Week 4.1: Project Steady state simulation of flow over a throttle body

Aim

To simulate a steady state fluid flow along the given elbow channel geometry with a fixed throttle valve (fully opened state).

Introduction

Throttle valves are designed to regulate the supply of fluid flow (air-fuel mixture) to an engine and are often operated by a handwheel or a lever. Controlling the supply of fluid is crucial as it dictates the power output of the engine. Analyzing the fluid flow across the throttle valve is important so as to decrease the pressure losses in the system and increase the overall efficiency and smooth working of the engine.

In the current study, a steady-state simulation of the throttle valve in the fully opened state will be conducted.

Method

Domain and Mesh

The 3D geometry of the elbow channel was provided and can be seen in the image below.

An unstructured cartesian grid was generated over the geometry using three layers of fixed embedding with a scaling of 3 at the walls of the throttle valve. The base mesh sizing was set to 2e-3m and the resulting mesh contained 45k cells as seen below.

CFD Setup

All Simulations were conducted using Converge v3.0. The fluid used in the domain was air with default properties. The pressure at the inlet was set to 1.5 bar and the pressure outlet was set to 1 bar. The elbow and throttle valve walls in the channel were set to no-slip condition.

The steady-state density-based PISO solver was used for the spatial discretization of the flow parameters. Turbulence in the flow was estimated using the two-equation RNG K-Epsilon Model. Momentum, density, turbulence, energy, and species were estimated using the SOR scheme while pressure was estimated using the converge bicgstab scheme.

Convergence was monitored using monitors of average velocity, pressure, and mass flow rate at the outlet. The solution was deemed to converge when the monitors varied under 0.001 units across iterations.

Results

The images below show the monitors of velocity, pressure, and mass flow rate at the outlet to ensure convergence.

The image below shows the velocity contour from the simulation.

A stagnation point can be observed around the throttle valve walls and is attributed to the blockage of the flow in the channel by the valve. The velocity is seen to increase downstream towards the outlet and is caused by the specified lower pressure boundary condition at the outlet.

The image below shows the pressure contour from the simulation.

A gradual decrease in the overall pressure contour can be observed from the inlet to the outlet. A local increase in pressure and a subsequent decrease in pressure can be seen at the throttle valve which can be attributed to the stagnation of the flow.

The image below shows the velocity streamlines from the simulation to visualize the flow around the throttle valve.

From the streamlines, it is observed that the flow around the throttle valve is fairly smooth since the throttle valve is in a fully opened state. The fully opened state of the valve causes a minimal blockage to the flow and hence all the streamlines are seen to pass along the valve easily. Partially closing the throttle valve will increase obstruction to the flow and decrease the mass flow at the outlet.

Conclusion

The steady-state simulation of airflow over the given elbow channel with a fixed throttle valve (fully opened state) was conducted using converge. Localized regions of flow stagnation were observed around the throttle valve and were deemed to have been caused by the blockage of the flow. This blockage is however minimal as the throttle was set to the fully opened state.