Straight Outlet Research Articles

Upgrading the Compressor Stage of the CAT250TJ Micro Gas Turbine Engine

AbstractDue to their simplicity and relative ease of manufacture, single-stage centrifugal and mixed flow micro gas turbine (MGT) engines are preferred in thrust-based remotely piloted aerial vehicles. A single-stage mixed-flow compressor upgrade for the 200 N CAT250TJ MGT engine is numerically evaluated and presented. An in-house developed mean line application and commercial CFD software is used for the design and performance evaluation of the proposed upgrade configurations. The CAT250TJ – Gen1 engine features a single-stage centrifugal compressor, annular combustor, and single stage axial turbine. Apart from an upgraded impeller, a new crossover diffuser configuration is introduced to replace the wedge-type, straight outlet diffuser configuration of the Gen1 engine. The new single vane crossover diffuser configuration provides a design point total-to-total efficiency and pressure ratio increase of 8.3% and 12.1%, respectively. A disadvantage of a single-vaned crossover diffuser compared to legacy diffusers is a narrower operating range. To alleviate this issue, various combinations of tandem and splitter vane crossover diffuser configurations are proposed. These provide an enhanced operating range, comparable with the operating range displayed by the Gen1 configuration. A turbine power matching analysis is additionally completed to ensure proper compressor integration. Gas turbine cycle software is used to evaluate the on-engine performance of the upgraded compressor configurations. It is shown that the new baseline, single vane crossover diffuser configuration provides a 10.74% increase in design point static thrust.

Performance analysis of a gas cyclone with a converging-diverging vortex finder

In this study, the influence of a novel converging-diverging (CD) vortex finder on the performance of a gas cyclone was studied using the computational fluid dynamics (CFD) method. In addition, the influence of the CD outlet pipe on the erosion rate of the cyclone was investigated. The cutoff diameter, pressure drop, and erosion rates of the new vortex finder design were compared with those of the conventional straight outlet pipe cyclone. The throat of the CD pipe was at the same level as the cyclone's roof. The simulation showed that the CD outlet pipe significantly reduced the cyclone pressure drop. The height and diameter of the converging part of the vortex finder affected the cyclone pressure drop and separation efficiency. Increasing the converging part's inlet diameter reduced the outer vortex tangential velocity and the cyclone separation efficiency. Increasing the converging part inlet diameter reduced turbulent intensity at different cyclone levels. The CD vortex finder with the shortest height and inlet diameter of the converging part (model C1) reduced the cutoff diameter from 6.2 µm to 5.9 µm. The CD outlet pipe with the largest height and inlet diameter of the converging part (model C6) reduced the pressure drop by 42.2% compared to the conventional cylindrical vortex finder. The erosion rate also decreased significantly with an increase in the converging part inlet diameter. However, the converging part height only slightly affected cyclone performance.

Analysis of Energy Loss Characteristics of Vertical Axial Flow Pump Based on Entropy Production Method under Partial Conditions.

The energy loss of the vertical axial flow pump device increases due to the unstable internal flow, which reduces the efficiency of the pump device and increases its energy consumption of the pump device. The research results of the flow loss characteristics of the total internal conduit are still unclear. Therefore, to show the internal energy loss mechanism of the axial flow pump, this paper used the entropy production method to calculate the energy loss of the total conduit of the pump device to clarify the internal energy loss mechanism of the pump device. The results show that the energy loss of the impeller is the largest under various flow conditions, accounting for more than 40% of the total energy loss of the pump device. The variation trend of the volume average entropy production and the energy loss is similar under various flow coefficients (KQ). The volume average entropy production rate (EPR) and the energy loss decrease first and then increase with the increase of flow, the minimum volume average entropy production is 378,000 W/m3 at KQ = 0.52, and the area average EPR of the impeller increases gradually with the increase of flow. Under various flow coefficient KQ, the energy loss of campaniform inlet conduit is the smallest, accounting for less than 1% of the total energy loss. Its maximum value is 63.58 W. The energy loss of the guide vane and elbow increases with the increase of flow coefficient KQ, and the maximum ratio of energy loss to the total energy loss of the pump device is 29% and 21%, respectively, at small flow condition KQ = 0.38. The energy loss of straight outlet conduit reduces first and then increases with the increase of flow coefficient KQ. When flow coefficient KQ = 0.62, it accounts for 27% of the total energy loss of the pump device, but its area average entropy production rate (EPR) and volume average entropy production rate (EPR) are small. The main entropy production loss in the pump device is dominated by entropy production by turbulent dissipation (EPTD), and the proportion of entropy production by direct dissipation (EPDD) is the smallest.

