Modeling fluid-structure-acoustic interaction is a highly challenging task and currently there is a lack of available benchmark datasets. For instance, to understand the processes of human phonation, it is essential to fully understand the fluid-structure-acoustic interaction process. In this article, a synthetic human phonation model is presented for benchmarking numerical methods in the field of aerodynamics, aeroacoustics and the highly-complex fluid-structure-acoustic interaction process of the voice production. The objective is to present the wide range of experimental data available, including the model geometry, the material characteristics, quantitiesreferred to the vocal fold dynamics, fluid mechanical quantities and the acoustic field. Firstly, the experimental setup is specified. Secondly, the experimental data is described in detail, accompanied by illustrations. Having the dataset in hand, finally, it is shown how to use this data to validate a computational phonation model called simVoice successfully. In conclusion, this benchmarking dataset offers the opportunity to validate structural dynamics, aerodynamics and aeroacoustics of a highly-complex fluid-structure-acoustic interaction simulation, obtained from different mathematical formulations and numerical procedures.

The image source method (ISM) is often used to simulate room acoustics due to its ease of use and computational efficiency. The standard ISM is limited to simulations of room impulse responses between point sources and omnidirectional receivers. In this work, the ISM is extended using spherical harmonic directivity coefficients to include acoustic diffraction effects. These effects occur in practice when transducers are mounted on audio devices of finite spatial extent, e.g., modern smart speakers with loudspeakers and microphones. The proposed method is verified using finite element simulations of various loudspeaker and microphone configurations in a shoebox-shaped room. It is shown that the accuracy of the proposed method is related to the sizes, shapes, number, and positions of the devices inside a room. A simplified version of the proposed method, which can significantly reduce computational effort, is also presented. The proposed method and its simplified version can simulate room transfer functions more accurately than currently available image source methods and can aid the development and evaluation of speech and acoustic signal processing algorithms, including speech enhancement, acoustic scene analysis, and acoustic parameter estimation.

Acoustic reciprocity states that the transfer function between a source and a receiver remains unchanged if the two are interchanged. An extension of acoustic reciprocity to the spherical harmonic domain has been derived in the literature between a directional source and a directional receiver. The present letter derives a reciprocal relation between source and receiver directivity coefficients, which facilitates the derivation of a transfer function in the spherical harmonic domain using directivity coefficients obtained via reciprocity. Additionally, reciprocity between transfer functions is extended for more general source and receiver directivities, which include acoustic scattering effects.

Pulsating heat pipes (PHPs) are increasingly used for the thermal management of hot spots. A major goal in the design process of PHPs is the handling of high heat fluxes and, thus, improved thermal resistance. The thermal resistance can be reduced by increasing the latent or convective heat transfer. Two design approaches with that goal are presented in this study: a flower-shaped PHP design to increase the latent heat transfer and a star-shaped PHP design to increase the convective heat transfer. We compare the proposed designs to a state-of-the-art, meander-shaped PHP design. Thereby, we quantify the thermal performance and the flow pattern of the different PHP designs. The copper PHPs were filled with acetone and tested horizontally and vertically. The filling ratios varied from 0 % to 90 % and the heat inputs increased from 50 W to 200 W. Our results illustrate that the flower-shaped PHP design reduces the thermal resistance by 7 % in horizontal and 12 % in vertical position. We found a strong interrelation between flow pattern and heat transfer in PHPs. Our study shows that phase change plays a key role for the thermal resistance. Based on that, we provide design criteria to optimize the thermal capabilities of PHPs with a special focus on hot spots.(c) 2022 Elsevier Ltd. All rights reserved.

Generating noise samples is crucial in developing and testing noise reduction algorithms or training deep learning models. This work proposes a wind noise generation model with airflow speed-dependent features. A linear predictive analysis of wind noise measured in a wind tunnel at different flow velocities was carried out. This analysis showed that temporal and spectral features depend on the flow speed. The prediction residual’s statistics and the filter coefficients are first extracted and then modeled based on the flow speed. The obtained models are then combined to synthetically generate wind noise given a time-varying flow speed profile as input, in contrast to an existing framework where temporal and spectral features were assumed speed-invariant. A subjective evaluation is carried out to assess the perceptual authenticity of the generated noise compared to the existing method.

