ANS:A - non-steady uniform

Gradually varying fluid flow typically falls under the category of non-steady non-uniform flow. Here’s an explanation of each type of flow:

1. Steady Uniform Flow: This type of flow has constant velocity magnitude and direction at any given point in the flow field and does not change over time. The flow properties are uniform throughout the domain.
2. Steady Non-uniform Flow: In steady non-uniform flow, the velocity magnitude and/or direction vary at different points in the flow field, but these variations do not change with time.
3. Non-steady Uniform Flow: This refers to flow where the velocity magnitude and direction are uniform initially but change with time, becoming non-uniform over time.
4. Non-steady Non-uniform Flow: This type of flow involves variations in velocity magnitude and direction both spatially and temporally. The flow properties change both with respect to location in the flow field and over time.

Gradually varying fluid flow refers to a situation where the flow properties (such as velocity, pressure, and cross-sectional area) change gradually over some length or time scale. This could occur, for instance, in channels with varying cross-sectional area, gradually changing slopes, or in gradually expanding or contracting sections of a flow passage. Therefore, the correct type of flow for gradually varying fluid flow is non-steady non-uniform flow.