Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session G18: Biofluids: Speech and Vocal |
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Chair: Michael Krane, Penn State University Room: 28D |
Monday, November 19, 2012 8:00AM - 8:13AM |
G18.00001: Aeroacoustic measurements in a human airway model Michael McPhail, Elizabeth Campo, Michael Krane Flow and acoustic measurements are presented for a vocal tract-like geometry with a rigid constriction as a prelude to a study of a compliant constriction that models the vocal folds. Optical flow measurements were taken at the inlet of the constriction and downstream in the jet region. Pressure and acoustic measures were taken on either side of the constriction. Volume flow, two-dimensional flow fields, and radiated sound will be presented for a range of driving pressures. Measurements are used to assess the resistance of the constriction and the measures of the aeroacoustic source. The measurements serve as a validation case for computational aeroacoustic simulations. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G18.00002: Aeroacoustic behavior of vocal fold models from acoustic measurements Michael Krane, Elizabeth Campo, Michael McPhail Measurements of the sound field of the Penn State Human Airway Model (HAM) are used to deduce the aeroacoustic behavior of vibrating vocal fold models. In particular, the distinctions between reflection, transmission and source behavior are sought as a means to quantify source-filter interaction. The acoustic measurements are conducted using 5 microphones located along the airway model axis. Phase-corrected signals from these microphones are used to compute the right-and left-running wave components on either side of the model vocal folds. In combination with theory, these cross-spectra are used to estimate the frequency dependence of the vocal fold reflection and transmission coefficients, as well as the aeroacoustic ``voice'' monopole and dipole source spectra. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G18.00003: Empirical estimates of aeroacoustic source behavior for vocal fold models having male and female geometry Elizabeth Campo, Michael McPhail, Michael Krane Measurements in the Penn State Human Airway Model (HAM) are used to estimate the aeroacoustic source spectra for vocal fold models models built to mimic the behavior of adult male and female humans. A central unanswered question in voice production is how to reliably predict how a change in physiology results in a change in the sound of the voice. Even differences such as those between normal adult males and females are still not fully explained. A combination of trangslottal pressure, radiated sound, volume flow and high speed imaging measurements in the HAM are presented. The theoretical basis for the source estimates is presented to show how the measurements lead to source strength estimates. This study is a first step in establishing how modifications in vocal fold geometry affect the voice's aeroacoustic source strength. [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G18.00004: Vocal Folds Simulations with Contact Algorithm Jubiao Yang, Lucy Zhang Our modified IFEM numerical algorithm was able to simulate vocal folds vibration, and demonstrates relations among vibration frequencies and several fluid and solid parameters successfully. However, although interactions between the solid, i.e. the vocal folds, and the fluid, i.e. air, are well handled, contacts and forces between solid parts, namely vocal folds, have been neglected based on the assumption that their influence is very limited, which may not hold true. To more accurately predict motion and deformation of the vocal folds, and to evaluate its effects on airflow, a contact algorithm is implemented to model when the glottis is completely shut off. The algorithm is developed to decide whether solid parts have made contact, to calculate the interaction force in between, and to decide when they again set apart. This contact algorithm correctly models the interaction between the vocal folds instead of neglecting the unrealistic overlapping of two solid parts, and shows the deformation of vocal folds caused both by the airflow and by the impact with each other. Our result capture the accurate vocal folds behaviors when two vocal folds are approaching each other in full-space cases, and when a vocal fold is approaching the symmetry-line wall in half-space cases. [Preview Abstract] |
Monday, November 19, 2012 8:52AM - 9:05AM |
G18.00005: A coupled experimental-numerical framework for fluid-structure interaction studies: towards a pseudo-self-oscillating vocal fold facility David Sommer, Sean D. Peterson Voiced speech is a complex process that involves coupled interactions between expelled air and the vocal fold structure. Numerical simulations of this process are difficult due to the unsteady nature of the flow and boundary conditions, while experimental investigations are generally limited in the structural modeling. To bridge this gap, an experimental platform is investigated that couples a mechanical flow facility featuring instrumented and actuated walls, with a numerical structure solver. Specifically, a proof-of-concept experimental apparatus consisting of a flat plate oriented normal to a uniform jet is developed. The plate is instrumented with pressure sensors, which record the pressure distribution caused by the impinging jet. A real-time controller reads the pressure distribution and computes the integrated force on the plate. The resulting force is applied to a numerical structure model comprising a spring-mass-damper system, in which the dynamical parameters can be adjusted in software. The axial position and velocity of the plate are updated in real time based upon the numerical dynamics solution. In the future, this experimental facility will be extended to model two degrees of freedom asymmetric vocal fold motion with full fluid coupling. Pressure sensors distributed across the solid interface, as opposed to direct force sensors, will help explicate the effect of fluid-structure coupling on tissue loading and flow properties, thus allowing for more detailed validation and improvement of computational models. