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The Effects of Viscosity and Three-Dimensionality on Shockwave-Induced Panel Flutter

Boyer, Nathan Robert

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Aero/Astro Engineering.
Impinging oblique shockwaves are commonplace in both external and internal flow paths on high-speed vehicles, and their prevalence will only increase with the continued pursuit of readily deployable flight vehicles. These shockwaves cause sharp pressure rises that create intense localized structural loads. Recently, impinging shocks waves have been identified as a mechanism to induce panel flutter, which presents a major concern for fatigue failure and increased noise generation. Critical to this is the fact that loss of panel stability occurs at different operating conditions and panel stiffness compared to classical panel flutter. To date, research on shock-induced panel flutter has been limited to a two-dimensional, semi-infinite assumption. Additionally, most existing simulations on the topic are restricted to inviscid flow. This dissertation documents expanded understanding of shock-induced panel flutter phenomena by exploring the effects of three-dimensionality and viscosity on the aeroelastic system. The analysis is carried out numerically using the Air Force Research Laboratory FDL3DI code. The first configuration considered is Mach 2 inviscid flow over a square panel. The panel is simply supported on all four edges, and the shockwave is set to impinge along the mid-chord. A parametric sweep is performed over non-dimensional dynamic pressure and incident shock angle. Mean, standard deviation, and time history of the panel response are presented. Additionally, the panel response is projected onto the natural mode shapes in order to gain deeper insight into the characteristics of the structural response. Fluid pressure snapshots are also provided. In general, the panel flutter response is qualitatively similar to previous studies on the semi-infinite configuration. Flutter amplitude is slightly lower and flutter frequency slightly higher for the three-dimensional configuration in all cases. Additionally, the critical non-dimensional dynamic pressure is increased for all shock strengths when compared to the two-dimensional inviscid configuration. This is likely a result of increased stiffness from the panel edge constraints. Despite similarities to the semi-infinite configuration along the centerline, significant spanwise variations occur in both the fluid and structural response of the three-dimensional configuration. Natural panel mode (2,3) makes a significant contribution to the flutter response for all the cases with shock impingement. This is attributed to bending of the reflected shockwave due to surface deformation. Fluid pressure variations in the span from the aeroelastic coupling propagate spanwise and downstream away from the panel. These fluctuations could yield a response in neighboring panels. Moreover, the propagating fluctuations could affect engine performance in internal flow applications. The second configuration considered is for laminar incoming flow over a semi-infinite panel at Mach 2 and a Reynolds number Re=120, 000. The panel is simply supported on the front and rear edges, and the shockwave is set to impinge at the panel midpoint. A similar parametric sweep over non-dimensional dynamic pressure and incident shock impingement angle are performed. The panel response is analyzed using statistical, temporal, and modal analysis. Fluid pressure, velocity, and separation length are also studied. The boundary layer remains laminar for the cases without shock impingement. However, with impinging shockwaves, the boundary layer becomes transitional downstream. Interestingly, the development of a transitional boundary layer induces a rich structural response with higher-order modes compared to cases without a shockwave or with a shockwave in inviscid flow. Flutter amplitude and frequency behave non-monotonically with both non-dimensional dynamic pressure and shock strength, and large fluctuations occur in both. This non-monotonic behavior is attributed to the active panel modes switching significantly across the parameter space. Furthermore, steady aeroelastic response is observed past the critical non-dimensional dynamic pressure for sufficiently high shock strengths. This re-stabilization may be caused by a large increase in mean deflection. Mean separation length beneath the shock foot varies significantly only for the largest studied shock strength. It is observed to be inversely correlated to flutter amplitude and directly correlated with mean deflection. The studies on three-dimensional inviscid flow and two-dimensional laminar flow are tied together by considering a three-dimensional configuration with incoming laminar flow. Results are generated at a single shock strength and two dynamic pressures, selected based on the previous sets of results discussed. The dominant mode shape for the smaller non-dimensional dynamic pressure is a high natural panel mode in both directions similar to the results of the semi-infinite viscous study. However, the dominant mode of the higher non-dimensional dynamic pressure is mode (2,3) which is consistent with the inviscid three-dimensional study. This indicates that viscous effects may become less important with increasing non-dimensional dynamic pressure.
Jack McNamara, Ph.D. (Advisor)
Datta Gaitonde, Ph.D. (Advisor)
Miguel Visbal, Ph.D. (Committee Member)
Jen-Ping Chen, Ph.D. (Committee Member)
131 p.

Recommended Citations

Citations

  • Boyer, N. R. (2019). The Effects of Viscosity and Three-Dimensionality on Shockwave-Induced Panel Flutter [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu156616766854713

    APA Style (7th edition)

  • Boyer, Nathan. The Effects of Viscosity and Three-Dimensionality on Shockwave-Induced Panel Flutter. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu156616766854713.

    MLA Style (8th edition)

  • Boyer, Nathan. "The Effects of Viscosity and Three-Dimensionality on Shockwave-Induced Panel Flutter." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156616766854713

    Chicago Manual of Style (17th edition)