Influence of Rotation Speed on Flow Field and Hydraulic Noise in the Conduit of a Vertical Axial-Flow Pump under Low Flow Rate Condition

The complex flow inside the axial-flow pump device will cause the problem of hydraulic noise; in order to explore the influence of the law of rotation speed on the internal flow characteristics and hydraulic noise of the axial-flow pump conduit, a combination of Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) was used to numerically solve the flow field and internal sound field in the pump device. The results showed that the flow in the elbow inlet conduit was smooth at different rotation speeds, and there was no obvious unstable flow. The higher the rotation speed, the more disordered the flow pattern in the left half of the elbow, which intensifies the unstable flow in the straight outlet conduit. The impeller is the main sound source of the internal hydrodynamic noise of the vertical axial-flow pump device. When the sound source propagates upstream and downstream along the conduit, the Total Sound Source Intensity (TSSI) gradually decays with the increase of distance; the greater the rotation speed is, the faster the Total Sound Source Intensity (TSSI) decays. When the rotation speed was increased from 1450 r/min to 2200 r/min, the TSSI in the straight outlet conduit was attenuated by 8.9 dB, 13.9 dB, and 16.0 dB respectively, and the TSSI in the elbow inlet conduit was attenuated by 11.0 dB, 13.5 dB, and 25.9 dB respectively. The vortex structure in the conduit induces flow noise and delays the attenuation of TSSI in the propagation process; with the increase of rotation speed, this delay will be more obvious.

Air Flow Analysis and Effect of Angle on Rotation Vane Blade Through 90-Degree by Computational Fluid Dynamic

The effects of different angles of rotation vane blades on the flow characteristics in a pipe bend were numerically examined in this work using computational fluid analysis (CFD). The model's geometry included a straight inlet pipe of 1 m length, a 90° pipe bend with a 0.1 m cross-section diameter, a straight outlet pipe of 1 m length, and the installation of rotating vane blades at 10° and 33° angles. The simulation's input parameters include fluid viscosity (0.000017894 kg/m.s), fluid density (1.225 kg/m3), and inlet fluid velocity (10, 14, 20, 24, 26, and 30 m/s). The simulations' output parameters include velocity and pressure measured at two points: section A-A (before the pipe bend) and section B-B (after pipe bend). The findings demonstrate that the velocity and pressure distribution is somewhat uneven at section B-B owing to the presence of the rotating vane. The most efficient rotation vane blade angle is 10° since it has the lowest velocity, static pressure, and pressure drop.

Investigation into the Influence of Division Pier on the Internal Flow and Pulsation in the Outlet Conduit of an Axial-Flow Pump

The outlet conduit is an important construction connecting the outlet of the pump guide vane and the outlet pool; in order to study the hydraulic performance of the straight outlet conduit of the axial-flow pump device, this paper adopts the method of numerical simulation and analyzes the influence of the division pier on the pressure and velocity distribution inside and near the wall of the straight outlet conduit based on three design schemes. Four pressure pulsation measuring points were arranged in the straight outlet conduit, and the low-frequency pulsation characteristic information inside the straight outlet conduit with and without the division pier was extracted by wavelet packet reconstruction. The results show that the addition of a division pier has an effect on the hydraulic loss, near-wall pressure and velocity distribution in the straight outlet conduit. A small high-pressure zone is formed near the wall at the starting position of the division pier, and a large high-speed zone is formed on the left side at the starting position of the division pier. The length of the division pier has no significant effect on the flow distribution of the straight outlet conduit and the pressure and velocity distribution near the wall. Under different working conditions, each monitoring point has the maximum energy in the sub-band (0~31.25 Hz). With the increase of the flow rate, the total pressure energy of the straight outlet conduit decreases gradually. Under each condition, the difference of the energy proportion of the horizontal monitoring points of the straight outlet conduit is small, and the difference of the energy proportion of the two monitoring points at the top and bottom of the outlet channel is relatively large. The energy of the two monitoring points in the straight outlet conduit with a division pier is smaller than that of the two monitoring points in the straight outlet conduit without a division pier. There are differences in the main frequency and the power spectrum corresponding to the main frequency of the monitoring points in the straight outlet conduit, and the reasonable setting of the division pier is conducive to reducing the pressure pulsation of the flow in the straight outlet conduit and is beneficial to the safe and stable operation of the pump device.

