Analysis of a Subsonic Expansion Jet Under the Influence of a Finite Wall at the Exit

With the advent of short takeoff and landing, thrust vectoring has become an integral part of aircraft systems. Various schemes are employed to achieve jet offset, one of which is by fluidic control using mechanisms such as perturbing boundary layer or providing a control bleed. The work presented in this paper provides an unconventional method of offsetting the main jet by inducing virtual Coanda effect by introducing a finite wall. It also lays down the importance of aspect ratio which determines whether the flow will bend or go straight. The proposed scheme requires neither moving parts nor control bleed making this a cutting edge discovery. The case presented here addresses the influence of finiteness of domain following expansion on the flow characteristics. It comprises a small inlet pipe to ensure full development of flow before expansion; and a main domain with a finite wall below, but is open above. So, not just the front but the top face too, is open to atmosphere. For various lengths, domain depth is increased till the flow switches from touching the wall to a straight jet. This is repeated for multiple inlet velocities and turbulent intensities. The expansion ratio is taken to be quite large so that it does not influence the results. It is observed that for a given velocity and length, there exists a critical depth before which flow sticks to the wall permanently. If the depth of wall is more than this critical depth then, the flow completely ignores the presence of wall and goes straight. It is also observed that this critical ratio is independent of the velocity and domain size to a large extent.