Mean Static Pressure Research Articles

Implantation of Pipeline Flow-Diverting Stents Reduces Aneurysm Inflow Without Relevantly Affecting Static Intra-aneurysmal Pressure

Flow-diverting stent (FDS) implantation is an endovascular treatment option for intracranial aneurysms. However, little is known about the hemodynamic effects. To assess the effect of stent compression on FDS porosity, to evaluate the influence of single and overlapping implantation of FDS on intra-aneurysmal flow profiles, and to correlate stent porosity with changes in static mean intra-aneurysmal pressure. Intra-aneurysmal time-density curves were recorded in a pulsatile in vitro flow model before and after implantation of FDSs (Pipeline Embolization Device; ev3) in 7 different types of aneurysm models. Reductions in the maximum contrast inflow and time to maximum intra-aneurysmal contrast were calculated. Micro--computed tomography was performed, and compression-related FDS porosity was measured. The influence of FDS placement on mean static intra-aneurysmal pressure was measured. FDS compression resulted in an almost linear reduction in stent porosity. Stent porosity (struts per 1 mm) correlated significantly with the reduction of aneurysm contrast inflow (R = 0.81, P < .001) and delay until maximum contrast (R = 0.34, P = .001). Circulating intra-aneurysmal high-velocity flow was terminated in all sidewall models after implantation of a single stent. Superimposition of 2 stents reduced maximum intra-aneurysmal contrast by 69.1 ± 3.1% (mean ± SD) in narrow-necked sidewall aneurysm models, whereas no substantial reduction in maximum intra-aneurysmal contrast was observed in wide-necked sidewall aneurysm models. Intra-aneurysmal mean static pressure did not correlate with FDS porosity or number of implanted stents. Implantation of FDS effectively reduces aneurysm inflow in a porosity-dependent way without relevantly affecting static mean intra-aneurysmal pressure. FDS, flow-diverting stentMAP, mean arterial pressurePED, Pipeline Embolization Device.

Computational Analysis of Flow Structure in a Curved Subsonic Diffusing Duct

In the present investigation the distribution of mean velocity, static pressure and total pressure are experimentally studied on a C-shape diffuser of 40° angle of turn with an area ratio of 1.284 and centerline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent and then a series of parametric investigations are conducted with same centre line length and inlet diameter but with different area ratios varying from 1.25 to 2.0 and angle of turn 30° to 75°. The measurements were taken at Reynolds number 2.25 × 105 based on inlet diameter and mass average inlet velocity. Predicted results of coefficient of mass averaged static pressure recovery (48%) and coefficient of mass averaged total pressure loss (12%) are in good agreement with the experimental results of coefficient of mass averaged static pressure recovery (45%) and coefficient of mass averaged total pressure loss (11%) respectively. Standard k-e model in fluent solver was chosen for validation. From the parametric investigation it is observed that for the increase in area ratio from1.25 to 2.0, static pressure recovery increases sharply but with the increase of angle of turn pressure recovery decreases steadily. The coefficient of total pressure loss almost remains constant with the change in area ratio and angle of turn for similar inlet conditions.

Mean Flow and Turbulence Measurements in a Turbulent Free Cruciform Jet

The results of measurements of all three components of the mean velocity vector, the Reynolds normal and primary shear stresses and the mean static pressure in a turbulent free jet, issuing from a sharp-edged cruciform orifice, are presented in this paper. The measurements were made with an x-array hot-wire probe and a pitot-static tube in the near flow field of the jet. The Reynolds number, based upon the equivalent diameter of the orifice, was 1.70 × 105. In addition to the quantities measured directly, the mean streamwise centreline velocity decay, the jet half-velocity widths, the jet spreading rate, the mean streamwise vorticity, the mass entrainment rate, the integral momentum flux and the one-dimensional energy spectra have been derived from the measured data. The results show that the mean streamwise centreline velocity decay rate of the cruciform jet is higher than that of a round jet issuing from an orifice with the same exit area as that of the cruciform orifice. The mean streamwise velocity field changed shape continuously from a cruciform close to the orifice exit plane to circular at 12 and half equivalent diameters downstream. The mean streamwise vorticity field, up to about three equivalent diameters downstream of the orifice exit plane, consists of four pairs of counter-rotating cells, which are aligned with the four edges in the centre of the cruciform orifice.