Suspension flow through an asymmetric T-junction

The flow of a suspension through a bifurcating channel is studied experimentally and by computational methods. The geometry considered is an ‘asymmetric T’, as flow in the entering branch divides to either continue straight or to make a right angle turn. All branches are of the same square cross-section of side length $D$, with inlet and outlet section lengths $L$ yielding $L/D=58$ in the experiments. The suspensions are composed of neutrally buoyant spherical particles in a Newtonian liquid, with mean particle diameters of $d=250~\unicode[STIX]{x03BC}\text{m}$ and $480~\unicode[STIX]{x03BC}\text{m}$ resulting in $d/D\approx 0.1$ to $d/D\approx 0.2$ for $D=2.4~\text{mm}$. The flow rate ratio $\unicode[STIX]{x1D6FD}=Q_{\Vert }/Q_{0}$, defined for the bulk, fluid and particles, is used to characterize the flow behaviour; here $Q_{\Vert }$ and $Q_{0}$ are volumetric flow rates in the straight outlet branch and inlet branch, respectively. The channel Reynolds number $Re=(\unicode[STIX]{x1D70C}DU)/\unicode[STIX]{x1D702}$ was varied over $0<Re<900$, with $\unicode[STIX]{x1D70C}$ and $\unicode[STIX]{x1D702}$ the fluid density and viscosity, respectively, and $U$ the mean velocity in the inlet channel; the inlet particle volume fraction was $0.05\leqslant \unicode[STIX]{x1D719}_{0}\leqslant 0.30$. Experimental and numerical results for single-phase Newtonian fluid both show $\unicode[STIX]{x1D6FD}$ increasing with $Re$, implying more material tending toward the straight branch as the inertia of the flow increases. In suspension flow at small $\unicode[STIX]{x1D719}_{0}$, inertial migration of particles in the inlet branch affects the flow rate ratio for particles ($\unicode[STIX]{x1D6FD}_{\mathit{particle}}$) and suspension ($\unicode[STIX]{x1D6FD}_{\mathit{suspension}}$). The flow split for the bulk suspension satisfies $\unicode[STIX]{x1D6FD}>0.5$ for $\unicode[STIX]{x1D719}_{0}<0.16$ while $\unicode[STIX]{x1D719}_{0}=0.16$ crosses from $\unicode[STIX]{x1D6FD}\approx 0.5$ to $\unicode[STIX]{x1D6FD}>0.5$ at $Re\approx 100$. For $\unicode[STIX]{x1D719}_{0}\geqslant 0.2$, $\unicode[STIX]{x1D6FD}<0.5$ at all $Re$ studied. A complex dependence of the mean solid fraction in the downstream branches upon inlet fraction $\unicode[STIX]{x1D719}_{0}$ and $Re$ is observed: for $\unicode[STIX]{x1D719}_{0}<0.1$, the solid fraction in the straight downstream branch initially decreases with $Re$, before increasing to surpass the inlet fraction at large $Re$ ($Re\approx 500$ for $\unicode[STIX]{x1D719}_{0}=0.05$). At $\unicode[STIX]{x1D719}_{0}>0.1$, the solid fraction in the straight branch satisfies $\unicode[STIX]{x1D719}_{\Vert }/\unicode[STIX]{x1D719}_{0}>1$, and this ratio grows with $Re$. Discrete-particle simulations employing immersed boundary and lattice-Boltzmann techniques are used to analyse these phenomena, allowing rationalization of aspects of this complex behaviour as being due to particle migration in the inlet branch.

