Time-averaged Pressure Research Articles

Histomorphometry of Feline Chronic Kidney Disease and Correlation With Markers of Renal Dysfunction

Chronic kidney disease is common in geriatric cats, but most cases have nonspecific renal lesions, and few studies have correlated these lesions with clinicopathological markers of renal dysfunction. The aim of this study was to identify the lesions best correlated with renal function and likely mediators of disease progression in cats with chronic kidney disease. Cats were recruited through 2 first-opinion practices between 1992 and 2010. When postmortem examinations were authorized, renal tissues were preserved in formalin. Sections were evaluated by a pathologist masked to all clinicopathological data. They were scored semiquantitatively for the severity of glomerulosclerosis, interstitial inflammation, and fibrosis. Glomerular volume was measured using image analysis; the percentage of glomeruli that were obsolescent was recorded. Sections were assessed for hyperplastic arteriolosclerosis and tubular mineralization. Kidneys from 80 cats with plasma biochemical data from the last 2 months of life were included in the study. Multivariable linear regression (P < .05) was used to assess the association of lesions with clinicopathological data obtained close to death. Interstitial fibrosis was the lesion best correlated with the severity of azotemia, hyperphosphatemia, and anemia. Proteinuria was associated with interstitial fibrosis and glomerular hypertrophy, whereas higher time-averaged systolic blood pressure was associated with glomerulosclerosis and hyperplastic arteriolosclerosis.

Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

AbstractThe objective of this numerical study is to increase the base pressure on a backward-facing step via linear feedback control, to be ultimately translated to a drag reduction on a blunt-based bluff body. Two backward-facing step cases are simulated: a laminar two-dimensional (2D) flow at a Reynolds number of ${\mathit{Re}}_{\theta } = 280$, and a turbulent three-dimensional (3D) flow at ${\mathit{Re}}_{\theta } = 1500$ using large-eddy simulation. The control is effected by a full-span slot jet with zero-net-mass-flux, and two jet locations are examined. Linear system identification is performed to characterize the flow response to actuation, used to synthesize a control law. The control strategy is based on the premise that an attenuation of the instantaneous pressure fluctuations on the base of the step should lead to an increase in the time-averaged base pressure. Open-loop harmonic forcing is examined within a broad frequency range for both the 2D and 3D flows, which are found to respond differently to actuation. The controllers based on disturbance attenuation lead to sensible increases in base pressure (up to 70 % in 2D and 20 % in 3D) with higher efficiency than the best results achieved in open-loop. The results support the conjecture about the link between the base pressure fluctuations and mean, although it is shown that such a black-box model approach is not suitable for optimization without further physical insight.

Parametric Study of Laser Energy Deposition in Mach 8 Bow Shock

A numerical study was performed to investigate the effect of laser energy deposition in a Mach 8 bow shock. The computational model was extracted from the experiment in which a nominal two-dimensional Mach 8 flow over a cylinder with diameter of 76 mm was studied. The surface pressure was in good agreement with experiments, and the standoff distance agreed well with the theoretical value. The process of blast wave propagation and bow shock distortion was analyzed for energy deposition. The effect of energy level, deposition location and pulsing frequency was studied. For a single pulse of energy deposition, results showed that the reduction of the time-averaged surface pressure increases beyond certain energy level, while the deposition location had less effect on the time-averaged pressure. For a continuously pulsed deposition, the surface pressure in the stagnation region was reduced with increase of frequency. A 33% pressure reduction was achieved with a frequency of 100 kHz. The envelop of the blast w...

Experimental study on time-averaged pressures in stepped spillway

Steps located in the non-aerated flow region of a chute are prone to cavitation damage. Two models operated with various Froude numbers and bottom slopes were employed to measure the pressure on the steps. The minimum and maximum pressures on the horizontal step surfaces occurred at the chute beginning and at the chute end, respectively. These characteristics were also found in the fully-developed flow region. The time-averaged pressure on the horizontal step surfaces is negative at the chute start, and then becomes positive along the flow direction in the non-uniform flow region. On the vertical step surfaces, the pressure is always negative at the top and remains negative along the entire vertical surface if the unit discharges are high enough in the non-uniform flow region. These results differ from the pressure characteristics in the uniform aerated flow region.