Computational Analysis of Flow Structure in a Curved Subsonic Diffusing Duct

In the present investigation the distribution of mean velocity, static pressure and total pressure are experimentally studied on a C-shape diffuser of 40° angle of turn with an area ratio of 1.284 and centerline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent and then a series of parametric investigations are conducted with same centre line length and inlet diameter but with different area ratios varying from 1.25 to 2.0 and angle of turn 30° to 75°. The measurements were taken at Reynolds number 2.25 × 105 based on inlet diameter and mass average inlet velocity. Predicted results of coefficient of mass averaged static pressure recovery (48%) and coefficient of mass averaged total pressure loss (12%) are in good agreement with the experimental results of coefficient of mass averaged static pressure recovery (45%) and coefficient of mass averaged total pressure loss (11%) respectively. Standard k-e model in fluent solver was chosen for validation. From the parametric investigation it is observed that for the increase in area ratio from1.25 to 2.0, static pressure recovery increases sharply but with the increase of angle of turn pressure recovery decreases steadily. The coefficient of total pressure loss almost remains constant with the change in area ratio and angle of turn for similar inlet conditions

Numerical characterization of a planar turbulent offset jet over an oblique wall

In the present study, mean velocity and turbulence characteristics of an oblique offset jet with an offset ratio of 7.0 and oblique angle, α=10° have been numerically investigated in details. A comparative study of mean flow parameters, and turbulence stresses along the jet centerline has also been performed to investigate the effect of variation of oblique angle. The Reynolds number considered for the present study is 15000 for which the flow field becomes fully turbulent. Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Spanwise integral of mean momentum, static pressure, Reynolds stress and energy have been computed along the downstream direction. Similarity of streamwise velocity and velocity component parallel to the oblique offset plate has been observed in the wall jet region of the reattached flow. The jet growth rate has been presented in terms of half-width, the decay of maximum velocity, variation of maximum velocity location and growth of length scale. Effect of variation of oblique angles on the streamwise variation of static pressure and skin friction coefficient have been compared for different angles. In the wall jet region streamwise variation of centerline turbulent intensities shows increased values with increase in oblique angle while turbulence intensities along the jet centerline in the preimpingement region remain unaffected by change in oblique angles. Near-wall velocity profiles have been presented by logarithmic law profiles and velocity defect law. Velocity distribution of oblique offset jet in inner coordinates shows differences with that of the boundary layer as well as plane wall jet.

Passive Control of High-Speed Separated Flows Using Splitter Plates

An experimental investigation was conducted to study the effects of passive splitter plates placed in the recirculation region behind a blunt-based axisymmetric body in supersonic flow. The goals of this research were to obtain a better understanding of the physical phenomena that govern these massively separated high-speed flows and to determine the flow-control authority of this passive device. Triangular splitter plates dividing the near wake into 1/2, 1/3, and 1/4 cylindrical regions were designed to exploit specific stability characteristics of this flow, to alter the base pressure, and ultimately to affect base drag. Mean static pressure measurements acquired from the base and splitter plate surfaces were the primary metric to assess the influence of these plates. Schlieren imaging, surface flow visualization, and pressure-sensitive paint measurements were also employed to document the near-wake flowfield, surface flow structure, and surface pressure, respectively. The insertion of these splitter plates only slightly affected the base pressure and near-wake flowfield, which suggests that the recirculation region may not be the most sensitive area to apply this flow control methodology.

