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opposite to the blowing side, and the magnitude of the side force increases with
STABtLITY AND CONTROL PROBLEMS AT HIGH ANGLES OF ATTACK   745
LEFT OR RIGHT SIDE AT.F.S. = 5.0
9
     cv
a) CR VS a,p = O
2* Soparadon on tho
     blowiW s.fde d~hyod
      by pt ontrairumN
       3-  HTOh vort~x movoi to a
 2         kNNt podW.
.    4-  Lov vwt~x movu to a
             hkrhot prmlkn
5- Soparatkn on th~
    non-blowing sido
id~rrnc~d
                                            b) Flow near the forebody apex
Figr 8.76   Nozzlejet blowing for forebody vortex control on the F-16 aircraft 49,Sn
746           PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
the blowing parameter Cy, which is defined as
                                                           C", = mj Vj                                             (8.18)
                                                                         ",       qao S
where mj is the jet mass flow rate, vj is the jet velocity, qoo iS the freestream
dynanuc7pressure, and S is the reference area*
      The physical fiow mechanism associated with the tangential aft blowing concept
is schema/cally shown in Fig. 8.76b. The basic principle behind the jet blowing
concept is the jet entrainment effect. The jet induces an inward velocity field
in its proximity and continuously entrains the surrounding fluid as it blows aft
(downstream). As a result, the vortex on the blowing side moves closer to the body
surface. Consequendy, the other vortex on the nonblowing side gets pushed away
from the body surface, giving rise to a side force in the direction of blowing.
      An example of slot blowing for the F-16 aircraft is presented in Fig.  8.77. The
blowing on the right causes a yawing moment to the right and vice versa  The slot
extends from FS 5 to FS 39lo /he slot blowing operates on the principle of circula-
tion control. As shownin Fig. 8.77b, the blowing energizes the boundary-layer flow
near the surface so that the flow separation is delayed. On the nonblowing side, the
 fiow patt.ern remains more orless the same as in thebasic case. As a result, the vortex
on the blowing side is located closer to the body. On the other side, the vortex gets
pushed further away, gMng rise to a side force directed towards the blowing side.
   Forebody suction.   An example of the application of forebody suction for
vortex control is shown in Fig. 8.78a  The vehicle configuration to which the
forebody suction was applied is the High Incidence Research Model (HIRM) of
RAE, U.K The suction ports are located near the apex of the nose.
     The nonzero side force when the suction is offis due to the naturally occurring
vortex asymmetry. The effect ofsuction on theleftis to produce a negative yawing
moment (towards the suction side) and vice versa
     The forebody suction,like forebody blowing, works on the principle of circula-
tion control, wherein the boundary-layer fiow is pulled towards the surface to keep
it attached to a greater extent and delay the flow separation on the suction side. As
a result, a side force develops towards the suction 9rde.
    The interest in using TVC has arisen mainly from the requirement to increase
　
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