[s-cars] While we are on the subject of WGFVs...

[Paul Gailus]

I think we have to be a little careful in such discussions,
because with air flow you need to consider both the static pressure
and the dynamic pressure (which is proportional to the velocity squared).

In order to get any airflow from the external atmosphere into
the compressor inlet, the static pressure at the inlet has to be lower
than the ambient atmospheric pressure.
The only way you can get air flow into the compressor inlet without
having a static pressure there less than atmospheric would be to
have an external source of dynamic pressure supplying high velocity
air (i.e., another blower).

I agree that you would want to minimize unnecessary external pressure
drops in the inlet ducting that restrict the flow. However, near the
compressor inlet the static pressure is going to be significantly
below atmospheric at large flows.

To maximize flow, you would want a bell-mouthed transition
(velocity stack) from the atmosphere to the compressor inlet
to minimize energy losses along the way.
The total pressure (static plus dynamic) will then be the same along
the transition from the external atmosphere to the compressor inlet.
At the inlet of the bell, there will be mostly static pressure and little
dynamic pressure (i.e., low velocity). At the outlet of the bell, there
will be a lower static pressure in exchange for the increased
velocity (i.e., dynamic pressure) based on conservation of energy and
Bernoulli's principle.

Paul 

-----Original Message-----
>From: Mark Strangways <Strangconst at rogers.com>
>Sent: Jan 13, 2006 7:52 AM
>To: Djdawson2 at aol.com, Eric_R_Kissell at whirlpool.com
>Cc: s-car-list at audifans.com
>Subject: Re: [s-cars] While we are on the subject of WGFVs...
>
>The last place you want a negative pressure (as related to atmosphere) is in 
>the inlet to the turbo.
>It will rob you of boost, and if the turbo is at or near the operating 
>extreme limits it can push it over.
>I contend that there is not much negative pressure to be found there, this 
>is why I fought so hard over the whole vacuum issue as it relates to the 
>wastegate. Until Dave sprung the little venturi concept on us, that changes 
>things.
>
>Mark
>----- Original Message ----- 
>From: <Eric_R_Kissell at whirlpool.com>
>To: <Djdawson2 at aol.com>
>Cc: <s-car-list at audifans.com>
>Sent: Friday, January 13, 2006 7:35 AM
>Subject: Re: [s-cars] While we are on the subject of WGFVs...
>
>
>>
>> It would be interesting to see how the vacuum created to the WG by the
>> venturi effect in the WGFV compares to the vacuum that exist in the line 
>> to
>> the compressor inlet, i.e. how much bigger is the venturi vacuum than
>> compressor inlet vacuum?
>>
>> I have to assume that the venturi creates more vacuum than the compressor
>> inlet, else the WGFV would not require the venturi effect.  This makes
>> sense relative to the venturi systems used by "inexpensive shop tools" you
>> mentioned.
>>
>> Thanks,
>> Eric
>>
>>
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>
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