Wall Pressure Profile Research Articles

Angular Remodeling in Single Stent-Assisted Coiling Displaces and Attenuates the Flow Impingement Zone at the Neck of Intracranial Bifurcation Aneurysms

Self-expanding intracranial stent-assisted coiling of bifurcation aneurysms has recently been shown to straighten target cerebral vessels, a phenomenon with unknown hemodynamic effect. To investigate the impact of angular remodeling in aneurysms treated with single stent-assisted coiling with the use of computational fluid dynamic techniques. Fourteen patients (7 women, mean age 55) who underwent stent coiling of 14 wide-necked bifurcation aneurysms were included based on the availability of high-resolution 3-dimensional rotational angiography. Pretreatment data sets underwent virtual aneurysm removal to isolate the effect of stenting. Wall shear stress and pressure profiles obtained from constant flow input computational fluid dynamic analysis were analyzed for apical hemodynamic changes. Stenting increased the bifurcation angle with significant straightening immediately after treatment and at follow-up (107.3° vs. 144.9°, P < .001). The increased stented angle at follow-up led to decreased pressure drop at the bifurcation apex (12.2 vs. 9.9 Pa, P < .003) and migration of the flow impingement zone (FIZ) toward the contralateral nonstented daughter branch by a mean of 1.48 ± 0.2 mm. Stent-induced angular remodeling decreased FIZ width separating peak apical wall shear stress (3.4 vs. 2.5 mm, P < .004). Analysis of FIZ distance measured from the parent vessel centerline showed it to be linearly (r = .58, P < .002) and FIZ width inversely correlated (r = .46, P < .02) to vessel bifurcation angle. Stent-induced angular remodeling significantly altered bifurcation apex hemodynamics in a favorable direction by blunting apical pressure and inducing the narrowing and migration of the FIZ, a novel response to intracranial stenting that should be added to intimal hyperplasia and flow diversion.

Numerical prediction on the interaction between the incident shock wave and the transverse slot injection in supersonic flows

The incident shock wave has a great impact on the transverse injection flow field in supersonic flows, and it can improve the mixing efficiency between the incoming flow and the fuel. In the current study, the interaction between the incident shock wave and the transverse slot injection has been investigated numerically, and the influences of the size and the location of the ramp on the wall pressure profiles in the transverse slot injection flow field have been performed. Additionally, the swept angle of the ramp is set to be 15.784°, 28.158° and 35.974°, respectively. The obtained results show that the size of the ramp has a great impact on the transverse injection flow field, and the shock wave formed upstream of the injection slot moves towards the entrance of the channel with the increase of the swept angle of the ramp and the jet-to-crossflow pressure ratio. The transverse injection flow field is disturbed when the incident shock wave formed at the leading edge of the ramp is strong enough, and the separation regions both upstream and downstream of the injection slot increase with the increase of the intensity of the incident shock wave. The incident shock wave has a large impact on the mixing improvement between the incoming supersonic flow and the fuel.

Influences of the turbulence model and the slot width on the transverse slot injection flow field in supersonic flows

Transverse slot injection scheme is very important for the mixing process between the air and the fuel in supersonic flows. The effect of the turbulence model and slot width on the transverse slot injection flow field has been investigated numerically based on the grid independency analysis, and the predicted results have been compared with the experimental data available in the open literature. The obtained results show that the grid scale makes only a slight difference to the wall pressure profiles for all jet-to-crossflow pressure ratios employed in this study, and the wall pressure profile with low jet-to-crossflow pressure ratio is predicted accurately by the RNG k–ε turbulence model, the SST k–ω turbulence model for the flow field with high jet-to-crossflow pressure ratio. High jet-to-crossflow pressure ratio can increase the jet penetration depth in supersonic flows, and the gradient of the length of the upstream separation region is larger than that of the height of the Mach surface. At the same time, when the jet-to-crossflow pressure ratio is maintained constant, the jet penetration depth increases with the increase of the slot width.

Wall Pressure Profile Around Cylindrical Rods in Yawed Gas Flow

The distribution of wall pressures in yawed flow through an array of cylindrical tubes inclined at different angles between 30° and 90° was experimentally studied using air at atmospheric pressure for 2290 ≤ Re ≤ 6100. The experiments show that the pressure coefficient is strongly influenced by the inclination angle, and only marginally affected by the flow rate within the tested range. The pressure behavior at the gap was calculated by assuming curved streamlines and inviscid flow, showing good agreement with measurements performed at the rod wall in the gap position.

