Numerical Simulation of Natural Convection in Stationary and Rotating Cavities

2004 ◽  
Author(s):  
Zixiang Sun ◽  
Alistair Kifoil ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Centrifugal Force ◽  
Large Scale ◽  
Transfer Rates ◽  
Buoyancy Driven Flows ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
Large Scale Flow ◽  
Rayleigh Numbers ◽  
Good Agreement

In compressor inter-disc cavities with a central axial throughflow it is known that the flow and heat transfer is strongly affected by buoyancy in the centrifugal force field. As a step towards developing CFD methods for such flows, buoyancy-driven flows under gravity in a closed cube and under centrifugal force in a sealed rotating annulus have been studied. Numerical simulations are compared with the experimental results of Kirkpatrick and Bohn (1986) and Bohn et al (1993). Two different CFD codes have been used and are shown to agree for the stationary cube problem. Unsteady simulations for the stationary cube show good agreement with measurements of heat transfer, temperature fluctuations, and velocity fluctuations for Rayleigh numbers up to 2 × 1010. Similar simulations for the rotating annulus also show good agreement with measured heat transfer rates. The CFD results confirm Bohn et al’s results, showing reduced heat transfer and a different Rayleigh number dependency compared to gravity-driven flow. Large scale flow structures are found to occur, at all Rayleigh numbers considered.

Effect of an Oscillating Flow Direction on Leading Edge Heat Transfer

1984 ◽  
Vol 106 (1) ◽  
pp. 222-228 ◽  
Author(s):  
M. L. Marziale ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Strouhal Number ◽  
Large Scale ◽  
Flow Direction ◽  
Leading Edge ◽  
Periodic Variation ◽  
Scale Model ◽  
Transfer Rates ◽  
Large Scale Model ◽  
Turbulence Length

An experimental investigation was conducted to examine the effect of a periodic variation in the angle of attack on heat transfer at the leading edge of a gas turbine blade. A circular cylinder was used as a large-scale model of the leading edge region. The cylinder was placed in a wind tunnel and was oscillated rotationally about its axis. The incident flow Reynolds number and the Strouhal number of oscillation were chosen to model an actual turbine condition. Incident turbulence levels up to 4.9 percent were produced by grids placed upstream of the cylinder. The transfer rate was measured using a mass transfer technique and heat transfer rates inferred from the results. A direct comparison of the unsteady and steady results indicate that the effect is dependent on the Strouhal number, turbulence level, and the turbulence length scale, but that the largest observed effect was only a 10 percent augmentation at the nominal stagnation position.

Scalable Microfluidic Platform for Flexible Configuration of and Experiments with Microtissue Multiorgan Models

2018 ◽  
Vol 24 (1) ◽  
pp. 79-95 ◽  
Author(s):  
Christian Lohasz ◽  
Nassim Rousset ◽  
Kasper Renggli ◽  
Andreas Hierlemann ◽  
Olivier Frey
Keyword(s):  
Large Scale ◽  
Plastic Material ◽  
Microtiter Plate ◽  
Scale Production ◽  
Experimental Conditions ◽  
Precise Control ◽  
Open Design ◽  
Gravity Driven ◽  
Gravity Driven Flow

Microphysiological systems hold the promise to increase the predictive and translational power of in vitro substance testing owing to their faithful recapitulation of human physiology. However, the implementation of academic developments in industrial settings remains challenging. We present an injection-molded microfluidic microtissue (MT) culture chip that features two channels with 10 MT compartments each and that was designed in compliance with microtiter plate standard formats. Polystyrene as a chip material enables reliable, large-scale production and precise control over experimental conditions due to low adsorption or absorption of small, hydrophobic molecules at or into the plastic material in comparison with predecessor chips made of polydimethylsiloxane. The chip is operated by tilting, which actuates gravity-driven flow between reservoirs at both ends of every channel, so that the system does not require external tubing or pumps. The flow rate can be modulated by adjusting the tilting angle on demand. The top-open design of the MT compartment enables efficient MT loading using standard or advanced pipetting equipment, ensures oxygen availability in the chip, and allows for high-resolution imaging. Every channel can be loaded with up to 10 identical or different MTs, as demonstrated by culturing liver and tumor MTs in the same medium channel on the chip.

Liquid Crystal Visualization of Surface Heat Transfer on a Concavely Curved Turbulent Boundary Layer

1984 ◽  
Vol 106 (3) ◽  
pp. 619-627 ◽  
Author(s):  
J. C. Simonich ◽  
R. J. Moffat
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Surface Heat ◽  
Transfer Rates ◽  
Surface Heat Transfer ◽  
Experimental Heat ◽  
Surface Heat Transfer Coefficient ◽  
Transfer Measurement

An experimental heat transfer study on a concavely curved turbulent boundary layer has been performed. A new, instantaneous heat transfer measurement technique utilizing liquid crystals was used to provide a vivid picture of the local distribution of surface heat transfer coefficient. Large scale wall traces, composed of streak patterns on the surface, were observed to appear and disappear at random, but there was no evidence of a spanwise stationary heat transfer distribution, nor any evidence of large scale structures resembling Taylor-Gortler vortices. The use of a two-dimensional computation scheme to predict heat transfer rates in concave curvature regions seems justifiable.

