Mayf:
great "find" on the turbocompressor surge info-- too often we hot-rodders
just have to treat words like "surge" as if they have incomprehensible,
mystical meanings. (Part of the job security for the compressor
specialists, I suspect.)
Your analysis of the implications (for lsr folks) w/resp. to centrif.
compressor selection sound logical, also. I have been coming to about the
same conclusion, based on analysis of the turbo literature that I have (none
of which gives such an easy-to-understand definition of "surge", btw.)
Russ, #1226B
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net]On Behalf Of DrMayf
Sent: Friday, June 27, 2003 10:34 AM
To: land-speed@autox.team.net
Subject: Compressor Surge Definition
A few days ago we were chatting about turbos and compresso surge. I surfed
around and found this really good explanation from Borg Warner Turbo
Systems:
"Surge line
The map width is limited on the left by the surge line. This is basically
"stalling" of the air flow at the compressor inlet. With too small a volume
flow and too high a pressure ratio, the flow can no longer adhere to the
suction side of the blades, with the result that the discharge process is
interrupted. The air flow through the compressor is reversed until a stable
pressure ratio with positive volume flow rate is reached, the pressure
builds up again and the cycle repeats. This flow instability continues at a
fixed frequency and the resultant noise is known as "surging". "
Ok, this means that if you have a centrifugal compressor and you are at some
level of prformance and you release the throttle to the closed position, the
air in the duct works backs up and with no place to go, the compressor blade
cannot "grip" the air and move it forward and can in some instances reverse
the flow (harmful if carried on to long). When the compressor either slows
down or the flow is reestablished bye either the opening of the throttle
blades or opening a blow off valve then the surge condition disappears. If
the compressor is sized to big for the system and it over pressurizes the
system then surge can also occur. However the waste gate, in this case acts
to limit the performance of the compressor by keeping it at a value that
does allow over boost. It does this by releasing exhaust gas before it can
enter the turbine section of the turbo, thus keeping it at some lower level
of operating performance.
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