Flow Amplitude Research Articles

Scaling behaviour of rotating convection in a spherical shell with different Prandtl numbers

Rayleigh–Bénard convection in a rotating spherical shell provides a simplified model for convective dynamics of planetary and stellar interiors. Over the past decades, the problem has been studied extensively via numerical simulations, but most previous simulations set the Prandtl number $Pr$ to unity. In this study we build more than 200 numerical models of rotating convection in a spherical shell over a wide range of $Pr$ ( $10^{-2}\le Pr \le 10^2$ ). By increasing the Rayleigh number $Ra$ , we characterise four different flow regimes, starting from the linear onset to multiple modes, then transitioning to the geostrophic turbulence and eventually approaching the weakly rotating regime. In the multiple modes regime, we show evidence of triadic resonances in numerical models with different $Pr$ , which may provide a generic mechanism for the transition from laminar to turbulence in rotating convection. We analyse scaling behaviours of the heat transfer and convective flow speeds in numerical simulations, paying particular attention to the $Pr$ dependence. We find that the so-called diffusion-free scaling for the heat transfer cannot reconcile all numerical models with different $Pr$ in the geostrophic turbulence regime. However, the characteristic flow speeds at different $Pr$ roughly follow a unified scaling that can be described by visco-Archimedean–Coriolis force balances, though the scaling tends to approach the Coriolis-inertial-Archimedean force balance at low $Pr$ . We also show that transition behaviours from rotating to non-rotating convection depend on $Pr$ . The transition criteria based on heat transfer and flow morphology would be rather different when $Pr>1$ , but the two criteria are consistent for cases with $Pr\le 1$ . Both scaling behaviours and transition behaviours suggest that the heat transfer is controlled by the boundary layers while the convective flow speeds are mainly determined by the force balance in the bulk for cases with $Pr>1$ , which is in line with recent experimental results with moderate to high $Pr$ . For cases with $Pr \le 1$ , both the heat transfer and convective velocities are approaching the inviscid dynamics in the bulk. We also briefly analysed the magnitude and scaling of zonal flows at different $Pr$ , showing that the zonal flow amplitude rapidly increases as $Pr$ decreases.

Extraction and characteristic analysis of the nonlinear acoustic impedance of circular orifice in the presence of bias flow

The acoustic behavior of the circular orifice is influenced by the bias flow and high amplitude sound excitation. The present study proposes an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation to extract the nonlinear acoustic impedance of circular orifice. Impact coefficients of the bias flow on the acoustic impedance of circular orifice are defined as the ratio of the acoustic impedance difference between the cases in the presence and absence of bias flow under high amplitude sound excitation to that under low amplitude sound excitation. The effects of bias flow Mach number, orifice diameter, plate thickness, and porosity on the impact coefficients under different amplitude sound excitations are studied, and the impact coefficients could collapse all the predictions by using the non-dimensional sound particle velocity. The fitting formulas of nonlinear acoustic impedance of circular orifice are presented by using nonlinear regression analysis.

Characteristics of lung resistance and elastance associated with tracheal stenosis and intrapulmonary airway narrowing in ex vivo sheep lungs

BackgroundUnderstanding the characteristics of pulmonary resistance and elastance in relation to the location of airway narrowing, e.g., tracheal stenosis vs. intrapulmonary airway obstruction, will help us understand lung function characteristics and mechanisms related to different airway diseases.MethodsIn this study, we used ex vivo sheep lungs as a model to measure lung resistance and elastance across a range of transpulmonary pressures (5–30 cmH2O) and ventilation frequencies (0.125–2 Hz). We established two tracheal stenosis models by inserting plastic tubes into the tracheas, representing mild (71.8% lumen area reduction) and severe (92.1%) obstructions. For intrapulmonary airway obstruction, we induced airway narrowing by challenging the lung with acetylcholine (ACh).ResultsWe found a pattern change in the lung resistance and apparent lung elastance as functions of ventilation frequency that depended on the transpulmonary pressure (or lung volume). At a transpulmonary pressure of 10 cmH2O, lung resistance increased with ventilation frequency in severe tracheal stenosis, whereas in ACh-induced airway narrowing the opposite occurred. Furthermore, apparent lung elastance at 10 cmH2O decreased with increasing ventilation frequency in severe tracheal stenosis whereas in ACh-induced airway narrowing the opposite occurred. Flow-volume analysis revealed that the flow amplitude was much sensitive to ventilation frequency in tracheal stenosis than it was in ACh induced airway constriction.ConclusionsResults from this study suggest that lung resistance and apparent elastance measured at 10 cmH2O over the frequency range of 0.125-2 Hz can differentiate tracheal stenosis vs. intrapulmonary airway narrowing in ex vivo sheep lungs.