Effect of aorto-iliac bifurcation and iliac stenosis on flow dynamics in an abdominal aortic aneurysm

Physiological flows in rigid diseased arterial flow phantoms emulating an abdominal aortic aneurysm (AAA) under rest conditions with aorto-iliac bifurcation and iliac stenosis are examined in vitro through 2D PIV measurements. Flow characteristics are first established in the model resembling a symmetric AAA with a straight outlet tube. The influence of aorto-iliac bifurcation and iliac stenosis on AAA flow dynamics is then explored through a comparison of the nature of flow patterns, vorticity evolution, vortex core trajectory and hemodynamic factors against the reference configuration. Specifically, wall shear stress and oscillatory shear index in the bulge portion of the models are of interest. The results of this investigation indicate overall phenomenological similarity in AAA flow patterns across the models. The pattern is characterized by a central jet and wall-bounded vortices whose strength increases during the deceleration phase as it moves forward. The central jet impacts the wall of AAA at its distal end. In the presence of an aorto-iliac bifurcation as well as iliac stenosis, the flow patterns show diminished strength, expanse and speed of propagation of the primary vortices. The positions of the instantaneous vortex cores, determined using the Q-function, correlate with flow separation in the bulge, flow resistance due to a bifurcation, and the break in symmetry introduced by a stenosis in one of the legs of the model. Time-averaged WSS in a healthy aorta is around 0.70 N m−2 and is lowered to the range ±0.2 N m−2 in the presence of the downstream bifurcation with a stenosed common iliac artery. The consequence of changes in the flow pattern within the aneurysm on disease progression is discussed.

Entry and exit flows in curved pipes

Solutions are presented for both laminar developing flow in a curved pipe with a parabolic inlet velocity and laminar transitional flow downstream of a curved pipe into a straight outlet. Scalings and linearized analyses about appropriate base states are used to show that both cases obey the same governing equations and boundary conditions. In particular, the governing equations in the two cases are linearized about fully developed Poiseuille flow in cylindrical coordinates and about Dean’s velocity profile for curved pipe flow in toroidal coordinates respectively. Subsequently, we identify appropriate scalings of the axial coordinate and disturbance velocities that eliminate dependence on the Reynolds number $Re$ and dimensionless pipe curvature $\unicode[STIX]{x1D6FC}$ from the governing equations and boundary conditions in the limit of small $\unicode[STIX]{x1D6FC}$ and large $Re$. Direct numerical simulations confirm the scaling arguments and theoretical solutions for a range of $Re$ and $\unicode[STIX]{x1D6FC}$. Maximum values of the axial velocity, secondary velocity and pressure perturbations are determined along the curved pipe section. Results collapse when the scalings are applied, and the theoretical solutions are shown to be valid up to Dean numbers of $D=Re^{2}\unicode[STIX]{x1D6FC}=O(100)$. The developing flows are shown numerically and analytically to contain spatial oscillations. The numerically determined decay of the velocity perturbations is also used to determine entrance/development lengths for both flows, which are shown to scale linearly with the Reynolds number, but with a prefactor ${\sim}60\,\%$ larger than the textbook case of developing flow in a straight pipe.

