Coriolis Effects on the Flow Field Inside a Rotating Triangular Channel for Leading Edge Cooling

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Matteo Pascotto ◽  
Alessandro Armellini ◽  
Claudio Mucignat ◽  
Luca Casarsa
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Flow Structure ◽  
Cross Section ◽  
Working Conditions ◽  
Rotation Axis ◽  
Leading Edge ◽  
Channel Cross Section ◽  
Smooth Channel ◽  
Static Conditions

The flow field inside a rotating smooth radial channel with a triangular shaped cross section is investigated. Test conditions resemble those pertaining to the passages used for the internal cooling of the gas turbine blade's leading edge. Heat transfer data are also available from the literature on the same geometry and at comparable working conditions and have been profitably used for a combined aerothermal analysis. The model consists of a straight smooth channel with an equilateral triangle cross section. The rotation axis is aligned with one of the triangle bisectors. Two dimensional particle image velocimetry (PIV) and stereo-PIV were used in order to characterize the inlet flow (in static conditions) and the rotation-induced secondary flow in the channel cross section at Re = 20,000, Ro = 0.2 and Re = 10,000, Ro = 0.4. A wider range of working conditions (Re = 10,000–40,000, Ro = 0.2–0.6) was explored by means of Reynolds averaged Navier–Stokes (RANS) simulations carefully validated by the available PIV data. The turbulence was modeled by means of the shear stress transport (SST) model with a hybrid near-wall treatment. The results show that the rotation-induced flow structure is rather complicated and show relevant differences compared to the flow models that have been considered thus far. Indeed, the secondary flow turned out to be characterized by the presence of two or more vortex cells, depending on channel location and Ro number. No separation or reattachment of these structures is found on the channel walls but they have been observed at the channel apexes. The stream-wise velocity distribution shows a velocity peak close to the lower apex and the overall flow structure does not reach a steady configuration along the channel length. This evolution is fastened (in space) if the rotation number is increased while changes of the Re number have no effect. Finally, due to the understanding of the flow mechanisms associated with rotation, it was possible to provide a precise justification of the channel thermal behavior.

Flow Visualization by Means of Contactless Inductive Flow Tomography in the Presence of a Magnetic Brake

2015 ◽  
Vol 15 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Matthias Ratajczak ◽  
Thomas Wondrak ◽  
Klaus Timmel ◽  
Frank Stefani ◽  
Sven Eckert
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Flow Field ◽  
Continuous Casting ◽  
Flow Structure ◽  
Cross Section ◽  
Two Dimensional ◽  
Slab Casting ◽  
Two Dimensional Flow

AbstractIn continuous casting DC magnetic fields perpendicular to the wide faces of the mold are used to control the flow in the mold. Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable. The contactless inductive flow tomography (CIFT) allows to reconstruct the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow-induced magnetic fields outside the mold. For a physical model of a mold with a cross section of 140 mm×35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm×100 mm demonstrating the upward scalability of CIFT.

scholarly journals Aerothermal Investigations of Mixing Flow Phenomena in Case of Radially Inclined Ejection Holes at the Leading Edge

1999 ◽  
Author(s):  
Dieter E. Bohn ◽  
Karsten A. Kusterer
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Side ◽  
Blade Surface ◽  
Cooling Fluid ◽  
Flow Phenomena ◽  
Vortex Systems

A leading edge cooling configuration is investigated numerically by application of a 3-D conjugate fluid flow and heat transfer solver, CHT-Flow. The code has been developed at the Institute of Steam and Gas Turbines, Aachen University of Technology. It works on the basis of an implicit finite volume method combined with a multi-block technique. The cooling configuration is an axial turbine blade cascade with leading edge ejection through two rows of cooling holes. The rows are located in the vicinity of the stagnation line, one row is on the suction side, the other row is on the pressure side. The cooling holes have a radial ejection angle of 45°. This configuration has been investigated experimentally by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The numerical domain includes the internal cooling fluid supply, the radially inclined holes and the complete external flow field of the turbine vane in a high resolution grid. Periodic boundary conditions have been used in the radial direction. Thus, end wall effects have been excluded. The numerical investigations focus on the aerothermal mixing process in the cooling jets and the impact on the temperature distribution on the blade surface. The radial ejection angles lead to a fully three dimensional and asymmetric jet flow field. Within a secondary flow analysis it can be shown that complex vortex systems are formed in the ejection holes and in the cooling fluid jets. The secondary flow fields include asymmetric kidney vortex systems with one dominating vortex on the back side of the jets. The numerical and experimental data show a good agreement concerning the vortex development. The phenomena on the suction side and the pressure side are principally the same. It can be found that the jets are barely touching the blade surface as the dominating vortex transports hot gas under the jets. Thus, the cooling efficiency is reduced.