Simulations of Flow and Noise Generated by Automobile outside Rear-View Mirrors

Numerical simulations of the flow and noise generated by two different automotive outside rear-view mirrors are investigated. The mirrors were mounted on the top of a specially designed table for simulations and wind tunnel tests. A decoupled two-stage methodology is applied that requires CFD simulations to collect pressure variations at solid surfaces followed by an acoustic post-processing of the data recorded. For the flow simulations, URANS (Unsteady RANS), DES (Detached Eddy Simulation) and LES (Large Eddy Simulation) turbulence modeling approaches are used. This study is part of an on-going project to develop a transient CFD procedure to accurately predict wind noise generated by the exterior surfaces of a moving ground vehicle. The Curle's formulation in low Mach number limit is used to calculate the acoustic pressure generated by the pressure fluctuations at solid walls. Reasonable agreement (within 5 dB) between measurements and predictions has been achieved both for the flow and sound characteristics (with denser mesh quality). It is found that the URANS and DES approaches underestimate surface pressure fluctuations and therefore, result in underestimated sound pressure levels. The LES approach on the other hand (particularly with the dynamic subgrid viscosity model) provides better agreement for the time-averaged surface pressure distributions and for the sound pressure levels.

Numerical visualization of boundary layer transition when negative Magnus effect occurs

We previously identified the appearance of negative Magnus lift on a sphere rotating about an axis perpendicular to an incoming flow at a critical Reynolds number using large-eddy simulation and obtained the statistically time-averaged lift and pressure coefficients around the sphere. We have now numerically investigated the unsteady characteristics of the boundary layer around a rotating sphere at three Reynolds numbers (1.0 × 104, 2.0 × 105, and 1.14 × 106). At a Reynolds number in the subcritical or supercritical region, the direction of the lift force followed the Magnus effect independent of the rotational speed. In contrast, at the critical Reynolds number when a particular rotational speed was imposed, negative lift was observed and a boundary-layer transition occurred only on one side of the sphere, as indicated by the visualization of the vortical structures around the sphere. A change in these structures and a shift of the separation points along with a change in the Reynolds number or rotational speed of the sphere were investigated in the context of boundary-layer transition by using visualization around the sphere. Graphical Abstract text

High Order Numerical Study of Gas Squeeze Film with Flexural Boundary Condition

Ultrasonic levitation system based on Near Field Acoustic Levitation is investigated in this study. A disc is levitated at a height much smaller than the acoustic wavelength where NFAL effect is dominant. A high-order analytical and numerical study on the levitation force induced by gas squeeze film is performed. By taking into account the modal solution on the vibrator whose disunity of the surface displacement can not be ignored, detailed boundary condition of gas squeeze film can achieve a high accuracy in final calculations of time-averaged pressure distribution, load capacity and stiffness of the system. A finite element analysis is compared with analytical solution. By discussing NFAL behavior in gas squeeze films, explanation of essential levitation characters in flexural vibrators is presented, which is important for future study on wafer’s non-contact transportation based on acoustic levitation.

Tip Vortex Cavitation Suppression by Active Mass Injection

Injection of water and aqueous polymer solutions in to the core of a trailing vortex was found to delay the inception of tip vortex cavitation (TVC). Optimal levels of mass injection reduced the inception cavitation number from 3.5 to 1.9, or a reduction of 45%. At the optimal fluxes, injection of water alone produced a reduction of 35%, and the addition of polymer solution led to a reduction of 45%. Stereo particle image velocimetry was employed to examine the flow fields in the region of TVC inception and infer the average core pressure, and planar PIV was used to examine the flow unsteadiness in this region. The time-averaged pressure coefficients for the vortex core pressure were estimated and compared to the pressure needed for TVC inception and full development. Measurement of flow variability in the TVC inception region indicated that relatively low fluxes of mass injection in the TVC roll-up region led to a substantial decrease in flow unsteadiness in the core region near the observed location of inception, and this corresponded to a substantial decrease in the inception pressure. Increased injection of water or polymer solutions led to a modest increase in the average vortex core radius, which was discernable in the measured pressure needed for developed cavitation.

Optically interrogated MEMS pressure sensor array

A novel pressure measurement technique is presented for wireless recording of time-averaged surface pressure distributions in wind tunnel surveys. An array of silicon micro-plate resonators acts as pressure sensing element. The pressure is recorded by measuring the sensor diaphragms’ resonance frequency using optical interferometry. Dependent on the quasi-static deflection caused by a pressure load, the resonance frequency varies with an average pressure sensitivity of 3 Hz/Pa in a frequency range between 30 and 150 kHz. A smart-pixel CMOS camera, narrow-band acoustic noise excitation and a specific sensor surface structure allow for the interrogation of a large number of sensors in parallel without the need for alignment between sensor and detector. Experimental tests reveal increased sensing performance with acoustic excitation of the higher vibration modes.