Vibrations during yogurt fermentation have been reported to disturb the gelation by inducing large, visible particles. Such vibrations are generated by the machinery used for the industrial manufacture and can cause structural excitation of the fermentation tanks. To study the effect of vibrations on yogurt structure, an experimental setup was constructed consisting of a cylindrical tank (height: 600 mm). The bottom of the tank was excited by a shaker, resulting in a vertical vibration propagation. Skim milk was vibrated during fermentation at 30 Hz and different amplitudes. Vibrated gels showed syneresis up to similar to 5%. Samples were taken at different height positions of the fermenter, processed into stirred yogurt, and analyzed. The number of large particles was primarily related to the set vibration amplitude, however, particle formation was more pronounced in the lower and upper area. Yogurts with a high particle number exhibited a reduced water-holding capacity and apparent viscosity. Moreover, the fluid dynamic effects of vibrations were investigated by particle image velocimetry. Vibrations led to uniform to-and-fro motions, whereas chaotic flow was observed at the surface. Finally, the impact of vibrations on the gelation mechanism is discussed.

Oscillating heat pipes (OHP) are increasingly used for the thermal management of hot spots. Thereby, a local evaporation zone occurs that is still not fully understood due to complex interactions of flow patterns and heat transfer. This study quantifies the thermal performance and the flow behavior of oscillating heat pipes with a centrally located hot spot heater. The copper OHPs were filled with acetone and tested with different orientations. The filling ratios varied from 0% to 90%, the heat inputs increased from 25 W to 200 W. Our results illustrate that the flow velocity values and the resulting thermal resistance are highly interrelated. Within one channel, there is a wide range of velocity values from 30 mm/s to 1200 mm/s; the thermal resistance decreases with higher average flow velocity. By characterizing the flow regime, we show that a reliable start-up depends on the initial vapor liquid pattern. Depending on the initial pattern, an individual temperature difference is required for the start-up, even for similar operating conditions. The analysis of the stopping behavior shows that a uniform temperature difference of 14 K is required for a stable fluid oscillation. Our study substantiates a strong interrelation between flow pattern and heat transfer in OHPs, which also shows a strong potential for future optimizations of OHP applications.

Sound generation during voiced speech remains an open research topic because the underlying process within the human larynx is hardly accessible for direct measurements. In the present study, harmonic sound generation during phonation was investigated with a model that replicates the fully coupled fluid-structure-acoustic interaction (FSAI). The FSAI was captured using a multi-modal approach by measuring the flow and acoustic source fields based on particle image velocimetry, as well as the surface velocity of the vocal folds based on laser vibrometry and high-speed imaging. Strong harmonic sources were localized near the glottis, as well as further downstream, during the presence of the supraglottal jet. The strongest harmonic content of the vocal fold surface motion was verified for the area near the glottis, which directly interacts with the glottal jet flow. Also, the acoustic back-coupling of the formant frequencies onto the harmonic oscillation of the vocal folds was verified. These findings verify that harmonic sound generation is the result of a strong interrelation between the vocal fold motion, modulated flow field, and vocal tract geometry.

The operating limits of oscillating heat pipes (OHP) are crucial for the optimal design of cooling systems. In particular, the dryout limit is a key factor in optimizing the functionality of an OHP. As shown in previous studies, experimental approaches to determine the dryout limit lead to contradictory results. This work proposes a compact theory to predict a dryout threshold that unifies the experimental and analytical data. The theory is based on the influence of vapor quality on the flow pattern. When the vapor quality exceeds a certain limit (x = 0.006), the flow pattern changes from slug flow to annular flow and the heat transfer decreases abruptly. The results indicate a uniform threshold value, which has been validated experimentally and by the literature. With that approach, it becomes possible to design an OHP with an optimized filling ratio and, hence, substantially improve its cooling abilities.