Characterizing the dynamic property of the vortex tail in a gas cyclone by wall pressure measurements

To explore a determination method for cyclone vortex tail, the wall pressures at different axial and radial positions of a cylinder-on-cone cyclone were measured and analyzed by the Fast Fourier Transform (FFT) and probability density analyses in this paper. The cyclone vortex tail was also visualized by a red ink tracer. The results show that the cyclone wall pressure does not change in the cylindrical section and gradually decreases in the conical section. The magnitudes of wall pressure at different azimuths are almost identical, indicating an axisymmetrical wall pressure radial profile in these parts of the cyclone. Whereas in the lower part of the cone and/or the upper part of dipleg, there is a sudden fall of wall pressure and non-axisymmetrical pressure radial profile. The minimum wall pressure occurs at about 270° azimuth in this region. Underneath in the next part of the dipleg, the wall pressure rapidly rises and returns to axisymmetry. These characteristics indicate that the vortex tail is bended to wall, turns around in this region, and can be used as evidences of the vortex tail. The position determined by the pressure measurement is close to the position of the rotating ring observed in the tracing experiment. It is also found that the frequency of the inner vortex is different from that of the outer vortex. The inner vortex flow fluctuates stronger and faster than its outer partner. At the vortex tail zone, the vortex breaks and the inner vortex fluctuation is involved in the wall pressure signal. Therefore, the position and dynamic property of the vortex tail can be well identified from the wall pressure measurement. The pressure measurement could provide some solid experimental basis for assessing relations of natural vortex length.

Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics.

The necessary degree of arytenoid cartilage abduction (ACA) to restore airway patency at maximal exercise has not been determined. Use computational fluid dynamics modelling to measure the effects of different degrees of ACA on upper airway characteristics of horses during exercise. Maximal ACA by laryngoplasty is necessary to restore normal peak airflow and pressure in Thoroughbred racehorses with laryngeal hemiplegia. The upper airway was modeled with the left arytenoid in 3 different positions: maximal abduction; 88% cross-sectional area of the rima glottis; and 75% cross-sectional area of the rima glottis. The right arytenoid cartilage was maximally abducted. Two models were assumed: Model 1: no compensation of airway pressures; and Model 2: airway pressure compensation occurs to maintain peak airflow. The cross-sectional pressure and velocity distributions for turbulent flow were studied at peak flow and at different positions along the airway. Model 1: In the absence of a change in driving pressure, 12 and 25% reductions in cross-sectional area of the larynx resulted in 4.11 and 5.65% reductions in peak airflow and 3.68 and 5.64% in tidal volume, respectively, with mild changes in wall pressure. Model 2: To maintain peak flow, a 6.27% increase in driving tracheal pressure was required to compensate for a cross-sectional reduction of 12% and a 13.63% increase in driving tracheal pressure was needed for a cross-sectional area reduction of 25%. This increase in negative driving pressure resulted in regions with low intraluminal and wall pressures, depending on the degree of airway diameter reduction. Assuming no increase in driving pressure, the decrease in left ACA reduced airflow and tidal volume. With increasing driving pressure, a decrease in left ACA changed the wall pressure profile, subjecting the submaximally abducted arytenoid cartilage and adjacent areas to airway collapse. The surgical target of ACA resulting in 88 % of maximal cross-sectional area seems to be appropriate.

Rheometry of non-Newtonian electrokinetic flow in a microchannel T-junction

Two-dimensional finite element simulations of electrokinetic flow in a microchannel T-junction of a fluid with a Carreau-type nonlinear viscosity are presented. The motion of the electrical double layer at the channel walls is approximated by velocity wall slip boundary conditions. The fluid experiences a range of shear rates as it turns the corner, and the flow field is shown to be sensitive to the non-Newtonian characteristics of the Carreau model. A one-to-one mapping between the Carreau parameters and the end wall pressure is demonstrated through statistical analysis of the pressure profile for a broad range of physical and operating parameters. Such a mapping allows the determination of the Carreau parameters of an unknown fluid if the end wall pressure profile is known; thus a highly efficient viscometric device may be constructed. A graphical technique to show that the inverse problem is well posed is shown, and a method for solving the inverse problem is presented. The challenges that must be overcome before a practical device can be constructed are discussed.

Overview of the National Centralized Tokamak programme

An overview is given of the National Centralized Tokamak (NCT) programme as a research programme for advanced tokamak research to succeed JT-60U. The mission of NCT is to establish high beta steady-state operation for DEMO and to contribute to ITER. The machine flexibility is pursued in aspect ratio and shape controllability for the demonstration of the high-β steady-state, feedback control of resistive wall modes, wide current and pressure profile control capability and also very long pulse steady-state operation. Existing JT-60 infrastructure such as the heating and current drive system, power supplies and cooling systems will be best utilized for this modification.

超音速燃焼器内の自発着火領域に関する数値解析

The present paper deals with the numerical investigation of autoignition region between a backward-facing step and perpendicular wall injectors in a supersonic combustor. A series of simulation changing the dynamic pressure ratio of the injectant to the main stream is carried out. Wall pressure profiles and injectant concentration in the recirculation region between the step and the injectors show agreement with experimental results. The results by tracking streamline clarifies the correlation between the ratio of circulating cycle to the variation of injectant concentration in the horseshoe vortex and the residence time of mixture measured at the fixed point. The residence time increases from 0.3 msec at the dynamic pressure ratio of 0.1 to 1.2 msec at 0.7. When the dynamic pressure ratio exceeds 0.7, the residence time becomes constant because the size of the horseshoe vortex and injectant concentration does not vary.

