Thermohydrodynamic Lubrication Analysis Incorporating Thermal Expansion Across the Film

1994 ◽  
Vol 116 (4) ◽  
pp. 681-688 ◽  
Author(s):  
Nen-Zi Wang ◽  
Ali A. Seireg
Keyword(s):  
Thermal Expansion ◽  
Heat Generation ◽  
Central Zone ◽  
Computational Procedure ◽  
Computational Domain ◽  
Fluid Films ◽  
Pressure Profiles ◽  
Fluid Film Thickness ◽  
Experimental Findings ◽  
Peak Pressures

The study reported in this paper deals with the development of a thermohydrodynamic computational procedure for evaluating the pressure, temperature and velocity distributions in fluid films with fixed geometry between the stationary and moving bearing surfaces. The velocity variations and the heat generation are assumed to occur in a central zone with the same length and width as the bearing but with a significantly smaller thickness than the fluid film thickness. The thickness of the heat generation (shear) zone is developed empirically for the best fit with experimentally determined peak pressures for a journal bearing with a fixed film geometry operating in the laminar regime. A transient thermohydrodynamic computational model with a transformed rectangular computational domain is utilized. The analysis can be readily applied to any given film geometry. The computed distribution of the pressure in the film is in excellent agreement with the experimental findings for different oils and speeds. The developed procedure gives an analytical basis for explaining the “Fogy effect” where significant pressures can be generated in slider bearings with parallel surfaces as a result of the thermal expansion of the film in the direction of the thickness. The procedure confirms the experimentally determined square root relationship between the pressure and the sliding velocity reported in references [1–4]. The normalized pressure profiles computed for the different conditions of the journal bearings are identical to those obtained by isoviscous theory.

Thermohydrodynamic Analysis of Surface Roughness in the Flow Field

2005 ◽  
Vol 127 (2) ◽  
pp. 293-301
Author(s):  
Joon Hyun Kim ◽  
Joo-Hyun Kim
Keyword(s):  
Surface Roughness ◽  
Flow Field ◽  
Film Thickness ◽  
Shear Zone ◽  
Rough Surfaces ◽  
Hydrodynamic Pressure ◽  
Computational Procedure ◽  
Fluid Films ◽  
Lubricating Film ◽  
Fluid Film Thickness

The study deals with the development of a thermohydrodynamic (THD) computational procedure for evaluating the pressure, temperature, and velocity distributions in fluid films with a very rough geometry. A parametric investigation is performed to predict the bearing behaviors in the lubricating film with the absorbed layers and their interfaces as determined by rough surfaces with Gaussian distribution. The layers are expressed as functions of the standard deviations of each surface to characterize flow patterns between both rough surfaces. Velocity variations and heat generation are assumed to occur in the central (shear) zone with the same bearing length and width. The coupled effect of the surface roughness and shear zone dependency on the hydrodynamic pressure and temperature has been found in the noncontact mode. The procedure confirms the numerically determined relationship between the pressure and film gap, provided that its roughness magnitude is smaller than the fluid film thickness.

Interferometric calibration of a strainmeter transducer

1971 ◽  
Vol 61 (4) ◽  
pp. 937-955
Author(s):  
Stanley Smookler ◽  
John V. Kline
Keyword(s):  
Thermal Expansion ◽  
Theoretical Analysis ◽  
Interference Pattern ◽  
Central Zone ◽  
Steel Tube ◽  
Peak Width ◽  
Strain Measurements ◽  
Fabry Perot

abstract A capacitive-strainmeter transducer is calibrated using a variable-spacing, Fabry-Perot interferometer. Optical flats are mounted on a spring parallelogram. Thermal expansion of a steel tube deforms the parallelogram, smoothly displacing one of the optical flats. This modulates the intensity of the 5016 àline, observed at the central zone of the interference pattern, and thus produces sharp peaks on a pen recorder. A theoretical analysis of the peak width, based on the work of Chabbal (1958), agrees with that recorded by the interferometer. This calibration permits earth-strain measurements to an accuracy of 1 per cent.

Dynamics of Machine Tool Spindle/Bearing Systems Under Thermal Growth

1997 ◽  
Vol 119 (4) ◽  
pp. 875-882 ◽  
Author(s):  
Bert R. Jorgensen ◽  
Yung C. Shin
Keyword(s):  
Thermal Expansion ◽  
Dynamic Response ◽  
Heat Generation ◽  
High Speed ◽  
Transfer Model ◽  
Good Prediction ◽  
High Speeds ◽  
Spindle Bearing ◽  
Thermal Growth ◽  
Bearing Stiffness

Increased use of high-speed machining creates the need to predict spindle/bearing performance at high speeds. Spindle dynamic response is a function of the nonlinear bearing stiffness. At high speeds, thermal expansion can play an important role in bearing stiffness. A complete bearing load-deflection analysis including thermal expansion is derived and is coupled with an analysis of spindle dynamic response. Steady-state temperature distribution is found from heat generation at the contact point and from a quasi three-dimensional heat transfer model. Numerical solutions give a good prediction of thermal growth and heat generation in the bearing. Predicted high-speed spindle frequencies show good agreement with experimentation. The effects of loading condition and bearing material type on bearing stiffness are also shown.