The human phonation is characterized by periodical oscillations of the vocal folds with a complete glottis closure. In contrast, a glottal insufficiency (GI) represents an oscillation without glottis closure resulting in a breathy and weak voice. In this study, flow-induced oscillations of silicone vocal folds were modeled with and without glottis closure. The measurements comprised the flow pressure in the model, the generated sound, and the high-speed footage of the vocal fold motion. The analysis revealed that the sound signal for vocal fold oscillations without closure exhibits a lower number of harmonic tones with smaller amplitudes compared to the case with complete closure. The time series of the pressure signals showed small and periodical oscillations occurring less frequently and with smaller amplitude for the GI case. Accordingly, the pressure spectra include fewer harmonics similar to the sound. The analysis of the high-speed videos indicates that the strength of the pressure oscillations correlates with the divergence angle of the glottal duct during the closing motion. Physiologically, large divergence angles typically occur for a pronounced mucosal wave motion with glottis closure. Thus, the results indicate a correlation between the intensity of the mucosal wave and the development of harmonic tones.

Voiced speech is the result of a fluid-structure-acoustic interaction in larynx and vocal tract (VT). Previous studies show a strong influence of the VT on this interaction process, but are limited to individually obtained VT geometries. In order to overcome this restriction and to provide a more general VT replica, we computed a simplified, averaged VT geometry for the vowel /a/. The basis for that were MRI-derived cross-sections along the straightened VT centerline of six professional tenors. The resulting mean VT replica, as well as realistic and simplified VT replicas of each tenor were 3D-printed for experiments with silicone vocal folds that show flow-induced oscillations. Our results reveal that all replicas, including the mean VT, reproduce the characteristic formants with mean deviations of 12% when compared with the subjects' audio recordings. The overall formant structure neither is impaired by the averaging process, nor by the simplified geometry. Nonetheless, alterations in the broadband, non-harmonic portions of the sound spectrum indicate changed aerodynamic characteristics within the simplified VT. In conclusion, our mean VT replica shows similar formant properties as found in vivo. This indicates that the mean VT geometry is suitable for further investigations of the fluid-structure-acoustic interaction during phonation.

In the present paper, we aim to characterize the mechanisms of sound generation during voiced human speech, which is referred to as phonation. This has been achieved in a combined experimental-numerical approach, which applies a PIV-based flow field to numerically compute the acoustic source field and simulate the radiation of the resulting sound field. By adapting state-of-the-art formulations, the acoustic source is fully separated from non-acoustic fluid-mechanical pressure fluctuations. The most intense source was found directly at the vocal folds. In addition, slightly less intense sources were found along the shear layers of the glottal jet. The resulting spectrum of the radiated sound shows similar characteristics as the validating experimental microphone measurement below 1 kHz.

In voice research, analytically-based models are efficient tools to investigate the basic physical mechanisms of phonation. Calculations based on lumped element models describe the effects of the air in the vocal tract upon threshold pressure (Pth) by its inertance. The latter depends on the geometrical boundary conditions prescribed by the vocal tract length (directly) and its cross-sectional area (inversely). Using Titze’s surface wave model (SWM) to account for the properties of the vocal folds, the influence of the vocal tract inertia is examined by two sets of calculations in combination with experiments that apply silicone-based vocal folds. In the first set, a vocal tract is constructed whose cross-sectional area is adjustable from 2.7 cm2 to 11.7 cm2. In the second set, the length of the vocal tract is varied from 4.0 cm to 59.0 cm. For both sets, the pressure and frequency data are collected and compared with calculations based on the SWM. In most cases, the measurements support the calculations; hence, the model is suited to describe and predict basic mechanisms of phonation and the inertial effects caused by a vocal tract.