Pressure-sensitive paint measurement on co-rotating disks in a hard disk drive

There is much demand for improvement in the performance of a hard disk drive (HDD) along with recent rapid developments of information technology. While high-speed disk rotation of a HDD is necessary to accommodate such needs, it causes disk flutter induced by pressure fluctuation on disks and degrades reliability of a HDD. In order to understand the mechanism of the fluttering phenomenon, it is important to know pressure field on the rotating disk. However, it is impossible to measure the pressure by ordinary methods such as pressure taps. Pressure-sensitive paint (PSP) is a pressure measurement technique based on the oxygen quenching of luminescence and enables us to measure the pressure non-invasively. In general, however, the temperature sensitivity of PSP makes it difficult to measure the precise pressure on the surface with temperature distribution. We measured the time-averaged pressure on the disk rotating at 10 000–20 000 rpm for the first time by adopting a temperature-insensitive PSP composed of pyrene sulfonic acid (PySO 3H) as a luminophore. It was found that the pressure forms a concentric circular distribution and decreases toward the center of the disk. Additionally, we elucidate how disk rotational speed and spacing between co-rotating disks influence on the pressure field.

A laboratory experiment of shear-induced natural ventilation

When the wind direction is parallel to the opening façade, the wind shear near the building opening generates turbulence and entrains air across the opening. This kind of shear-induced ventilation cannot be predicted by the orifice equation because the time-averaged pressure difference across the opening is close to zero. This study uses wind tunnel experiments and the tracer gas decay method to investigate the ventilation rate of shear-induced ventilation. The influences of opening area A, external wind speed U and wind direction on the ventilation rates Q, of single-sided and two-sided openings are systemically examined. The experimental results indicate that the dimensionless ventilation rate, Q*=Q/UA, of shear-induced ventilation is independent of the wind speed and opening area, and the value of Q* of two-sided openings is larger than that of a single-sided opening. In addition, a cosine law was used to predict the ventilation rate of building with two-sided openings under various wind directions, and the results are compared with the prediction of the multizone ventilation model COMIS.

Analysis of turbulent flow through a square-sectioned duct with installed 90-degree elbow

This paper presents the results of a theoretical and experimental investigation of the flow of air through a square-sectioned duct with installed bend. A special test stand was built which allowed testing two different bends with dimensionless mean radius values 2.01 and 1.5. To measure the volumetric flow rate, a measuring orifice plate was installed for control purposes. Additionally, numerical integration of the continuity equation, equations of motion, and equations of selected turbulence models was carried out using FLUENT. As a result of the numerical calculations, time-averaged velocity fields, pressures, and components of the turbulent stress tensor in a developing hydrodynamic flow through a square-sectioned duct with installed bend were determined. The numerical results obtained were subjected to detailed verification by comparison with experimental results obtained on the constructed test stand and those available in the literature.

Aerodynamic Analysis of an Innovative Low Pressure Vane Placed in an s-Shape Duct

In this paper the aerodynamics of an innovative multisplitter low pressure (LP) stator downstream of a high pressure turbine stage is presented. The stator row, located inside a swan necked diffuser, is composed of 16 large structural vanes and 48 small airfoils. The experimental characterization of the steady and unsteady flow fields was carried out in a compression tube rig under engine representative conditions. The one-and-a-half turbine stage was tested at three operating regimes by varying the pressure ratio and the rotational speed. Time-averaged and time-accurate surface pressure measurements are used to investigate the aerodynamic performance of the stator and the complex interaction mechanisms with the high pressure (HP) turbine stage. Results show that the strut blade has a strong impact on the steady and unsteady flow fields of the small vanes depending on the vane circumferential position. The time-mean pressure distributions around the airfoils show that the strut influence is significant only in the leading edge region. At off-design condition (higher rotor speed) a wide separated region is present on the strut pressure side and it affects the flow field of the adjacent vanes. A complex behavior of the unsteady surface pressures was observed. Up to four pressure peaks are identified in the time-periodic signals. The frequency analysis also shows a complex structure. The spectrum distribution depends on the vane position. The contribution of the harmonics is often larger than the fundamental frequency. The forces acting on the LP stator vanes are calculated. The results show that higher forces act on the small vanes but largest fluctuations are experienced by the strut. The load on the whole stator decreases 30% as the turbine pressure ratio is reduced by approximately 35%.

Computational and experimental study of supersonic flow over axisymmetric cavities

Laminar and turbulent computations are presented for annular rectangular-section cavities, on a body of revolution, in a Mach 2.2 flow. Unsteady ‘open cavity flows’ result for all laminar computations for all cavity length-to-depth ratios, L/D (1.33, 10.33, 11.33 and 12.33). The turbulent computations produce ‘closed cavity flows’ for L/D of 11.33 and 12.33. Surface pressure fluctuations at the front corner of the L/D = 1.33 cavity are periodic in some cases depending on the cavity length and depth, the boundary layer at the cavity front lip and the cavity scale. The turbulent computations are supported by experimental schlieren images, obtained using a spark light source, and time-averaged surface pressure data.