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G18.00006: Three-Dimensional Flow Separation Induced by a Model Vocal Fold Polyp Kelley C. Stewart, Byron D. Erath, Michael W. Plesniak The fluid-structure energy exchange process for normal speech has been studied extensively, but it is not well understood for pathological conditions. Polyps and nodules, which are geometric abnormalities that form on the medial surface of the vocal folds, can disrupt vocal fold dynamics and thus can have devastating consequences on a patient's ability to communicate. A recent in-vitro investigation of a model polyp in a driven vocal fold apparatus demonstrated that such a geometric abnormality considerably disrupts the glottal jet behavior and that this flow field adjustment was a likely reason for the severe degradation of the vocal quality in patients. Understanding of the formation and propagation of vortical structures from a geometric protuberance, and their subsequent impact on the aerodynamic loadings that drive vocal fold dynamic, is a critical component in advancing the treatment of this pathological condition. The present investigation concerns the three-dimensional flow separation induced by a wall-mounted prolate hemispheroid with a 2:1 aspect ratio in cross flow, i.e. a model vocal fold polyp. Unsteady three-dimensional flow separation and its impact of the wall pressure loading are examined using skin friction line visualization and wall pressure measurements. [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G18.00007: Resolving pressure from DPIV measurements in a dynamically scaled-up vocal fold model Lori Lambert, Michael Krane, Erica Sherman, Timothy Wei This presentation highlights application of control volume analysis to DPIV measurements in a dynamically scaled human vocal fold model. For the first time spatially and temporally resolved pressure field information can be extracted from voice experiments. The vocal fold model was built around a computer driven mechanism that replicates both the transverse vibrations as well as the streamwise rocking of human vocal folds. A range of experiments were conducted corresponding to 50 -- 200 Hz life frequencies. Volumetric flow rate and maximum velocity measurements will be presented for several control surfaces in the glottal flow. The direction of the glottal jet (coand\u{a}) was noted for each instantaneous oscillation cycle. The pressure forces acting in the glottis were calculated using the streamwise and transverse linear momentum equations and control volume analysis. In addition to serving as a baseline study, data from these experiments provide the comparison for follow on studies of diseased and abnormal vocal fold vibrations. [Preview Abstract] |
Monday, November 19, 2012 9:31AM - 9:44AM |
G18.00008: Natural and forced asymmetries in flow through a vocal fold model Bethany Drain, Lori Lambert, Michael Krane, Timothy Wei Much of the complexity and richness of voice production stems from asymmetries in flow through the vocal folds. There are naturally occurring asymmetries, such as the Coanda effect ($i.e.$ deviation of the glottal jet from the centerline as air passes through the nominally symmetric vocal folds). There are also asymmetries which arise from disease or dysfunction of the vocal folds. This study uses DPIV measurements in a dynamically scaled-up human vocal fold model to compare the flow characteristics between symmetric versus asymmetric oscillations.~ For this study, asymmetries were introduced by running one vocal fold out of phase with the other. Three phase lags, 0\r{ }, 18\r{ } and 36\r{ }, were examined over a range of frequencies corresponding to the physiological frequencies of 50-200 Hz. Control volume analysis was applied and time traces of terms from the conservation of linear momentum equation were generated. This allowed analysis of how differences in the glottal jet flow manifest themselves in the fluid pressure field. In addition, further examination of the Coanda effect in the context of fluid pressure will be discussed. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G18.00009: In Vitro Microfluidic Models of Mucus-Like Obstructions in Small Airways Molly K. Mulligan, James B. Grotberg, Josu\'e Sznitman Liquid plugs can form in the lungs as a result of a host of different diseases, including cystic fibrosis and chronic obstructive pulmonary disease. The existence of such fluid obstructions have been found as far down in the bronchiole tree as the sixteenth generation, where bronchiole openings have diameters on the order of a hundred to a few hundred microns. Understanding the propagation of liquid plugs within the bifurcating branches of bronchiole airways is important because their presence in the lungs, and their rupture and break-up, can cause injury to the epithelial cells lining the airway walls as a result of high wall shear stresses. In particular, liquid plug rupture and break-up frequently occurs at airway bifurcations. Until present, however, experimental studies of liquid plugs have generally been restricted to Newtonian fluids that do not reflect the actual pseudoplastic properties of lung mucus. The present work attempts to uncover the propagation, rupture and break-up of mucus-like liquid plugs in the lower generations of the airway tree using microfluidic models. Our approach allows the dynamics of mucus-like plug break-up to be studied in real-time, in a one-to-one in vitro model, as a function of mucus rheology and bronchial tree geometry. [Preview Abstract] |
Monday, November 19, 2012 9:57AM - 10:10AM |
G18.00010: Yield Stress Effects on Mucus Plug Rupture Yingying Hu, Shiyao Bian, John C. Grotberg, Shuichi Takayama, James B. Grotberg Mucus plugs can obstruct airways, resulting in lost gas exchange and inflammation. Yield stress, one of the significant rheological properties of mucus, plays a significant role in plug rupture. We use carbopol 940 gels as mucus simulants to study dynamics of mucus plug rupture in experiments. Yield stress increases with gel concentration increasing (0.1{\%}$\sim $0.3{\%}). The yield stress of the 0.2{\%} gel is about 530 dyn/cm$^{2}$, which can simulate normal mucus. A 2D PDMS channel is used to simulate a collapsed airway of the 12$^{th}$ generation in a human lung. Plug rupture is driven by a pressure drop of 1.6$\times $10$^{4}\sim $2.0$\times $10$^{4}$ dyn/cm$^{2}$. Initial plug length varies from half to two times the half channel width. A micro-PIV technique is used to acquire velocity fields during rupture, from which wall shear stress is derived. Plug shortening velocity increases with the pressure drop, but decreases with yield stress or the initial plug length. Wall shear stress increases with yield stress, which indicates more potential damage may occur to epithelial cells when pathologic mucus has a high yield stress. Near the rupture moment, a wall shear stress peak appears at the front of the film deposited by the plug during rupture. [Preview Abstract] |
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