# How I can determine the free surface level?

In summary, the conversation discusses a prototype of a hydroelectric plant and the need to simulate turbulent flows. The geometry consists of two zones, one with water and one with air, and a gate is used to control the flow. The speaker is seeking advice on boundary conditions and the use of a dynamic mesh. They also ask if the geometry can be considered an open channel and how to determine the free surface and bottom level at the outlet.
Hello

My geometry is a prototype of a hydroelectric plant. It consists of a tank, penstock, a gate and a test section; my aim is to simulate turbulent flows on this prototype. My geometry consists of two zones, a zone filled with water (red color) and a zone filled with air (blue color). The water will start to flow when I pull the gate to the top. At first, I want to know what boundary conditions I should give to this geometry and what boundary conditions I should give to the gate. Do I have to use a dynamic mesh to give a motion to this gate and which UFD example should I use?

Secondly, can I consider this geometry as an open channel? If yes, how I can determine the free surface level and the bottom level at outlet?

Sorry for my English.

Can you help me please? Thanks

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There needs to be a gate valve at the turbine input to control the flow through the turbine. That gate and turbine restricts the flow and so allows the penstock to remain full of water during operation.

The gate at the top of the penstock will not need to be closed except when servicing the bottom gate or the penstock.

After the gate at the top of the penstock there needs to be an open vertical pipe, reaching higher than the top of the tank. That will allow air to enter the penstock without restriction when the upper gate is closed. It will prevent the embarrassing partial vacuum collapse of the penstock structure if the upper gate is closed before the lower gate.

No, you cannot consider this as an open channel flow because the water is flowing in a pipe.

## 1. How do I physically measure the free surface level of a liquid?

To determine the free surface level of a liquid, you can use a variety of instruments such as a ruler, graduated cylinder, or a dipstick. Simply place the instrument in the liquid and record the measurement at the point where the liquid meets the air.

## 2. What factors can affect the accuracy of my free surface level measurement?

The accuracy of your free surface level measurement can be affected by factors such as the shape and size of the container holding the liquid, any obstructions on the surface of the liquid, and the visibility of the meniscus (curved surface) of the liquid.

## 3. Can I use a mathematical formula to calculate the free surface level?

No, a mathematical formula cannot accurately determine the free surface level of a liquid. This is because the free surface level is influenced by external factors such as air pressure, temperature, and the properties of the liquid itself.

## 4. How can I ensure precise and consistent free surface level measurements?

To ensure precise and consistent free surface level measurements, it is important to use the same instrument and method for each measurement. Additionally, taking multiple measurements and averaging them can help to reduce any errors or variations.

## 5. Is it necessary to determine the free surface level of a liquid?

In some cases, determining the free surface level of a liquid may not be necessary. However, in scientific and engineering contexts, it is often important to know the precise location of the liquid's surface in order to make accurate calculations and predictions.

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