Venturi Nozzle Multiphase Flow Analysis

Description

Venturi Nozzle Multiphase Flow Analysis Using ANSYS Fluent

Introduction

This report presents a comprehensive Computational Fluid Dynamics (CFD) analysis of a venturi nozzle using ANSYS Fluent. The study aims to investigate the complex multiphase flow behavior of air and water through the nozzle geometry, providing insights into the performance and flow characteristics of this important hydraulic device.

The simulation geometry, designed using ANSYS Design Modeler, consists of a venturi-shaped nozzle with a long, narrow tube and a constricted section. The domain includes an air inlet at the top and a water inlet on the left side, allowing for the investigation of the interaction between the two phases. The geometry is optimized to capture the flow acceleration through the constriction and the subsequent expansion.

ANSYS Meshing was employed to generate a high-quality mesh comprising 829,367 cells. This mesh density provides sufficient resolution to accurately capture the multiphase flow dynamics, turbulence effects, and pressure variations within the domain. The mesh quality ensures efficient computation and helps in resolving the complex flow patterns expected in the venturi nozzle.

Methodology

A pressure-based, steady-state solver was employed to capture the flow characteristics of the venturi nozzle.

The Coupled scheme was selected for pressure-velocity coupling, providing robust and efficient convergence for the multiphase flow simulation.

The Realizable k-epsilon turbulence model with Enhanced Wall Treatment was chosen to accurately represent the turbulent nature of the flow, especially in the constricted section of the venturi.

The Volume of Fluid (VOF) multiphase model with implicit formulation for volume fraction parameters was used to handle the interaction between the air and water phases. This approach is well-suited for capturing the interface between the two fluids and predicting their behavior throughout the domain.

Results

The air volume fraction contours reveal the distribution of air throughout the venturi nozzle. A high concentration of air is observed at the top inlet and in the upper portion of the long tube. As the flow progresses through the constriction, there’s a notable reduction in the air fraction, indicating acceleration and possible mixing with water.

The pressure contours demonstrate the characteristic pressure distribution in a venturi system. A high-pressure region is observed at the water inlet and the beginning of the long tube. As the flow approaches the constriction, there’s a significant pressure drop, followed by a gradual pressure recovery in the expanding section. This pressure variation is crucial for the venturi effect and the nozzle’s operation.

The velocity contours illustrate the flow acceleration through the venturi. Low velocities are observed at the inlets and in the wider sections of the tube. A dramatic increase in velocity is evident in the constricted section, with the highest velocities occurring at the throat of the venturi. This acceleration is fundamental to the energy conversion process in the nozzle.

The simulation captures the essential venturi effect, with clear indications of flow acceleration and pressure changes through the constriction.

The interaction between air and water phases is evident, particularly in the mixing region near the constriction.

The pressure distribution aligns with theoretical expectations for a venturi system, validating the simulation’s accuracy.

The velocity profile shows the characteristic acceleration through the constriction, which is crucial for the operation of venturi nozzles.

The air mass flow rate at the inlet (0.00048099167 kg/s) and the volume-averaged air flow velocity (0.68884552 m/s) provide quantitative insights into the air phase behavior.

The area-weighted average velocity at the air inlet (1.0432147 m/s) indicates a significant acceleration from the initial water inlet velocity, demonstrating the venturi’s effect on flow speed, demonstrating the venturi’s effect on flow speed.