Title

Flow characteristics of a transverse water jet into an unconfined water channel

Date of Award

2015

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Engineering

Faculty

Faculty of Health, Engineering and Science

First Advisor

Dr Mehdi Khiadani

Second Advisor

Dr Alireza Mohyeddin

Abstract

The flow pattern of a transverse jet in a crossflow is complex due to the interaction between the jet and the crossflow. This interaction plays a significant role in practical fluid mixing including effluent discharge in water, film cooling and chemical mixing chamber. In this research, the flow patterns of a transverse jet in an open channel were studied experimentally and numerically. For this detailed study, three velocity ratios 2, 3 and 4 and two water depths 100 and 200 mm were considered. The objectives of this study were:

  • To explore the velocity distribution for different velocity ratios
  • To analyse the turbulence characteristics of the water jet in a crossflow
  • To simulate the flow dynamics using three turbulence models (k - E. k – w and RSM)
  • To compare the experimental results with the predictions arising from the turbulence models.

The experiments were conducted in Edith Cowan University’s Hydraulic Laboratory using a 13 m horizontal flume with a recirculating water system. A vertical circular pipe (23 mm diameter) was used as the jet and placed at 8.5 m from the flume inlet, normal to the crossflow. For the experimental measurements, a 2D Laser Doppler Velocimeter (LDV) was used. The numerical simulations of the flow field were carried out using ANSYS FLUENT 14.5.

The outcomes of the study were:

  • The trajectory of the jet centreline and the penetration of the jet were dependent on the velocity ratio
  • For the same velocity ratio, the penetration of the jet varied with the depth but the overall relationship between these variables was complex
  • Analysis of turbulence characteristics showed that turbulence behaviour greatly influenced mixing and entrainment of the jet flow
  • None of the three turbulence models, in their current form, can adequately describe the full flow behaviour. However, the k - E. model performed better than the other two models for the velocity and turbulence analysis of a jet in a crossflow.

Usually, a flash jet from the bottom of a channel, induces a recirculation region at the upstream side of the channel; however, with a transverse jet in this study no upstream recirculation region was observed. The strength of the reverse flow region was influenced by the degree of blockage of the crossflow by the jet. The upstream flow deceleration rate was coupled to the jet blockage factor and the magnitude of the adverse pressure gradient on the trailing edge of the jet. This implies that either the jet blockage or the adverse pressure gradient was not strong enough to create an upstream reverse flow near the jet exit close the free surface. The velocity ratios considered in this study were ranges from low to high velocity ratios. The different flow features observed due to those velocity ratios enhance the knowledge of basic fluid dynamics. The results provide the information that the flow behaviour due to the different velocity ratios depends on the crossflow Reynolds number and the flow configuration. With the knowledge of this result, the relative importance of the flow propagation and mixing in the crossflow can be evaluated. The influence of the velocity ratio in a crossflow in an unconfined situation may aid to understand the design estimation of such flow field. The jet trajectories provide the information of penetration depths that can be used to figure out the proper mixing process of such situations.

LCSH Subject Headings

Hydraulics.

Water jets.

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