An Experimental Investigation of Pressure Distributions in a Journal Bearing Operating in the Transition Regime

1986 ◽  
Vol 200 (4) ◽  
pp. 251-264 ◽  
Author(s):  
J B Roberts ◽  
P J Mason
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Journal Bearing ◽  
Transition Regime ◽  
Pressure Measurements ◽  
Eccentricity Ratio ◽  
Clearance Ratio ◽  
Viscosity Parameter ◽  
Pressure Distributions ◽  
Friction Factors

Experimental results are presented, relating to friction factors and circumferential pressure distributions, for a plain cylindrical journal bearing with a central circumferential inlet groove. The length-diameter ratio of each journal bearing land was 0.25 and the clearance ratio was 0.0031. The friction factor results showed the existence of a distinct ‘transition regime’, characterized by a pronounced ‘hump’ in the friction factor-Reynolds number relationship. Pressure measurements recorded when operating in this transition regime revealed the inadequacy of many existing ‘turbulent’ theories for superlaminar lubrication. By using a short-bearing theory a good correlation of the pressure distribution results was obtained, in terms of a non-dimensional viscosity parameter, kz, which is dependent on both the eccentricity ratio and Reynolds number. The magnitude of kz in this regime was considerably higher than the corresponding value for laminar flow, and was similar to the magnitude predicted from a simple theory based on relating kz to the variation of measured friction factor with Reynolds number.

Pressure Distributions in a Superlaminar Journal Bearing

1982 ◽  
Vol 104 (2) ◽  
pp. 187-195 ◽  
Author(s):  
J. B. Roberts ◽  
R. E. Hinton
Keyword(s):  
Reynolds Number ◽  
Total Pressure ◽  
Pressure Field ◽  
Journal Bearing ◽  
Pressure Measurements ◽  
Inertial Effects ◽  
Empirical Theory ◽  
Number Range ◽  
Pressure Distributions ◽  
Friction Factors

The main features of a comprehensive set of pressure measurements, obtained from a short, plain journal bearing, are presented. The pressure field in the lubricant film was measured in both the circumferential and axial directions over a Reynolds number range of 40–50,000. In cases where the film is noncavitating the pressure distributions are separated into viscous and inertial components. The inertial components are found to agree fairly well with an approximate short bearing theory. Axially averaged, total pressure distributions are compared with the predictions of a simple, empirical theory based on measured friction factors and incorporating inertial effects.

The Characteristics of a Statically Loaded Journal Bearing with Superlaminar Flow

1980 ◽  
Vol 22 (2) ◽  
pp. 79-94 ◽  
Author(s):  
R. E. Hinton ◽  
J. B. Roberts
Keyword(s):  
Friction Factor ◽  
Journal Bearing ◽  
Load Capacity ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Experimental Results ◽  
Empirical Theory ◽  
Clearance Ratio ◽  
Friction Factors ◽  
Theoretical Predictions

Experimental results are presented, relating to the friction factor, load capacity and attitude angle, for a plain, cylindrical journal bearing with a central, circumferential inlet groove. The length to diameter ratio of the journal bearing was 1/3 and the clearance ratio was 0.011. By the use of various lubricants, including water, Reynolds numbers ranging from 40 to 50 000 were attained. Comparisons with various theoretical predictions are given. It is shown that a simple, empirical theory, which incorporates measured friction factors, gives better agreement with the experimental load capacity results than previous theories.

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

Flowfield and Pressure Measurements in a Rotating Two-Pass Duct With Staggered Rounded Ribs Skewed 45Degrees to the Flow

2004 ◽  
Vol 128 (2) ◽  
pp. 340-348 ◽  
Author(s):  
Tong-Miin Liou ◽  
Y. Sian Hwang ◽  
Yi-Chen Li
Keyword(s):  
Friction Factor ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Friction Loss ◽  
Main Stream ◽  
Pressure Measurements ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Distributions

Laser-Doppler velocimetry and pressure measurements are presented of the local velocity and wall pressure distributions in a rotating two-pass square duct with staggered ribs placed on the leading and trailing walls at an angle of 45deg to the main stream. The ribs were square in cross section with the radii of rounds and fillets to rib height ratios of 0.33. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are documented in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. For CFD reference, the periodic fully developed flow condition is absent for the present length of the rotating passage roughened with staggered 45deg ribs. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the staggered 45deg ribs arrangement over the in-line one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature for passages ribbed with staggered 45deg ribs. The staggered 45deg ribs are found to reduce the friction loss to about 88%±1% of the in-line 45deg ribs for the rotating passage under the same operating conditions. The respective contributions of the angled ribs and passage rotation on the passage friction loss are identified.

