Fluid Kinematics And Dynamics: Introduction

KINEMATICS AND DYNAMICS

INTRODUCTION

Fluid kinematics refers to the features of a fluid in motion. It only deals with the motion of fluid particles without taking into account the forces causing the motion. Considerations of velocity, acceleration, flow rate, nature of flow and flow visualization are taken up under fluid kinematics.

A fluid motion can be analyzed by one of the two alternative approaches, called Lagrangian and Eulerian.

In Lagrangian approach, a particle or a fluid element is identified and followed during the course of its motion with time as demonstrated in Fig.1

Fig. 1. Lagrangian Approach (Study of each particle with time)

Fig. 2. Eulerian Approach (Study at fixed station in space)

Eg: To know the attributes of a vehicle to be purchased, you can follow the specific vehicle in the traffic flow all along its path over a period of time.

Difficulty in tracing a fluid particle (s) makes it nearly impossible to apply the Lagrangian approach. The alternative approach, called Eulerian approach consists of observing the fluid by setting up fixed stations (sections) in the flow field (Fig. 2).

Motion of the fluid is specified by velocity components as functions of space and time. This is considerably easier than the previous approach and is followed in Fluid Mechanics.

Eg: Observing the variation of flow properties in a channel like velocity, depth etc, at a section.