New and improved channel cross section with piecewise linear or smooth sides

2011 ◽  
Vol 38 (6) ◽  
pp. 690-697 ◽  
Author(s):  
Said M. Easa
Keyword(s):  
Cross Section ◽  
Piecewise Linear ◽  
Unit Cost ◽  
Channel Cross Section ◽  
Smooth Curves ◽  
Rate Of Increase ◽  
Smooth Channel ◽  
Wide Range ◽  
Area And Perimeter ◽  
Side Section

This paper presents a new and improved channel cross section with m-segment linear sides and horizontal bottom (MSLS). For large m, the section sides become smooth curves, thus providing the designer with flexibility in using either piecewise linear or smooth channel sides with the same formulation. General simple formulas for the area and perimeter are presented for section sides with m linear segments. An optimization model, which implements the general formulas and minimizes the construction cost, is presented and applied using an example. For sections with piecewise linear sides, where the surface lining unit cost increases as the number of sides increases, the MSLS section was found to be more economical than a section with two-segment linear sides when the rate of increase in cost is not large. The smooth MSLS was found to be always more economical than the two-segment parabolic side section and the parabolic side section. The MSLS, which is more economical, yet simpler, than other section types is useful for a wide range of applications involving small and large channels.

Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions—Part I: High-Resolution Particle Image Velocimetry Measurements

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Ignacio Mayo ◽  
Gian Luca Gori ◽  
Aude Lahalle ◽  
Tony Arts
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Cross Section ◽  
Turbulence Intensity ◽  
Particle Image ◽  
Channel Cross Section ◽  
Recirculation Bubble ◽  
Rotation Numbers ◽  
Image Velocimetry ◽  
Static Conditions

The present work is part of a detailed aerothermal investigation in a model of a rotating internal cooling channel performed in a novel facility setup which allows test conditions at high rotation numbers (Ro). The test section is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with eight ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitch-to-height ratio is 10. In this first part of the paper, the flow over the wall region between the sixth and seventh ribs in the symmetry plane is investigated by means of two-dimensional particle image velocimetry (PIV). Tests were carried out at a Reynolds number (Re) of 15,000 in static and rotating conditions, with a maximum Ro of 0.77. Results are in good agreement with the data present in literature at the same Reynolds number and with rotation numbers of 0 (static conditions) and 0.38 in a channel with the same geometry as in the present work. When Ro is increased from 0.38 to 0.77, the main velocity and turbulence fields show important changes. At a rotation number of 0.77, although the extension of the recirculation bubble after the sixth rib on the trailing side does not vary significantly, it covers the full inter-rib area on the leading side in the streamwise direction. The turbulence intensity on the leading side shows a low value with respect to the static case but roughly at the same level as in the lower Ro case. On the trailing side, the maximum value of the turbulence intensity slightly decreases from Ro  = 0.38 to Ro  = 0.77, the wall shear layer is restabilized along the second half of the pitch due to the high rotation, and the secondary flows are redistributed causing spanwise vortex compression. The observed result is the rapid decay of turbulent fluctuations in the second half of the inter-rib area.

Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Ranjan Saha ◽  
Jens Fridh ◽  
Torsten Fransson
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Film Cooling ◽  
Guide Vane ◽  
Leading Edge ◽  
Field Measurements ◽  
Co2 Concentration ◽  
Horseshoe Vortex ◽  
Mainstream Flow ◽  
Nozzle Guide

An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes (NGVs) to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge (TE) can be used to visualize the mixing of the coolant flow with the mainstream. Flow field measurements are performed in the downstream plane with a five-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side (PS) of the vane TE where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge (LE) does not reach the PS endwall, potentially creating a local hotspot.

Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade

2012 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Ranjan Saha ◽  
Jens Fridh ◽  
Torsten Fransson
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Film Cooling ◽  
Guide Vane ◽  
Leading Edge ◽  
Field Measurements ◽  
Co2 Concentration ◽  
Pressure Side ◽  
Trailing Edge ◽  
Nozzle Guide

An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge can be used to visualize the mixing of the coolant flow with the mainstream. Flow field measurements are performed in the downstream plane with a 5-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side of the vane trailing edge where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge does not reach the pressure side endwall, potentially creating a local hotspot.