Non-Intrusive Heat Transfer Coefficient Determination in a Packed Bed of Spheres

2010 ◽  
Author(s):  
David J. Geb ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Packed Bed ◽  
Computational Procedure ◽  
Spherical Particles ◽  
Average Heat Transfer Coefficient ◽  
Heat Generation Rate ◽  
Average Heat

Non-intrusive measurements of the internal average heat transfer coefficient [1] in a randomly packed bed of spherical particles are made. It is desired to establish accurate results for this simple geometry so that the method used can then be extended to determine the heat transfer characteristics in any porous medium, such as a compact heat exchanger. Under steady, one-dimensional flow the spherical particles are subjected to a step change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The average heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory with the experimental results. More specifically, the average heat transfer coefficient is adjusted within the computational procedure until the predicted values of the fluid outlet temperature match the experimental values. The only information needed is the basic material properties, the flow rate, and the experimental data. The computational procedure alleviates the need for solid and fluid phase temperature measurements, which are difficult to make and can disturb the solid-fluid interaction. Moreover, a simple analysis allows us to proceed without knowledge of the heat generation rate, which is difficult to determine due to challenges associated with calibrating an inductively-coupled, sample specific, heat generation system. The average heat transfer coefficient was determined, and expressed in terms of the Nusselt number, over a Reynolds number range of 20–600. The results compared favorably to the work of Whitaker [2] and Kays and London [3]. The success of this method, in determining the average heat transfer coefficient in a randomly packed bed of spheres, suggests that it can be used to determine the average heat transfer coefficient in other porous media.

Remarks on a theory of elasticity for fluid films

1995 ◽  
Vol 449 (1936) ◽  
pp. 223-231 ◽  
Keyword(s):  
Theory Of Elasticity ◽  
Mechanical Problem ◽  
Fluid Films ◽  
Elastic Fluid ◽  
Experimental Findings

A theory of elastic fluid films that generalizes classical notions of capillarity is described. For the purely mechanical problem, restrictions on energy-minimizing states are obtained. These restrictions are in accord with the experimental findings of K wok et al . (1994).

Aggregate Intensification of Natural Convection Between Air and a Vertical Parallel-Plate Channel by Inserting an Auxiliary Plate at the Mouth and Appending Colinear Insulated Plates at the Exit

2000 ◽  
Author(s):  
Assunta Andreozzi ◽  
Oronzio Manca ◽  
Antonio Campo
Keyword(s):  
Nusselt Number ◽  
Parallel Plate ◽  
Navier Stokes ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Heated Plate ◽  
Computational Domain ◽  
Plate Height ◽  
Pressure Profiles ◽  
Plate Channel

Abstract This paper addresses the examination of heat transfer in parallel-plate channels using a combination of two passive schemes: (1) the insertion of an auxiliary plate at the mouth and (2) the appendage of colinear insulated plates at the exit. The investigation is made by numerically solving the full elliptic Navier-Stokes and energy equation in a I-type computational domain. The channel is symmetrically heated by uniform heat flux. The working fluid is air. The results are reported in terms of induced mass flow rate and maximum wall temperatures. Further, the local Nusselt number, the mean Nusselt number and pressure profiles are presented. The analyzed Grashof numbers based on the heated plate height are 103 and 106.

Effects of the Forcing Frequency on Pulsating Impinging Jet Behavior and the Boundary Layer on the Target Curved Wall

2018 ◽  
Author(s):  
N. Kharoua ◽  
L. Khezzar ◽  
Z. Nemouchi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Vortex Breakdown ◽  
Scale Model ◽  
Strong Mixing ◽  
Computational Domain ◽  
Cold Air ◽  
Eddy Simulation ◽  
Pressure Profiles ◽  
Target Wall

In the present work, time-dependent responses of Nusselt number, friction coefficient and pressure profiles to the passage of groups of coherent structures along a curved impingement wall, is considered. It is meant to replicate a more realistic picture of the flow. The jet considered belongs to heating applications where the jet flow temperature is higher than that of the impingement wall. The flow was simulated using Large Eddy Simulation with the Dynamic Smagorinsky sub-grid-scale model. The plane jet was forced at frequencies increasing gradually to a maximum of 2200 Hz with an amplitude equal to 30% of the mean jet velocity. The computational domain was divided into 16.5 million hexahedral computational cells whose resolution was assessed based on the turbulence scales. It was found that for low forcing frequencies (e.g., 200Hz), coherent forced primary vortices induced by the pulsations are separated by less organized vortices naturally induced similar to those of the unforced jet. It could be seen that the natural vortices have moderate effects on the boundary layer development on the impingement surface starting at relatively short distances from the stagnation point compared to the forced vortices. Increasing the forcing frequency to 1000Hz reduces the distance separating successive forced vortices causing the pairing phenomenon to occur at a certain distance along the target wall. Increasing the forcing frequency further to 2200Hz makes the pairing phenomenon followed by vortex breakdown to occur at shorter distances along the target wall. The smaller forcing frequencies yield large and strong distant vortices which affect the dynamical field noticeably in conjunction with an important deterioration of heat transfer due to their strong mixing effect and entrainment of cold air from the surroundings. On the other hand, high frequencies generate smaller vortices which are relatively close to each other. Thus, they have a weaker effect allowing the growth of the boundary layer on the target wall up to a distance equal to four times the jet-exit width where the minimum heat transfer is observed. In fact, the small successive vortices form a sort of shield preventing the cold air from the surroundings to reach the target wall until their breakdown.

