Effect of Radial Clearance on the Flow Between Corotating Disks in Fixed Cylindrical Enclosures

2002 ◽  
Vol 124 (3) ◽  
pp. 719-727 ◽  
Author(s):  
Mohammad Al-Shannag ◽  
Joan Herrero ◽  
Joseph A. C. Humphrey ◽  
Francesc Giralt
Keyword(s):  
Finite Thickness ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Disk Surface ◽  
Plane Boundary ◽  
Radial Clearance ◽  
Surface Shear ◽  
Entire Flow ◽  
Flow Domain ◽  
Computationally Intensive

Numerical results are obtained for the isothermal laminar flow of air between a pair of disks attached to and rotating with a hub in a fixed cylindrical enclosure. The presence of radial clearances or “gaps” between the rims of the disks and the curved enclosure wall, and the finite thickness of the disks, are considered in the calculations. The gaps allow time- and circumferentially-dependent axially-directed air flow exchanges between the contiguous inter-disk spaces. As a consequence, axisymmetric calculations of the flow, whether using boundary conditions in the gaps or extended to include the entire flow domain, fail to faithfully reproduce the experimentally measured radial variations of the mean and rms circumferential velocity components in the inter-disk space. Likewise, three-dimensional calculations using the symmetry-plane boundary condition in the gaps also fail to reproduce these variations. In contrast, computationally intensive three-dimensional calculations of the entire flow domain, including the gaps, yield results in very good agreement with the measured mean and rms velocities. These three-dimensional calculations reveal large velocity fluctuations in the gap regions accompanied by corresponding large fluctuations of the inter-disk flow, reflecting a destabilization of the structure and dynamics of the latter by the former. The axisymmetric calculations as well as those using the symmetry-plane condition in the gap are included in this study principally to elucidate their shortcomings in simulating the three-dimensional flows considered; they are not the main goal of the study. Notwithstanding, the physically approximate, full domain axisymmetric calculations yield useful qualitative results. They show that increasing gap size decreases disk surface shear and the associated disk torque coefficient, but at the cost of destabilizing the inter-disk flow. This observation is in agreement with earlier findings and is better understood as the result of the present study.

Effects of Geometrical Structure on Flows Around a Rotating Disk in an Enclosure

2007 ◽  
Author(s):  
T. Watanabe ◽  
H. Furukawa ◽  
M. Suzuki
Keyword(s):  
Phase Velocity ◽  
Geometrical Structure ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Side Wall ◽  
Rotating Disk ◽  
Disk Surface ◽  
Practical Applications ◽  
Entire Flow ◽  
Radial Gap

Flows around a rotating disk in a cylindrical enclosure are typical models of flows found in fluid machinery and chemical reactors. They have their practical applications and draw engineering interests. When the radius of the disk is infinite, it is known that circular rolls, spiral rolls, turbulent spirals and turbulent spots appear. In this case, the parameters governing the flows are the Reynolds number based on the angular velocity of the disk and the axial gap between the disk surface and the end wall of the enclosure. We consider, in this paper, a more practical configuration. The disk has its thickness comparable with the axial height of the enclosure, and the radial gap between the disk rim and the side wall of the enclosure is not negligible. Vortex flows are driven by the centrifugal force around the disk rim, and they are expected to have effects on the entire flow. We performed numerical and experimental studies and investigated the unsteady three-dimensional behaviors. A new criterion to identify flow patterns is introduced and the Hopf bifurcation points from the axisymmetric flows to the three-dimensional flows are determined. The phase velocity of the spiral rolls are measured by a time-dependent analysis. The influence of the geometrical structure on the phase velocity is estimated. New types of flows are found, where bead-like vortices appear and spiral rolls with positive and negative front angles coexist.

scholarly journals Three-Dimensional Stress Concentration Around a Cylindrical Hole in a Semi-Infinite Elastic Body

1966 ◽  
Vol 33 (4) ◽  
pp. 855-865 ◽  
Author(s):  
C. K. Youngdahl ◽  
E. Sternberg
Keyword(s):  
Integral Transform ◽  
Finite Thickness ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Integral Form ◽  
The Body ◽  
Cylindrical Hole ◽  
Normal Displacement ◽  
Plane Boundary ◽  
Dimensional Solution

