<div>The ambient pressure fluctuations within a wind tunnel test environment can severely affect the boundary layer transition witnessed on test articles The Boeing/AFOSR Mach 6 Quiet Tunnel was designed to minimize these fluctuations, also referred to as noise, and is the world's premier facility for studying hypersonic boundary layer transition in a quiet flow environment. All experiments performed for this work were conducted at this facility.</div><div><br></div><div> </div><div> The freestream flow field of this tunnel has been characterized multiple times since its creation, however an extensive three-dimensional spatial sweep has never been conducted. A pitot rake model was designed to allow for an extensive spatial survey of tunnel noise. This model created measurement capabilities that were previously unknown to the BAM6QT facility, including the ability to take concurrent freestream pitot probe measurements. The performance of this new measurement method was evaluated, and suggestions for future verification tests are made. The pitot rake appears to suffer from probe-probe interactions in certain configurations, and has demonstrated variation in measurements that depends on the individual sensor used.</div><div><br></div><div> </div><div> This new measurement apparatus was used to investigate the effect that cavities in the tunnel wall created by the installation of new optical windows had on the freestream noise level. A control dataset corresponding to a perfectly conformal tunnel wall was not collected during this work. The experiments conducted provide evidence that the tunnel wall cavities do increase the noise downstream of their location by approximately 100%, however a control dataset is needed to verify this finding.</div><div><br></div><div> </div><div> In addition to tunnel characterization, a novel flat plate model was evaluated for use in the BAM6QT. This model was intended for use as a platform for observing second mode instability growth. These experiments show that the initial flat plate geometry proved incompatible with the BAM6QT as the tunnel could not achieve nominal flow conditions with the model installed. The flat plate model was streamlined to rectify the startup issue, but no evidence of the second mode instability was found. A 2.5° half angle cone is being designed to replace the flat plate model as a platform for the continuation of this project.</div>

<p dir="ltr">Pressure transducer, infrared heat transfer, and schlieren imaging data for a flared cone and cone-cylinder-flare in Mach 6 quiet flow are presented. Flared cone pressure transducer results show second-mode RMS values comparable to that found in prior experimental work. Second-mode frequency is found to linearly increase with increasing freestream unit Reynolds number, and frequency varies little between sensors for a given freestream unit Reynolds number. Turbulent intermittency begins to increase at a freestream unit Reynolds number 2x10⁶/m greater than the unit Reynolds number corresponding to peak second-mode RMS. peak RMS. High-speed schlieren imaging on the downstream section of the flared cone shows the second-mode disturbance following trends in power which correlate with PCB RMS. Infrared heat transfer results contain the azimuthal heating streak pattern observed for the flared cone in prior research, but the hot-cold-hot streak pattern is not seen due to limited model length. Streak heating occurs downstream of second-mode peak RMS over the freestream unit Reynolds number range of 6.4x10⁶/m to 10.4x10⁶/m. The heat transfer of streaks is found to vary significantly from streak to streak, while mean streak heating variation with freestream unit Reynolds number is small.</p><p dir="ltr">PCB results of the cone-cylinder-flare show intermittent turbulence at a freestream unit Reynolds number of 16.0x10⁶/m. Examination of shear-layer and second-mode instabilities show significant increases in RMS moving downstream along the flare and with increasing freestream unit Reynolds number. High-speed schlieren imaging of the shear-layer reattachment region on the flare show the presence of the shear-layer and second-mode instabilities when the model is configured with a sharp nose tip. The instabilities are not present with a blunt 5 mm radius nose tip. Heat transfer is observed to increase along the downstream portion of the flare. The sharp nose tip configuration has higher heat transfer rates than the 5 mm radius nose tip configuration.</p>