Re: Aerodynamics

To: tesla-at-poodle.pupman-dot-com
Subject: Re: Aerodynamics
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 30 Mar 1997 17:46:42 -0600
Approved: tesla-at-stic-dot-net
Subject: 
            Re: Aerodynamics
       Date: 
            Fri, 28 Mar 1997 09:10:22 -0800
       From: 
            Skip Greiner <sgreiner-at-wwnet-dot-com>
Organization: 
            Greiner, Ltd.
         To: 
            Tesla List <tesla-at-pupman-dot-com>

> 
> All,
> 
> I have always held that rotary gaps of the simple type, as built by the
> majority of the Tesla community, often flame, flare, or exhibit "follow
> around" for several reasons.  The most obvious is poor design and lack
> of
> forethought in the tank circuit itself.  The other reason is Aerodynamic
> fluid flow problems!
> 
> We all want to seen the rotary as a big fan in addition to a spark gap.
> This fan cools the electrodes and keeps a steady flow of churning air at
> the
> stationary points. How many of us view the system as an series of
> instantaneous events?
> 
> If we invision the moving point as a slab sided cylinder in motion, the
> fluid flow dynamics will show a low pressure region extending well
> behind
> the point.  the faster the point moves the lower the pressure in the
> region
> and the more extended it becomes.  Furthermore, we all know that in air,
> at
> reduced pressures, the electric conduction is more readily supported due
> to
> reduced mean free path.  This remains the case until we get to below 1
> or 2
> mm of pressure and then the situation reverses and the resistance of the
> arc
> goes up quickly due to reduced charge carriers.
> 
> Thus, as the points are firing and the gap tries to spearate, the low
> pressure region following in the wake of the moving cylinder electrode
> allows conduction to continue long after the points are beyond normal
> spark
> over.  All this seems to occur in the low pressure region.
> 
> The biggest flamer gaps I have seen have been high speed gaps with big
> electrodes!   Realizing what the cause might be, I have always used
> electrodes smaller than 1/4" and lately in magnifier work, have opted
> for
> .180 tungsten rod up to 12KW.  I also opt for a much slower gap or rotor
> speed and a larger wheel diameter.  I often operate at no more than 1800
> rpm
> on a 1 foot rotor and use multiple gaps in series with the rotary and
> run
> lethal rotary gap spacings in the .010" range.  I never have experienced
> flare, flaming or "follow around" up to the maximum of 15 KW which I ran
> on
> Nemesis a few times.
> 
> We might do well to think about this problem a bit.  I am planning some
> aerodynamically designed electrodes in future.
> 
> Richard Hull, TCBOR

Richard

An excellent point. One of my sons is an aerodynamicist. I will be
presenting him with the problem today and ask him to make
recommendations as to electrode shape, size and velocity. There should
also be a way to provide baffles on the rotor to break up the low
pressure area behind the moving point, the same way it's done on cars
and airplanes. Will publish his comments on the list.

Skip