This paper contains a three-dimensional solution, exact within classical elastostatics, for the stresses and deformations arising in a half-space with a semi-infinite transverse cylindrical hole, if the body—at infinite distances from its cylindrical boundary—is subjected to an arbitrary uniform plane field of stress that is parallel to the bounding plane. The solution presented is in integral form and is deduced with the aid of the Papkovich stress functions by means of an especially adapted, unconventional, integral-transform technique. Numerical results for the nonvanishing stresses along the boundary of the hole and for the normal displacement at the plane boundary, corresponding to several values of Poisson’s ratio, are also included. These results exhibit in detail the three-dimensional stress boundary layer that emerges near the edges of the hole in the analogous problem for a plate of finite thickness, as the ratio of the plate thickness to the diameter of the hole grows beyond bounds. The results obtained thus illustrate the limitations inherent in the two-dimensional plane-strain treatment of the spatial plane problem; in addition, they are relevant to failure considerations and of interest in connection with experimental stress analysis.

scholarly journals Steady flow separation patterns in a 45 degree junction

2000 ◽  
Vol 411 ◽  
pp. 1-38 ◽  
Author(s):  
C. ROSS ETHIER ◽  
SUJATA PRAKASH ◽  
DAVID A. STEINMAN ◽  
RICHARD L. LEASK ◽  
GREGORY G. COUCH ◽  
...  
Keyword(s):  
Flow Separation ◽  
Stokes Equations ◽  
Bypass Graft ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Measured Velocity ◽  
Curved Tube

Numerical and experimental techniques were used to study the physics of flow separation for steady internal flow in a 45° junction geometry, such as that observed between two pipes or between the downstream end of a bypass graft and an artery. The three-dimensional Navier–Stokes equations were solved using a validated finite element code, and complementary experiments were performed using the photochromic dye tracer technique. Inlet Reynolds numbers in the range 250 to 1650 were considered. An adaptive mesh refinement approach was adopted to ensure grid-independent solutions. Good agreement was observed between the numerical results and the experimentally measured velocity fields; however, the wall shear stress agreement was less satisfactory. Just distal to the ‘toe’ of the junction, axial flow separation was observed for all Reynolds numbers greater than 250. Further downstream (approximately 1.3 diameters from the toe), the axial flow again separated for Re [ges ] 450. The location and structure of axial flow separation in this geometry is controlled by secondary flows, which at sufficiently high Re create free stagnation points on the model symmetry plane. In fact, separation in this flow is best explained by a secondary flow boundary layer collision model, analogous to that proposed for flow in the entry region of a curved tube. Novel features of this flow include axial flow separation at modest Re (as compared to flow in a curved tube, where separation occurs only at much higher Re), and the existence and interaction of two distinct three-dimensional separation zones.

scholarly journals Experimental and Numerical Investigation about Small Clearance Journal Bearings under Static Load Conditions

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Carlo Alberto Niccolini Marmont Du Haut Champ ◽  
Fabrizio Stefani ◽  
Paolo Silvestri
Keyword(s):  
Three Dimensional ◽  
Journal Bearings ◽  
Radial Clearance ◽  
Small Scale ◽  
Test Rig ◽  
Small Clearance ◽  
Dimensional Simulation ◽  
Dynamic Loading Conditions ◽  
Static And Dynamic Loading ◽  
Good Agreement

The aim of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., microgas turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed and the performance of its bearings was investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial rotor kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for thermoelasto-hydrodynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this paper, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RKs, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results.

Optimization of the Three-Dimensional Flow Path in the Scroll-Nozzle System of a Radial Inflow Turbine

1984 ◽  
Vol 106 (2) ◽  
pp. 511-515 ◽  
Author(s):  
E. A. Baskharone
Keyword(s):  
Flow Analysis ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Three Dimensional Flow ◽  
Multiply Connected ◽  
Dimensional Flow ◽  
Nozzle Configuration ◽  
Flow Domain ◽  
Radial Inflow Turbine ◽  
Compressibility Effects

A three-dimensional inviscid flow analysis in the combined scroll-nozzle system of a radial inflow turbine is presented. The coupling of the two turbine components leads to a geometrically complicated, multiply-connected flow domain. Nevertheless, this coupling accounts for the mutual effects of both elements on the three-dimensional flow pattern throughout the entire system. Compressibility effects are treated for an accurate prediction of the nozzle performance. Different geometrical configurations of both the scroll passage and the nozzle region are investigated for optimum performance. The results corresponding to a sample scroll-nozzle configuration are verified by experimental measurements.

