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Background: Rodent ultrasonic vocalizations (USVs) are crucial to their social communication and a widely used translational tool for linking gene mutations to behavior. To maximize the causal interpretation of experimental treatments, we need to understand how neural control affects USV production. However, both the aerodynamics of USV production and its neural control remain poorly understood. Results: Here, we test three intralaryngeal whistle mechanisms—the wall and alar edge impingement, and shallow cavity tone—by combining in vitro larynx physiology and individual-based 3D airway reconstructions with fluid dynamics simulations. Our results show that in the mouse and rat larynx, USVs are produced by a glottal jet impinging on the thyroid inner wall. Furthermore, we implemented an empirically based motor control model that predicts motor gesture trajectories of USV call types. Conclusions: Our results identify wall impingement as the aerodynamic mechanism of USV production in rats and mice. Furthermore, our empirically based motor control model shows that both neural and anatomical components contribute to USV production, which suggests that changes in strain specific USVs or USV changes in disease models can result from both altered motor programs and laryngeal geometry. Our work provides a quantitative neuromechanical framework to evaluate the contributions of brain and body in shaping USVs and a first step in linking descending motor control to USV production. [ABSTRACT FROM AUTHOR]

Air-moving devices such as fans are routinely characterised experimentally in terms of their sound power, and sound quality which depends on both broadband and tonal noise levels. The International Organization for Standardization method 5136, widely used in industry and academia, estimates sound power in third-octave bands radiated into a duct. Since the International Organization for Standardization method is not designed for tone measurements and overlooks the unevenness of the modal power distribution, an extended method has been developed and implemented based on mode decomposition. The 'two-port' source model is formulated to include higher-order modes and applied for the first three modes which require six independent stationary measurements on each side or 'port'. The resulting experimental rig is much shorter than the International Organization for Standardization rig and does not require anechoic terminations. Both methods have been used to characterise the same fan, and the results compared to understand tone measurement shortfall of the International Organization for Standardization rig. [ABSTRACT FROM AUTHOR]

An algorithm to compute the silent base flow sources of sound in a jet is introduced. The algorithm is based on spatiotemporal filtering of the flow field and is applicable to multifrequency sources. It is applied to an axisymmetric laminar jet and the resulting sources are validated successfully. The sources are compared to those obtained from two classical acoustic analogies, based on quiescent and time-averaged base flows. The comparison demonstrates how the silent base flow sources shed light on the sound generation process. It is shown that the dominant source mechanism in the axisymmetric laminar jet is 'shear-noise,' which is a linear mechanism. The algorithm presented here could be applied to fully turbulent flows to understand the aerodynamic noise-generation mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The physical sources of sound are expressed in terms of the non-radiating part of the flow. The non-radiating part of the flow can be obtained from convolution filtering, as we demonstrate numerically by using an axi-symmetric jet satisfying the Navier–Stokes equations. Based on the frequency spectrum of the source, we show that the sound sources exhibit more physical behaviour than sound sources based on acoustic analogies. To validate the sources of sound, one needs to let them radiate within the non-radiating flow field. However, our results suggest that the traditional Euler operator linearized about the time-averaged part of the flow should be sufficient to compute the sound field. [Copyright &y& Elsevier]

Noise from high-lift devices such as slats and flaps can contribute significantly to the overall aircraft sound pressure levels, particularly during approach. The acoustic spectrum of the noise radiated from slats exhibits two distinct features. There is a high-frequency tonal noise component and a high-energy broadband component ranging from low- to midfrequencies. The objective is to predict the broadband slat noise. The broadband noise is predicted using a two-step process. First, the noise sources are modeled based on the local turbulence information. Then, the sound from these sources is propagated by assuming that the flow past the wing is uniform. A boundary element method is used to find Green's function for wave propagation in a moving medium in the presence of the wing. The noise in the far field is then predicted by forming a convolution of Green's function with the modeled sources. The attractive feature of this prediction scheme is the quick computational time, which makes it suitable for new design and control strategies. [ABSTRACT FROM AUTHOR]

Abstract: Three simplified wave-packet models of the coherent structures in subsonic jets are presented. The models comprise convected wave-packets with time-dependent amplitudes and spatial extents. The dependence of the radiated sound on the temporal variations of the amplitude and spatial extent of the modulations are studied separately in the first two model problems, being considered together in the third. Analytical expressions for the radiated sound pressure are obtained for the first and third models. Results show that temporally localised changes in the wave-packet can lead to radiation patterns which are directional and which comprise high-amplitude bursts; such intermittency is observed in subsonic jets at the end of the potential core, and so the models may help explain the higher noise levels and intermittent character of the sound radiated to low emission angles for subsonic jets. By means of an efficiency metric, relating the radiated acoustic power to the fluctuation energy of the source, we show that the source becomes more powerful as its temporal localisation is increased. This result extends that of Sandham et al. (Journal of Sound and Vibration 294(1) (2006) 355–361) who found similar behaviour for an infinitely extended wavy-wall. The pertinence of the model is assessed using two sets of data for a Mach 0.9 jet. One corresponds to a direct numerical simulation (DNS) of a Reynolds number 3600 turbulent jet and the other to a large eddy simulation (LES) of a Reynolds number 4×105 jet. Both time-averaged and time-dependent amplitudes and spatial extents are extracted from the velocity field of the numerical data. Computing the sound field generated by the wave-packet models we find for both simulations that while the wave-packet with a time-averaged envelope shows discrepancies of more than an order of magnitude with the sound field, when the wave-packet ‘jitters’ in a way similar to the intermittency displayed by the simulations, we obtain agreement to within 1.5dB at low axial angles. This shows that the ‘jitter’ of the wave-packet is a salient source feature, and one which should be modelled explicitly. [Copyright &y& Elsevier]