Time-resolved stereo PIV measurements of the horseshoe vortex system at multiple locations in a low-aspect-ratio pin–fin array

2015 ◽  
Vol 57 (1) ◽  
Author(s):  
Corey D. Anderson ◽  
Stephen P. Lynch
Keyword(s):  
Aspect Ratio ◽  
Horseshoe Vortex ◽  
Vortex System ◽  
Time Resolved ◽  
Piv Measurements ◽  
Pin Fin ◽  
Low Aspect Ratio ◽  
Pin Fin Array

scholarly journals Heat Transfer From Low Aspect Ratio Pin Fins

2007 ◽  
Author(s):  
Michael E. Lyall ◽  
Alan A. Thrift ◽  
Atul Kohli ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Gas Turbines ◽  
Channel Height ◽  
Internal Cooling ◽  
Number Range ◽  
Pin Fin ◽  
Heat Transfer Augmentation ◽  
Low Aspect Ratio ◽  
Pin Fins

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 to 30,000. Both pressure drop and spatially-resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Endwall Heat Transfer Measurements in a Staggered Pin Fin Array With an Adiabatic Pin

2007 ◽  
Author(s):  
Forrest E. Ames ◽  
Chad A. Nordquist ◽  
Lindsay A. Klennert
Keyword(s):  
Heat Transfer ◽  
Turbulent Transport ◽  
Infrared Camera ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Vortex System ◽  
Flow Acceleration ◽  
Pin Fin ◽  
Pin Fin Array

Full surface endwall heat transfer distributions have been acquired in a staggered pin fin array with the use of an infrared camera. Values are presented at Reynolds numbers of 3000, 10,000 and 30,000 based on pin diameter and average velocity through adjacent pins. Average endwall Nusselt numbers agree closely with archival values at each Reynolds number. Locally averaged heat transfer levels show a substantial increase from the inlet through the first few rows and finally a nearly streamwise periodic condition in the second half of the eight row geometry. Increasing levels of heat transfer in the inlet region can be attributed to the leading edge vortex system, flow acceleration around pins, and the generation of turbulence. Distributions of turbulence intensity and turbulent scale are shown to help document the turbulent transport conditions through the array. Detailed endwall Nusselt number distributions are presented and compared at the three Reynolds numbers for the first four and last four rows. These detailed heat transfer distributions highlight the influence of the horseshoe vortex system in the entrance region and the wake generated turbulence throughout the pin fin array. Local velocity and turbulence distributions are presented together with local Stanton number and skin friction coefficient data to examine the aggressive nature of the turbulent mixing.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Time Resolved ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Unsteady Heat Transfer Around Low Aspect Ratio Cylinders in an Array

2016 ◽  
Author(s):  
Shawn Siroka ◽  
Melissa Shallcross ◽  
Stephen Lynch
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Flux ◽  
Pin Fin ◽  
Low Aspect Ratio ◽  
Minimum Heat

Cylindrical pins, often called pin fins, are used to create turbulence and promote convective heat transfer within many devices, ranging from computer heat sinks to the trailing edge of jet engine turbine blades. Previous experiments have measured the time-averaged heat transfer over a single pin as well as the flow fields around the pin. However, in this study, focus is placed on the instantaneous heat flux around the centerline of a low aspect-ratio pin within an array. Time-mean and unsteady convective heat flux are measured around the circumference of an isothermal heated test pin via a microsensor located at the surface. The pin is positioned at various locations within a staggered array in a large-scale wind tunnel. Reynolds numbers from 3,000 to 50,000, based on pin diameter and maximum velocity between pins, are tested with a streamwise spacing of 1.73 diameters between rows, a spanwise spacing of 2 diameters, and a pin height of 1 diameter. The time-averaged and standard deviation of convective heat flux around the pin is higher over most of the pin surface for pins in downstream row positions of an array relative to the first row pin, except in the wake which has similar levels for all rows. For a given pin position in the array, as the Reynolds number increases, the point of minimum heat transfer moves circumferentially upstream on the pin fin, corresponding to earlier transition of the pin boundary layer. Also, for a given Reynolds number, the minimum heat transfer point on the pin circumference moves upstream for pins further into the array, due to the high turbulence levels within the array which cause early transition. For a single pin row with no downstream pins, heat transfer fluctuations are very high on the backside of the pin due to the significant unsteadiness in the pin wake, but heat transfer fluctuations are suppressed for a pin with downstream rows due to the confining effects of the close spacing. The results from this study can be used to design pin-fin arrays that take advantage of unsteadiness and increase overall convective heat transfer for various industry components.

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