A. A. Thrift

Heat Transfer From 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 and 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.

Effects of an Axisymmetric Contoured Endwall on a Nozzle Guide Vane: Convective Heat Transfer Measurements

Heat transfer is a critical factor in the durability of gas turbine components, particularly in the first vane. An axisymmetric contour is sometimes used to contract the cross sectional area from the combustor to the first stage vane in the turbine. Such contouring can lead to significant changes in the endwall flows, thereby altering the heat transfer. This paper investigates the effect of axisymmetric contouring on the endwall heat transfer of a nozzle guide vane. Heat transfer measurements are performed on the endwalls of a planar and contoured passage whereby one endwall is modified with a linear slope in the case of the contoured passage. Included in this study is upstream leakage flow issuing from a slot normal to the inlet axis. Each of the endwalls within the contoured passage presents a unique flow field. For the contoured passage, the flat endwall is subject to an increased acceleration through the area contraction, while the contoured endwall includes both increased acceleration and a turning of streamlines due to the slope. Results indicate heat transfer is reduced on both endwalls of the contoured passage relative to the planar passage. In the case of all endwalls, increasing leakage mass flow rate leads to an increase in heat transfer near the suction side of the vane leading edge. DOI: 10.1115/1.4002966

Effects of an Axisymmetric Contoured Endwall on a Nozzle Guide Vane: Adiabatic Effectiveness Measurements

Gas turbine designs seek improved performance by modifying the endwalls of nozzle guide vanes in the engine hot section. Within the nozzle guide vanes these modifications can be in the form of an axisymmetric contour as the area contracts from the combustor to the turbine. This paper investigates the effect of axisymmetric endwall contouring on the cooling performance of a film cooled endwall. Adiabatic effectiveness measurements were performed in a planar passage for comparison to a contoured passage whereby the exit Reynolds numbers was matched. For the contoured passage, measurements were performed on both the flat endwall and on the contoured endwall. Fully expanded film cooling holes were distributed on the endwall surface preceded by a twodimensional slot normal to the inlet axis. Results indicated that the coolant coverage from the upstream leakage slot was spread over a larger area of the contoured endwall in comparison to the flat endwall of the planar passage. Film cooling effectiveness on the flat endwall of the contoured passage showed minimal differences relative to the planar passage results. The contracting endwall of the contoured passage, however, showed a significant reduction with average film cooling effectiveness levels approximately 40% lower than the planar passage at low film cooling flow rates. In the case of all endwalls, increasing leakage and film cooling mass flow rates led to an increase in cooling effectiveness and coolant coverage. NOMENCLATURE Ah area of film cooling hole C true vane chord CD discharge coefficient Cp pressure coefficient, (Ps – Ps,in)/0.5ρU 2

A Methodology to Measure Aerodynamic Forces on Cylinders in Channel Flow

While the measurement of drag and lift forces on a body in external flow is common practice, the same cannot be said for aerodynamic forces on bodies in internal flows. The inherent difficulty in making force measurements on a body in an internal channel flow is decoupling the body from the bounding walls. The methodology presented in this paper uses a technique to overcome this constraint to accurately measure two components of force on a single cylinder within a single row array, with an aspect ratio (height-to-diameter ratio) of 1. Experiments were conducted with air over a range of Reynolds numbers between 7500 and 35,000 and for three different spanwise pin spacings. Experimental results indicated an increase in cylinder drag with a reduction in spanwise pin spacing. The gas turbine and electronics industries use cylinders or pin fins in internal flow channels to increase heat transfer augmentation through high turbulence and increased surface area. The flow fields in these obstructed channels are difficult to predict, so these measurements can be used to directly compare with predicted drag and lift forces.