[Diy_efi] Pressure readings perpendicular to airflow

[Grant Beaty]

> A probe perpendicular to the flow measures "static" pressure. Yes, static
> pressure goes lower as velocity goes up in an adiabatic flow.

Doh, I should have known that.

> A probe directed into the flow will measure 'total' pressure--which is
> equal to dynamic (velocity) pressure plus static pressure.
>
> A change in velocity converts part of the static pressure into dynamic
> pressure or vice versa.
>
> Greg

Hmm, Corky's book seems to suggest that measuring static pressure is valid
(from his testing methods on pade 165), while Humphie's book says "The
pressure ratio is obtained from the outlet total absolute pressure divided
by the inlet total absolute pressure, and represents the actual pressure
ratio from compressor inlet to outlet devoid of any ducting losses. Total
pressure is the sum of the measured static pressure plus the dynamic head."
on page 65.

So an intercooler reduces the dynamic pressure (through cooling and reducing
velocity) while ideally keeping the same static pressure correct? The quote
from Automotive Turbocharging & Supercharging Systems just doesn't seem
right to me. Isn't the total pressure a constant from one side of the turbo
to the other (if we ignore how much the compessor heats up the air)?

Thanks,
Grant Beaty


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