Disturbed Dynamic Brain Activity and Neurovascular Coupling in End-Stage Renal Disease Assessed With MRI.

Pathophysiological mechanisms underlying cognitive impairment in end-stage renal disease (ESRD) remain unclear, with limited studies on the temporal variability of neural activity and its coupling with regional perfusion. To assess neural activity and neurovascular coupling (NVC) in ESRD patients, evaluate the classification performance of these abnormalities, and explore their relationships with cognitive function. Prospective. Exactly 33 ESRD patients and 35 age, sex, and education matched healthy controls (HCs). The 3.0T/3D pseudo-continuous arterial spin labeling, resting-state functional MRI, and 3D-T1 weighted structural imaging. Dynamic (dfALFF) and static (sfALFF) fractional amplitude of low-frequency fluctuations and cerebral blood flow (CBF) were assessed. CBF-fALFF correlation coefficients and CBF/fALFF ratio were determined for ESRD patients and HCs. Their ability to distinguish ESRD patients from HCs was evaluated, alongside assessment of cerebral small vessel disease (CSVD) MRI features. All participants underwent blood biochemical and neuropsychological tests to evaluate cognitive decline. Chi-squared test, two-sample t-test, Mann-Whitney U tests, covariance analysis, partial correlation analysis, family-wise error, false discovery rate, Bonferroni correction, area under the receiver operating characteristic curve (AUC) and multivariate pattern analysis. P < 0.05 denoted statistical significance. ESRD patients exhibited higher dfALFF in triangular part of left inferior frontal gyrus (IFGtriang) and left middle temporal gyrus, lower CBF/dfALFF ratio in multiple brain regions, and decreased CBF/sfALFF ratio in bilateral superior temporal gyrus (STG). Compared with CBF/sfALFF ratio, dfALFF, and sfALFF, CBF/dfALFF ratio (AUC = 0.916) achieved the most powerful classification performance in distinguishing ESRD patients from HCs. In ESRD patients, decreased CBF/fALFF ratio correlated with more severe renal impairment, increased CSVD burden, and cognitive decline (0.4 < |r| < 0.6). ESRD patients exhibited abnormal dynamic brain activity and impaired NVC, with dynamic features demonstrating superior discriminative capacity and CBF/dfALFF ratio showing powerful classification performance. 1 TECHNICAL EFFICACY: Stage 1.

Analysis of a Bifurcation and Stability of Equilibrium Points for Jeffrey Fluid Flow through a Non-Uniform Channel

This study aims to analyze how the parameter flow rate and amplitude of walling waves affect the peristaltic flow of Jeffrey’s fluid through an irregular channel. The movement of the fluid is described by a set of non-linear partial differential equations that consider the influential parameters. These equations are transformed into non-dimensional forms with appropriate boundary conditions. The study also utilizes dynamic systems theory to analyze the effects of the parameters on the streamline and to investigate the position of critical points and their local and global bifurcation of flow. The research presents numerical and analytical methods to illustrate the impact of flow rate and amplitude changes on fluid transport. It identifies three types of streamline patterns that occur: backwards, trapping, and augmented flow resulting from changes in the value of flow rate parameters.