Frictional Pressure Drop in Micro-Channel

2004 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Hiroki Takahashi ◽  
Yoshiaki Ohno
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Frictional Pressure Drop ◽  
Turbulent Transition ◽  
Friction Factors ◽  
Turbulent Flow Regime ◽  
Form Pressure ◽  
Laminar And Turbulent Flow ◽  
Flow Through

The friction characteristics of water in a sub-millimeter scale channel were investigated experimentally. The friction factors and the critical Reynolds number were measured using water flow through circular tubes with diameters of 0.5, 0.25 and 0.17 mm. The experimental results show that the measured friction factor for water agreed well with the conventional Poiseuille (λ = 64/Re) and Blasius (λ = 0.316 Re−0.25) equations in laminar and turbulent flow regime; the laminar-turbulent transition Reynolds number was approximately 2300 for diameter 0.5 mm. For diameter 0.25 mm, the friction factor evaluated by the form pressure drop also agreed well with the Poiseuille equation. For diameter 0.17 mm, the measured total friction factor was close to the Poiseuille prediction.

Steady and Unsteady Surface Pressure Distributions Around Rectangular Prisms With Sharp Edges at Reynolds Number Up to 2.5×106

2006 ◽  
Author(s):  
Annick D’Auteuil ◽  
Guy L. Larose
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Surface Pressure ◽  
Angle Of Attack ◽  
Pressure Measurements ◽  
Oncoming Flow ◽  
Pressure Distributions ◽  
Unsteady Surface Pressure ◽  
Sharp Edges ◽  
Flow Reattachment

The commonly-held assumption that the aerodynamics of rectangular prisms with sharp edges are insensitive to Reynolds number is shown to have limitations. Flow reattachment on the top and/or bottom of the prisms can be related to Reynolds number, Re. Steady and unsteady surface pressure measurements were carried out on nine different rectangular prisms for Re from 0.3×106 to 2.5×106 at several angles of attack, in smooth and turbulent flow. It was observed that the reattachment was dependent on parameters such as fineness ratio, edge treatment, angle of attack, turbulence of the oncoming flow and Reynolds number. Permanent reattachment occurred for prisms with fineness ratio of 4 and fluctuating reattachment took place for rectangular prisms with fineness ratio as low as 2.

Flowfield and Pressure Measurements in a Rotating Two-Pass Duct With Staggered Rounded Ribs Skewed 45° to the Flow

2004 ◽  
Author(s):  
Tong-Miin Liou ◽  
Yi-Sian Hwang ◽  
Yi-Chen Li
Keyword(s):  
Friction Factor ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Friction Loss ◽  
Main Stream ◽  
Pressure Measurements ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Distributions

Laser-Doppler velocimetry and pressure measurements are presented of the local velocity and wall pressure distributions in a rotating two-pass square duct with staggered ribs placed on the leading and trailing walls at an angle of 45° to the main stream. The ribs were square in cross-section with the radii of rounds and fillets to rib height ratios of 0.33. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are documented in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. For CFD reference, the periodic fully developed flow condition is absent for the present length of the rotating passage roughened with staggered 45° ribs. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the staggered 45° ribs arrangement over the in-line one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature for passages ribbed with staggered 45° ribs. The staggered 45° ribs are found to reduce the friction loss to about 88%±1% of the in-line 45° ribs for the rotating passage under the same operating conditions. The respective contributions of the angled ribs and passage rotation on the passage friction loss are identified.

scholarly journals Leakage Characteristic of Helical Groove Seal Designed in Reactor Coolant Pump

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Meng Zhang ◽  
Xiao-fang Wang ◽  
Sheng-li Xu ◽  
Shuo Yin
Keyword(s):  
Reynolds Number ◽  
High Pressure ◽  
Friction Factor ◽  
Helix Angle ◽  
Operation Condition ◽  
Coolant Pump ◽  
Reactor Coolant ◽  
Friction Factors ◽  
Helical Groove ◽  
Groove Seal