Downstream decay of fully developed Dean flow

Direct numerical simulations were used to investigate the downstream decay of fully developed flow in a $180^{\circ }$ curved pipe that exits into a straight outlet. The flow is studied for a range of Reynolds numbers and pipe-to-curvature radius ratios. Velocity, pressure and vorticity fields are calculated to visualize the downstream decay process. Transition ‘decay’ lengths are calculated using the norm of the velocity perturbation from the Hagen–Poiseuille velocity profile, the wall-averaged shear stress, the integral of the magnitude of the vorticity, and the maximum value of the $Q$-criterion on a cross-section. Transition lengths to the fully developed Poiseuille distribution are found to have a linear dependence on the Reynolds number with no noticeable dependence on the pipe-to-curvature radius ratio, despite the flow’s dependence on both parameters. This linear dependence of Reynolds number on the transition length is explained by linearizing the Navier–Stokes equations about the Poiseuille flow, using the form of the fully developed Dean flow as an initial condition, and using appropriate scaling arguments. We extend our results by comparing this flow recovery downstream of a curved pipe to the flow recovery in the downstream outlets of a T-junction flow. Specifically, we compare the transition lengths between these flows and document how the transition lengths depend on the Reynolds number.

Development of secondary flows in viscoelastic curved ducts and the influence of outlet region

This paper presents numerical simulations of Newtonian and viscoelastic flows through a 180° curved duct of square cross section with a long straight outlet region. A particular attention is paid to the development of the flow in the output rectangular region after the curved part. The viscoelastic fluid is modeled using the constitutive equation proposed by Phan–Thien–Tanner (PTT). The numerical results, obtained with a finite-volume method, are shown for three different Dean numbers (125,137,150) and for three Deborah numbers (0.1,0.2,0.3). The necessary outlet length to impose boundary conditions is presented and discussed for these cases. Streamlines and vortex formation are shown to illustrate and analyze the evolution of the secondary flow in this region.

Performance assessment of vortex settling chambers

In present investigation an attempt has been made to study the variation in sediment removal efficiency of vortex settling chamber with the locations of the inlet and outlet channels and to develop a new model for predicting the removal efficiency of the vortex settling chamber. Existing equations for removal efficiency are checked for their accuracy using experimental data collected in present study along with data available in literature. The computed efficiency by existing equations was found to be inconsistent with the corresponding observed ones. Therefore, a new equation is proposed in this study. Experiments were conducted on two geometrical models of the vortex chamber. In the first type of the extractor model, both the inlet and outlet overflow channels were kept in an alignment following a straight line tangential to the vortex chamber. In the second type of extractor model, the straight inlet channel joined the vortex chamber tangentially at its one side. The straight outlet channel was taken off tangentially from the upstream end of the chamber at 90° from the inlet channel. It was observed that the efficiency of the geometrical Model-II has been obtained higher because in this model the sediment particle may travel long helicoidal path and thus, resulting in higher settling length, smaller turbulence, and large residence time in comparison to geometrical Model-I. The proposed equation is found to produce results with a maximum error of ±35% for about 100% of the total data. The qualitative performance of the present predictor indicated that it has lowest MAPE (25.03), RMSE (0.150), and highest R2 (0.753) as compared to other existing predictors.

Barrier shoreline evolution constrained by shoreface sediment reservoir and substrate control: The Miquelon-Langlade Barrier, NW Atlantic

ABSTRACT Billy, J., Robin, N., Certain, R., Hein, C. and Berne, S., 2013. Barrier shoreline evolution constrained by shoreface sediment reservoir and substrate control: the Miquelon-Langlade Barrier, NW Atlantic. The Saint-Pierre-et-Miquelon Archipelago (France) is located in the NW Atlantic Ocean, proximal to the Cabot Straight outlet of the Gulf of Saint-Lawrence, and 50 km south of Newfoundland (Canada). The Miquelon-Langlade Barrier is a 12-km-long, 100–2500-m-wide, north-south–oriented isthmus connecting two bedrock islands (Miquelon to the north; Langlade to the south). This study aims to improve our understanding of shoreface-shoreline sediment exchange processes by comparing medium-term (1949–2011) shoreline changes, determined from aerial photographs and differential GPS data, with total shoreface sediment reservoir volumes estimated using seismic along the west coast of the Miquelon-Langlade Barrier. Spatial variability between the northern and southern sectors of the study site are seen both in...

