Some questions about Eddy3D

Grasshopper
#1

I think eddy3d is a great plug-in for outdoor ventilation analysis. Now I need do some validation before outdoor wind analysis by Eddy3d. I found the validation file in Eddy3d is based on Jiang’s paper.

As far as my opinion，the Jiang’s paper is good for outdoor and indoor wind ventilation validation，but not for the outdoor wind analysis which related with the building blocks.

The research always use the “AIJ guidelines for practical applications of CFD” to do outdoor wind validation.I want use eddy3d to do the validation. But I have some questions about it. Maybe someone can help，THX for anyone who pay attention to my questions.

1.

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In Eddy3D we can set gradient wind，but we can only set one Z reference and U reference. In “AIJ guidelines” it gives me the list of Z reference and U reference. So which Z reference should I choose？Or do you know how to solve this problem？

2.

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In Eddy3D，the plug-in let me define block size and the cell size，does the cell size means the cell on the building surface？The result is 4 now， the 4 means 4 times or 4 levels？

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The Eddy3D need define the accuracy of the mesh， so what is the meaning of the “ACCbuilding” and other “ACC-XXXX”？

If I set 4，is it means 4 level cell or the cell size is 4？

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In Eddy3D， the plug-in can define Relaxation factors， the default setting is Fluent， so What is the different between Fluent and OpenFOAM setting？

There is “Solution and Algorithm control”，but the example did not set this， do I need set something or just let it be default？

5. I always used Fluent to do the CFD simulation. In Fluent，if I set 1000 iteration and maybe before 1000 the result is convergence， the simulation will stop. But I think Eddy3D will not stop before iteration setting. Do anyone have any suggestion about this part？

THX for anyone who can help me and I will keep in this validation simulation and I will upload my file when the questions have been solved~~~

PS ： the attachment files are “AIJ guidelines” validation case. And after I did this validation I will upload the data. THX~~~~

JimmyCaseD(Highrise Blocks).3dm (44.2 KB)

2 Likes
#2

Hi Jimmy,

Thanks for getting some more validation going, you can find results to compare over here [1]!
First off, check this website for the basic equations we are dealing with.

In Eddy3D we can set gradient wind，but we can only set one Z reference and U reference. In “AIJ guidelines” it gives me the list of Z reference and U reference. So which Z reference should I choose？Or do you know how to solve this problem？

What you are setting with your components are Uref, Zref, and z0 (disregard zG for now).
Plotting U over z with the values from above should give you your ABL.

image, for example try something like this.

In Eddy3D，the plug-in let me define block size and the cell size，does the cell size means the cell on the building surface？The result is 4 now， the 4 means 4 times or 4 levels？

Yes, it means 4 levels.

The Eddy3D need define the accuracy of the mesh， so what is the meaning of the “ACCbuilding” and other “ACC-XXXX”？

Here, you define the levels you have just decided upon.

In Eddy3D， the plug-in can define Relaxation factors， the default setting is Fluent， so What is the different between Fluent and OpenFOAM setting？

This is a complex topic, feel free to find more information here.

There is “Solution and Algorithm control”，but the example did not set this， do I need set something or just let it be default？

Please leave it as default for now.

I always used Fluent to do the CFD simulation. In Fluent，if I set 1000 iteration and maybe before 1000 the result is convergence， the simulation will stop. But I think Eddy3D will not stop before iteration setting. Do anyone have any suggestion about this part？

It would! The internal setting for convergence is set to 1e-4 for p and 1e-5 for the remaining variables.

Best,

Patrick

[1] Kastner, P., Dogan, T. (2019). A cylindrical meshing methodology for annual urban computational fluid dynamics simulations. Journal of Building Performance Simulation, 13(1), 59-68.

2 Likes
#3

@Jimmy871013 did you validate the AIJ cases ?

1 Like
#4

While we are working on the CFD project with EDDY3D, we found some difficulties in sorting wind data(velocity and direction).

We are wondering if you can share how different wind direction data were interpolated to 8760 hours of wind speed and directions. We are very interested to find hourly directions from weather data. Since it was not possible to find from eddy3d or we might not know how to get it from eddy3d.

We have tried many different approaches, but we were not successful. It will be great if you can share or guide any papers or documents that we can calculate hourly directions.

Let us know if you can give us any advice.

Thank you.

#5

Hi Keunhyuk,

You are probably interested in this component:

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We are wondering if you can share how different wind direction data were interpolated to 8760 hours of wind speed and directions. We are very interested to find hourly directions from weather data. Since it was not possible to find from eddy3d or we might not know how to get it from eddy3d.

It seems that you are interested in WFA (Wind Reduction Factors Annual). You will receive a DataTree with a branch for every hour that contains values for every probing point. The wind direction for every branch may or may not been simulated by you. If you have not simulated it, Eddy3D will approximate it for you. What is happening is described here [1], see section ‘Wind velocities’.

…Going forward, the 8 RANS simulations served as a nearest neighbor lookup table of wind velocities in concert with the annual weather data. For each probing point, we probed the simulated velocity from the 8 CFD simulations. This multidimensional array is used to calculate the dimensionless wind velocity for every probing point by dividing the simulated velocity magnitude by the scaled-down inlet velocity with the logarithmic wind power profile. This yields a spatial wind reduction matrix with information for every probing point for each of the 8 wind directions. From here, we converted the spatial matrix into a temporal matrix. For every hour of the year and its corresponding wind direction, we looked up the nearest neighbor CFD simulation and multiplied the velocities from the spatial velocity matrix with the wind velocity from the weather data that has been scaled down to the probing height. This operation yields a temporal velocity matrix with wind reduction data from which
the wind velocities for the UTCI calculation are retrieved [10]. …

For the approximation, you can choose if you prefer a simple ‘nearest neighbor lookup’ or a interpolation of the two nearest neighbor wind directions for every hour in the year with a right click on the component.

Let me know if you have any other questions.

Best,

Patrick

[1] Kastner, P., & Dogan, T. (2020) Predicting Space Usage by Multi-Objective Assessment of Outdoor Thermal Comfort around a University Campus.