Re: Preliminary analysis of aerodynamics of sparrow strainers (or not)

Jay Scheevel

Hi Micheal,


Not back yet, but I will give a short response to clarify.. Corrections for the differences in chord were made external to Javafoil. I explain my procedures in the first of the documents that I linked to. I realized that Reynolds number is scale dependent (that is kind of the point, isn’t it?), so I have had to use a Reynolds number in Javafoil, that allows me to reach approximately 1 million effective Reynolds number for the Q2 configuration multifoil. To do this the cord is not unit for either airfoil of the multifoil pairs. So, to achieve the entire airplane in a internally consistent model, I cut the half span down to thirds using three models to approximate taper washout and tip efficiency loss (all of these are consolidated externally in spreadsheets with corrections incorporated there).


I modeled multifoils using the LS1 airfoil digitized directly from the hotwire templates in my set of plans. This is overlain in the plot below where the hotwire template is black and the coords used in Javafoil are in red. This figure is from my paper, part 1, that I linked previously. The black square Cp’s are from wind tunnel measurements on the same airfoil at Re=1 e6.  BTW in this comparison, I am using the same relative coords that I sent to you, except below I have scaled it to unit chord in order to compare apples to apples.





From: <> On Behalf Of Michael Dunning
Sent: Thursday, March 10, 2022 7:06 PM
Subject: Re: [Q-List] Preliminary analysis of aerodynamics of sparrow strainers (or not)


Funny; I had that same thought after I went to bed...

However, I used the coordinates from Jay's stock LS(1) airfoil file directly with no changes...except one: re-scaling them up to a unit chord on import. I noticed that both the files without the sparrow strainer ended at x = 0.7116. I figured that the one with the sparrow strainer was at a unit chord length (x = 1.0) and the other two just had the strainer deleted. Plotting them all side by side, that doesn't look to be the case :(

I'm also a bit puzzled by Jay's references to the Eppler main wing, so it probably has something to do with tweaks needed for his modeling framework. I'm starting to lean towards this discrepancy stemming from differences in reference chord length. This sort of thing is how I learned about 'Reynold's Number' vs. 'Reynold's Number per foot' the hard way.

We'll just have to wait for Jay to get back.
#2827 (still thinking about planning on visualizing how to finish building)

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