Temperature measurements in a hypersonic gun tunnel using heat-transfer methods

1967 ◽  
Vol 27 (3) ◽  
pp. 503-512 ◽  
Author(s):  
B. E. Edney
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Mach Number ◽  
Heat Losses ◽  
Transfer Rates ◽  
Gun Barrel ◽  
Compression Cycle ◽  
Initial Shock ◽  
Working Section ◽  
Good Agreement

The theory of Fay & Riddell (1958) is used to calculate stagnation temperatures from stagnation-point heat-transfer rates measured in the working section of a hypersonic gun tunnel at a Mach number of 9·8. Measurements using both thin-film gauges and calorimeters are described. The temperatures measured using this technique are found to be lower than predicted by Lemcke (1962) from measurements of shock strengths and final pressures in the gun barrel. This discrepancy is attributed to heat losses in the barrel during the initial shock compression cycle. A simple theory is developed to take into account these losses. There is good agreement between this theory and the experimental results.

Measurement and Prediction of the Influence of Catalytic and Dry Low NOx Combustor Turbulence on Vane Surface Heat Transfer

2003 ◽  
Vol 125 (2) ◽  
pp. 221-231 ◽  
Author(s):  
Forrest E. Ames ◽  
Chao Wang ◽  
Pierre A. Barbot
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Test Case ◽  
Data Set ◽  
Transfer Rates ◽  
Pressure Distributions ◽  
Dimensional Boundary ◽  
Nozzle Guide ◽  
System Configurations ◽  
Nozzle Guide Vanes

New combustion systems developed for low emissions have produced substantial changes to the characteristics of inlet turbulence entering nozzle guide vanes. This paper documents the characteristics of turbulence generated by mock combustion system configurations representative of recently developed catalytic and dry low NOx combustors. Additionally, heat transfer rates are determined on the surface of a vane subjected to inlet turbulence generated by these mock combustor configurations. Six different inlet turbulence conditions with levels ranging up to 14% are documented in this study and vane heat transfer rates are acquired at exit chord Reynolds numbers ranging from 500,000 to 2,000,000. Heat transfer distributions show the influence of turbulence level and scale on heat transfer augmentation and transition. Cascade aerodynamics are well documented and match pressure distributions predicted by a commercial CFD code for this large-scale low-speed facility. The vane pressure distribution could be characterized as a conventional or fully loaded distribution. This comprehensive data set is expected to represent an excellent test case for vane heat transfer predictive methods. Predictive comparisons are shown based on a two-dimensional boundary layer code using an algebraic turbulence model for augmentation as well as a transition model.

Numerical Investigation of Variable Property Effects on Laminar Natural Convection of Gases Between Two Horizontal Isothermal Concentric Cylinders

1986 ◽  
Vol 108 (4) ◽  
pp. 783-789 ◽  
Author(s):  
D. N. Mahony ◽  
R. Kumar ◽  
E. H. Bishop
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boussinesq Approximation ◽  
Variable Properties ◽  
Transfer Rates ◽  
Concentric Cylinders ◽  
Weighted Mean Temperature ◽  
Laminar Natural Convection ◽  
Rayleigh Numbers ◽  
Gap Width

A numerical finite difference investigation has been conducted to determine the effects of variable properties on the laminar natural convection of gases between horizontal isothermal concentric cylinders. Velocity profiles, temperature profiles, and heat transfer rates have been computed for diameter ratios of 1.5, 2.28, 2.6, and 5.0 and Rayleigh numbers based on gap width up to 1.8 × 105. The temperature difference ratio θo was varied from 0.2 to 3.0, and the range of validity of the Boussinesq approximation was determined to be θo = 0.2. A volume-weighted mean temperature was shown to be the most effective reference temperature to reduce the heat transfer data for each diameter ratio to a single curve of the form keq = C RaLn, for 0.2 ≤ θo ≤ 3.0 and RaL = 2.0 × 105.

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

2020 ◽  
Author(s):  
Tom Hickling ◽  
Li He
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Internal Flow ◽  
Systematic Investigation ◽  
Small Scale ◽  
Rotating Cavity ◽  
Ekman Layers ◽  
Inertial Wave ◽  
Wall Flow ◽  
Large Scale Flow

Abstract Heat transfer inside rotating cavities plays an important role in gas turbine engineering. Flows in both compressors and turbine internal flow cavities exhibit self-generated large-scale inertial wave structures, and buoyancy effects are often important. Across the open literature on the topic, there seems to be no clear consensus on what the most suitable modelling fidelity is — although it is a widely held opinion that URANS approaches are less suitable than LES, many authors have succeeded in getting reasonable heat transfer results with URANS. There is also little knowledge of the validity of hybrid URANS/LES type approaches (such as DES) when it comes to predicting the heat transfer in these flows, and furthermore, on the sensitivity of the flow model validity to local driving aerothermal mechanisms in different parts of the cavity. This paper presents the results of a systematic investigation of a rotating cavity with axial throughflow at a Grashof number of 3 × 109. It is found that, for the case investigated, the disk Ekman layers remain laminar. This causes the disk heat transfer to be relatively insensitive to the modelling fidelity used with URANS, DES, and LES giving similar results. The effect of the disk thermal boundary condition is also investigated — it is found to have a significant effect on the direction of the near-wall flow at high radii, despite the large-scale flow structure within the cavity remaining essentially unchanged. This feedback of the disk heat transfer to the near-disk aerodynamics implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, URANS fails to resolve the heat transfer enhancement from small-scale buoyancy driven streaks, whilst these are captured by LES. DES also captures these streaks, as the URANS layer within which they are located returns a very small eddy viscosity, and behaves in a similar manner to LES.

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