Experimental Characterization of the Coolant Film Issuing From a Cooling Tile

2004 ◽  
Author(s):  
K. H. Chua ◽  
J. Carrotte ◽  
P. Denman ◽  
A. Spencer
Keyword(s):  
Large Scale ◽  
Subsequent Development ◽  
Aerodynamic Characteristics ◽  
Linear Increase ◽  
Wall Film ◽  
Surface Data ◽  
Mainstream Flow ◽  
Conventional Cooling ◽  
Hot Surface ◽  
Tile Surface

In modern, low emission, gas turbine combustion systems the amount of air available for cooling of the flame tube liner is limited. This has led to the development of more complex systems, such as cooling tiles, as opposed to the use of more conventional cooling slots. Within a cooling tile the flow passes around a large number of pedestals located between 2 skins that promote the removal of heat from the hot surface. This flow is then discharged from a slot at the rear of the tile to form the coolant film. This paper characterises the flow passing through a tile and, in particular, the coolant film that is formed along the tile surface. Data is presented for both a standard tile geometry and one in which the coolant film is enhanced by effusion cooling. A large-scale facility incorporating a 10 times full size cooling tile has been developed. The aerodynamic characteristics of the coolant film have been defined using pneumatic probes, hot wire anemometry and PIV instrumentation, while gas tracing is used to indicate mixing of the coolant film with the mainstream flow. For low mainstream turbulence the results show that the initial condition of the cooling film dominates the subsequent development and mixing of the film along the tile length. Relative to this configuration, high mainstream turbulence levels with large turbulent scales were introduced by placing a cylinder upstream of the tile. The turbulent mainstream flow quickly penetrates the coolant film and a more rapid break up of the coolant film is observed. This includes an almost linear increase in thickness of the coolant film together with a linear reduction in wall film effectiveness along the tile length. Relative to this conventional tile the use of effusion cooling was shown to restore the film effectiveness along the rear of the tile. In addition to the time averaged characteristics the time dependent behaviour of the coolant film was also investigated. In particular, unsteadiness associated with vortex shedding within the mainstream flow was observed within the coolant film and adjacent to the tile surface.

Aerodynamic characteristics of a large-scale, twin tilt-nacelle V/STOL model

1981 ◽  
Author(s):  
M. FALARSKI ◽  
M. DUDLEY ◽  
W. BUCHMANN ◽  
A. PISANO
Keyword(s):  
Large Scale ◽  
Aerodynamic Characteristics

scholarly journals Large-Scale and Deep-Seated Gravitational Slope Deformations on Mars: A Review

Geosciences ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 174
Author(s):  
Marco Emanuele Discenza ◽  
Carlo Esposito ◽  
Goro Komatsu ◽  
Enrico Miccadei
Keyword(s):  
Large Scale ◽  
High Quality ◽  
Surface Data ◽  
Geomorphological Processes ◽  
Gravitational Processes ◽  
Quality Surface ◽  
High Quality Surface ◽  
Mars Missions

The availability of high-quality surface data acquired by recent Mars missions and the development of increasingly accurate methods for analysis have made it possible to identify, describe, and analyze many geological and geomorphological processes previously unknown or unstudied on Mars. Among these, the slow and large-scale slope deformational phenomena, generally known as Deep-Seated Gravitational Slope Deformations (DSGSDs), are of particular interest. Since the early 2000s, several studies were conducted in order to identify and analyze Martian large-scale gravitational processes. Similar to what happens on Earth, these phenomena apparently occur in diverse morpho-structural conditions on Mars. Nevertheless, the difficulty of directly studying geological, structural, and geomorphological characteristics of the planet makes the analysis of these phenomena particularly complex, leaving numerous questions to be answered. This paper reports a synthesis of all the known studies conducted on large-scale deformational processes on Mars to date, in order to provide a complete and exhaustive picture of the phenomena. After the synthesis of the literature studies, the specific characteristics of the phenomena are analyzed, and the remaining main open issued are described.

