The finite obstacle effect on the aerodynamic performance of a normal hovering wing is studied using the immersed boundary method. Phenomena of a two-dimensional wing hovering above, under, or on the side of a circular obstacle are presented. Parameters including obstacle size, distance, location, and flapping angle are investigated to study how the aerodynamic force and flow field are affected. The diameter of the obstacle ranges from 0.5c to 12c and the distance between the centroid of the wing and obstacle surface from 0.5c to 6c (c is the wing chord length). Previous observations of ground effects including force enhancement, reduction, and recovery occur similarly when the wing hovers above the obstacle of diameter greater than 2c. However, finite obstacles affect the aerodynamic performance differently when the size shrinks to a critical value. Force drops when the wing moves close and rises when moving away, opposite to the ground effect. As flapping angle amplitude increases, the force change tends to be consistent for different-sized obstacles. The top or side effect shows a different influence on the force change. Force monotonically increases as the distance decreases when the wing hovers under the obstacle. The side effect places a less important factor on the aerodynamic performance. All force changes under such circumstance are less than 13% referring to nonobstacle result. The gap between the leading or trailing edge of the wing and obstacle surface plays a significant role in the leading and trailing edge vortices generating, shedding, and pairing, which greatly affects the force change.

Fish swim with four main gaits—anguilliform, subcarangiform, carangiform, and thunniform—produced by waves along varying portions of the body. However, how muscle activation length influences swimming performance remains poorly understood. We present a reconfigurable robotic fish that replicates all four gaits in a single platform by rapidly tuning its body stiffness. Vacuum-driven layer jamming muscles in four tensegrity joints enable quick (≤1 s) stiffness modulation (stiffness ratio of 46.6) and gait switching. In thunniform gait, the robot reaches 1.24 body lengths per second, whereas in anguilliform gait, it achieves agile maneuvering with a turning radius of 0.26 body lengths. Fluid simulations show that the thunniform gait generates stronger vortices and 142% more thrust compared with anguilliform motion at 5 Hz, explaining its high-speed performance. The robot dynamically adapts gaits during locomotion—using thunniform for fast traversal and anguilliform for obstacle negotiation—demonstrating environmental adaptability. This work advances understanding of aquatic multimodal locomotion.

With the rapid development of artificial intelligence, machine learning algorithms are becoming more widely applied in the modification of turbulence models. In this paper, with the aim of improving the prediction accuracy of the Reynolds-averaged Navier–Stokes (RANS) model, a semi-implicit treatment of Reynolds stress anisotropy discrepancy model is developed using a higher-order tensor basis. A deep neural network is constructed and trained based on this discrepancy model. The trained model parameters are embedded in a computational fluid dynamics solver to modify the original RANS model. Modification computations are performed for two cases: one interpolation and one extrapolation of different Reynolds numbers. For these two cases, the ability of the modified model to capture anisotropic features has been improved. Moreover, when compared with the mean velocity of large eddy simulations (LES), the root mean square error of the modified model is significantly lower than the original RANS model. Meanwhile, the modified model can better simulate flow field separation and fluctuation in the shear layer and has better prediction accuracy for the reattachment point and the mean velocity profile compared with the original RANS model. In addition, the modified model also improves the prediction accuracy for the mean pressure coefficient and mean friction coefficient of the underlying wall surface. The previously trained model is also directly performed for the modification computation of the two massive separation periodic hill flows. It is shown that the results simulated by the modified model and LES approach are more consistent in both trend and magnitude than the original RANS model and LES approach.

This work investigates separate and combined effects of the vane surface roughness and thermal barrier coating (TBC) on the cooling performance of a film-cooled high-pressure turbine vane using computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis. The cooling effectiveness and heat transfer coefficient, where are predicted within an investigated range of the roughness height from 5 to 20 µm, are compared with those of the smooth vane. Results show that the roughness height increases local heat transfer coefficients in general in the suction side (SS) and the rear-half portion of the pressure side (PS), thereby reducing the cooling effectiveness. The results are different from those in the suction-side vicinity of the leading edge (LE) to further downstream of the pressure side due to uncertain local heat transfer coefficients. In addition, thermal sensitivity to the roughness height and TBC is investigated based on the volume basis in the roughness height range which is extended to 120 µm. Results show that without TBC, a 120 µm increase in the roughness height causes 24 K and 20 K rises of the average and maximum vane temperatures, respectively. With TBC, the average and maximum vane temperatures are reduced as much as 18 K and 27.8 K, respectively.

Since the theoretical aeroelasticity for flapping-wing aerodynamics was introduced in the 1920s, the effects of flexibility on aeroelasticity have been paid more attention to aerodynamic design. In recent years, the trait of the wing flexibility is applied for small-scale wings of biomimetic flyers including micro air vehicles and mini unmanned aerial vehicles. Until now, the aerodynamic performance and great agility of these flyers, which are beneficially used for military missions and other civilian applications, have been improved through surrogate flapping wings with the favorable effects of the flexibility. As per the aeroelasticity principle for the forward flying, the chordwise flexibility of an elastic flapping wing can generate thrust and lift redistributions, whereas the spanwise flexibility can result in variations of the angle of attack and the shift of phase along the wingspan direction. Consequently, all vortices generated by the flapping wing i.e. (1) leading-edge vortices, (2) tip vortices, and (3) trailing-edge vortices are blended supportively, thereby improving the aerodynamic performance and agility. Hence, the growth of research and development of the aerodynamic performance and agility for these flyers under the influence of flexible wings increases through experimental and computational studies dynamically and rapidly. This review aims to highlight the important role of the flexibility in the recent progress in wing aerodynamics of these flyers through several wing models done by famous groups of experts in this field. In addition, this review includes the acoustics of the wings under the flexibility effects which is considered as a new key for better flyer design and improvement. A comprehensive understanding of the integrated aerodynamics and acoustics under the wing flexibility is, therefore, needed.