Boundary Layer Transition Flight Experiment Research Articles

Boundary Layer Transition Preflight Experiments in a Mach-6 Quiet Tunnel

Experiments on a subscale model of the U.S. Air Force Office of Scientific Research Boundary Layer Transition flight experiment were made in the Boeing/Air Force Office of Scientific Research Mach-6 Quiet Tunnel. Infrared thermography and temperature-sensitive paint were used to measure the surface temperature and heat transfer and provide images of streamwise streaks with the model at 0, 2, and 4 deg angle of attack. Variations in heating patterns were measured for yaw and roll angles. All smooth body cases remained laminar under quiet flow, but symmetric turbulent wedges were seen in noisy flow. Discrete surface pressure sensors measured possible instabilities on the model surface at locations that correspond to computed instability growth. It was discovered that the geometry was sensitive to forward- and rearward-facing steps near the swept leading edges. Controlled forward- and rearward-facing steps were created and tested. No transition was measured under quiet flow for any rearward-facing step at 0 deg angle of attack. Early transition was measured for the forward-facing steps, and correlations were developed for scaling step effects to the flight vehicle.

Secondary Side Considerations for Boundary Layer Transition Flight Experiment

The Boundary Layer Transition (BOLT) Flight Experiment is to launch soon on a sounding rocket to obtain hypersonic data on a complex geometry with swept leading edges and concave surfaces. BOLT was designed to provide two distinct experimental surfaces on opposite sides of the vehicle. One side of BOLT, referred to as the primary side experiment, was specifically dedicated to boundary-layer transition at hypersonic conditions in the absence of intentionally added surface roughness. The other side, the secondary side experiment, was selected to investigate roughness effects, in the form of rearward-facing steps. Step effects are an important consideration for both sides, as joints near the nose were required to alleviate aerothermodynamic heating. The secondary side joints were made larger than the primary side to provide additional insight into the impact of rearward-facing steps during flight. The secondary side experiment is the focus of the present Paper, which provides details into design decisions made to finalize the geometry and instrumentation for flight.

Aerothermodynamic Ground Tests in Support of the Boundary Layer Transition Flight Experiment

The U.S. Air Force Research Laboratory/U.S. Air Force Office of Scientific Research has sponsored the Boundary Layer Transition (BOLT) experiment to investigate hypersonic boundary-layer transition on a low-curvature, concave surface with swept leading edges. This paper provides a review of aerothermodynamic ground-test contributions by NASA Langley Research Center to the design of the BOLT flight experiment. Several test entries into the NASA Langley Aerothermodynamics Laboratory 20 Inch Mach 6 Air Tunnel are discussed. Global surface heating distributions on subscale BOLT models were measured using either phosphor thermography or infrared thermography at a range of model attitudes and freestream Reynolds numbers. An initial test entry provided the first experimental measurements of transition on the BOLT geometry. A second test entry investigated the effects of distributed surface roughness along the swept leading edges. A third test entry provided an evaluation of the aeroheating environment on the aerodynamic fairings and a portion of the flight vehicle downstream of the BOLT experiment. These entries were intended to support the development and design of flight hardware and instrumentation for the BOLT flight experiment.