Nozzle-Exit Boundary-Layer Effects on a Controlled Supersonic Jet

Abstract

The effect of nozzle-exit boundary-layer thickness on the evolution of a round Mach 1.3, Reynolds number 1 × 10 6 jet is examined without and with control. For the latter, the flapping mode is considered at the preferred column mode frequency (Strouhal number 0.3). The boundary-layer thickness is varied from a very small value to 25% of the diameter. For the no-control cases, the distance between the nozzle lip and the initial appearance of breakdown is proportional to the boundary-layer thickness, which is consistent with theory and previous results by other researchers at Mach 0.9. However, the subsequent growth toward the centerline is faster for the thicker boundary layers. With flapping mode control, increasing the thickness of the boundary layer has different effects on the flapping and nonflapping planes. The rapid spreading of the jet observed on the flapping plane with thin boundary layers is greatly diminished as the nozzle-exit layer is thickened. Conversely, the rate of spreading on the nonflapping plane is increased. Likewise, the characteristic vortical rings observed with thin layers in experiment and simulations become less prominent with thicker layers, indicating reduced control authority. Thus, increasing the boundary-layer thickness reduces the differences between controlled and uncontrolled cases.

Investigation of a Twinjet Configuration with and without Flow Control

“…Hence, it is speculated that the presence of this steep gradient of spreading is responsible for the earlier collapse. Previous works employing explicit laminar boundary layer profiles on single jets have reported no significant variation in the column length for supersonic jets 46 The existence of the boundary layer results in some more key differences between the FBL and the baseline cases. The profiles of mean velocity for the FBL case show a stark difference close to the nozzle exit relative to those for the baseline case (Fig.…”

Flow Similarity in Strong Swept-Shock/Turbulent-Boundary-Layer Interactions

“…Finally, because the development of coherent structures in a turbulent shear layer is dependent on the thickness of the shear layer and the convective velocity [73,74], these results should prove to have interesting ramifications for mid-frequency unsteadiness of the separated shear layer and shock system. The scaling of the outer shear layer with incoming boundary-layer thickness (2-D free-interaction theory) suggests the formation of shear layer coherence with frequencies similar to that observed in 2-D STBLIs.…”