Developing Force and Moment Measurement Capabilities in the Boeing/Afosr Mach-6 Quiet Tunnel

Nathaniel T Lavery, Purdue University

Abstract

Force and moment measurement capabilities are quintessential in wind tunnel testing. A force and moment balance had never been tested in the BAM6QT before this research. The work accomplished in this thesis performed the first force and moment testing in the BAM6QT and laid the groundwork for a better balance to be acquired in the near future. The BAM6QT is a quiet tunnel, meaning it is capable of low disturbance freestream flow. This feature makes it ideal for research in boundary layer transition. The intersection of hypersonic aerodynamic loading and the effects of freestream noise on the boundary layer will create many opportunities for new research. The BAM6QT will be the only hypersonic quiet tunnel with force and moment capabilities. Having the right balance for the conditions in the BAM6QT is imperative for successful implementation. Many types of force and moment balances exist and are explained in the introduction of this work. A 6-component, internal strain gauge balance was loaned from Calspan to facilitate this research. The strain gauge balance is a type well suited for conventional tunnels. The research explored if the general purpose nature of the strain gauge balance would be suitable for the BAM6QT. A BAM6QT run lasts 4 to 6 seconds and is comprised of several intervals of steady stagnation pressure near 190 ms in duration. In test durations below 200 ms, strain gauge balances decrease in accuracy without the use of acceleration compensation. It was sought to determine if the BAM6QT tunnel would require acceleration compensation to achieve load measurements. This would be the case if each interval incurred an impulse of inertial loads with a low enough frequency to not be filtered out before the next impulse. For five components: Normal force (NF), pitching moment (PM), side force (SF), yawing moment (YM), and rolling moment (RM), it was not found that acceleration compensation was required. Low frequency inertial loads were not apparent. In the tracking of cone and tunnel movement via high speed video, no low frequency vertical movement was identified. Axial force (AF) was inconclusive. A consistent 5.3 Hz oscillation was present in AF running loads. This frequency is the same as the frequency of quasi-steady intervals resulting from the expansion fan reflection in the driver tube. Tunnel movement was detected at the frequency. However, the movement was not large enough to cause inertial loads comparable to the amplitude of oscillation. If this is an oscillation in aerodynamic loading, acceleration compensation would be of little gain. A balance must operate within an established load range or risks damage. Error in the balance measurements is proportional to the maximum load range. Because the startup loads of the BAM6QT were suspected to be large but were unknown, a balance with a substantial load range was selected to provide a large factor of safety. The cost of the large load range was increased measurement error. Running loads were near 1% or less of the maximum load range. The bias and precision error of the balance was a larger than the magnitude of the running load for all but AF. Bias error for the low range was estimated from bench-top testing and was significantly lower than the bias error over the full range.

Degree

M.Sc.

Advisors

Chynoweth, Purdue University.

Subject Area

Fluid mechanics|Mechanics

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