We developed and evaluated an anodized-aluminum pressure-sensitive paint (AA-PSP) with new formulations of free-base porphyrin, ${\mathrm{H}}_2\mathrm{TCPP}$, as an optical unsteady pressure sensor. The luminophore ${\mathrm{H}}_2\mathrm{TCPP}$ has quite a short fluorescent lifetime (2.4 ns on the condition of the AA-PSP). The fluorescence spectroscopy result shows that the excitation wavelength of ${\mathrm{H}}_2\mathrm{TCPP}$ corresponds to violet-colored (425 nm) and green-colored (longer than 520 nm) lights. The pressure sensitivity is sufficiently high for the pressure sensor (0.33–0.51%/kPa) and the temperature sensitivity is very low (0.07–1.46%/K). The photodegradation of the AA-PSPs is not severe in both excitation light sources of the green LED and the Nd:YAG laser. The resonance tube experiment result shows the cut-off frequency of the AA-PSPs is over 9.0 kHz, and the results of the shock tube experiment show the 10 µs order time constant of the normal shock wave.

The present study investigated the effects of active flow control by high-frequency flapping jets on a supersonic cavity flow. The discharging position was varied at the leading edge, the bottom wall upstream side, the bottom-wall downstream side, and the trailing edge. The flapping jets’ frequencies were varied at 0 (non-flapping case), 15, and 22 kHz, respectively. Discharging non-flapping jets at the leading edge and the bottom wall upstream side remarkably enhanced pressure fluctuations and density gradients. The reverse flow near the bottom wall and the amplitude of the recirculation inside the cavity were enhanced when non-flapping jets were discharged at the leading edge. Discharging non-flapping jets at the bottom wall downstream side reduced the pressure fluctuations of the frequency lower than 8 kHz. Discharging flapping jets changed flowfields, although the flow control effects of discharging positions were dominant. The flapping-jet discharging at the leading edge reduced the size of the primary recirculation. Discharging flapping jets at the bottom wall downstream side showed further suppression effects on fluctuations than the non-flapping-jet discharging case. There were no significant effects on the pressure fluctuations when the jets were discharged at the trailing edge.

Base pressure fluctuations associated with the large-scale wake structures behind a freestream-aligned circular cylinder and aerodynamic force fluctuations related to them are experimentally investigated in the wind tunnel tests. Measurements at ReD=6.97×104 and 1.04×105 were conducted using pressure-sensitive paint (PSP) and a magnetic suspension and balance system (MSBS) for creating a supportless condition. The obtained pressure fields were mainly analyzed by a modal decomposition combining azimuthal Fourier decomposition and proper orthogonal decomposition (POD). The pressure fluctuations caused by large-scale vortex shedding were observed from the results of frequency analysis for mode coefficients. The states of the fluctuations were classified into three patterns, which are anticlockwise/clockwise circular and flapping patterns. These patterns have been observed in the previous studies for velocity fluctuations in the wake of a freestream-aligned circular cylinder. The conditional sampling analysis revealed that the trend in the amplitude of the pressure fluctuations is different by the state, and the flapping pattern causes a large pressure difference across the cylinder axis. Furthermore, the relationship between the antisymmetric pressure fluctuations and lift fluctuations, which act in the lateral direction of the cylinder, is confirmed.