Numerical study on flow instability in parallel helical tubes under ocean conditions

The superimposed coupling of flow oscillations generated by transient external forces under ocean conditions and flow oscillations in parallel helical tubes during two-phase flow instability may lead to more complex flow oscillation phenomena in parallel helical tubes. However, there is still a lack of understanding regarding the effect of ocean conditions on the two-phase flow instability within parallel helical tubes. The two-phase flow instability in parallel helical tubes under ocean conditions is numerically investigated in the present study. The effects of ocean conditions on the flow behavior and instability threshold in parallel helical tubes are studied with mass flux 200 kg/m2s and inlet subcooling within 5–70 °C. The results show that the mass flow rate decreases as the inclination angle increases. A larger rolling amplitude or shorter period increases the flow and temperature oscillation amplitude. Two characteristic frequencies are found in the natural circulation flow instability under the rolling motion. As the rolling amplitude increases, the compound flow oscillation amplitude is larger and more chaotic with a certain phase shift. The effect of stationary inclining on the flow instability threshold is rather significant than rolling effect. The results of the present study can serve as a significant reference for the operation and design of the helical-coiled once-through steam generator under ocean conditions.

Experimental study on thermal performance of plate evaporator under yawing and heaving conditions

To elucidate the role of marine sloshing in thermal performance of plate evaporators, an experimental system of flow boiling in plate evaporator was constructed, integrating with a six-degree-of-freedom motion platform. The effects of sloshing modes (yawing and heaving), mass flow rate, sloshing frequency, amplitude, and intensity on the boiling performance of plate evaporator were examined and investigated. The experimental results indicate that, both yawing and heaving motions significantly enhance the boiling heat transfer performance of the R410A plate evaporator. In the yawing motion, the frequency and amplitude both play a role in bolstering the heat transfer capabilities of the evaporator. As the intensity of the sloshing increases, the heat transfer performance of the plate evaporator significantly improves compared to stable conditions, with enhancements ranging from 6% to 33%. As the intensity of the sloshing increases, the heat transfer performance of the plate evaporator significantly improves compared to stable conditions, with enhancements ranging from 7% to 84%. Notably, the impact of heaving motion on heat transfer enhancement surpasses that of the yawing motion. In addition, a heat transfer correlation for the R410A was introduced to evaluate the boiling heat transfer in plate evaporator under the yawing and heaving conditions.

Second order and transverse flow visualization through three-dimensional particle image velocimetry in millimetric ducts

Despite recent advances in 3D particle image velocimetry (PIV), challenges remain in measuring small-scale 3D flows, in particular flows with large dynamic range. This study presents a scanning 3D-PIV system tailored for oscillatory flows, capable of resolving transverse flows less than a percent of the axial flow amplitude. The system was applied to visualize transverse flows in millimetric straight, toroidal, and twisted ducts. Two PIV analysis techniques, stroboscopic and semi-Lagrangian PIV, enable the quantification of net motion as well as time-resolved axial and transverse velocities. The experimental results closely align with computational fluid dynamics (CFD) simulations performed in a digitized representation of the experimental model. The proposed method allows the examination of periodic flows in systems down to microscopic scale and is particularly well-suited for applications that cannot be scaled up due to their complex, multi-physics nature.

Feasibility of capturing vessel expansion with 4D-CTA: Phantom study to determine reproducibility, spatial and temporal resolution.

Dynamic Computed Tomography Angiography (4D CTA) has the potential of providing insight into the biomechanical properties of the vessel wall, by capturing motion of the vessel wall. For vascular pathologies, like intracranial aneurysms, this could potentially refine diagnosis, prognosis, and treatment decision-making. The objective of this research is to determine the feasibility of a 4D CTA scanner for accurately measuring harmonic diameter changes in an in-vitro simulated vessel. A silicon tube was exposed to a simulated heartbeat. Simulated heart rates between 40 and 100 beats-per-minute (bpm) were tested and the flow amplitude was varied, resulting in various changes of tube diameter. A 320-detector row CT system with ECG-gating captured three consecutive cycles of expansion. Image registration was used to calculate the diameter change. A vascular echography set-up was used as a reference, using a 9MHz linear array transducer. The reproducibility of 4D CTA was represented by the Pearson correlation (r) between the three consecutive diameter change patterns, captured by 4D CTA. The peak value similarity (pvs) was calculated between the 4D CTA and US measurements for increasing frequencies and was chosen as a measure of temporal resolution. Spatial resolution was represented by the Sum of the Relative Percentual Difference (SRPD) between 4D CTA and US diameter change patterns for increasing amplitudes. The reproducibility of 4D CTA measurements was good (r ≥ 0.9) if the diameter change was larger than 0.3mm, moderate (0.7 ≤ r<0.9) if the diameter change was between 0.1 and 0.3mm, and low (r<0.7) if the diameter change was smaller than 0.1mm. Regarding the temporal resolution, the amplitude of 4D CTA was similar to the US measurements (pvs ≥ 90%) for the frequencies of 40 and 50bpm. Frequencies between 60 and 80bpm result in a moderate similarity (70% ≤ pvs<90%). A low similarity (pvs<70%) is observed for 90 and 100bpm. Regarding the spatial resolution, diameter changes above 0.30mm result in SRPDs consistently below 50%. In a phantom setting, 4D CTA can be used to reliably capture reproducible tube diameter changes exceeding 0.30mm. Low pulsation frequencies (40 or 50bpm) provide an accurate measurement of the maximum tube diameter change.