The detailed analysis of sound generation in human phonation is severely limited as the accessibility to the laryngeal flow region is highly restricted. Consequently, the physical basis of the underlying fluid–structure–acoustic interaction that describes the primary mechanism of sound production is not yet fully understood. Therefore, we propose the implementation of a hybrid acoustic PIV procedure to evaluate aeroacoustic sound generation during voice production within a synthetic larynx model. Focusing on the flow field downstream of synthetic, aerodynamically driven vocal folds, we calculated acoustic source terms based on the velocity fields obtained by time-resolved high-speed PIV applied to the mid-coronal plane. The radiation of these sources into the acoustic far field was numerically simulated and the resulting acoustic pressure was finally compared with experimental microphone measurements. We identified the tonal sound to be generated downstream in a small region close to the vocal folds. The simulation of the sound propagation underestimated the tonal components, whereas the broadband sound was well reproduced. Our results demonstrate the feasibility to locate aeroacoustic sound sources inside a synthetic larynx using a hybrid acoustic PIV approach. Although the technique employs a 2D-limited flow field, it accurately reproduces the basic characteristics of the aeroacoustic field in our larynx model. In future studies, not only the aeroacoustic mechanisms of normal phonation will be assessable, but also the sound generation of voice disorders can be investigated more profoundly.

Within the human larynx, the ventricular folds serve primarily as a protecting valve during swallowing. They are located directly above the sound-generating vocal folds. During normal phonation, the ventricular folds are passive structures that are not excited to periodical oscillations. However, the impact of the ventricular folds on the phonation process has not yet been finally clarified. An experimental synthetic human larynx model was used to investigate the effect of the ventricular folds on the phonation process. The model includes self-oscillating vocal fold models and allows the comparison of the pressure distribution at multiple locations in the larynx for configurations with and without ventricular folds. The results indicate that the ventricular folds increase the efficiency of the phonation process by reducing the phonation threshold level of the pressure below the vocal folds. Two effects caused by the ventricular folds could be identified as reasons: (1) a decrease in the mean pressure level in the region between vocal and ventricular folds (ventricles) and (2) an increase in the glottal flow resistance. The reason for the first effect is a reduction of the pressure level in the ventricles due to the jet entrainment and the low static pressure in the glottal jet. The second effect results from an increase in the glottal flow resistance that enhances the aerodynamic energy transfer into the vocal folds. This effect reduces the onset threshold of the pressure difference across the glottis.

Wind noise in hearing aids occurs even at low wind speeds and is a confounding factor for hearing aid wearer, hence leading to a reduction of speech intelligibility. In this submission, a study on the correlation of the flow field around a hearing aid to its acoustic output is made. The BTE (behind the ear) hearing aid is mounted on an artificial head with three different ear geometries. The flow field is captured using a two component PIV (particle image velocimetry) system. For exposing critical flow phenomena, a POD (proper orthogonal decomposition) of the PIV measurement data is made. The hearing aid output is measured with a microphone inside the artificial head. On the one hand, wind noise in hearing aids is generated by the fluctuating velocity field of the boundary layer on the hearing aid. On the other hand, based on the PIV data and the POD results, flow patterns around the artificial head and the hearing aid are detected, which cause further noise, that is captured by the hearing aid microphones. With these findings, modifications on the hearing aid geometry are deduced, that lead to a decrease in wind noise and hence to a better speech intelligibility.

The sound spectra obtained in a synthetic larynx exhibited subharmonic tones that are characteristic for diplophonia. Although the generation of subharmonics is commonly associated with asymmetrically oscillating vocal folds, the synthetic elastic vocal folds showed symmetrical oscillations. The amplitudes of the subharmonics decreased with an increasing lateral diameter of the supraglottal channel, which indicates a strong dependence of the supraglottal boundary conditions. Investigations of the supraglottal flow field revealed small cycle-to-cycle variations of the static pressure in the region of the pulsatile glottal jet as the origin of the first subharmonic tone. It is located at half the fundamental frequency of the vocal fold oscillation. A principle component analysis of the supraglottal flow field with the fully developed glottal jet revealed a large recirculation area in the second spatial eigenvector which deflected the glottal jet slightly in a perpendicular direction of the jet axis. The rotation direction of the recirculation area changed with different oscillation cycles between clockwise and counterclockwise. As both directions were uniformly distributed across all acquired oscillation cycles, a cycle-wise change can be assumed. It is concluded that acoustic subharmonics are generated by small fluctuations of the glottal jet location favored by small lateral diameters of the supraglottal channel.

