A test investigation is performed to the convective heat transfer in a confined crossflow channel with a specific dimensionless height of 3, produced from a 2×2 square-array impinging jets with dimensionless pitches of 4. Particular focus is played on the heat transfer enhancement by using the passively extended jet pipes and the actively center-positioned synthetic jet in the continuous-jet square array, as well as their combination schemes. Square-array jet Reynolds number (Re) ranges from 3 000 to 10 000, and the synthetic jet acoustic actuator is driven at a fixed frequency of 250 Hz. Correspondingly, the synthetic jet velocity ratios (defined as the ratio of synthetic jet characteristic velocity to square-array jet ejecting velocity) are varied from 2.0 to 0.6. From the jet pipe extension, the dimensionless normal distance between jet outlet and targeting wall is adjusted in a range of 1–3. Within the scope of this study, the heat transfer enhancement roles are clearly illustrated. Under Re=3 000, the synthetic jet integration demonstrates a significantly stronger heat transfer augment role than the jet pipe extension, taking on dominant heat transfer enhancement mechanism in the combination scheme. With respect to the baseline situation (no synthetic jet integration and no jet pipe extension), the area-averaged Nusselt number on a specified zone could be increased up to 200% when the crossflow velocity ratio (defined as the ratio of crossflow inlet velocity to square-array jet ejecting velocity) beyond 0.67. Whereas under Re=10 000, the jet pipe extension plays dominant heat transfer enhancement mechanism on the otherwise. the area-averaged Nusselt number could be increased up to 100% at crossflow velocity ratio of 0.5 in relation to the baseline situation. Meanwhile, in the square array with the extended jet pipes, the role of synthetic jet integration is very faint. The most possibilities wherein the combination of synthetic jet integration and jet pipe extension could exhibit obviously its significance on heat transfer enhancement appear when both schemes display equivalent heat transfer augment roles. For instance, under Re=5 000 and crossflow velocity ratio ranging from 0.6 to 0.8, the combination scheme shows an obviously further improvement on heat transfer enhancement, in related to the single scheme either in active or passive.

To reveal the fluid structure coupling mechanism of multi-leaf wavy foil type dynamic pressure gas bearings, a coupling analysis method was established for the shear flow and elastic foil combination deformation in the rotating-static multi-wedge channel of this type of bearing. The parameter distribution of the unsteady flow field of the rotating-static gap gas film and the unsteady deformation of the elastic foil combination were numerically studied. The research results confirm that there was a strong aero-elastic coupling effect in dynamic pressure gas bearings of the multi-leaf wave foil type. When multiple wedge-shaped channels were coupled with eccentricity, different elastic foils correspond to multiple discrete high/low pressure zones in the gas film. The high pressure zone was located in the convergence area of the channel, while the low pressure zone was located at the sudden expansion step connected to adjacent foils. The local expansion of flow channels in the high-pressure zone induced flow separation and increases shear flow instability. The fluid-elastic coupling weakened the pulsation amplitude in the high-pressure region of the gas film, and strengthened the pressure pulsation amplitude in the low-pressure region. The 1st and 2nd elastic foils deformed in the direction of the bearing sleeve, while the 4th and 5th elastic foils deformed in the direction of the rotating shaft, which corresponds to the distribution of the high-pressure and low-pressure areas of the rotating-static air film. The low-pressure zone of the static gas film induced separation between the top foil and its adjacent overlapping foil. The influence of rotational speed, eccentricity, clearance scale, and elastic foil stiffness on the fluid-elastic coupling performance of bearings was obtained. The gas film pressure in the fluid domain is positively correlated with the bearing capacity, speed, and eccentricity, while negatively correlated with the clearance scale. High rotational speed and large eccentricity induced an increase in the peak value of the low-pressure region in the gas film. In aero-elastic coupling, there was a certain lag in the vibration frequency of the top foil compared to pressure pulsation. And the amplitude of foil vibration and gas film pressure pulsation in the high-pressure region of the fluid domain were greater than that in the low-pressure region of the fluid domain. The results in this study provide theoretical basis and technical quidance for the design of airborne multi-leaf wave foil dynamic pressure gas.