Flow and Heat Transfer in a Ribbed Channel With Complex Structure Characters

2020 ◽  
Author(s):  
Yu chao Liu ◽  
Tao Guo ◽  
Zong yu Han ◽  
Hui ren Zhu
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Cross Section ◽  
Heat Transfer Performance ◽  
Channel Structure ◽  
Channel Cross Section ◽  
Internal Cooling ◽  
Transfer Performance ◽  
The Real ◽  
The Asymmetry

Abstract The ribbed channels are widely used in the internal cooling structure of turbine blade. Many investigations on this kind of channel were carried on in the channel with rectangle cross section and straight inlet. Nevertheless, in mid-chord region of a real blade, the channel characters are more complex and may affect the heat transfer performance in the channel. The heat transfer investigation in a channel with 3 legs was conducted by numerical simulation. Aim to get the influence of channel structure feature to heat transfer and flow characteristics, the channel was simplified from a real turbine internal cooling channel and main structure features were kept. In order to make the velocity in the first leg close to that in the real structure, the entrance is changed to the contraction entrance. The first leg of channel section is simplified as trapezoid. The legs are connected by 2 U-turns with bend angle for imitating the bend because of the airfoil in real blade. A supplement hole in the inlet of 3rd leg was kept as same as the real channel. Some coolant was supplement to the 3rd leg. Furthermore, 3 rib arrangements (45° ribs, 135° ribs and V-shape ribs) were studied for presenting the interaction between rib arrangement and channel structure character. The results show that: 1) the shape of the inlet cross section has a continuous effect on the irregular velocity in the first leg, the velocity pattern cause by inlet may interact with the secondary flow caused by ribs and lead to different heat transfer distribution compared with the channel with uniform inlet velocity and rectangle cross section. The heat transfer performance in channel with 135° ribs is different from that in the channel with 45° ribs. 2) In the second leg, the secondary flow is generated at the inlet by the bending structure of the leg connection. This secondary flow may suppress or promote the secondary flow produced by ribs. The composed secondary flow leads to the asymmetry flow pattern in the channel and causes the different heat transfer performance in two ribbed walls. 3) In the third leg, the interaction between the flow coming from the supplement hole, the secondary flow caused by ribs and the flow coming from upstream form the complex flow structure. The different rib angle affects the position of high-velocity area. 4) The heat transfer distribution is asymmetry because of the asymmetry channel cross section and bending connecting of legs. The heat transfer performance is different between that in channel with 45° ribs and 135° ribs, whereas is same in the channel with rectangle cross section. Generally speaking, the heat transfer performance is best in the channel with V-shape ribs and is worst in the channel with 45° ribs.

Time-Space Evolution of Secondary Flow Structures in a Two-Stage Low-Speed Turbine

2006 ◽  
Author(s):  
Pierpaolo Puddu ◽  
Chiara Palomba ◽  
Franco Nurzia
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Flow Structure ◽  
Time Dependent ◽  
Flow Structures ◽  
Two Stage ◽  
Time Space ◽  
Secondary Flow Structure ◽  
Unsteady Effects ◽  
Turbine Model

The aim of this work is to highlight the unsteady effects related to wake-blade and blade rows interactions, but also the time-space evolution of secondary flow structures in a two-stage low-speed turbine model designed and constructed to perform unsteady measurements with different techniques [1]. In this case attention has been addressed to the analysis of the flow field in the first stage of the turbine model. Measurements are performed with aerodynamic probes downstream of the first stator and using a single slanted hot-wire anemometer downstream of the first rotor. Time-dependent relative flow field downstream of the first rotor (obtained from phase-locked averaging technique) have been reconstructed for different relative positions between stator and rotor blades. From these results the time-dependent secondary flow vectors have been obtained as well. The mean reference flow used to determine the secondary flow structure has been evaluated for each frame by mass-averaged technique. The evolution of the secondary flow structure due to the influence of the upstream and downstream stators on the first rotor has been investigated. The main unsteady effects put in evidence the variation of the intensity and spatial extension of the vortex flow structure.

Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions: Part II — Detailed LCT Measurements

2015 ◽  
Author(s):  
Ignacio Mayo ◽  
Aude Lahalle ◽  
Gian Luca Gori ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Flow Direction ◽  
Channel Cross Section ◽  
Wall Region ◽  
Static Case ◽  
Ribbed Channel ◽  
Static Conditions

The present two-part work deals with a detailed characterization of the flow field and heat transfer distribution in a model of a rotating ribbed channel performed in a novel setup which allows test conditions at high Rotation numbers (Ro). The tested model is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with 8 ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitch to height ratio is 10. In this second part of the study, the heat transfer distribution over the wall region between the 6th and 7th ribs is obtained by means of Liquid Crystal Thermography (LCT). Tests were firstly carried out at a Reynolds number of 15000 and a maximum Ro of 1.00 to evaluate the evolution of the heat transfer with increasing rotation. On the trailing side, the overall Nusselt number increases with rotation until a limit value a 50% higher than in the static case, which is achieved after a value of the Rotation number of about 0.3. On the leading side, the overall Nusselt number decreases with increasing rotation speed to reach a minimum which is approximately 50% of the one found in static conditions. The velocity measurements at Re=15000 and Ro=0.77 provided in Part I of this paper are finally merged to provide a consistent explanation of the heat transfer distribution in this model. Moreover, heat transfer measurements were performed at Reynolds numbers of 30000 and 55000, showing approximately the same trend.

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