The Effect of Reynolds Number on the Aerodynamic Performance of Micro Radial Flow Fans

2005 ◽  
Author(s):  
K. Hanly ◽  
R. Grimes ◽  
E. Walsh ◽  
B. Rodgers ◽  
J. Punch
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Radial Flow ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Fundamental Change ◽  
Geometric Similarity ◽  
Flow Phenomena ◽  
Conventional Cooling ◽  
High Degree

Elevated heat dissipation and simultaneous reductions in package sizes are well documented for a range of electronics systems. The problem is heightened in portable systems where the space available for the implementation of an active cooling methodology is limited and conventional cooling products are too large. Using micro scale radial flow fans is a potential solution. However, little is known about the aerodynamic effects of reducing the fan scale and therefore Reynolds number to the extent required for typical portable electronic applications. This paper investigates this issue, by quantifying the reduction in aerodynamic performance which accompanies the reductions in scale. To do this, geometrically similar radial flow fans were fabricated with diameters ranging from 80 to 10mm. Measurements of the rotors’ geometries are presented, showing a high degree of geometric similarity between the fans. The aerodynamic performance of each of the fans was measured. Non-dimensional performance of each of the larger fans were almost identical, while the performance plot of the smallest fan differed significantly from the others. The paper tentatively concludes that a fundamental change in flow phenomena has emerged in the smallest scale fan which has altered its aerodynamic characteristics.

scholarly journals Airborne Electromagnetic and Radiometric Peat Thickness Mapping of a Bog in Northwest Germany (Ahlen-Falkenberger Moor)

2020 ◽  
Vol 12 (2) ◽  
pp. 203 ◽  
Author(s):  
Bernhard Siemon ◽  
Malte Ibs-von Seht ◽  
Stefan Frank
Keyword(s):  
Large Scale ◽  
Spatial Information ◽  
Borehole Data ◽  
Northwest Germany ◽  
Surface Data ◽  
Airborne Electromagnetic ◽  
Lateral Extent ◽  
Elevated Surface ◽  
Airborne Electromagnetic Data ◽  
Gradient Approach

Knowledge on peat volumes is essential to estimate carbon stocks accurately and to facilitate appropriate peatland management. This study used airborne electromagnetic and radiometric data to estimate the volume of a bog. Airborne methods provide an alternative to ground-based methods, which are labor intensive and unfeasible to capture large-scale (>10 km2) spatial information. An airborne geophysical survey conducted in 2004 covered large parts of the Ahlen-Falkenberger Moor, an Atlantic peat bog (39 km2) close to the German North Sea coast. The lateral extent of the bog was derived from low radiometric and elevated surface data. The vertical extent resulted from smooth resistivity models derived from 1D inversion of airborne electromagnetic data, in combination with a steepest gradient approach, which indicated the base of the less resistive peat. Relative peat thicknesses were also derived from decreasing radiation over peatlands. The scaling factor (µa = 0.28 m−1) required to transform the exposure rates (negative log-values) to thicknesses was calculated using the electromagnetic results as reference. The mean difference of combined airborne results and peat thicknesses of about 100 boreholes is very small (0.0 ± 1.1 m). Although locally some (5%) deviations (>2 m) from the borehole results do occur, the approach presented here enables fast peat volume mapping of large areas without an imperative necessity of borehole data.

Analysis of Flutter-Induced Limit Cycle Oscillations in Gas-Turbine Structures With Friction, Gap, and Other Nonlinear Contact Interfaces

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
E. P. Petrov
Keyword(s):  
Gas Turbine ◽  
Limit Cycle ◽  
Large Scale ◽  
Direct Calculation ◽  
Aerodynamic Characteristics ◽  
Frequency Domain Method ◽  
Nonlinear Contact ◽  
Limit Cycle Flutter ◽  
Interface Parameters ◽  
First Time

A frequency-domain method has been developed to predict and comprehensively analyze the limit-cycle flutter-induced vibrations in bladed disks and other structures with nonlinear contact interfaces. The method allows, for the first time, direct calculation of the limit-cycle amplitudes and frequencies as functions of contact interface parameters and aerodynamic characteristics using realistic large-scale finite element models of structures. The effects of the parameters of nonlinear contact interfaces on limit-cycle amplitudes and frequencies have been explored for major types of nonlinearities occurring in gas-turbine structures. New mechanisms of limiting the flutter-induced vibrations have been revealed and explained.

Investigation of Wedge Probe Wall Proximity Effects: Part 2—Numerical and Analytical Modeling

1997 ◽  
Vol 119 (3) ◽  
pp. 605-611 ◽  
Author(s):  
P. D. Smout ◽  
P. C. Ivey
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Outer Wall ◽  
Aerodynamic Characteristics ◽  
Proximity Effects ◽  
Wake Flow ◽  
Scale Model ◽  
Flow Structures ◽  
Flow Features ◽  
Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large-scale model probes were tested to understand the mechanisms responsible for this effect, by which free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified that control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

Aerodynamic characteristics of a large-scale, twin tilt-nacelle V/STOL model

1982 ◽  
Vol 19 (8) ◽  
pp. 627-633
Author(s):  
Michael D. Falarski ◽  
Michael R. Dudley ◽  
W. Buchmann ◽  
A. Pisano
Keyword(s):  
Large Scale ◽  
Aerodynamic Characteristics

scholarly journals A Case Study of Subtropical Frontogenesis during a Blocking Event

