Re: PV Dirigible Prop Alternative To Super Pressure

From	jimp@specsol.spam.sux.com
Newsgroups	sci.physics
Subject	Re: PV Dirigible Prop Alternative To Super Pressure
Date	2016-06-11 05:00 +0000
Organization	A noiseless patient Spider
Message-ID	<qgis2d-315.ln1@mail.specsol.com> (permalink)
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Bret Cahill <bretcahill@aol.com> wrote:
>> >> >> For the third time, why is the Reynolds number of any sphere, of any size,
>> >> >> and of any material always the same number?
>> >> > 
>> >> > If the diameter or "characteristic dimension" is larger or smaller, you get a larger or smaller Nre.
>> >> > 
>> >> > If the velocity in inversely proportional to diameter then the Nre is the same for all sizes of that shape in that fluid, i.e. a golf ball going 300 km/hr has the same Nre as a cyclist helmet going 30 km/hr and the air holes in the helmet actually _reduce_ drag like the dimples on the golf ball reduce drag.
>> >> > 
>> >> > Maybe you meant the Reynolds number can be applied to any size object.
>> >>  
>> >> The Reynolds number is directly proportional to the diameter of the
>> >> cross section, so the comment about size is incorrect.
>> >> 
>> >> Equal sized spheres, no matter the material, be they soap bubbles or lead,
>> >> have the same Reynolds number.
>> > 
>> > The speeds would need to be the same as well, a rare coincidence because
>> > soap bubbles always move slowly w/ respect to wind speed.
>> 
>> As the Reynolds number is directly proportional to velocity, 
> 
> then different speeds => different Nre.
> 
>> comparing
>> Reynolds numbers at differing speeds 
> 
> A golf ball going 300 km/hr has the same Nre as a cyclist helmet going
> 30 km/hr because the helmet ix 10X bigger than the ball.
> 
> The air holes in the helmet actually _reduce_ drag like the dimples on
> the golf ball reduce drag.
> 
> The reason is the speeds and diameters are different but the Nre are
> the same, 50K - 100K where dimpling works.
 
As Reynolds number is dependant on speed as you have realized, comparing
Reynolds numbers of things at different speeds is pointless.

As Reynolds number is dependant on speed as you have realized, talking
about the Reynolds number of something without specifying speed is
pointless.


-- 
Jim Pennino

Thread

PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-04 12:47 -0700
  Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-05 02:11 +0000
    Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-04 22:22 -0700
      Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-05 17:36 +0000
        Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-05 13:52 -0700
          Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-05 22:56 +0000
            Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-08 00:57 -0700
              Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-08 19:27 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Mahipal <mahipal7638@gmail.com> - 2016-06-08 19:16 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-09 02:52 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Mahipal <mahipal7638@gmail.com> - 2016-06-09 06:55 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-09 16:22 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Mahipal <mahipal7638@gmail.com> - 2016-06-09 13:23 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-09 21:14 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Mahipal <mahipal7638@gmail.com> - 2016-06-09 14:49 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-09 19:46 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-10 05:53 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-10 10:07 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-10 17:49 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-10 21:22 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-10 19:40 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-11 05:00 +0000
                Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-11 01:13 -0700
                Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-11 17:38 +0000
  Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-08 00:58 -0700
    Re: PV Dirigible Prop Alternative To Super Pressure noTthaTguY <abu.kuanysh05@gmail.com> - 2016-06-08 07:23 -0700
    Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-08 14:18 -0700
      Re: PV Dirigible Prop Alternative To Super Pressure Sergio <invalid@invalid.com> - 2016-06-08 16:26 -0500
      Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-08 21:41 +0000
        Re: PV Dirigible Prop Alternative To Super Pressure benj <nobodyxx@gmail> - 2016-06-08 20:23 -0400
          Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-09 00:34 +0000
            Re: PV Dirigible Prop Alternative To Super Pressure benj <nobodyxx@gmail> - 2016-06-08 21:07 -0400
              Re: PV Dirigible Prop Alternative To Super Pressure "hanson" <hanson@quick.net> - 2016-06-08 19:22 -0700
              Re: PV Dirigible Prop Alternative To Super Pressure jimp@specsol.spam.sux.com - 2016-06-09 02:36 +0000
  Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-08 14:42 -0700
    Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-09 20:20 -0700
      Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-10 10:10 -0700
        Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-11 11:02 -0700
      Re: PV Dirigible Prop Alternative To Super Pressure Bret Cahill <bretcahill@aol.com> - 2016-06-10 20:11 -0700

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