David Helmer

Validation Experiment for Shock Boundary Layer Interactions: Sensitivity to Upstream Geometric Perturbations

The sensitivity of two shock boundary layer interactions (SBLIs) { a compression corner interaction and an incident shock interaction { to small geometric perturbations (h < 0:2 0) was investigated using particle image velocimetry (PIV) measurements. Tests were performed in a continuously operated Mach 2.1 wind tunnel with a low aspect ratio test section. The primary oblique shock was generated by a 1.1mm high 20 degree compression wedge on the top wall of the tunnel, and small bumps were introduced upstream on the opposite wall. A total of 100 perturbed cases were tested; 45 for the compression corner interaction and 55 for the incident shock interaction. This dataset is well suited to be used for the validation of CFD codes which are intended to be used in design and analysis of systems with stochastic inputs. Both the compression corner and incident shock interactions were very sensitive to perturbations in a given region (-69mm < xp < -54mm), and insensitive to perturbations outside of it. Depending upon the location of the perturbations, the compression corner interaction could be strengthened or weakened signicantly. Areas of high wall-normal velocity in the incident SBLI were intensied as larger perturbations were added in the sensitive region. For all perturbations, the incident shock interaction either moved upstream or stayed in the same location. The deviation in the position of this SBLI from its unperturbed location was a strong function of both the location and size of the perturbations.

Experimental investigations of mixing in turbulent jets with buoyancy

This paper presents measurements of molecular mixing in turbulent buoyant jets of helium issuing into air, using planar laser imaging of the jet uid mole fraction elds. The o ws considered are nominally momentum-driven, so buoyancy eects are presumed to be conned to the small scales of the o w. The measurements focus on the developing region of the jet, which is of particular interest to o ws with combustion. The results suggest that buoyancy aects the details of the evolution of the mixing eld even while the mean eld maintains scaling properties consistent with non-buoyant jets. Specically , the mean jet uid mole fraction proles, and the proles of mole fraction uctuations, show a sharper jet/ambient uid interface relative to non-buoyant jets, possibly indicative of reduced entrainment. The mole fraction uctuations along the jet centerline are also weaker than those reported in non-buoyant jets. Statistics of jet uid mole fractions, conditional on spatial location within the jet, provide one view of the spatial evolution of the jet, while the eld nature of the measurements allows us to investigate the eect of spatial ltering, such as that inherent in large-eddy simulations (LES), on the elds of the turbulent uctuations. The results are intended to inform ongoing eorts to model the mixing process in o ws with density dierences, such as combustion systems.