naca-wr-l-5
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Numerical Evaluation of the Wake Survey Equations for Subsonic Flow Including the Effect of Energy Addition
Direct-reading tables and charts are presented for
determining the drag or thrust coefficients from wake-
survey measurements in the subsonic speed range. For
flows wherein no energy is added, the point drag coef-
ficient is shown to be an explicit function of the stream
Mach number M , the static-pressure coefficient at the
wake station % , and the total-pressure—loss coeffi-
cient AH/fio, WLere AB is the total-pressure loss
and q0 is the stream dynamic pressure. values of the
point drag coefficient are tabulated for a wide range
of values of these parameters. Inasmuch as the tabulated
coefficients (either drag or thrust) represent the point
values, Which are independent of the integration of the
wake, the charts or tables in the form presented are
general in application.
For flows wherein energy is added, such as flows
behind propellers or heated radiators, an additional
parameter, which is a function of the stagnation-
temperature rise, must be considered. values of the
point drag coefficient that include the effects of the
addition of energy are tabulated.
In the field of aeronautical research,wake pressure
surveys have been used increasingly for determining
profile drag, internal drag, Jet thrust, and related
factors. The evaluation of the drag or thrust from
pressure surveys is based on the solution of the momentum
equation. For high-speed flows, in which the air must be
considered compressible, the evaluation of the drag or
thrust must include the variation in the density of the
air; this variation in the density necessarily complicates
the solution of the momentum equation. For flows wherein
energy has been added, the density variation is of
importance even for the low-speed conditions.
Because a large number of pressure readings are
usually required to make a complete Wake survey, it is
essential that solutions of the wake-survey equations
for all types of flow be presented in a form to permit
rapid and accurate computation. Various simplifying
techniques have been developed for evaluation of the
drag coefficient from wake pressure measurements by
means of charts or tables, but these methods have required
excessive interpolation or computation due to the form
of the parameters employed.
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