Hemodynamic characteristics in ruptured and unruptured intracranial aneurysms: a prospective cohort study utilizing the AneurysmFlow™ tool.

Hemodynamic factors significantly influence the onset, progression, and rupture of intracranial aneurysms (IAs). Current rupture risk prediction scores focus primarily on the clinical, anatomical and morphological aspects. This study aimed to investigate the hemodynamic characteristics differences between ruptured and unruptured IAs. Conducted from July 2021 to July 2022, this prospective cohort study involved patients with ruptured and unruptured IAs undergoing digital subtraction angiography (DSA). Hemodynamic characteristics were assessed using the AneurysmFlow™ tool. Hemodynamic, clinical, anatomical and morphological parameters were compared between ruptured and unruptured IA groups. The study included 127 patients with 135 aneurysms (67 ruptured, 68 unruptured). Complex flow patterns (type 3 and 4) were observed more frequently in ruptured aneurysms compared to unruptured aneurysms (odds ratio [OR], 5.57; 95% confidence interval [CI], 2.49-12.45; P < 0.001) in univariate analysis, and were also more common in unruptured aneurysms associated with daughter sacs features (P = 0.015). The mean aneurysm flow amplitude (MAFA) was lower in ruptured aneurysms, and associated with lower flow velocity in the parent artery related to vasospasm. MAFA in the aneurysmal dome or any additional daughter sacs was lowest compared to other regions inside the aneurysms. The technical failure rate of AneurysmFlow™ measurements was 8.5% (12 out of 139 patients). Additionally, hypertension (OR, 0.42; 95% CI, 0.30-0.54; P < 0.001), bifurcation location (AcomA/ACA/MCA/PcomA/posterior circulation) (OR, 0.17; 95% CI, 0.05-0.29; P = 0.005), and irregular shape (OR, 0.19; 95% CI, 0.05-0.35; P = 0.012) were identified as independently associated with rupture. Complex flow patterns identified on the AneurysmFlow™ tool are significantly more common in ruptured and unruptured aneurysms associated with daughter sac features. The lowest MAFA in the aneurysmal dome and daughter sacs likely indicates specific pathophysiological changes within the aneurysm wall associated with rupture incidence. Hypertension, bifurcation location, and an irregular shape are independently associated with the risk of rupture. Further multicenter studies with larger sample sizes are needed to validate these findings. ACA = anterior cerebral artery; AcomA = anterior communicating artery; IAs = intracranial aneurysms; ICA = internal carotid artery; MAFA = mean aneurysm flow amplitude; MCA = middle cerebral artery; PcomA = posterior communicating artery; RIAs = ruptured intracranial aneurysms; SAH = subarachnoid hemorrhage; UIAs = unruptured intracranial aneurysms.

