14.3.5. Velocity Distributions

So since it is a 0 that means I can draw this the velocity distributions velocity contours okay iso velocity contours I can draw the velocity contours that means maybe this velocity is equal to 2 meter per second next maybe 1.5, 1, 0.5 meter per second. This is what the contours of equal velocities that is what you can be because near to the boundary velocity is 0. So you can have a velocity distribution like you can have a velocity for this case also you can have a velocity distributions like that is what I always encourage you to just draw the safe try to understand it how the velocity distributions are happening it okay.

In open channel flow, the distribution of velocity can be visualized using contours known as iso-velocity contours. These contours represent lines connecting points of equal velocity at various depths of flow. Near the boundary of the channel, the velocity is zero due to the no-slip condition which states that fluid in contact with the boundary does not move. As you move away from the boundary into the main body of the flow, the velocity increases and can be represented through contours, which can help visualize flow characteristics clearly.

Imagine watching a river flow. Right at the edge where the water meets the bank, the water is still – that's the 'no-slip' condition. As you look out towards the middle of the river, the water is moving swiftly. If you could draw lines connecting places that have the same speed, you would see those lines curving because the speed changes across the width and depth of the river.

So, the basically we can have a different classifications of the flow we will discuss more details. why we need it subcritical supercritical and the flow conditions.

The hydraulic radius is defined as the cross-sectional area of flow divided by the wetted perimeter. This concept is crucial in understanding how flow behaves in different conditions, such as subcritical (calm) and supercritical (fast-moving) flows. The hydraulic radius helps to calculate other parameters of flow in an open channel, making it easier for engineers to design channels and predict flow characteristics efficiently.

Think of a garden hose; if you partially cover the end of the hose with your thumb, the speed of the water shooting out increases because the area the water can flow through is smaller. In open channel flow, wider or older infrastructures may behave differently than new, narrow ones. Understanding the hydraulic radius allows civil engineers to consider how changes in channel shape and size affect water flow, much like adjusting the nozzle on a hose.

As we discuss very beginning of dimensional analysis we use the flow proud numbers for classifications of these like flow proud numbers if is equal to the 1 then is a critical if it is a greater than 1 is supercritical less than 1 is subcritical.

Flow in open channels can be classified into three main categories based on flow velocity and gravitational effects: subcritical flow (less than critical speed), critical flow (at critical speed), and supercritical flow (greater than critical speed). Critical flow represents a balance state where any increase in energy causes a transition to supercritical flow, while subcritical flow is characterized by lower velocities and depth. Understanding these classifications helps predict flow behavior, energy movement, and potential hazards, such as flooding.

Imagine a racetrack with cars. If the cars are moving slowly (subcritical), they can easily navigate turns. At critical speed, they balance speed and control just right. But if they speed up too much (supercritical), they might risk losing control. Similarly, engineers need to understand these flow types to design safe and efficient waterways, just like ensuring cars are kept at the right speed for safety.

Anyway that is maybe a simple way to explaining you not going through this pressure is equal to the atmospheres and the pressure flow energy is not significant in this case that is the reasons maybe it is come that but let me not we have these the cover does not matter it okay.

In open channel flows, one important aspect is understanding pressure conditions at the water's surface, which is usually atmospheric pressure. Unlike in pipes where pressure can build up, in open channels, the surface pressure is atmospheric, making it essential to focus on gravitational forces and drag from channel surfaces. This understanding is crucial when analyzing how quickly water flows and how it interacts with the channel bed and banks, as these factors significantly affect energy loss in flow.

Think about a swimming pool. The water surface is exposed to the atmosphere, and we directly see its depth without worrying about pressure buildup inside because it has no covering. Just like a pool, understanding these pressure conditions in open channel flow helps civil engineers predict how water behaves as it moves, ensuring effective designs for channels, rivers, and drainage systems.

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