Unsteady Pressure Measurements With a Fast Response Cooled Probe in High Temperature Gas Turbine Environments

This paper presents the first experimental engine and test rig results obtained from a fast response cooled total pressure probe. The first objective of the probe design was to favor continuous immersion of the probe into the engine to obtain a time series of pressure with a high bandwidth and, therefore, statistically representative average fluctuations at the blade passing frequency. The probe is water cooled by a high pressure cooling system and uses a conventional piezoresistive pressure sensor, which yields, therefore, both time-averaged and time-resolved pressures. The initial design target was to gain the capability of performing measurements at the temperature conditions typically found at high pressure turbine exit (800–1100°C) with a bandwidth of at least 40 kHz and in the long term at combustor exit (2000 K or higher). The probe was first traversed at the turbine exit of a Rolls-Royce Viper turbojet engine at exhaust temperatures around 750°C and absolute pressure of 2.1 bars. The probe was able to resolve the high blade passing frequency (≈23 kHz) and several harmonics of up to 100 kHz. Besides the average total pressure distributions rom the radial traverses, phase-locked averages and random unsteadiness are presented. The probe was also used in a virtual three-hole mode yielding unsteady yaw angle, static pressure, and Mach number. The same probe was used for measurements in a Rolls-Royce intermediate pressure burner rig. Traverses were performed inside the flame tube of a kerosene burner at temperatures above 1600°C. The probe successfully measured the total pressure distribution in the flame tube and typical frequencies of combustion instabilities were identified during rumble conditions. The cooling performance of the probe is compared with estimations at the design stage and found to be in good agreement. The frequency response of the probe is compared with cold shock-tube results and a significant increase in the natural frequency of the line-cavity system formed by the conduction cooled screen in front of the miniature pressure sensor were observed.

Design of the rotor blades of a mini hydraulic bulb-turbine

The rotor blades of a mini hydraulic turbine were designed using a quasi-three-dimensional method. The meridional flow is computed by a streamline curvature method and the blade-to-blade flow by a singularity method. The rotor blade sections are the NACA 66 (MOD) with a = 0.8 meanline. The camber and the stagger angle of the blade sections are adjusted to fulfil the prescribed angular momentum distributions, at the rotor inlet and outlet sections, and zero-incidence flow angle, at the blade leading edge. Turbine head and efficiency versus flow rate curves were obtained for different rotor blade stagger angles at constant rotational speed. Radial distributions of time-averaged velocity and pressure, measured at the rotor exit section with a five-hole probe, are also presented. The design and the experimental results are compared with three-dimensional inviscid flow numerical results computed by the FLUENT code. The domain is discretized by unstructured meshes with a maximum of 2.5 × 10 6 elements. The numerical results show good agreement with the design values and the experimental results, validating the design hypothesis of small radial velocity in the flow through the rotor.

Comparison of hemodynamic endpoints between normal subject and tetralogy patient using Womersley velocity profile and MR based flow measurements.

Right ventricular (RV) enlargement and pulmonary valve insufficiency (PI) are well-known, unavoidable long term sequelae encountered by patients who undergo tetralogy of Fallot (TOF) surgery. Despite their lifelong need for cardiac surveillance and occasional re-intervention, there is a paucity of numerical data characterizing blood flows in their pulmonary arteries (PA). Specifically, although PA regurgitation is well-known to be ubiquitously present in adult repaired TOF (rTOF) patients yet, there have been only limited numerical studies to fully characterize this process. The few studies available have utilized idealized, simplistic geometric models or overly simplistic boundary conditions that fail to account for flow reversals near the arterial walls as observed in in-vitro and MRI based in-vivo studies. The objective of this study was to establish and validate a numerical methodology of PA blood flow using actual patient specific geometry and flow measurements obtained using phase-contrast MRI, employing Womersley type velocity profiles that model flow reversals near walls. The results from computation were validated with measurements. For the normal subject, the time averaged right PA pressure from computation (13.8 mmHg) and experiment (14.6 mmHg) differed by 6%. The time-averaged main PA pressure from computation (16.5 mmHg) and experiment (16.3 mmHg) differed by 1%. The numerically computed left PA regurgitant fraction was 89% compared to measured 77.5%, while the same for the rTOF was 43% (computation), compared to 39.6% (measured). We conclude that the use of numerical computations using the Womersley boundary condition allows reliable modeling of the pathophysiology of PA flow in rTOF.