The effect of operating conditions on heat transfer for parallel plate heat exchangers of thermoacoustic standing wave systems

Thermoacoustic systems represent a promising technology for clean cooling and/or power generation. However, understanding of the behavior of oscillatory flow inside the system under high drive ratio operating conditions, at elevated mean pressures, range of frequencies, and high flow amplitudes, remains limited and poses challenges for designing efficient systems with minimal losses. This paper presents a numerical investigation into the flow and heat transfer characteristics across a coupled cold and hot parallel-plate heat exchanger operating under standing-wave type oscillatory flow conditions. The models were developed for various conditions, spanning frequencies from 13 Hz to 100 Hz and mean pressures between 1 and 20 bar, using both nitrogen and helium as working fluids. The study reveals significant phenomena such as heat accumulation and annular effects in both temperature and velocity/vorticity fields. These findings were discussed in the context of their impact on the heat transfer performance of the heat exchanger. Specifically, the emergence of vortices was examined in relation to mean pressure, alongside jet-like velocity profiles and natural convection effects. Furthermore, the paper includes a comparative analysis between the heat transfer model employed in this study and previous works, aiming to validate the findings. This research enhances the understanding of fluid dynamics and heat transfer phenomena within heat exchangers of thermoacoustic devices, thereby contributing to advancements in future design improvements.

Acoustics-driven multifunctional microreactor bioinspired by Phylum Porifera for bidirectional pumping and mixing production of silica nanofluids

The Phylum Porifera is one of the most primitive multicellular animals without a mouth, digestive cavity, or central nervous system. Its pores are strewn with flagella inside. Phylum Porifera wiggles its flagella to inhale the seawater, which brings in oxygen, bacteria, microscopic algae, and other organic debris to feed on. Inspired by this natural system, a microreactor based on sharp-edge has been developed and applied in microfluidics to achieve bidirectional pumping and mixing. Here we demonstrate a multifunctional microreactor for bidirectional pumping and mixing that mimics the internal flagella of the Phylum Porifera. The microreactor is designed based on microscale nonlinear acoustics to achieve functionalities via the acoustic streaming generated by the vibration of sharp-edge under the acoustic field. Numerical simulation is conducted to investigate the effect of sharp-edge numbers, dip angles, spreading angles, spacing of sharp-edges, and channel width on the pumping performance. And the bidirectional pumping is verified by experiments. Similarly, numerical simulation and experimental validation are conducted to investigate the effect of flow rate, amplitude, and sharp-edge density on mixing performance. Finally, to verify the application potential and good mixing performance of the developed microreactor, silica nanofluids were synthesized with excellent stability and uniform particle size distribution. These results not only provide important guidelines for the rational design of functional nanomaterials, but also shed new light on the development of efficient microreactors.

Parameter resolution of simulated responses to periodic hydraulic tomography signals in aquifers

An accurate assessment of the hydraulic properties of aquifers is required to represent groundwater flow and solute transport. This study investigates periodic hydraulic tomography performed between wells to obtain accurate images of hydraulic properties. Tomographic experiments with different period and amplitude of sinusoidal test flow, hydraulic properties and well configurations were simulated with a numerical flow model. An l-curve analysis of the obtained heads and sensitivities identified the optimal parameter resolution and served as a basis for comparing the experiments. The results show that the transient phase of signals with short periods provides the most information about the resolution of the aquifer. The resolution could be further improved if tests with different periods were properly combined in the analysis. The study concludes that periodic tomography provides valuable insight into the spatial resolution of hydraulic conductivity and its vertical anisotropy and specific storage, but the choice of signal characteristics is critical.

Frequency and amplitude of flashing-induced instability in an open natural circulation loop

Several nuclear reactor designs rely on passive containment cooling systems. The so-called containment wall condenser relies on natural circulation loops to extract heat from high-temperature steam in the containment to a water tank at ambient pressure. In such passive systems, phase changes can happen and cause flow instabilities in the cooling loop. The flashing-induced instability occurs when the heated fluid in the riser suddenly vaporizes due to a hydrostatic pressure decrease. This instability causes periodic flow peaks, which are of major concern but whose characteristics have not been studied quantitatively.This paper presents two analytical models that predict the flashing frequency and a maximum flow amplitude from geometry and basic operating parameters such as power level and reservoir temperature. The expressions are derived from a physical analysis and do not involve any calibration constants. The flashing frequency appears to be driven by the power level, the inlet temperature and the riser pipe geometry. For the amplitude, the maximum flow rate can be expressed in a Froude number that depends only on the total pressure losses. These models are validated against PASI experiments and system-scale simulations with the CATHARE 3 code, both performed as part of the European Commission funded PASTELS project. Additional data from numerous experimental studies in the literature are used to extend the validity range of the frequency model.Successfully validated against experimental data and additional simulations, these models provide an explicit relationship between oscillations characteristics and design parameters, making them valuable tools for nuclear engineers.

