Ignacio Mayo

Two-Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with eight ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10%. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state liquid crystal thermography (LCT) was employed to quantify a detailed 2D distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the sixth and eighth rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15,000, 20,000, 30,000, and 40,000. The maximum rotation number values were ranging between 0.12 (Re = 40,000) and 0.30 (Re = 15,000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case, the secondary flows are responsible for high heat transfer gradients on the investigated area.

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

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 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 second part of the study, the heat transfer distribution over the wall region between the sixth and seventh ribs is obtained by means of liquid crystal thermography (LCT). Tests were first carried out at a Reynolds number of 15,000 and a maximum Ro of 1.00 to evaluate the evolution of the heat transfer with increasing rotation. On the trailing side (TS), the overall Nusselt number increases with rotation until a limit value of 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 (LS), 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 = 15,000 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 30,000 and 55,000, showing approximately the same trend.

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

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.Copyright

Spatially Resolved Heat Transfer Coefficient in a Rib-Roughened Channel Under Coriolis Effects

Heat transfer in a magnified rotating ribbed channel is studied by means of liquid crystal thermometry. The test section consists of four Plexiglas walls, forming a rectangular cross section, mounted on a large rotating disk together with the complete necessary measurement chain. The investigated wall is equipped with ribs perpendicular to the main flow direction, it is heated in such a way to achieve a uniform heat flux boundary condition. Facing the need of two-dimensional experimental heat transfer data, tets were carried out in order to quantify the convective heat transfer distribution on the wall between two consecutive ribs under rotating conditions. Different Rotation numbers (0, 0.06, 0.11 and 0.17) were tested at a Reynolds number of 15,000. For the selected heat flux and rotation rates, and based on previous aerodynamic and thermal investigations presented in open literature, no effect of buoyancy is expected, while the Coriolis forces play an important role in the determination of heat transfer. The rotating cases were performed in both senses of rotation in order to allow the studied wall to act as both a trailing and a leading side. At the highest Rotation number, the results confirm that heat transfer is enhanced up to 17% along the trailing side compared with the non-rotating case. This is due to the secondary flows and shear layer instability instigated by the Coriolis forces. On the other hand, heat transfer on the leading side is reduced up to 19% at the highest rotation number; this is caused by the stabilization of the shear layer and the contribution of the secondary flows.Copyright

Heat Transfer Analysis Of A Rotating Ribbed Channel By Means Of Large Eddy Simulations

The present work studies the three-dimensional flow field and heat transfer in a model of an internal cooling channel in rotation by means of Large Eddy Simulations (LES). The selected geometry corresponds to a section of an experimental facility documented in the open literature. The channel presents a low aspect ratio cross section, one ribbed wall and square ribs placed perpendicularly to the main flow direction. In order to reduce the computational cost, the length of the computational domain is equal to the rib pitch of the laboratory model, whereas periodic boundary conditions are provided at the inlet and outlet of the domain. The simulations are carried out under the same conditions as in the experiments, namely at a Reynolds number equal to 15,000 and a Rotation number equal to 0.3. The first objective of this work is to provide the three dimensional flow field that experiments were not able to retrieve, and to discuss its impact on the wall heat transfer. Moreover, the dimensionless mean temperature fields in static and rotating conditions are introduced. Secondly, this work aims to study the suitability of an open source Computational Fluid Dynamics (CFD) solver to investigate the heat transfer phenomena in turbine internal cooling. With the selected LES turbulence model and boundary conditions, the present simulations provide a good agreement with the detailed experimental data.

Two Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different Rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with 8 ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10 per cent. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state Liquid Crystal Thermography was employed to quantify a detailed two dimensional distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the 6th and 8th rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15000, 20000, 30000 and 40000. The maximum Rotation number values were ranging between 0.12 (Re = 40000) and 0.30 (Re = 15000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the Rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case the secondary flows are responsible for high heat transfer gradients on the investigated area.Copyright