# Need help on boundary layer meteorology

• lalula2
In summary: Beyond that, in general, it would be very difficult to predict the exact effects of boundary conditions on a simulation.

#### lalula2

Hi, i am mech undergrad student, currently i am doing my thesis for CFD simulation of wind flow in urban area by using FLUENT. I am trying to apply logarithmic velocity profiles for my inlet boundary condition.
My question is that from the formula of logarithmic wind profile, the velocity will become negative when it less than certain height due to the ln function. Do i need to use power law profiles to describe the velocity profile under certain height?
Thanks.

Best regards.

This is a question you should find the answer to through journal papers.

Why are you applying a logarithmic inlet condition? It doesn't make much sense to me. If you are trying to get the inlet condition to be as close as the actual velocity profile, then don't worry about.

Expand your domain to include some space outside of your physical domain. Send in a uniform constant flow and let it do what i wants.

I trying so save my computational time by create my own udf for the boundary condition and based on those journals i read.
Beside that, my moderator criticized my velocity profiles and ask me to rectify the problem as he said my velocity above my study area are not logic.
For actual urban area, the building height is relatively low compare to the atmosphere boundary layer.

Well, having said that, you could just kind of substitute height for height above the surface, e.g.
Rather than
$$u(i,j,k) = log(z(i,j,k))$$
Have something like:
$$u(i,j,k) = log( z(i,j,k) - z(i,j,1) )$$

Do remember that boundary conditions are quite a problem in most computational codes, and many many problems can arise from them. Having said that, be very careful when analyzing results such that you ensure you're getting what you think you should.

I image there could be problems with reflections depending on the actual boundary condition implementation.

## 1. What is boundary layer meteorology?

Boundary layer meteorology is the study of the Earth's lowest layer of the atmosphere, known as the boundary layer. This layer is characterized by rapid changes in temperature, humidity, and wind speed, and plays a crucial role in weather and climate patterns.

## 2. Why is boundary layer meteorology important?

Boundary layer meteorology is important because it helps us better understand and predict weather and climate patterns. The boundary layer is where most of the Earth's weather occurs, and changes in this layer can have significant impacts on the environment and human activities.

## 3. How is the boundary layer formed?

The boundary layer is formed through a process called boundary layer mixing, which occurs when warm air rises and mixes with cooler air. This mixing creates a layer of air with different properties than the air above it, such as temperature and humidity.

## 4. What factors influence the boundary layer?

Several factors can influence the boundary layer, including solar radiation, surface characteristics (such as land or water), and atmospheric conditions (such as wind speed and stability). Human activities, such as urbanization and pollution, can also impact the boundary layer.

## 5. How is boundary layer meteorology studied?

Boundary layer meteorology is studied through a combination of observational data, computer models, and field experiments. Instruments such as weather balloons, satellites, and ground-based sensors are used to collect data on the boundary layer, which is then analyzed and incorporated into models to improve our understanding of its behavior.