This study addresses the supraglottal flow field that is downstream of aerodynamically driven, synthetic vocal folds. Two different methods based on Particle Image Velocimetry (PIV) are applied: Phase-averaged (PA) and Highspeed (HS) PIV. A comparative analysis of the measurement results is given to provide a more comprehensive understanding for future PIV measurements. Additionally, the acoustic source terms were calculated based on the HS-PIV data and its simulated far-field spectral behavior is compared to acoustic measurements. The supraglottal flow field was characterized by an asymmetric jet flow for PAand HS-PIV measurements. However, the maximum velocities as well as velocity fluctuations were averaged out in the phase-averaging procedure. In a first assessment of the acoustic sources in the supraglottal region, the Phase-averaged and Highspeed measurements yielded distinctly different results. While a strong acoustic source was detected near the glottis between the vocal folds in both measurement cases, the intensity of this source decreased for the phase-averaged flow field. Additionally, the acoustic sources in the jet region could only be captured by the High-speed PIV measurements. The simulation of the radiated sound with the HS-PIV acoustic sources used as in input revealed a partially proper match between the measured and the simulated spectra. However, several spectral characteristics could not be reproduced in the simulation, hinting to a non-aeroacoustic sound generation of these. Fig. 1 Exemplary state of the supraglottal flow field for a Phase-averaged PIV (left) and High-speed PIV (right) measurement

The fluid flow within the human larynx plays an essential role in the fluid-structure-acoustic interaction during voice production. This study addresses the supraglottal flow field downstream of aerodynamically driven, synthetic vocal folds based on the M5 model. The larynx replica is designed to provide full optical access to the flow region. Two different approaches based on Particle-Image-Velocimetry (PIV) were applied for measuring the flow: Phase-averaged (PA) and High-speed (HS) PIV. Beside a comparison of the supraglottal flow field, the acoustic sources were calculated based on both PIV approaches. Furthermore, the simulated far-field sound based on the HS-PIV data is compared to experimental results. Within both PIV approaches, the typical asymmetric jet flow was detected. However, transient flow field characteristics as high vorticity and maximal velocities peaks could only be observed in HS-PIV data. A strong aeroacoustic source was found immediately downstream of the glottis for both PIV approaches. However, the sources in the jet region could only be observed in the HS-PIV data owing to the averaging procedure for PA-PIV. The comparison between simulated and measured sound spectra revealed good agreement. In contrast, subharmonic tones could not be detected hinting to an additional non-aeroacoustic mechanism of sound generation.

The fluid flow within a human larynx plays an essential role in the fluid–structure–acoustic interaction during voice production. This study addresses the flow field downstream of aerodynamically driven, synthetic vocal folds. In order to quantitatively investigate the supraglottal formation of the flow field within one oscillation cycle of the vocal folds, a phase-locked PIV technique is introduced. The pseudo-time-resolved measurement results were averaged for each phase angle. When including a supraglottal channel, the jet was deflected from the centerline of the supraglottal channel and changed the direction of deflection in different cycles. The result is a bistable flow field. Therefore, a sorting method based on the mean cyclic supraglottal pressure difference was introduced. For both states of the flow field, a recirculation area was detected, interacting with the arising glottal jet in every oscillation cycle. This interaction could be identified as the major cause for supraglottal jet deflection, and the sense of rotation of the recirculation area defined the direction of deflection. The asymmetric structure of the flow field was caused by the geometric boundary condition, i.e., due to the present supraglottal channel. An additional key factor was found to be the contact between the two vocal folds in each oscillation cycle which interrupted the jet flow periodically. Removing the supraglottal channel resulted in a symmetric jet location. When avoiding vocal fold contact, the bistable behavior vanished and the jet was steadily deflected to one lateral side. In the present study, it cannot be confirmed that the Coanda effect is responsible for the deflection.