1.6. Inflow and Outflow Boundary Conditions

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. Therefore, due to the no slip condition the tangential component of the velocity at a stationary wall is set to 0.

In this chunk, we discuss how boundary conditions are essential in fluid dynamics, especially when the flow interacts with surfaces like walls. The 'no slip condition' is introduced, which implies that at a stationary wall, the fluid's velocity is zero at the wall itself. This means that fluid particles in contact with the wall do not slide along it; they are stationary relative to the wall. Hence, both normal (perpendicular) and tangential (parallel) components of the fluid's velocity are zero at these boundaries.

Think about how honey moves over a plate. If you place a spoon in a jar of honey, the honey touches the spoon and does not slide past it; rather, it remains still at the point of contact. Similarly, when fluid flows over a wall, it behaves in the same way where the velocity at the wall's surface is zero.

Now not talking about the inflow and the outflow boundary conditions. So, you see this is inlet this is outlet. So, here from here the inflow will be there, and from here outflow 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.

In this section, we are describing two specific types of boundary conditions in fluid mechanics: inflow and outflow conditions. An inflow condition describes how fluid enters a system, while an outflow condition describes how fluid exits the system. At these boundaries, both the velocity of the fluid and the pressure can be specified. This allows the simulation of various flow conditions, such as different flow rates in a pipe or an open channel.

Consider a garden hose. When you turn on the tap, water flows into the hose (inflow) at a certain rate (velocity) and pressure. If the hose is pointed at the ground, this water then flows out of the hose (outflow) at a certain rate when you open the nozzle. The rate at which water comes in and goes out can be adjusted or specified depending on your needs.

So, the inflow and outlet can be the specification can be in 2 forms, whether if whether we want to specify the inlet flow velocities at the inlet or outlet or the pressure. 1 typical example here is the for the pressure is the pipe flow. Here it is open channel flow.

When setting up a computational model, we have two main ways to specify inflow and outflow boundaries. We can either define the velocity of the flow entering or leaving the model or we can specify the pressure at these boundaries. This is crucial in simulating real-world scenarios where the inflow and outflow rates can vary greatly based on the system's design and operating conditions. The examples of pipe flow or open channel flow highlight how water can be managed differently based on the situation.

Imagine filling a pool with a garden hose. You can control how fast water flows into the pool by adjusting the tap (which represents controlling the flow velocity), or you could measure the height of the water in the pool to determine how much pressure is pushing flow in and out (representing pressure specifications). This flexibility in specifying conditions mimics what happens in actual hydraulic engineering scenarios.

So there is one question which I would want to know, solve solver discuss. So there is a CFD code which is used to solve a 2 dimensional in 2 dimension X and Y incompressible laminar flow without free surfaces. The fluid is Newtonian. So appropriate boundary conditions are used.

In this chunk, we look at a practical application involving computational fluid dynamics (CFD). The discussion revolves around solving fluid flow equations in a two-dimensional space (X and Y coordinates) for an incompressible fluid, which means the fluid's density remains constant. The situation implies a laminar flow where the fluid particles move smoothly in parallel layers. This is an important context in which boundary conditions significantly affect the outcomes of flow simulations.

Picture a smooth river flowing in a straight line. If you were to analyze the flow of this river, you would treat it as two-dimensional, looking at how water flows alongside the banks (the walls). By applying boundary conditions at the riverbanks—like how fast the water flows at certain points—you can predict changes in the river’s behavior under different rain conditions or water obstruction scenarios.

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