Vascular function and skeletal fragility: a study of tonometry, brachial hemodynamics, and bone microarchitecture.

Osteoporosis and cardiovascular disease frequently occur together in older adults; however, a causal relationship between these 2 common conditions has not been established. By the time clinical cardiovascular disease develops, it is often too late to test whether vascular dysfunction developed before or after the onset of osteoporosis. Therefore, we assessed the association of vascular function, measured by tonometry and brachial hemodynamic testing, with bone density, microarchitecture, and strength, measured by HR-pQCT, in 1391 individuals in the Framingham Heart Study. We hypothesized that decreased vascular function (pulse wave velocity, primary pressure wave, brachial pulse pressure, baseline flow amplitude, and brachial flow velocity) contributes to deficits in bone density, microarchitecture and strength, particularly in cortical bone, which is less protected from excessive blood flow pulsatility than the trabecular compartment. We found that individuals with increased carotid-femoral pulse wave velocity had lower cortical volumetric bone mineral density (tibia: -0.21 [-0.26, -0.15] standardized beta [95% CI], radius: -0.20 [-0.26, -0.15]), lower cortical thickness (tibia: -0.09 [-0.15, -0.04], radius: -0.07 [-0.12, -0.01]) and increased cortical porosity (tibia: 0.20 [0.15, 0.25], radius: 0.21 [0.15, 0.27]). However, these associations did not persist after adjustment for age, sex, height, and weight. These results suggest that vascular dysfunction with aging may not be an etiologic mechanism that contributes to the co-occurrence of osteoporosis and cardiovascular disease in older adults. Further study employing longitudinal measures of HR-pQCT parameters is needed to fully elucidate the link between vascular function and bone health.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Baffleless coils can operate as continuous oscillatory flow reactors to produce pharmaceutical products where process intensification is intended. A method to evaluate mixing performance and its impact on reaction conversion is residence time distribution (RTD) analysis. Liquid macromixing in a long baffleless coil reactor (L = 24 m, dt = 4.57 mm) at ranges of oscillation amplitude (11.75–58.75 mm), frequency (0–3.68 Hz), and net flow rate (30–120 g⋅min−1) was investigated based on measured RTDs fitted to the skewed normal distribution model. The impact of operating conditions on the RTD was supported by analyzing the liquid flow field derived from CFD simulations. The RTD variance under different oscillation conditions suggests a near plug flow pattern, although deviations from ideality such as skewness and long tailing were always observed. The model parameters, along with the RTD variance, were correlated to the operating conditions lumped in an oscillatory Dean number that used the flow amplitude as characteristic length (Deox). Values of Deox varied between 150 and 11000, and the RTD variance at the different net flow rates was minimized for 300 < Deox < 600, as also evidenced from the minimum cross-sectional variance of the simulated time-averaged axial velocity profile. Normalizing the data allowed comparison to similar coil studies with different geometrical dimensions and operating conditions, leading to generalized correlations for the RTD model parameters. Finally, chemical conversion was assessed for first- and second-order single phase reactions at different Damköhler numbers using the segregation and maximum mixedness micromixing models combined with the fitted RTDs. The performance of the coil remained consistent with a plug flow reactor despite its departures from ideal flow.

Contributions of Jupiter's Deep‐Reaching Surface Winds to Magnetic Field Structure and Secular Variation

AbstractNASA's Juno mission delivered gravity data of exceptional quality. They indicate that the zonal winds, which rule the dynamics of Jupiter's cloud deck, must slow down significantly beyond a depth of about 3,000 km. Since the underlying inversion is highly non‐unique additional constraints on the flow properties at depth are required. These could potentially be provided by the magnetic field and its Secular Variation (SV) over time. However, the role of these zonal winds in Jupiter's magnetic field dynamics is little understood. Here we use numerical simulations to explore the impact of the zonal winds on the dynamo field produced at depth. We find that the main effect is an attenuation of the non‐axisymmetric field, which can be quantified by a modified magnetic Reynolds number Rm that combines flow amplitude and electrical conductivity profile. Values below Rm = 3 are required to retain a pronounced non‐axisymmetric feature like the Great Blue Spot (GBS), which seems characteristic for Jupiter's magnetic field. This allows for winds reaching as deep as 3,400 km. A SV pattern similar to the observation can only be found in some of our models. Its amplitude reflects the degree of cancellation between advection and diffusion rather than the zonal wind velocity at any depth. It is therefore not straightforward to make inferences on the deep structure of cloud‐level winds based on Jupiter's SV.

