Physical Concepts and Basic

Fluid

Mechanics

71

The rate of change

of

flow velocity is the acceleration. Faster rate of

change in velocity gives rise to a greater acceleration in flow.

Such

acceleration can be either positive, i.e. when the velocity is increasing or

negative, i.e. when the velocity is reducing.

This can be appreciated from the flow velocity recording of aortic

velocity and its derivative. Fig.

3.3.4

shows the aortic flow and the flow

acceleration.

Fig.

3.3.4:

Aortic flow and its first derivative, the flow acceleration (dQ/dt). Aortic

pressure and rate

of

its pressure change (dP/dt) is

also

shown.

Thus acceleration is the rate

of

change of velocity. We have for the

accelerations associated with the longitudinal, radial and rotational

velocities (Zamir,

a,