We demonstrate the first device to our knowledge that uses a solar panel to power the electrochemical reduction of dissolved carbon dioxide (carbonate) into formate that is then used in the same device to operate a direct formate fuel cell (DFFC). The electrochemical reduction of carbonate is carried out on a Sn electrode in a reservoir that maintains a constant carbon balance between carbonate and formate. The electron-rich formate species is converted by the DFFC into electrical energy through electron release. The product of DFFC operation is the electron-deficient carbonate species that diffuses back to the reservoir bulk. It is possible to continuously charge the device using alternative energy (e.g., solar) to convert carbonate to formate for on-demand use in the DFFC; the intermittent nature of alternative energy makes this an attractive design. In this work, we demonstrate a proof-of-concept device that performs reduction of carbonate, storage of formate, and operation of a DFFC.

The potential of jet noise shielding from the Hybrid Wing Body (HWB) airplane is investigated in subscale experiments. The jet nozzle had a bypass ratio 10 and was operated at realistic takeoff exhaust conditions using helium-air mixtures. The shield, fabricated from a thin flat plate, had the generic shape of the HWB planform. Redistribution of the jet noise source is essential for achieving substantial noise reduction. Devices used to alter the jet noise source comprised chevrons (in mild and aggressive configurations) and a number of porous wedge fan flow deflectors. Using the estimated cumulative (downward plus sideline) EPNL reduction as a figure of merit, shielding of the plain nozzle yields a 2.4 dB reduction. Application of the aggressive chevrons increases the reduction to 6.5 dB, while the best wedge configuration improves this figure to 6.9 dB. Combination of wedge and aggressive chevrons yields a benefit of 7.6 dB. Examination of high-definition noise source maps shows a direct link between the insertion loss and the axial location of peak noise source. The aggressive chevrons cause an abrupt contraction of the noise source length at Strouhal number Sr=1.2, while the wedge induces a gradual contraction with increasing frequency. As a result, the insertion loss with the aggressive chevrons is stronger than with the wedge. However, because the wedge is inherently quieter than the chevrons, it gives a slightly better overall benefit. Surveys of the mean flow field show that the wedge, and its combination with chevrons, produces a significant reduction in the potential core length. On the other hand, the chevrons alone induce modest changes in the length of the high-speed region of the jet. Therefore, the mean velocity field by itself cannot provide useful information for inferring the noise source length for these complicated flows.

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Use of conventional scattering solvers for the problem of sound diffraction in the presence of a mean flow requires the use of variable transformations that reduce the wave equation to its canonical form. This enables the assessment of the mean-flow impact on the radiation of the isolated source as well as its diffraction by an object. Applications include the shielding of propulsion noise sources by the airframe. The focus of this study is the diffraction of a wavepacket noise source, simulating jet noise, from a surface having the general shape of the hybrid-wing-body (HWB) airplane. In addition, the canonical problem of monopole diffraction by a sphere is addressed. In both instances the potential solution for the mean flow is used in the transformations, and the boundary element method is used to compute the scattered fields. The study addresses the effect of the mean flow on the incident and total pressure fields and conducts a systematic assessment of the errors introduced by the transformations. The general trend is a compaction of the downstream influence of the noise source, leading to better shielding for the HWB problem. The overall error tends to be less than 5% for flight Mach number not exceeding 0.2. Nomenclature D j = jet diameter E, E = error field a = speed of sound f = cyclic frequency k = acoustic wavenumber = ω/a ∞ k x = axial wavenumber k r = radial wavenumber M = Mach number n = unit normal p = pressure r = radial distance in polar or spherical coordinate systems s = wing span Sr = Strouhal number t = time u = velocity vector U j = jet velocity x = (x, y, z) = position vector θ = polar angle relative to downstream axis ψ = azimuth angle φ = perturbation velocity potential ρ = density ω = angular frequency Subscripts ∞ = freestream i = incident field s = scattered field t = total field Modifiers ( ) = mean component ( ) = acoustic fluctuation component ( ) = axial Fourier transform ( ) = transformed domain