Publications

2012
W. J. Baars, Tinney, C. E., Ruf, J. H., Brown, A. M., and McDaniels, D. M., “Wall pressure unsteadiness and side loads in overexpanded rocket nozzles,” AIAA Journal, vol. 50, no. 1, pp. 61-73, 2012.Abstract
Surveys of both the static and dynamic wall pressure signatures on the interior surface of a subscale, cold-flow, and thrust-optimized parabolic nozzle are conducted during fixed nozzle pressure ratios corresponding to free shock separation and restricted shock separation states. The motive is to develop a better understanding for the sources of off-axis loads during the transient startup of overexpanded rocket nozzles. During free shock separation state, pressure spectra reveal frequency content resembling shock wave turbulent boundary-layer interaction. Presumably, when the internal flow is in restricted shock separation state, separation bubbles are trapped by shocks and expansion waves; interactions between the separated flow regions and the waves produce asymmetric pressure distributions. An analysis of the azimuthal modes reveals how the breathing mode encompasses most of the resolved energy and that the side load inducing mode is coherent with the response moment measured by strain gauges mounted upstream of the nozzle on a flexible tube. Finally, the unsteady pressure is locally more energetic during restricted shock separation, albeit direct measurements of the response moments indicate higher side load activity when in free shock separation state. It is postulated that these discrepancies are attributed to cancellation effects between annular separation bubbles.
PDF icon j2012aiaa-baarsv50n1.pdf
W. J. Baars, Tinney, C. E., and Wochner, M. S., “Nonlinear noise propagation from a fully expanded Mach 3 jet,” 50th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2012-1177, Nashville, TN, 2012.PDF icon c2012aiaa-nashvillebaars-1177.pdf
B. W. Donald, Baars, W. J., Tinney, C. E., and Ruf, J. H., “Acoustic characterization of sub-scale rocket nozzles,” 50th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2012-0544, Nashville, TN, 2012.PDF icon c2012aiaa-nashvilledonald-0544.pdf
S. M. Mula, Stephenson, J., Tinney, C. E., and Sirohi, J., “Dynamical and evolutionary characteristics of the tip vortex from a four bladed rotor in hover,” American Helicopter Society 68th Annual Forum. Fort Worth, TX, 2012.PDF icon c2012ahs-fortworthmula.pdf
J. H. Stephenson, Mula, S. M., Tinney, C. E., and Sirohi, J., “Far wake rotorcraft vortex tumbling,” 50th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2012-0425, Nashville, TN, 2012.PDF icon c2012aiaa-nashvillestephenson-0425.pdf
M. A. Villanueva, Tinney, C. E., Dolder, C. N., and Haberman, M. R., “Flowfield and wall pressure characteristics downstream of a boundary layer suction device,” 50th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2012-0743, Nashville, TN, 2012.PDF icon c2012aiaa-nashvillevillanueva-0743.pdf
A. Karpatne, Sirohi, J., Mula, S. M., and Tinney, C. E., “Investigation of tip vortex aperiodicity in hover,” American Helicopter Society 68th Annual Forum. Fort Worth, TX, 2012.PDF icon c2012ahs-fortworthkarpatne.pdf
N. Murray, Lyons, G., Tinney, C. E., Donald, B., Baars, W., Thurow, B., H., H., and Panickar, P., “A laboratory framework for synchronous near/far-field acoustics and MHz PIV in high-temperature shock-containing jets,” Proceedings of the Internoise 2012/ASME NCAD meeting. New York, NY, 2012.PDF icon c2012asme-nycmurray-1270.pdf
W. J. Baars and Tinney, C. E., “Scaling model for nonlinear supersonic jet noise,” Bulletin of the American Physical Society, Division of Fluid Dynamics, San Diego, CA, vol. 57. San Diego, CA, 2012.PDF icon a2012aps-sandiego-149497.pdf
2011
C. N. Dolder, Villanueva, M. A., Haberman, M. R., and Tinney, C. E., “Application of boundary layer suction for reducing hydrophone sensing noise,” in 162nd Meeting of the Acoustical Society of America, San Diego, CA, 2011, vol. 130:4, Pt 2.