Statistical analysis of brake squeal noise

Despite substantial research efforts applied to the prediction of brake squeal noise since the early 20th century, the mechanisms behind its generation are still not fully understood. Squealing brakes are of significant concern to the automobile industry, mainly because of the costs associated with warranty claims. In order to remedy the problems inherent in designing quieter brakes and, therefore, to understand the mechanisms, a design of experiments study, using a noise dynamometer, was performed by a brake system manufacturer to determine the influence of geometrical parameters (namely, the number and location of slots) of brake pads on brake squeal noise. The experimental results were evaluated with a noise index and ranked for warm and cold brake stops. These data are analysed here using statistical descriptors based on population distributions, and a correlation analysis, to gain greater insight into the functional dependency between the time-averaged friction coefficient as the input and the peak sound pressure level data as the output quantity. The correlation analysis between the time-averaged friction coefficient and peak sound pressure data is performed by applying a semblance analysis and a joint recurrence quantification analysis. Linear measures are compared with complexity measures (nonlinear) based on statistics from the underlying joint recurrence plots. Results show that linear measures cannot be used to rank the noise performance of the four test pad configurations. On the other hand, the ranking of the noise performance of the test pad configurations based on the noise index agrees with that based on nonlinear measures: the higher the nonlinearity between the time-averaged friction coefficient and peak sound pressure, the worse the squeal. These results highlight the nonlinear character of brake squeal and indicate the potential of using nonlinear statistical analysis tools to analyse disc brake squeal.

Wave‐driven porewater and solute circulation through rippled elastic sediment under highly transient forcing

Lay AbstractWaves over permeable and porous sediment induce movement of water through the pores of the sediment. This leads to circulation of seawater infiltrating into the sediment and then eventually exfiltrated back into the sea. This porewater circulation is caused by pressure variations along the surface of the seabed due to the passing of waves. However, previous studies have considered pressure along the seabed as steadily varying. This is not the case when flow associated with waves is turbulent, which is practically all the time. Using advanced computational modeling tools that more explicitly represent pressure variations occurring at short time intervals and the physical response of sediment to these pressure fluctuations, this study shows that pressure variations occurring at short timescales not considered before enhances the circulation and exchange of water between the seabed and the ocean. This also leads to larger exchange fluxes of dissolved material in the water circulating through the sediment. Since the seabed host many chemical and ecological processes that depend on the delivery of fluids and their dissolved content, accurate estimation of the importance and the rate at which these chemical and ecological processes occur would require a closer inspection of the effects of short time pressure fluctuations induced by turbulence and waves.

Laminar flow control via utilization of pipe entrance inserts (a comment on entrance length concept)

Flow field measurements behind pipe entrance inserts called as flow conditioners in a mean flow Reynolds number range 547 ≤ Re ≤ 9000 are presented herein. A tube bundle, a Laws’ perforated plate and an etoile were located at the entrance of a smooth circular pipe of inner diameter, D = 26.6 mm . The covered ranges of open area ratio, β and non-dimensional length, L / D were 0.49 ≤ β ≤ 0.74 and 0.123 ≤ L / D ≤ 2 respectively. The cross-sectional axial velocity u = u ( r ) profiles at the downstream stations of X / D = 75 , X / D = 375 , X / D = 680 together with pressure losses Δ P are referred to determine the influence of utilized designs. The flow conditioners have a single performance characteristic expressed through a relationship of pressure loss coefficient K = K ( Re β ) which provides a practical method for the calculation of time-averaged pressure loss, Δ P ̄ in an average error margin of ±18%. The laminar flow inside the pipe without an insert in the range of Re < 2450 is not fully developed sensed with u = u ( r ) profiles having a ±20% deviation from the Blasius profile for the lengths X / D < 680 . Meanwhile flow conditioners provide a fully developed laminar flow independent of Re and X observed in terms of downstream u = u ( r ) profiles with a better fit to the Blasius profile in a mean error margin of ±10%. The laminar flow control via flow conditioners is analyzed through a discussion in terms of the introduced local non-dimensional velocity parameters. The used methodology is based on the definition of entrance length Reynolds Number; Re X = ( X / D ) Re . The proposed equations “ Re X β = C ” (where C is a constant) can be used for the estimation of settling distance of the flow conditioners and laminar entrance length. The experimental data are in conformity with the magnitudes of C = 2.87 × 10 4 and C = 3 × 10 5 with the corresponding error margins of ±4% and ±6% respectively.