Shock-Wave Boundary-Layer Interaction Study on a Compression Corner Using Pressure-Sensitive Paint

Experiments have been performed to study a compression corner induced turbulent boundary layer interactions in a freestream Mach number of 2.05 without and with control. Two configurations of vortex generators (VG), in the form of an array of deltaramps placed upstream of the interaction region at 27.5δ or h/δ = 0.65, have been tested to control the interaction. Pressure sensitive paint (PSP) measurements were made using a binary paint developed in-house. Reasonably good agreement of PSP results with mean static pressure measurements has been observed. The spanwise wall pressure distribution immediately downstream of the control devices show a sinusoidal pattern indicating the generation of streamwise vortices from VG devices. The interaction of these vortices with the reverse flow in the separated region replaced a well-defined separation line for no control by a highly corrugated separation line. Relative to the no-control case, the peak rms value in the intermittent region of separation with control sh...

Application of CFD and Phenomenological Models in Studying Interaction of Two Turbulent Plane Jets

This paper presents a numerical and analytical study of structure and flow development in planar (2- dimensional) turbulent jets. The numerical results are used to develop a phenomenological solution, here referred as Bending Model, for twin turbulent plane jets. The effects of nozzle- nozzle spacing and injection angle are emphasized in numerical study. This study includes a wide range of nozzle- nozzle spacing, 4.25, 9 and 18.25 and injection angle between - 20 to 20. In the farfield, the k-e model predicts the velocity of the jet higher than the experimental results; however, the overall performance of k-e model is acceptable in the prediction of velocity field. Mean velocity and static pressure fields are presented. The Bending Model can predict the attachment of two plane jets for a wide range of nozzle-nozzle spacing and injection angle. Based on the model and modified Reichardt's hypothesis, the flow field in the domain is predicted. The results are compared with the numerical simulation of the k-є model and previous experimental results. The results show encouraging agreement with the numerical and experimental results.

Numerical Investigation of flow through Annular diffusing duct

In the present investigation the distribution of mean velocity, static pressure and total pressure are experimentally studied on an annular curved diffuser of 30° angle of turn with an area ratio of 1.283 and centerline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent and then a series of parametric investigations are conducted with same centre line length and inlet diameter but with different area ratios varying from 1.15 to 3.75. The measurements were taken at Reynolds number 2.25 x 105 based on inlet diameter and mass average inlet velocity. Predicted results of coefficient of mass averaged static pressure recovery (30%) and coefficient of mass averaged total pressure loss (21%) are in good agreement with the experimental results of coefficient of mass averaged static pressure recovery (26%) and coefficient of mass averaged total pressure loss (17%) respectively. Standard k-ε model in Fluent solver was chosen for validation. From the parametric investigation it is observed that static pressure recovery increases up to an area ratio of 2.86 and between the area ration 2.86 to 3.75, pressure recovery decreases steadily. The coefficient of total pressure loss almost remains constant with the change in area ratio for similar inlet conditions.

Pressure Measurements in Jet Diffusion Using a Developed Hot-Wire Static Pressure Sensor

The aim of this experimental study is to investigate the diffusion of jets, with particular attention focused on the relationship between the static pressure and the stream wise mean velocity on the development of a two-dimensional air jet. A jet with three injection Reynolds numbers (Re=1.0×104, 2.0×104, 3.0×104) was generated in a two-dimensional wind tunnel. The velocity distributions were measured by an X-type hot-wire anemometer. The static pressure distributions were measured by a static pressure probe developed in our laboratory, which incorporates a hot-wire anemometer. There are two important characteristics for the hot-wire static pressure probe. The one is that mean static pressure and the static pressure fluctuation can be measured at the same time. The other is that the probe is not affected by the flow and the changes of physical properties (thermal conductivity) of gases, because the sensing hot-wire is always in the air bias flow. The sensitivity of the fstatic pressure probe is 92.3 mV/Pa. The frequency response is flat from 16 Hz to 2.5 kHz. As a result of the experiment, it was found that negative static pressure exists in the turbulent shear layer. It is considered that the entrainment processes from the negative static pressure by the vortex structure motion of the turbulent shear layer.