2007 ◽  
Vol 135 (7) ◽  
pp. 2588-2609 ◽  
Author(s):  
George Tai-Jen Chen ◽  
Chung-Chieh Wang ◽  
An-Hsiang Wang
Keyword(s):  
Large Scale ◽  
Frontal Zone ◽  
Southern China ◽  
Sensible Heat Flux ◽  
Northern China ◽  
Sensible Heat ◽  
Surface Data ◽  
Sea Area ◽  
Blocking Event

Abstract During 8–14 June 2000, a 500-hPa blocking event occurred over Mongolia and northern China (near 45°N, 108°E), which was the only case over this region in June since 1981. As the block developed, the initially weak low-level mei-yu front over southern China evolved into a system with strong baroclinity and subsequently moved south. The frontal passage over Taiwan caused temperatures to drop by 10°C, the largest in June over two decades. Using gridded analyses, manually analyzed weather maps, and satellite and surface data, the present study investigates the evolution of this mei-yu front under the influence of the block. The 925-hPa frontogenetical function is computed and effects of different processes are discussed. As the blocking event developed, concurrent ridge–trough amplification in the lower–midtroposphere produced a reversed thermal pattern. The lower-tropospheric high moved southward, and large-scale confluence and deformation were enhanced between the northerly flow and the prefrontal southwesterly flow. The location of the block, to the west-southwest of the Okhotsk Sea area, allowed it to affect the front over southern China and caused it to penetrate inside 20°N, unusual for the month of June. The distribution of the frontogenetical function indicated that the mei-yu frontogenesis and the maintenance of the front were attributed to both deformation and convergence. These two processes together counteracted the strong frontolysis along the frontal zone from diabatic effects, caused by evaporative cooling of frontal precipitation on the warm side and stronger sensible heat transfer (and daytime heating over less cloudy areas) on the cold side of the front. When deformation, convergence, and diabatic effects were all combined, the net total frontogenesis peaked slightly ahead of the frontal zone, thus contributing to the southward propagation of the front in addition to the advection by postfrontal cold air in the present case. When the front moved into the South China Sea, the cross-frontal thermal gradient diminished rapidly, mainly due to the frontolytic effect from sensible heat flux over warm waters.

Investigation of Wedge Probe Wall Proximity Effects: Part 2 — Numerical and Analytical Modelling

1996 ◽  
Author(s):  
Peter D. Smout ◽  
Paul C. Ivey
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Outer Wall ◽  
Aerodynamic Characteristics ◽  
Proximity Effects ◽  
Wake Flow ◽  
Scale Model ◽  
Flow Structures ◽  
Flow Features ◽  
Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large scale model probes were tested to understand the mechanisms responsible for this effect, by which free stream pressure near the outer wall of a turbomachine may be over indicated by upto 20% dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified which control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

Boundary layers and wind in cylindrical Rayleigh–Bénard cells

2012 ◽  
Vol 697 ◽  
pp. 336-366 ◽  
Author(s):  
Sebastian Wagner ◽  
Olga Shishkina ◽  
Claus Wagner
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Large Scale ◽  
Linear Increase ◽  
Two Dimensions ◽  
Local Analysis ◽  
Bottom Plate ◽  
Special Focus ◽  
Layer Region ◽  
Rayleigh Benard

AbstractWe analyse the wind and boundary layer properties of turbulent Rayleigh–Bénard convection in a cylindrical container with aspect ratio one for Prandtl number $\mathit{Pr}= 0. 786$ and Rayleigh numbers ($\mathit{Ra}$) up to $1{0}^{9} $ by means of highly resolved direct numerical simulations. We identify time periods in which the orientation of the large-scale circulation (LSC) is nearly constant in order to perform a statistical analysis of the LSC. The analysis is then reduced to two dimensions by considering only the plane of the LSC. Within this plane the LSC is treated as a wind with thermal and viscous boundary layers developing close to the horizontal plates. Special focus is on the spatial development of the wind magnitude and the boundary layer thicknesses along the bottom plate. A method for the local analysis of the instantaneous boundary layer thicknesses is introduced which shows a dramatically changing wind magnitude along the wind path. Furthermore a linear increase of the viscous and thermal boundary layer thickness along the wind direction is observed for all $\mathit{Ra}$ considered while their ratio is spatially constant but depends weakly on $\mathit{Ra}$. A possible explanation is a strong spatial variation of the wind magnitude and fluctuations in the boundary layer region.

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