Dynamics of ionization wave splitting and merging of atmospheric-pressure plasmas in branched dielectric tubes and channels

Atmospheric-pressure fast ionization waves (FIWs) generated by nanosecond, high voltage pulses are able to propagate long distances through small diameter dielectric tubes or channels, and so deliver UV fluxes, electric fields, charged and excited species to remote locations. In this paper, the dynamics of FIW splitting and merging in a branched dielectric channel are numerically investigated using a two-dimensional plasma hydrodynamics model with radiation transport, and the results are compared with experiments. The channel consists of a straight inlet section branching 90° into a circular loop which terminates to form a second straight outlet section aligned with the inlet section. The plasma is sustained in neon gas with a trace amount of xenon at atmospheric pressure. The FIW generated at the inlet approaches the first branch point with speeds of ≈108 cm s−1, and produces a streamer at the inlet–loop junction. The induced streamer then splits into two FIW fronts, each propagating in opposite directions through half of the loop channel. The FIWs slow as they traverse the circular sections due to a shorting of the electric field by the other FIW. Approaching the loop–outlet junction, the two FIW fronts nearly come to a halt, induce another streamer which goes through further splitting and finally develops into a new FIW front. The new FIW increases in speed and plasma density propagating in the straight outlet channel. The electrical structure of the FIWs and the induced streamers during the splitting and merging processes are discussed with an emphasis on their mutual influence and their interaction with the channel wall. The FIW propagation pattern is in good agreement with experimental observations. Based on numerical and experimental investigations, a model for the splitting and merging FIWs in the branched loop channel is proposed.

Spray and Flame Structure of a Generic Injector at Aeroengine Conditions

In support of the development of CFD for aeroengine combustion, quantitative measurements of spray properties and temperature were made. A generic swirling air blast injector was designed and built to produce well defined inlet conditions and for ease of numerical description for the CFD development. The measurements were performed in an optically accessible single sector combustor at pressures of 4 and 10 bar and preheat temperatures of 550 and 650 K, respectively. Jet A-1 was used as fuel. The burner air to fuel ratio was 20 and the pressure loss was set to 3%. Sauter mean diameter profiles and liquid mass flux distributions were generated from the phase Doppler anemometry measurements of the evaporating spray drop sizes and velocities. With planar measurements of Mie scattering and kerosene-LIF, the distribution of kerosene (liquid and vapor phase) was imaged. Temperatures were measured with OH-LIF. The burner was designed with a straight outlet to exhibit lifted flames. Hence initial distributions of size, velocity and density of the spray were measured before it entered the flame. Almost complete prevaporization was seen at least for the four bar flame. Compared with atmospheric investigations, the smaller diameters of the droplets and the small streamline curvature of the configuration led to a more uniform behavior of the spray.

Numerical simulation of 3D viscous flow in tubular pumping station on dual-directional operation

The investigation of the three-dimensional fluid flow inside a tubular pumping station on dual-directional operation is described,based on the Reynolds time-averaged Navier-Stokes equations and the Realizable k-eturbulent flow model,applying the law-of-the-wall and sliding mesh technique.The pump model withSshape impeller vanes and bend guide-vanes behind the impeller was used.The main phenomena existent in pressure contours,velocity contours,velocity vectors and flow lines was showed.The influence of one another on pump with channel was discussed in the condition of installation in fact. The performance of the pumping station was estimated,and was compared with test data.The results of the simulation in- dicate the disturbance of flow at pump outlet to be a great in- fluence on the flow of the discharge channel,the flow in dif- fuser channel to be a greater sensitivity on inlet flow,this flow inside straight outlet channel of no guide-vanes to be composed of axial-whirling flow,circulation-vortex flow and axial-flow. There is more loss of head in discharge diffuser of the channel, comparing with that of the suction reducer.It is possible to predict correctly tubular pumping station performance by nu- merical simulation.