Assessment of turbulence model performance for transonic flow over an axisymmetric bump

AbstractA computational study has been performed to evaluate the predictive capabilities of some existing eddy-viscosity (both linear, LEVM, and non-linear, NLEVM) and Reynolds stress transport turbulence models (RSTM) by reference to a transonic shock-induced separated flow over a 10% axisymmetric bump. The calculations have been carried out during the course of a collaborative research programme including both UK universities and industry. The findings of the project demonstrate that improved results can be obtained for such flows by using more advanced turbulence models. For linear eddy-viscosity models, only the SST approach gave good predictions of shock location, recirculation size and pressure recovery, although this was accompanied by deficiencies in the prediction of post-shock velocity profile shape. Non-linear eddy-viscosity models, particularly at the cubic level, provided a more consistent level of agreement with experiments over the range of shock location, wall pressure and velocity profile parameters. Some improvement was also seen in the prediction of turbulence quantities, although only a move to an RSTM closure model reproduced the measured peak stress levels accurately. It was notable that the use of low-Re variants of the models (instead of wall functions) produced no significant improvement in predictions. There are, however, some shortcomings in all models, particularly in the development of flow after reattachment, which was always predicted to be too slow.

Turbulent pipe flow manipulation: some experimental and computational results for single manipulator rings

The effect on developing turbulent pipe flow of blade manipulator devices has been investigated both experimentally and computationally with a view towards reducing pipeline transmission losses. Wall pressure and mean axial velocity profiles have been obtained for nine manipulator configurations. Numerical calculations have been performed for two of these manipulator configurations using a finite volume method that incorporates a low Reynolds number model of turbulence. The results suggest that nett drag reduction may be possible in this flow although at present this seems unlikely. It remains to be answered whether any benefit can be achieved in fully developed flow for which both experimental and computational studies are now underway.

Pressure-flow relationships in a laryngeal airway model having a diverging glottal duct

A laryngeal airway model was constructed using polyester resin in order to empirically test current pressure-flow equations of the larynx. The model was five times larger than life size and had 13 pressure holes to allow measurement of wall pressure profiles. The glottis had a diffuser shape with a 40° divergence angle. This glottal shape is prominent during glottal closure within a vibratory cycle. Three glottal diameters were used: 0.0054, 0.0200, and 0.0918 cm (prototype values). There were essentially two regions of laryngeal pressure for steady flow conditions. The subglottal pressure acted on the laryngeal surfaces upstream of the entrance to the glottis, and the supraglottal pressure acted on the laryngeal surfaces within the diverging region of the glottis. Flow separation near the glottal entrance is suspected. Large negative pressures were not found in the glottis, and the two-duct, glottal pressure-flow equations of Ishizaka and Matsudaira were not well supported. The translaryngeal pressure drop coefficient essentially was dependent only on Reynolds number. [Work supported by NIH and The Voice Foundation.]

A one-dimensional analysis of granular flow in bunkers

Recent work by Morrison and Richmond on a theory of granular flow has been used to analyze a bunker system consisting of a verfical-sided bin and a wedge or conically shaped hopper. Also, wall friction has been included in the basic equations and these have been used to design profiles for constant-pressure hoppers as well as to analyze the bunkers mentioned above. Using average stresses and mass flow rates on any horizontal section, closed-form solutions have been obtained for wall pressures and material velocities. These are easily evaluated for given material and bunker conditions to determine numerical results, and contain sufficient versatility to provide both analytical and design capabilities. For given bunker geometries and material properties, transient and steady-state wall-pressure profiles and flow rates can be computed. For desired flow rates of given materials, bunker geometries can be calculated. The results include expressions for minimum openings and wall slopes to prevent arching, and are sufficiently general to treat different wall-friction values in the hopper and bin sections. Comparisons with available experimental data and previous theoretical results show reasonable agreement, including the wall-pressure jump at the transition point from bin to hopper, particularly when test conditions approximate the restrictions imposed by the one-dimensionality of the solution.

In-vivo determination of error in the measurement of urethral pressure by the method of Brown and Wickham.

A method of determining the error caused by the infusion of water into the urethra during urethral wall pressure and urethral pressure profile measurements is described and discussed. The test is conducted in vivo and the measured pressure is related to the actual urethral wall pressure. The "intrinsic error" is found to be approximately 1-0 cm H2O for every ml/min of infusion rate. Incidental findings concerned with changes in urethral resistance are also reported.

Impact of a freely expanding gas on a wall

A study is made of the flow which results when an initially uniform gas expands into a vacuum through a complete one-dimensional rarefaction wave, and then strikes either a solid wall or a similar opposite facing rarefaction. A Knudsen number K n is defined by the ratio of the undisturbed mean free path to the distance between the center of the rarefaction and the wall. The direct simulation Monte Carlo method has been used to obtain numerical solutions over a range of K n from 10−4 to 103. Results for the wall pressure profile were also obtained from experiment and from approximate continuum calculations. The pressure profile on the wall or the line of symmetry was found to be insensitive to assumptions about the initial highly rarefied stage of the reflection. On the other hand, when considering the temperature history of the gas adjacent to the wall, a proper molecular analysis of the initial stage of reflection was required for all values of the Knudsen number.