2 Aerodynamics
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Fig. 2.60 Supersonic jet flow of the engine nozzle
and other parameters of the airflow. For subsonic flow field and supersonic flow field, the propagation range of disturbance is different. In a
uniform flow field, it is assumed that the gas is stationary and the disturbance source is moving. The small disturbance emitted by the disturbance
source propagates around at the speed of sound, and its influence area has
the following four situations (as shown in Fig. 2.61).
(1) Static disturbance source (Ma = 0)
From a certain moment, the disturbance wave surface emitted in the
first n seconds is a concentric sphere with the disturbance source O as
the center and na as the radius. As long as the time is long enough,
any point in the space will be affected by the disturbance source, that
is, the influence area of the disturbance source is the whole flow field.
(2) Subsonic disturbance source (Ma < 1, V < α)
In the first N seconds, the spherical wave with a radius of na emitted
by the disturbance source should move down from O to the On point
along the direction of the incoming flow, OOn = nV. Because of nV
< na, the disturbance can still cover the whole flow field. The small
disturbance of subsonic flow field can be found in the whole flow
field, and the turbulence of the airflow has been felt before the arrival
of the disturbance source, so the flow direction and airflow parameters
will be changed gradually to meet the requirements of the disturbance
source.