Moderator: Torsten
IMHO this is an inertia problem.Why does casting a 30 ft head that weighs 300 grains ‘feel’ so much heavier than a 60 ft head that weighs 300 grains?
Vince,However, you have taken the form drag coefficient that you are using for the line as being in laminar flow,
Torsten has given a nominal Reynolds number of 32,000 in his form drag calculation and 500 million for the skin drag calculation so I would think that would put them well into the turbulent flow region for both forms of drag.At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent.
I quite agree but you are using a Cd of 1 for your form drag which is for laminar flow, instead of somewhere between 0.1 and 0.3 for a cylinder in turbulent flow as described at Post 8. (viewtopic.php?f=11&t=3858#p68458)gordonjudd wrote: ↑Thu Jan 05, 2023 6:03 pm Torsten has given a nominal Reynolds number of 32,000 in his form drag calculation and 500 million for the skin drag calculation so I would think that would put them well into the turbulent flow region for both forms of drag.
I’m not sure what the splitter plate represents in your 2nd figure but the studies are dated. “Mueller TJ, Pohlen LJ, Cnigliaro PE, Jansen Jr BJ (1983) The influence of free-stream dis- turbances on low Reynolds number airfoil experiments, Exp. Fluids 1: 3-14.” Is a better reference.It is clear that there is very little laminar flow. a result anticipated due to the testing in an already turbulent flow which will produce early transition.
That is of course your prerogative but my position is that a Cd of 1 has produced results that have not been verified in the real world, not only in the lift studies but also in the dangle where the line does not straighten even at our highest casting speeds. Given that the line is flexible, a force acting upon it will cause the line to move in order to reduce that force, and there’s little evidence of that occurring in the fly leg, except in strong winds.In summary, as long as not someone would convince me that the "drag crisis" actually happens for fly lines I'll stick to the Cd value of 1……..I can't and I don't want to draw any conclusions about other works here, this would be fully OT and outside the scope of this thread.
Torsten,In summary, as long as not someone would convince me that the "drag crisis" actually happens for fly lines I'll stick to the Cd value of 1.
Vince,Neither the first figure (laminar flow), nor putting boundary control devices on to your cylinder (3rd figure - right hand side) represent the same turbulent freestream turbulence conditions that you have used for skin drag analysis:
So are you implying that turbulent flow doesn't happen until you reach the crisis flow region for Reynolds numbers above 3.5e-05 even though other researchers say the flow is fully turbulent for Reynolds number values above 300?It’s worth looking at Torstens last diagram for lower values, I’ve circled the part that indicates turbulent freestream airflow
Freestream flow is upstream of the object being measured or tested. Looking at the diagram you have presented, it is for upstream laminar flow (circled in red)gordonjudd wrote: ↑Wed Jan 04, 2023 5:17 pm At least in the measurements made by Gaddis the opposite was true. He found:It is clear that there is very little laminar flow. a result anticipated due to the testing in an already turbulent flow which will produce early transition.