Numerical Study on the Effect of Bend Angle on Turbulent Flow through Oscillating Bend

The effect of the bend angle on the unsteady developing turbulent air flow through oscillating circular-sectioned curved pipes with the various angles of 180°, 135° and 90° was investigated numerically. The bends had a diameter of 106 mm and a curvature radius ratio of 6.0 with long, straight upstream and downstream sections. Results of the mean velocity and static pressure were obtained at a Reynolds number of 31200 and at various longitudinal stations. The velocity of the primary flow was illustrated in the form of contour map and vector diagram. From the inlet plane of the three oscillating bends to the angle of 45°, the velocity fields in 180°, 90° and 135° bends are similar. The high velocity regions, however, occur near the upper and lower parts in 90° and 180° bends, respectively.

Heat transfer characteristics of synthetic jet impingement cooling

Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet, and is potentially useful for cooling applications. The impingement heat transfer characteristics of a synthetic jet are studied in this work. Toward that end, the behavior of the average heat transfer coefficient of the impinged heated surface with variation in the axial distance between the jet and the heated surface is measured. In addition, radial distribution of mean and rms velocity and static pressure are also measured. The experiments are conducted for a wide range of input parameters: the Reynolds number (Re) is in the range of 1500–4200, the ratio of the axial distance between the heated surface and the jet to the jet orifice diameter is in the range of 0–25, and the length of the orifice plate to the orifice diameter varies between 8 and 22 in this study. The maximum heat transfer coefficient with the synthetic jet is found to be upto 11 times more than the heat transfer coefficient for natural convection. The behavior of average Nusselt number is found to be similar to that obtained for a continuous jet. The exponent of maximum Nusselt number with Re varies between 0.6 and 1.4 in the present experiments, depending on the size of the enclosure. A direct comparison with a continuous jet is also made and their performances are found to be comparable under similar set of conditions. Such detailed heat transfer results with a synthetic jet have not been reported earlier and are expected to be useful for cooling of electronics and other devices.

이중제트에서 노즐과 노즐사이의 각도 변화에 따른 유동 특성

The characteristics of flow on unventilated dual jets was experimentally investigated. The two nozzles each with an aspect ratio of 20 were separated by 6 nozzle widths. Reynolds number based on nozzle width was set to 5,000 by nozzle exit velocity. All measurements were made over a range of nozzle-to-nozzle angles from 0˚ to 25˚. The particle image velocimetry and pressure transducer were employed to measure turbulent velocity components and mean static pressure, respectively. It was shown that a recirculation zone with sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plated. As nozzle-to-nozzle inclined angles were decreased, it was found that the spanwise turbulent intensity is greater than the streamwise turbulent intensity in the merging region. In the combined region, the velocity of dual jets agree well with that of single jet, but the turbulence intensity of dual jets not agree with that of single jet.

An investigation of the flow characteristics in the bootdeck region of a scale model notchback saloon vehicle

The results of an experimental investigation of the bootdeck flow structure of a 36 per cent scale model notchback car are presented together with a general review of advanced laser diagnostic techniques suitable for large-scale wind tunnel flow measurement. The tests were used to characterize the flow behaviour over the Reynolds number range 0.74 × 106-4.93 × 106 in the Cranfield University 2.4 m × 1.8 m wind tunnel. The experiments involved flow visualization, rear bootdeck and backlight three-dimensional stereoscopic particle image velocimetry (PIV) measurements, and mean static and unsteady static pressure measurements. Initial results from the flow visualization suggested flow asymmetries originating in the backlight region that were sensitive to the Reynolds number. The PIV data and static pressure data, however, showed little or no sensitivity of flow to Reynolds number with consistent flow structure and levels of unsteadiness from the backlight to the rear bootdeck region. At this stage no definitive reasons can be given for the discrepancies between the flow visualization and the other data, although the flow visualization data were particularly difficult to interpret near the backlight, and the near-wake structure may be bi-stable in this Reynolds number range. More detailed three-dimensional stereoscopic, time-resolved PIV flow data are now planned to quantify conclusively the correct flow structure and its sensitivities.