Numerical analysis of developing turbulent flow in a 180° bend tube by an algebraic Reynolds stress model

A numerical analysis has been performed for three-dimensional developing turbulent flow in a 180° bend tube with straight inlet and outlet section used by an algebraic Reynolds stress model. To our knowledge, numerical investigations, which show the detailed comparison between calculated results and experimental data including distributions of Reynolds stresses, are few and far between. From this point of view, an algebraic Reynolds stress model in conjunction with boundary-fitted co-ordinate system is applied to a 180° bend tube in order to predict the anisotropic turbulent structure precisely. Calculated results are compared with the experimental data including distributions of Reynolds stresses. As a result of this analysis, it has been found that the calculated results show a comparatively good agreement with the experimental data of the time-averaged velocity and the secondary vectors in both the bent tube and straight outlet sections. For example, the location of the maximum streamwise velocity, which appears near the top or bottom wall in the bent tube, is predicted correctly by the present method. As for the comparison of Reynolds stresses, the present method has been found to simulate many characteristic features of streamwise normal stress and shear stresses in the bent tube qualitatively and has a tendency to under-predict its value quantitatively. Judging from the comparison between the calculated and the experimental results, the algebraic Reynolds stress model is applicable to the developing turbulent flow in a bent tube that is known as a flow with a strong convective effect. Copyright © 2005 John Wiley & Sons, Ltd.

Numerical computations of flow in rotating ducts with strong curvature

The artificial compressibility method is used to analyze internal flows in rotating ducts having strong curvature. This study was concerned with the laminar flow of an incompressible Newtonian fluid having constant viscosity in circular and square ducts with a 908 bend. The emphasis of the present simulation is to determine the effect of rotation and through‐flow rate on the fluid physics and friction characteristics in the straight channel and in the curved geometric regions. The Reynolds numbers ranged from 100 to 790 and the Rossby numbers from 0 to 0.4. Coriolis forces arising from rotation produce a non‐symmetric secondary flow in the bend that increases the loss coefficient as compared with the values for non‐rotation. In addition, the wall friction losses in the straight outlet section are increased, and both effects are directly proportional to the Rossby number.

SEROUS LINED EXTRAMURAL ILEAL VALVE: A NEW CONTINENT URINARY OUTLET

Purpose We report the functional results following the use of serous lined extramural valve as an antireflux technique and urinary outlet for continent urinary diversion. Materials and Methods The procedure was performed in 18 men and 5 women. The technique entails fashioning 2 serous lined extramural troughs in a detubularized W-shape ileal reservoir. A tapered ileal segment is embedded in 1 trough as an antireflux valve and the ureters are anastomosed to its proximal end. Another tapered ileal segment or the appendix is embedded in the second trough and acts as a continent cutaneous outlet. Results No operative or postoperative mortality was observed. One patient had prolonged ileus which was treated conservatively. All patients were evaluable with a mean followup of 19 months. All patients but 1 were continent day and night. No catheterization difficulties were reported. Evacuation intervals were 4 to 5 hours. Radiographic evaluation demonstrated a continent complaint reservoir, stable and straight outlet, and absence of pouch and ureteral reflux. Conclusions This procedure is technically feasible, surgically versatile, applicable for urinary diversion or conversion and associated with satisfactory outcome.

Numerical Analysis of Three-Dimensional Turbulent Flow in a 180.DEG.-Bent Tube Using by an Algebraic Reynolds Stress Model.

A numerical analysis has been performed for three dimensional developing turbulent flow in a 180° bent tube with straight inlet and outlet sections using by an algebraic Reynolds stress model. To our knowledge, only very few numerical investigations exist in which the detailed comparison between calculated results and experimental data contained Reynolds stresses. In numerical analysis, an algebraic Reynolds stress model in conjunction with a boundary-fitted coordinate system is applied to a 180° bent tube in order to solve the anisotropic turbulent structure precisely. As a result of this analysis, it is found that the calculated results show a comparatively good agreement with the experimental data of the time averaged velocity and the secondary vectors in the bent tube and the straight outlet sections. For example, the location of the maximum streamwise velocity, which appears near the top or bottom wall in the bent tube, is predicted correctly by the present method. As for the comparison of Reynolds stresses, the present model has been found to simulate many characteristic features of streamwise normal stress and shear stresses in the bent tube satisfactorily, but has a tendency to underpredict its value. Judging from the comparison between the calculated and the experimental results, the algebraic Reynolds stress model is applicable to the developing turbulent flow in a bent tube which is known as a flow with a strong convective effect.