Helical groove seal is designed in reactor coolant pump to control the leakage along the front surface of the impeller face due to its higher resistance than the circumferentially grooved seal. The flow and the friction factors in helical groove seals are predicted by employing a commercial CFD code, FLUENT. The friction factors of the helical groove seals with helix angles varying from 20 deg to 50 deg, at a range of rotational speed and axial Reynolds number, were, respectively, calculated. For the helically grooved stator with the helix angle greater than 20 deg, the leakage shows an upward trend with the helix angle. The circumferentially grooved stator has a lower resistance to leakage than the 20 deg and 30 deg stators. It can be predicated that, for a bigger helix angle, the friction factor increases slightly with an increase in high axial Reynolds number, which arises from the high-pressure operation condition, and the friction factor is generally sensitive to changes in the helix angle in this operation condition. The study lays the theoretical foundation for liquid seal design of reactor coolant pump and future experimental study to account for the high-pressure condition affecting the leakage characteristic.

Laminar, Transitional and Turbulent Friction Factors for Gas Flows in Smooth and Rough Microtubes

2008 ◽  
Author(s):  
Marco Lorenzini ◽  
Gian Luca Morini ◽  
Sandro Salvigni
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Turbulent Regime ◽  
Turbulent Friction ◽  
Compressibility Effect ◽  
Flow Acceleration ◽  
Friction Factors ◽  
Macro Scale ◽  
Fully Developed Turbulent Flow ◽  
Microscale Transport

Theoretical and experimental works on microscale transport phenomena have been carried out in the past decade in the attempt to analyse possible new effects and to assess the influence of scaling on the classical correlations which are used in macro-scale heat and fluid flow, following the need to supply engineers with reliable correlations to be used in the design of micro-scale devices. These results were sometimes in mutual contrast, as is the case for the determination of the friction factor, which has been found to be lower, higher or comparable to that for macroscopic channels, depending on the researchers. In this work the compressible flow of nitrogen inside circular microchannels from 26 μm to 508 μm in diameter and with different surface roughness (<1%) is investigated for the whole range of flow conditions: laminar, transitional and turbulence. Over 5000 experimental data have been collected and analysed. The data confirmed that in the laminar regime the agreement with the conventional theory is very good in terms of friction factors both for rough and smooth microtubes. For the smaller microchannels (<100 μm) when Re is greater than 1300 the friction factor tends to deviate from the Poiseuille law because the flow acceleration due to compressibility effect gains in importance. The transitional regime was found to start no earlier than at values of the Reynolds number around 1800–2000. Both smooth and sudden changes in the flow regime have been found, as reported for conventional tubes. Fully developed turbulent flow was attained with both smooth and rough tubes, and the results for smooth tubes seem to confirm Blasius’s relation, while for rough tubes the Colebrook’s correlation is found to be only partially in agreement with the experimental friction factors. In the turbulent regime the dependence of the friction factor on the Reynolds number is less pronounced for microtubes with respect to the prediction of the Colebrook’s correlation and the friction factor tends only to depend on the microtube relative roughness.

An Experimental and Analytical Investigation of Friction Factors for Fully Developed Flow in Internally Finned Triangular Ducts

1986 ◽  
Vol 108 (3) ◽  
pp. 507-512 ◽  
Author(s):  
H. Chegini ◽  
S. K. Chaturvedi
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Analytical Investigation ◽  
Momentum Equation ◽  
Fully Developed Flow ◽  
Finite Difference Technique ◽  
Friction Factors ◽  
Experimental Values ◽  
Good Agreement

Friction factors for fully developed flow in triangular ducts with fins of various height and width are investigated for Reynolds numbers ranging from 150 to 90,000. Two triangular ducts having apex angles of 60 and 38.8 deg are studied. Results are presented in the form of standard plots of friction factor as a function of Reynolds number. Friction factor values for the smooth triangular duct cases are in good agreement with the existing results. For the finned-duct cases, the fully developed axial velocity profiles in laminar flow are determined by solving the x-momentum equation iteratively by the Gauss–Seidel finite-difference technique. The theoretically determined friction factors for these cases are in good agreement with the experimental values of friction factors based on pressure drop measurements.

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