Impact of a Collector Box on the Pressure Recovery of an Exhaust Diffuser System

2011 ◽  
Author(s):  
Bryan C. Bernier ◽  
Mark Ricklick ◽  
J. S. Kapat
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Experimental Tests ◽  
Total Pressure Loss ◽  
Pressure Recovery ◽  
Computational Domain ◽  
Complex Flow ◽  
Local Pressure ◽  
3 Dimensional ◽  
Pressure Profiles

The effects of an industrial gas turbine’s Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system. In this investigation, the exhaust diffuser remained constant through each test, with collector box geometries being varied. The same uniform velocity profile was maintained at the diffuser inlet for all geometries considered. The local pressure recovery through the diffuser with 4 axial ports at 4 circumferential locations was reported along with 14 locations in the accompanying ECB. A system performance analysis for each geometry was conducted using the total pressure loss from inlet to exit of the model. Velocity and total pressure profiles obtained with a hotwire anemometer and Kiel probe at the exit of the diffuser and at the exit of the ECB are also presented in this study. Three (3) different ECB geometries are investigated at a Reynolds number of 60,000. Results obtained from these experimental tests are used to validate the accuracy of a 3-dimensional RANS with realizable k-ε turbulence CFD model from the commercial software package Star-CCM+. The study confirms the existence of two strong counter-rotating helical vortices at the exit of the ECB which significantly affect the flow within the diffuser. Evidence of a strong recirculation zone within the ECB was found to force separation within the exhaust diffuser. Extending the length of the ECB proved to decrease the total pressure loss of the system by up to 19% experimentally. Additionally, the realizable k-ε turbulence was able to accurately represent the total pressure loss of the system within 5%. Despite the extremely complex flow field within the ECB, the computational domain reasonably represented the system in both magnitude and trends.

A Comparison between Measured and Computed Flow Fields in a Transonic Compressor Rotor

1980 ◽  
Vol 102 (4) ◽  
pp. 883-889 ◽  
Author(s):  
P. W. McDonald ◽  
C. R. Bolt ◽  
R. J. Dunker ◽  
H. B. Weyer
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Computational Procedure ◽  
Operating Conditions ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Pressure Profiles

The flow field within the rotor of a transonic axial compressor has been computed and compared to measurements obtained with an advanced laser velocimeter. The compressor was designed for a total pressure ratio of 1.51 at a relative tip Mach number of 1.4. The comparisons are made at 100 percent design speed (20,260 RPM) with pressure ratios corresponding to peak efficiency, near surge, and wide open discharge operating conditions. The computational procedure iterates between a blade-to-blade calculation and an intrablade through flow calculation. Calculated Mach number contours, surface pressure distributions, and exit total pressure profiles are in agreement with the experimental data demonstrating the usefulness of quasi three-dimensional calculations in compressor design.

scholarly journals Non-similar solutions for natural convection from a moving vertical plate with a convective thermal boundary condition

2016 ◽  
Vol 20 (6) ◽  
pp. 1847-1853
Author(s):  
Asterios Pantokratoras
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Thermal Expansion ◽  
Heat Generation ◽  
Wall Temperature ◽  
Vertical Plate ◽  
Internal Heat ◽  
Thermal Boundary Condition ◽  
Internal Heat Generation ◽  
Wall Heat Transfer

In a recent paper by Makinde (Thermal Science, 2011, Vol. 15, Suppl. 1, pp. S137-S143.) the effect of thermal buoyancy along a moving vertical plate with internal heat generation was considered. The plate thermal boundary condition was a convective condition with a heat transfer coefficient proportional to x-1/2 . The fluid thermal expansion coefficient was proportional to 1-x and the internal heat generation was assumed to decay exponentially across the boundary layer and proportional to x-1 in order that the problem accepts a similarity solution. In the present work, the same problem without heat generation is considered, with constant heat transfer coefficient and constant thermal expansion coefficient which is more realistic and has much more practical applications. The present problem is non-similar and results are obtained with the direct numerical solution of the governing equations. The problem is governed by the Prandtl number, the non-dimensional distance along the plate and a convective Grashof number, which is introduced for the first time. It is found that the wall shear stress, the wall heat transfer and the wall temperature, all increase with increasing distance and the wall temperature tends to 1. The influence of the convective Grashof number is to increase the wall shear stress and the wall heat transfer and to reduce the wall temperature.

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