one electric vacuum motor. The flow bench air source creates a pressure differential across the test object that causes air to flow through not only the test object but through the entire flow bench. At some point in the flow bench, the airflow velocity is measured. From the measured air velocity, the volume or mass of air that is flowing through the test object can be calculated. 

The next stage was to conduct the Grid dependency test, where, analysis begins with a coarse mesh and it is refined to finer mesh for each run until the results do not change significantly and depend of the grid size anymore. As the grid or mesh size approaches zero, the approximate solution is almost equal to the actual solution

 A local mesh with a refinement of 5 was considred optimal and used the least amount of computational data ( other values used were 6,7 and 8). The local mesh was used on the faces of the valve to give better readings as the pressure loss will develop mostly there, The meaning of meshing–or mesh generation–is: defining continuous geometric shapes (such as 3D models) using 1D, 2D, and 3D shapes (mesh faces). The finer the mesh, the more accurately the 3D model will be defined. 

 

Study:- As stated earlier, the project intent was to highlight the effect of valve lifts and mass flow rate so a parametric study was conducted for the valve lift distance. The distances of the valve lift were 0.01 to 0.08 mm for 7 divisions and the mass flow rate for each iteration and the chart was shown below.

 

	Design Point 1	Design Point 2	Design Point 3	Design Point 4	Design Point 5	Design Point 6	Design Point 7
D3@Sketch4@Flowbench_part.Part [m]	0.001	0.002166667	0.003333333	0.0045	0.005666667	0.006833333	0.008
SG Mass Flow Rate 1 [kg/s]	-0.019441238	-0.030701613	-0.051917424	-0.078695975	-0.100116022	-0.116986255	-0.129723848