Vibration-Induced Flow and Streaming in Oscillatory Flow of Thermoacoustics

Induced acoustic streaming flow in thermoacoustic systems occurs due to acoustic vibrations, causing changes to the mean flow in the systems. This phenomenon creates a tendency to generate net fluid flow that can cause energy change within certain areas inside the system. However, the effects of the entire system’s vibrations on the flow streaming are not yet fully understood, yet it is important for a more effective operation. This study experimentally investigated the flow streaming resulting from vibration in a standing-wave thermoacoustic test rig with a flow frequency of 23.6 Hz. The existence of flow streaming due to vibration which was not counted in the theoretical formula is shown and indicated by experimental values. The result shows that there is a correlation between the amplitude of the drive ratio (DR) and the velocity of the oscillation of the flow. Upon examining both the theoretical and the practical evidence, it becomes clear that there exists a marginal flow velocity in directions other than the main flow due to the vibration of resonator’s wall as measured at the intake and outflow areas of the stack. This marginal flow velocity amplifies as the drive ratio of flow increases and it may potentially explain the observed difference between measured flow amplitude and the theoretical value.

Myxomatous mitral valve disease and associated pulmonary hypertension might increase serum angiopoietin-2 in dogs.

To evaluate the relationships between the severity of myxomatous mitral valve disease (MMVD) and pulmonary hypertension (PH) and serum angiopoietin (Ang)-1 and Ang-2 concentrations in dogs with MMVD. 74 dogs (control, n = 12; MMVD, n = 62) were included. Serum Ang-1 and Ang-2 concentrations were estimated using the canine-specific ELISA kit. The concentrations were compared between dogs with MMVD and healthy dogs, and they were analyzed according to the severity of MMVD and PH. The median serum Ang-1 concentration did not differ among the study groups. The median serum Ang-2 concentration was higher in dogs with stage B2 MMVD (P = .041) and acute congestive heart failure (P = .002) than in control dogs. In addition, the median serum Ang-2 concentration was higher in MMVD dogs with PH than in those without PH (P = .031). Serum Ang-2 concentration was correlated with vertebral heart score (rs = 0.36, P = .004) and vertebral left atrial score (r = 0.50, P < .001) in dogs with MMVD, and correlated with vertebral heart score (r = 0.63, P = .01), maximum E wave amplitude of the diastolic transmitral flow (rs = 0.61, P = .018), ejection fraction (rs = -0.77, P < .001) and fractional shortening (rs = -0.56, P = .032) in dogs with acute congestive heart failure. Circulating Ang-2 levels increase in dogs with the severity of MMVD and the presence of PH.

Nonlinear Acoustic Behavior Prediction and Analysis of Straight Through Perforated Tube Silencer With Flow

Straight through perforated tube silencers are widely used in intake and exhaust noise control, and their acoustic behaviors are influenced by the gas flow and high amplitude sound remarkably. To investigate the acoustic attenuation performance of straight through perforated tube silencers in the presence of flow and high amplitude sound, an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation is employed and validated by comparing predictions and measurements. Transmission loss of the straight through perforated tube silencer under pure tone and multi-tone sound excitations is predicted. Results show that, under the pure tone sound excitations, the acoustic attenuations are affected remarkably by the high amplitude sound, and the nonlinear effects turn to weaken as flow velocity increases. With the sound pressure level (SPL) decreasing along the axis of the silencer, the acoustic nonlinearity in the orifice weakens gradually. The shedding vortices are restricted to the region near perforations because of the transport of flow. When the multi-tone sound excitation is enforced on the inlet, transmission loss of the silencer is different from the pure tone excitation at the same SPL of every compositional frequency.