
[Sponsors] 
How to digitize a complex pressure distribution plot 

LinkBack  Thread Tools  Search this Thread  Display Modes 
February 6, 2023, 04:40 
How to digitize a complex pressure distribution plot

#1 
New Member
Jakub
Join Date: Feb 2023
Posts: 1
Rep Power: 0 
Hi everyone,
I'm trying to digitise the total/stagnation pressure distributions of a boundary layer ingesting engine. I have a lot of experimental and computational data from past work but I'm struggling to convert it into a vtk format. My current approach is creating a csv file with engauge by manually drawing lines along each pressure contour line but the limitation is that it only creates separate lines when the contours are uniformly distributed or almost flat and the majority of my dataset is highly distorted. I'm using a simple MATLAB code which converts a csv file into a vtk file however, it only works when it has the same xcoordinate for every line. Since most of the pressure distributions at high angles of attack are nonuniform, engauge is not able to capture these contours separately and I can't create a suitable csv file for MATLAB to convert. I looked everywhere for a similar software to engauge but every other approach gives me separate x values for each line. Is there any other way I could digitize this data? I though of changing the MATLAB script to accept separate x values but I'm not sure how to go about it. Hopefully it makes sense. I uploaded an example of what I'm digitizing. Thank you in advance. 

February 6, 2023, 12:35 

#2 
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,672
Rep Power: 71 
Sorry, I am not sure to understand the format of your initial data.
Matlab is good for many matrix manipulation, also for graphic data but depending on your initial data maybe Tecplot could be of some help. 

February 6, 2023, 17:24 

#3 
Senior Member

I have no idea how you can accurately extract contour values from any location in the plot, but let us assume that you can, so that you have scattered data as follows:
Z1, Y1, f1 Z2, Y2, f2 ... Zn, Yn, fn where the f are the value you are extracting and the (z,y) couples are the location where they are being extracted from. What you can do with this data, if the (z,y) couples are scattered (i.e., with no particular order or distribution), is: 1) Do a delaunay triangulation and either just come out with the data on the resulting unstructured triangular grid or use it to reinterpolate the data linearly on whatever other grid 2) Directly interpolata the data to the desired grid The latter option involves putting up your data structure for an N nearest neighbor search and being able to interpolate from N scattered points, say with an RBF. The RBF route may work also with all the points, so with no need of any data structure, but you'll need to work more on the resulting system solution. I'm pretty sure that someone has already done this with Matlab and most or all the pieces are out there, whatever route you choose 

February 6, 2023, 18:51 

#4  
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,672
Rep Power: 71 
Quote:
Paolo I was thinking to Tecplot because of the unstructured data, the list being exactly what you wrote. Then, would be easy to work for each triangular element and getting isovalue line f(x,y)=a+b*x+c*y >y(x)= (f_v a b*x)/c 

February 7, 2023, 12:45 

#5  
Senior Member

Quote:
If Tecplot can digest a scattered set of points with data and come up with the resulting contours then, I guess, it is the simplest route. My original suggestion came from the fact that, in the past, I worked with MATLAB on the wasp .map file format for terrains, which is just a collection of isolines, hence I know that it is doable in MATLAB very easily. In my case I wanted to get an STL file of the terrain surface, but the matter is pretty much the same. 

February 7, 2023, 12:57 

#6 
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,672
Rep Power: 71 
Let see more details from the authors about his real goal.
Anyway, I think that it is a simple task using the linear law y(x;f_v) to extract the required set of data representing the isolines. 

Tags 
matlab code, postprocessing, pressure contour, vtk file 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Total pressure distribution at boundary as a named expression  ftopper  FLUENT  0  December 9, 2022 10:23 
Getting divergence while increasing the back pressure at pressure outlet  greenfields15  FLUENT  0  March 19, 2018 00:39 
outlet pressure Boundary settings velocity streamline under ambient temp.conditions  Vishnu_bharathi  CFX  12  November 21, 2017 07:56 
Small wiggles in pressure distribution  Rouven  Pointwise & Gridgen  5  August 29, 2015 12:51 
Bad pressure distribution in pump  oringo  FLUENT  2  March 2, 2013 11:38 