1.5. Wall Boundary Condition

Now, as I said I mentioned about being closed and you know being open there is a wall at the boundary these wall and other concepts you have read in your previous lectures of hydraulic engineering. So, we are going to talk about the wall boundary condition, since fluid cannot pass through a wall the normal component of the velocity relative to the wall is set to 0 and this is what is this called this is called no slip condition.

In fluid dynamics, when we talk about the wall boundary condition, we refer to the behavior of fluid flow near a solid boundary, such as the wall of a tank or a pipe. The key point to understand is that fluids cannot penetrate solid surfaces. Therefore, at the wall, the velocity of the fluid in the direction perpendicular to the wall (the normal component) is zero. This condition is known as the 'no slip condition', which means that the fluid in contact with the wall is stationary because it cannot move through the wall.

Think of a swimming pool. When a person stands still, their legs are in contact with the bottom of the pool. The water directly next to their legs does not move; it 'sticks' to their legs. This sticking effect represents the no slip condition. The water might flow quickly around other parts of the pool, but right by the person's legs, the water has no velocity.

Therefore, due to the no slip condition the tangential component of the velocity at a stationary wall is set to 0. So, you see there if there is an inlet here, there is a wall here there is an outlet. So, the velocity at this point does not matter what the velocity here is at this particular point anywhere around across this wall the velocity will be 0 due to no slip condition.

Continuing from the no slip condition, we also have the situation regarding the tangential component of fluid velocity at a stationary wall. In addition to the normal velocity (which is zero), the tangential velocity, which is the component of flow parallel to the wall, is also zero at the wall. This means that, regardless of how fast the fluid is moving in other parts of the flow, right at the wall itself, there is no motion. This reinforces the importance of boundaries in determining fluid flow behavior in computational models.

Imagine driving a car along a highway with a barrier on either side. As you approach the barrier, you can't drive through it; the car stops at the barrier. Similarly, the fluid cannot 'pass through' the wall and must stop. Just as there would be no forward movement against the barrier, the fluid next to the wall has a velocity of zero, representing the no slip condition.

No not talking about the inflow and the outflow boundary conditions. So, you see this is inlet this is outlet. So, the here from here the inflow will be there, and from here out flow will be there. In means coming in and out means going out. So, at a velocity inlet or outlet the velocity of the incoming or outgoing flow specified along the inlet outlet phase at pressure inlet and outlet the total pressure along the inlet and outlet phase specified.

Boundary conditions are not limited to just walls; they also include conditions at boundaries where fluid enters or exits a system, called inflow and outflow conditions. An inflow condition specifies the velocity of fluid entering the system, while an outflow condition does the same for fluid flowing out. Additionally, these conditions can also address pressure at the inlets and outlets, which is crucial in determining how the fluid behaves as it moves through the system.

Consider a garden hose. When you turn the tap on, that's your inflow condition—the speed and force of the water entering the hose. When you point the hose at a plant, the water flows out; this outflow condition could be controlled by how you adjust the hose nozzle. When pressure builds up inside the hose, it affects the flow rate, similar to how pressure specifications influence fluid behavior in a computational model.

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