Study of wind effects on different buildings of pitched roofs

The characteristics of wind flow past simplified models of one-side pitched roof buildings were examined in a wind tunnel that was designed and built at the Housing and Building Research Center (HBRC). The wind tunnel consists of a square cross section of 200 mm × 200 mm (a bellmouth intake, main entrance duct, a flow straightener, a transition section, and a suction fan). The tunnel was calibrated by a pitot-static tube, determining the flow rate and mean velocity upstream of the models. Static pressure distributions on the external surfaces of models were measured with a free stream velocity of 7 m/s. Smoke visualization tests were also carried to obtain qualitatively the flow patterns around a simulated building models. The flow visualization results gave a good qualitative agreement with measurements. The separation zone, the reattachment length, and the wake region width were clear in the visualization-obtained patterns. The temperature distribution at various points over the pitched roof was measured and the heat transfer coefficient was normalized by the heat transfer coefficient for a 0°. pitch roof. A CFD computer package (ANSYS) based on the finite element method was used to predict velocity contours and vectors in the model domain. The model was created in two-dimensions and meshed with about 15,000 quadratic elements. Convergence and stability of the solution were verified at a certain number of finite elements and iterations. It was found that as the angle of inclination of the roof increased, the mean static pressure on such roof has increased with an enlarged stagnation zone. The results show that a pitched roof of 30° has a much better heat transfer performance than one with 10°, 20°, and 40° for same base building model height and Reynolds number. Good agreement was found between the experimental and computational results.

Influence of leakage flow through labyrinth seals on rotordynamics: numerical calculations and experimental measurements

An extensive investigation of the influence of the leakage flow through a labyrinth seal at supply pressure of 12 bar on the rotordynamics was performed by using numerical calculations and experimental measurements. Toward this end, an experimental rotor setup was established in Shanghai Jiao Tong University. Two labyrinth seals were chosen for comparison, e.g., an interlocking seal and a stepped one. The numerical calculations based on the bulk-flow theory and the perturbation analysis were accomplished. Simultaneous acquisitions of the fluctuating static pressure at the stator wall and the displacement of the whirling rotor were made. The influence of the aerodynamic forcing on the rotor was analyzed in terms of the axial distribution of the mean static pressure, the circumferential distribution of the fluctuating pressure, the fist critical speed and the destabilization rotating speed of the rotor. The experimental results demonstrated that the sinusoidal distribution of the fluctuating static pressure on the stator wall was closely related to the whirling motion of the rotor. The first critical speed of the rotor was reduced by the aerodynamic forcing, resulting in intensified destabilization of the rotor system. Furthermore, the numerical analyses were in good agreement to the experimental measurements.

Experimental study of the near field and transition region of a free jet issuing from a sharp-edged elliptic orifice plate

The mixing characteristics in the near field and transition region, the region of interest in most jet mixing applications, of an isothermal, incompressible, free jet of air issuing from a sharp-edged elliptic orifice plate of aspect ratio 2 into still air surroundings have been studied experimentally using hot-wire anemometry and a pitot-static tube. For comparison, some experiments were performed in round jets issuing from a sharp-edged orifice plate and from a contoured nozzle. All the test jets were unforced and the Reynolds number, based on the equivalent diameter of the sharp-edged elliptic orifice plate which was the same as the diameter of the sharp-edged round orifice plate or the contoured round nozzle, was 1.88 × 10 5 . The three components of the mean velocity vector, time-averaged and phase-averaged fluctuating velocity data, autocorrelation coefficients and one-dimensional spectra of the fluctuating velocities and the mean static pressure were measured. The mean streamwise vorticity, mass entrainment rates and the jet half-velocity widths have been obtained from the measured data. The results show that mixing in an elliptic jet issuing from a sharp-edged orifice plate is higher than in round jets and in elliptic jets issuing from contoured nozzles. The near field and transition region of the elliptic jet were deduced to be dominated by the axisymmetric instability mode which triggers the generation of symmetric shear layer structures. The results also show the presence of coherent structures in the near field and transition region of the jet and the effect of these coherent structures on momentum transport in the jet.

