Numerical Investigation of a Rectangular Jet Exhausting over a Flat Plate with Periodic Surface Deformations at the Trailing Edge

Multiple competing factors are forcing aircraft designers to reconsider the underwing engine pod configuration typically seen on most modern commercial aircraft. One notable concern is increasing environmental regulations on noise emitted by aircraft. In an attempt to satisfy these constraints while maintaining or improving vehicle performance, engineers have been experimenting with some innovative aircraft designs which place the engines above the wings or embedded in the fuselage. In one configuration, a blended wing concept vehicle utilizes rectangular jet exhaust ports exiting from above the wing ahead of the trailing edge. While intuitively one would think that this design would reduce the noise levels transmitted to the ground due to the shielding provided by the wing, experimental studies have shown that this design can actually increase noise levels due to interactions of the jet exhaust with the aft wing surface and flat trailing edge. In this work, we take another look at this rectangular exhaust port configuration with some notional modifications to the geometry of the trailing edge to determine if the emitted noise levels due to jet interactions can be reduced with respect to a baseline configuration. We consider various horizontal and vertical offsets of the jet exit with respect to a flat plate standing in for the aft wing surface. We then introduce a series of sinusoidal deformations to the trailing edge of the plate of varying amplitude and wave number. Our results show that the emitted sound levels due to the jet–surface interactions can be significantly altered by the proposed geometry modifications. While sound levels remained fairly consistent over many configurations, there were some that showed both increased and decreased sound levels in specific directions. We present results here for the simulated configurations which showed the greatest decrease in overall sound levels with respect to the baseline. These results provide strong indications that such geometry modifications can potentially be tailored to optimize for further reductions in sound levels.

Tandem-wing interactions on aerodynamic performance inspired by dragonfly hovering

Dragonflies possess two pairs of wings and the interactions between forewing (FW) and hindwing (HW) play an important role in dragonfly flight. The effects of tandem-wing (TW) interactions on the aerodynamic performance of dragonfly hovering have been investigated. Numerical simulations of single-wing hovering without interactions and TW hovering with interactions are conducted and compared. It is found that the TW interactions reduce the lift coefficient of FW and HW by 7.36% and 20.25% and also decrease the aerodynamic power and efficiency. The above effects are mainly caused by the interaction between the vortex structures of the FW and the HW, which makes the pressure of the wing surface and the flow field near the wings change. During the observations of dragonfly flight, it is found that the phase difference ( γ ) is not fixed. To explore the influence of phase difference on aerodynamic performance, TW hovering with different phase differences is studied. The results show that at γ = 22.5°, dragonflies produce the maximum lift which is more than 20% of the body weight with high efficiency; at γ = 180°, dragonflies generate the same lift as the body weight.

Vortex trapping recaptures energy in flying fruit flies

Flapping flight is one of the most costly forms of locomotion in animals. To limit energetic expenditures, flying insects thus developed multiple strategies. An effective mechanism to reduce flight power expenditures is the harvesting of kinetic energy from motion of the surrounding air. We here show an unusual mechanism of energy harvesting in an insect that recaptures the rotational energy of air vortices. The mechanism requires pronounced chordwise wing bending during which the wing surface momentary traps the vortex and transfers its kinetic energy to the wing within less than a millisecond. Numerical and robotic controls show that the decrease in vortex strength is minimal without the nearby wing surface. The measured energy recycling might slightly reduce the power requirements needed for body weight support in flight, lowering the flight costs in animals flying at elevated power demands. An increase in flight efficiency improves flight during aversive manoeuvring in response to predation and long-distance migration, and thus factors that determine the worldwide abundance and distribution of insect populations.

Prototyping an S-Band Conformal Line Array Antenna on a Partial Wing Surface

This paper presents the design, prototyping, and testing of an S-Band conformal array on a partial wing surface. The array elements are series fed microstrip patch antennas fabricated entirely through additive manufacturing (AM) technology using a combination of fused deposition modeling and thermal spray. A robust material set of ULTEM 9085 and copper alloy is used for a good balance of mechanical/environmental robustness and RF performance, while also offering a viable path forward for a future fielded design. The focus of this paper is on AM multi-material fabrication, fundamental print settings and material characterization, and antenna testing. AM characterization coupons are utilized to improve the accuracy of the RF antenna model, which showed excellent agreement with the prototype measurements.

Prototyping an S-Band Conformal Line Array Antenna on a Partial Wing Surface

This paper presents the design, prototyping, and testing of an S-Band conformal array on a partial wing surface. The array elements are series fed microstrip patch antennas fabricated entirely through additive manufacturing (AM) technology using a combination of fused deposition modeling and thermal spray. A robust material set of ULTEM 9085 and copper alloy is used for a good balance of mechanical/environmental robustness and RF performance, while also offering a viable path forward for a future fielded design. The focus of this paper is on AM multi-material fabrication, fundamental print settings and material characterization, and antenna testing. AM characterization coupons are utilized to improve the accuracy of the RF antenna model, which showed excellent agreement with the prototype measurements.