Chris Lesperance
Registered
I recently started to try and figure out how to do accurate turbos with the Physics Spreadsheet. This is the table that starts on Cell M39 on the Engine2 tab. I’m hoping to add this here for documentation and hive mind the parts that might be missing.
I haven’t figured out how to do the Turbine Flow rate (Cell A48 to D98). If some one has suggestions, please post it and let me know.
First thing is research. Finding any graphs related to the make and model of your turbo. Usually there is a compressor map that is a standard layout for all turbos. As an example, it is the Figure 2 picture below.
Once you have this, it is trying to extract the numbers from your map graph. I've been using https://plotdigitizer.com/app lately. Maybe there are others out there, but any app that will convert a line graph to data. Load in the graph, and then set your X and Y limits. A reminder that the scale for the flow can be different. You’ll need to convert the X axis to kg/s if that is not available.
On the spreadsheet side, I believe you only need to fill in what you know. You don't have to utilize the full chart. Adding more will make it more detailed, but I do not believe it is necessary. In this example, with the map having the turbo RPM going to 150000 rpm, I filled in the Spool RPM (Cell O42) to 20000. You need to try and make that Spool RPM number come close to the RPMs that are listed on your compressor map to make guessing easier. The Corrected flow on the compressor map goes to ~0.5 kg/s. Putting "0.05" in Cell P42 gives a good break down for that.
Using 100k RPM as an example of what to do.
Surge flow - Red line - Column AG is the Compressor surge flow values. For this, you match the RPM on the spread sheet with where it intersects with the surge flow line. You take the X value, and put that in the AG column.
Pressure Ratio - Yellow - You'll take the corrected flow value on the sheet (Blue numbers/lines), and use that on your X axis on the map. Where that intersects with the RPM, gives you the pressure ratio. You will fill that in the chart for the RPM you are working with (Yellow cells).
Now where the pressure ratio is plotted, that will be within an area circle. That is the Efficiency (green values). This is a little guess work as the circles increase by a couple percent per line. How ever it falls, you put that in the chart for the RPM you are working with (green cells)
That should take care of 1 rpm line. That just need to be done for the rest of the rpms on your chart.
I hope I explained the way that I see things well enough. It just has to be done for all RPM values on the spreadsheet. Now the values before and after the plotted points, I do not have a good solution for. In my engine, I just took some inspiration from the provided turbo on the sheet. If you come up with a better or easier solution, I would love to hear it. Also note that if the RPM value on the sheet is not on the map (for example 40000rpm), that might take a little guess work. I don't have a good and easy solution for that either. I think I might have to ask ChatGPT for some suggestions.
Anyway, let me know if that works or if there are any questions. I'll do my best to answer!
I haven’t figured out how to do the Turbine Flow rate (Cell A48 to D98). If some one has suggestions, please post it and let me know.
First thing is research. Finding any graphs related to the make and model of your turbo. Usually there is a compressor map that is a standard layout for all turbos. As an example, it is the Figure 2 picture below.
Once you have this, it is trying to extract the numbers from your map graph. I've been using https://plotdigitizer.com/app lately. Maybe there are others out there, but any app that will convert a line graph to data. Load in the graph, and then set your X and Y limits. A reminder that the scale for the flow can be different. You’ll need to convert the X axis to kg/s if that is not available.
On the spreadsheet side, I believe you only need to fill in what you know. You don't have to utilize the full chart. Adding more will make it more detailed, but I do not believe it is necessary. In this example, with the map having the turbo RPM going to 150000 rpm, I filled in the Spool RPM (Cell O42) to 20000. You need to try and make that Spool RPM number come close to the RPMs that are listed on your compressor map to make guessing easier. The Corrected flow on the compressor map goes to ~0.5 kg/s. Putting "0.05" in Cell P42 gives a good break down for that.
Using 100k RPM as an example of what to do.
Surge flow - Red line - Column AG is the Compressor surge flow values. For this, you match the RPM on the spread sheet with where it intersects with the surge flow line. You take the X value, and put that in the AG column.
Pressure Ratio - Yellow - You'll take the corrected flow value on the sheet (Blue numbers/lines), and use that on your X axis on the map. Where that intersects with the RPM, gives you the pressure ratio. You will fill that in the chart for the RPM you are working with (Yellow cells).
Now where the pressure ratio is plotted, that will be within an area circle. That is the Efficiency (green values). This is a little guess work as the circles increase by a couple percent per line. How ever it falls, you put that in the chart for the RPM you are working with (green cells)
That should take care of 1 rpm line. That just need to be done for the rest of the rpms on your chart.
I hope I explained the way that I see things well enough. It just has to be done for all RPM values on the spreadsheet. Now the values before and after the plotted points, I do not have a good solution for. In my engine, I just took some inspiration from the provided turbo on the sheet. If you come up with a better or easier solution, I would love to hear it. Also note that if the RPM value on the sheet is not on the map (for example 40000rpm), that might take a little guess work. I don't have a good and easy solution for that either. I think I might have to ask ChatGPT for some suggestions.
Anyway, let me know if that works or if there are any questions. I'll do my best to answer!
I have a problem where the power wouldn't increase anymore after 1000bhp. I think I had once 1200bhp on my BMW 3.2 CSL Turbo physics (accidently and had to correct). I am writing this comment before I will start learning about these compressor parameters, I haven't been doing anything with those yet. And I hope to find answer in these lines, thanks to this thread hopefully a lot quicker. 