The Lid-Driven Cavity Flow: A Synthesis of Qualitative and Quantitative Observations

1984 ◽  
Vol 106 (4) ◽  
pp. 390-398 ◽  
Author(s):  
J. R. Koseff ◽  
R. L. Street
Keyword(s):  
Heat Flux ◽  
Flow Visualization ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Lower Boundary ◽  
Thymol Blue ◽  
Width Ratio ◽  
Cavity Depth ◽  
Driven Cavity ◽  
Turbulent Characteristics

A synthesis of observations of flow in a three-dimensional lid-driven cavity is presented through the use of flow visualization pictures and velocity and heat flux measurements. The ratio of the cavity depth to width used was 1:1 and the span to width ratio was 3:1. Flow visualization was accomplished using the thymol blue technique and by rheoscopic liquid illuminated by laser-light sheets. Velocity measurements were made using a two-component laser-Doppler-anemometer and the heat flux on the lower boundary of the cavity was measured using flush mounted sensors. The flow is three-dimensional and is weaker at the symmetry plane than that predicted by accurate two-dimensional numerical simulations. Local three-dimensional features, such as corner vortices in the end-wall regions and longitudinal Taylor-Go¨rtler-like vortices, are significant influences on the flow. The flow is unsteady in the region of the downstream secondary eddy at higher Reynolds numbers (Re) and exhibits turbulent characteristics in this region at Re = 10,000.

scholarly journals Rotation and Magnetic Field Effect on Surface Waves Propagation in an Elastic Layer Lying over a Generalized Thermoelastic Diffusive Half-Space with Imperfect Boundary

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
S. M. Abo-Dahab ◽  
Kh. Lotfy ◽  
A. Gohaly
Keyword(s):  
Magnetic Field ◽  
Surface Waves ◽  
Half Space ◽  
Attenuation Coefficient ◽  
Elastic Layer ◽  
Finite Thickness ◽  
Relaxation Times ◽  
Magnetic Field Effect ◽  
Plane Boundary ◽  
Special Cases

The aim of the present investigation is to study the effects of magnetic field, relaxation times, and rotation on the propagation of surface waves with imperfect boundary. The propagation between an isotropic elastic layer of finite thickness and a homogenous isotropic thermodiffusive elastic half-space with rotation in the context of Green-Lindsay (GL) model is studied. The secular equation for surface waves in compact form is derived after developing the mathematical model. The phase velocity and attenuation coefficient are obtained for stiffness, and then deduced for normal stiffness, tangential stiffness and welded contact. The amplitudes of displacements, temperature, and concentration are computed analytically at the free plane boundary. Some special cases are illustrated and compared with previous results obtained by other authors. The effects of rotation, magnetic field, and relaxation times on the speed, attenuation coefficient, and the amplitudes of displacements, temperature, and concentration are displayed graphically.

scholarly journals Computed Eccentricity Effects on Turbine Rim Seals at Engine Conditions With a Mainstream

1994 ◽  
Author(s):  
Zhou Guo ◽  
David L. Rhode ◽  
Fred M. Davis
Keyword(s):  
Reynolds Number ◽  
Temperature Rise ◽  
Three Dimensional ◽  
Computer Code ◽  
Interaction Effects ◽  
Navier Stokes ◽  
Radial Clearance ◽  
Turbine Wheel ◽  
Blade Root

A previously verified axisymmetric Navier-Stokes computer code was extended for three-dimensional computation of eccentric rim seals of almost any configuration. All compressibility and thermal/momentum interaction effects are completely, included, and the temperature, pressure and Reynolds number of the mainstream, coolant stream and turbine wheel are fixed at actual engine conditions. Regardless of the seal eccentricity, both ingress and egress are found between θ = −30° and 100°. which encompasses the location of maximum radial clearance at θ = 0°. All other θ locations within the rim seal show only egress, as does the concentric basecase for all circumferential locations. Further, the maximum ingress occurs near θ = 30° for all eccentricities. This is found to produce a blade root/retainer temperature rise from the concentric case of 390 percent at 50 percent eccentricity and a 77 percent rise at 7.5 percent eccentricity. In addition, the nature of an increased eccentricity causing a decreased seal effectiveness is examined, along with the corresponding increase of cavity-averaged temperature.

Influence of geometric parameters and operating conditions on the thermohydrodynamic behaviour of plain journal bearings

2000 ◽  
Vol 214 (5) ◽  
pp. 445-457 ◽  
Author(s):  
I Pierre ◽  
M Fillon
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Three Dimensional ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Thermal Dissipation ◽  
Radial Clearance ◽  
Geometric Factors ◽  
Essential Components ◽  
Mass Flowrate

Hydrodynamic journal bearings are essential components of high-speed machinery. In severe operating conditions, the thermal dissipation is not a negligible phenomenon. Therefore, a three-dimensional thermohydrodynamic (THD) analysis has been developed that includes lubricant rupture and re-formation phenomena by conserving the mass flowrate. Then, the predictions obtained with the proposed numerical model are validated by comparison with the measurements reported in the literature. The effects of various geometric factors (length, diameter and radial clearance) and operating conditions (rotational speed, applied load and lubricant) on the journal bearing behaviour are analysed and discussed in order to inform bearing designers. Thus, it can be predicted that the bearing performance obtained highly depends on operating conditions and geometric configuration.

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