W. J. Baars, Tinney, C. E., Murray, N. E., Jansen, B. J., and Panickar, P., “The effect of heat on turbulent mixing noise in supersonic jets,” 49th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2011-1029, 2011.PDF icon c2011aiaa-orlandobaars-1029.pdf
W. J. Baars, Tinney, C. E., and Ruf, J. H., “Time-frequency analysis of rocket nozzle wall pressures during start-up transients,” 13th European Turbulence Conference, Journal of Physics: Conference Series, vol. 318, no. 092001, 2011. Publisher's VersionAbstract
Surveys of the fluctuating wall pressure were conducted on a sub-scale, thrust-optimized parabolic nozzle in order to develop a physical intuition for its Fourier-azimuthal mode behavior during fixed and transient start-up conditions. These unsteady signatures are driven by shock wave turbulent boundary layer interactions which depend on the nozzle pressure ratio and nozzle geometry. The focus however, is on the degree of similarity between the spectral footprints of these modes obtained from transient start-ups as opposed to a sequence of fixed nozzle pressure ratio conditions. For the latter, statistically converged spectra are computed using conventional Fourier analyses techniques, whereas the former are investigated by way of time-frequency analysis. The findings suggest that at low nozzle pressure ratios –where the flow resides in a Free Shock Separation state– strong spectral similarities occur between fixed and transient conditions. Conversely, at higher nozzle pressure ratios –where the flow resides in Restricted Shock Separation– stark differences are observed between the fixed and transient conditions and depends greatly on the ramping rate of the transient period. And so, it appears that an understanding of the dynamics during transient start-up conditions cannot be furnished by a way of fixed flow analysis.
PDF icon c2011etc13-warsawbaars.pdf
C. N. Dolder, Haberman, M. R., Villanueva, M. A., and Tinney, C. E., “Turbulent pressure signature reduction using turbulent boundary layer suction control,” 49th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2011-0751, Orlando, FL, 2011.PDF icon c2011aiaa-orlandodolder-0751.pdf
S. M. Mula, Stephenson, J., Tinney, C. E., and Sirohi, J., “Vortex Jitter in Hover,” American Helicopter Society Southwest Region Technical Specialists Meeting. Fort Worth, TX, 2011.PDF icon c2011ahs-fortworthmula.pdf
W. J. Baars, Tinney, C. E., Ruf, J. H., Brown, A. M., and McDaniels, D. M., “Wall pressure unsteadiness and side loads in overexpanded rocket nozzles,” AIAA Houston Section Annual Technical Symposium. Gilruth Center, NASA-JSC, 2011.
2010
C. N. Dolder, Haberman, M. R., and Tinney, C. E., “Turbulent Boundary Layers over Receiver Arrays,” in 159th Acoustical Society of America Meeting, NOISE-CON, Baltimore, MD, 2010, vol. 127:3, Pt 2.
W. J. Baars, Stearman, R. O., and Tinney, C. E., “A review on the impact of icing on aircraft stability and control,” Journal of Aeroelasticity and Structural Dynamics, vol. 2, no. 1, pp. 35–52, 2010. Publisher's VersionAbstract
Several years of earlier research was conducted for the U.S. Air Force, related to the impact that warhead-induced damage had on the aeroelastic integrity of lifting surfaces and in turn the resulting upset of the complete aircraft. This prompted us to look at how similar aeroelastic events and aircraft upsets might be triggered by ice accumulation on specific parts of the aircraft. Although seldom studied, icing can also significantly impact the aircraft’s aeroelastic stability, and hence the overall aircraft stability and control, and can finally result in irreversible upset events. In this latter context, classical flutter events of the lifting surfaces and controls can occur due to ice-induced mass unbalance or control hinge moments and force reversals. Also, a loss of control effectiveness caused by limit cycle oscillations of the controls and lifting surfaces may appear, due to significant time-dependent drag forces introduced by separated flow conditions caused by the ice accumulation. A review is presented in this article on the mechanisms that initiate these ice-induced upset events when considering the class of small general aviation aircraft. The review is based on literature and earlier experimental work performed at The University of Texas at Austin. Two commonly observed ice-induced aircraft stability and control upset scenarios were selected to investigate. The first upset scenario that is presented involves an elevator limit cycle oscillation and a resulting loss of elevator control effectiveness. The second upset is related to a violent wing rock or an unstable Dutch Roll event.
PDF icon j2010asdj-baarsv2.pdf
J. Stephenson, Tinney, C. E., and Sirohi, J., “The near-field pressure of a small-scale rotor during hover,” 48th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2010-0008, Orlando, FL, 2010.PDF icon c2010aiaa-orlandostephenson-0008.pdf
W. J. Baars, Tinney, C. E., and Powers, E., “POD based spectral Higher-Order Stochastic Estimation,” 48th AIAA Aerospace Sciences Meeting and Exposition. AIAA Paper 2010-1292, Orlando, FL, 2010.PDF icon c2010aiaa-orlandobaars-1292.pdf
W. J. Baars, Tinney, C. E., Ruf, J. H., Brown, A. M., and McDaniels, D. M., “On the unsteadiness associated with shock-induced separation in overexpanded rocket nozzles,” 46th AIAA Joint Propulsion Conference and Exhibit. AIAA Paper 2010-6728, Nashville, TN, 2010.PDF icon c2010aiaa-nashvillebaars-6728.pdf

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