Experimental Study on Flow-Induced Disk Flutter Dynamics by Measuring the Pressure Between Disks

It is important to clarify the characteristics of flow-induced vibrations in hard disk drives in order to achieve an ultrahigh magnetic recording density. In particular, it is necessary to reduce the flow-induced disk vibrations referred to as disk flutter. This paper describes the correlation between the disk vibration amplitude and the pressure fluctuation between a pair of high-speed corotating disks. It also reveals the effects of the arm thickness and arm shape on the disk vibrations and the static pressure between the disks. The disk vibrations were measured using a laser Doppler vibrometer (LDV). The static pressure downstream of the arm between a pair of narrow disks was measured by a method in which a side-hole needle was used as a measurement probe. In addition, the direction of air flow along the trailing edge of the arm was measured using a hot-wire anemometer. The experimental results revealed that the arm inserted between the disks suppresses the disk vibrations. However, the shape and thickness of the arm did not quantitatively affect the disk vibrations. The root-mean-square (RMS) static pressure fluctuation downstream of the arm decreased remarkably, whereas the mean static pressure increased when the arm was inserted between the disks. Furthermore, the circumferential variations in both the RMS and mean static pressures reduced when the arm was inserted. Therefore, it is suggested that the disk vibrations are excited by an increase in the static pressure fluctuation, mean dynamic pressure, and circumferential variation in the static pressure between the disks. Consequently, the disk vibrations can be suppressed by inserting the arm or a spoiler.

Upstream nozzle shaping effects on near field flow in round turbulent free jets

Isothermal, incompressible round turbulent free jets of air, issuing from a sharp-edged orifice and from a contoured nozzle into still air surroundings, have been used to study the effects of upstream nozzle shaping on near field jet evolution experimentally. The Reynolds number, based on the diameter of the orifice or the nozzle, was 1.84 × 10 5 in both jets. Hot-wire anemometry and a pitot-static tube were used to obtain the measured quantities which included the mean streamwise velocity, the turbulent Reynolds normal and shear stresses, the autocorrelation coefficients and one-dimensional energy spectra of the fluctuating streamwise velocity and the mean static pressure. The mean streamwise velocity decay on the jet centerline and the jet half-velocity widths were obtained from the mean streamwise velocity data. To the extent that the results showed that mixing in the sharp-edged orifice round jet was higher than in the contoured nozzle round jet, upstream nozzle shaping was found to affect jet evolution in the near flow field. The distribution of the autocorrelation coefficients of the streamwise fluctuating velocity showed a marked difference in the evolution of the two jets, one of which had a uniform, and the other a non-uniform, exit plane mean streamwise velocity profile. The one-dimensional energy spectra results and also those of the distribution of the autocorrelation coefficients indicated the presence of coherent structures in the near field of the jets and the sharp-edged orifice jet was found to be more “energetic” than the contoured nozzle jet.

Near Field Measurements in an Equilateral Triangular Turbulent Freejet

The near-field mean flow and turbulence characteristics of a turbulent jet of air issuing from a sharp-edged equilateral triangular orifice into still air surroundings have been examined experimentally using hot-wire anemometry and a pitot-static tube. For comparison, some measurements were made in a round free air jet, also issuing from sharp-edged orifice. The Reynolds number, based on the equivalent diameter, was 1.84 x 10 5 in each jet. The three components of the mean velocity vector, the Reynolds normal and primary shear stresses, the distribution of the autocorrelation coefficients and the one-dimensional energy spectra of the fluctuating velocity signals, and the mean static pressure were measured. The mean streamwise vorticity, the half-velocity widths, mass entrainment into the jet, and the local shear in the mean streamwise velocity were obtained from the measured data