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The interaction between the transonic flow around a spring mounted OAT15A airfoil model and the resulting pitching motion of the model were investigated with the goal of understanding the dynamics of the occurring phenomena. The experiments were performed at a free-stream Mach number of 0.74, a Reynolds number of $$\mathrm{Re}_\mathrm {c}=3.1\times 10^6$$ Re c = 3.1 × 10 6 , and a mean angle of attack of $$5.8^\circ$$ 5 . 8 ∘ . A periodic pitch motion with an amplitude of the angle of attack of $$\pm \,0.9^\circ$$ ± 0 . 9 ∘ was observed for these flow conditions. The dominant structural frequency of the airfoil’s pitch motion was adjusted to be in the range of the natural buffet frequency of the flow with inhibited pitching motion of the model. The structural motion locks into the frequency of the shock buffet with the pitching degree of freedom at a dominant frequency of 115.5 Hz. Velocity field measurements by means of high repetition rate particle image velocimetry (PIV) were used to capture the motion of the shock and to determine the state of the boundary layer flow for the different phases of the model motion. The PIV results with high temporal resolution allow the detailed observation of the evolution of the different phases of the buffet cycle. Mean values and statistical quantities, spectra and space-time correlations were determined from the measurement data to analyze the flow effects. It was possible to estimate the convection velocity of turbulent structures in the detached boundary layer. Graphical abstract
The interaction between the transonic flow around a spring mounted OAT15A airfoil model and the resulting pitching motion of the model were investigated with the goal of understanding the dynamics of the occurring phenomena. The experiments were performed at a free-stream Mach number of 0.74, a Reynolds number of $$\mathrm{Re}_\mathrm {c}=3.1\times 10^6$$ Re c = 3.1 × 10 6 , and a mean angle of attack of $$5.8^\circ$$ 5 . 8 ∘ . A periodic pitch motion with an amplitude of the angle of attack of $$\pm \,0.9^\circ$$ ± 0 . 9 ∘ was observed for these flow conditions. The dominant structural frequency of the airfoil’s pitch motion was adjusted to be in the range of the natural buffet frequency of the flow with inhibited pitching motion of the model. The structural motion locks into the frequency of the shock buffet with the pitching degree of freedom at a dominant frequency of 115.5 Hz. Velocity field measurements by means of high repetition rate particle image velocimetry (PIV) were used to capture the motion of the shock and to determine the state of the boundary layer flow for the different phases of the model motion. The PIV results with high temporal resolution allow the detailed observation of the evolution of the different phases of the buffet cycle. Mean values and statistical quantities, spectra and space-time correlations were determined from the measurement data to analyze the flow effects. It was possible to estimate the convection velocity of turbulent structures in the detached boundary layer. Graphical abstract
The flow over a wing model with aspect ratio 2 and based on the supercritical airfoil (OAT15A) was experimentally investigated for a fixed Reynolds number ($$Re_\textrm{c}$$ R e c ) of $$3\times 10^{6}$$ 3 × 10 6 and numerous aerodynamic conditions. The angle of attack (AOA) and the Mach number ($$M_\mathrm {\infty }$$ M ∞ ) were varied between 5$$^{\circ }$$ ∘ and 6.5$$^{\circ }$$ ∘ , and between 0.72 and 0.75, respectively. Here we focused on the dynamics of the shock front at incipient and developed buffet conditions, by employing background-oriented schlieren measurements on the wing’s upper surface. The spanwise variations of the shock front statistics and its frequency content were examined. The shock oscillations appeared to be the superposition of multiple fluid modes, of which the most dominant was the classic 2-D buffet, which induced uniform chordwise oscillations of the shock front. The hypothesis was formulated that the remaining modes are linked to physical phenomena reported in the literature, namely the side-wall boundary layer and the vortices detected in the mid-span separated flow.
With the goal of understanding the dynamics of the transonic flow around an OAT15A airfoil model, velocity field measurements were performed by means of high repetition rate particle image velocimetry. The experiments were performed at free-stream Mach numbers from 0.70 to 0.77 and at a Reynolds number of Re$$_\textrm{c}\approx 3\times 10^6$$ c ≈ 3 × 10 6 . The variation of the Mach number allowed for an investigation in the pre-buffet, buffet and close to buffet-offset regime. A fixed version and a spring mounted version of the model were used to investigate the effect of the pitching degree of freedom on the shock buffet. The dominant structural frequency of the airfoil’s pitch motion was adjusted to be in the range of the natural buffet frequency of the flow with inhibited pitching motion of the model. Flow field measurements with an acquisition rate of $$4\,$$ 4 kHz allowed for the detection and analysis of the shape and the motion of the compression shock. With released pitching degree of freedom, shock buffet started at a lower Mach number and showed a larger amplitude for the shock oscillation. Furthermore, the shock motion appeared more harmonic compared to the model without pitching degree of freedom. For a Mach number of $$M_\infty =0.72$$ M ∞ = 0.72 and 0.74, the change of the angle of attack and the shock location correlated strongly with each other. From the measurements, the phase lag between both quantities during the coupled motion could be determined. From the correlation of the shock position at different heights, it can be concluded that the shock motion is controlled by events at the shock foot. The movement of the upper shock part is only a reaction to the movement of the lower part.
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