Aerodynamic Force and Pressure Loss Measurements on Low Aspect Ratio Pin Fin Arrays
The desire to achieve higher heat transfer augmentation for turbine blades is fueled by the increased power output and efficiency that is achievable with high turbine inlet temperatures. The use of internal cooling channels fitted with pin fin arrays serves as one method of accomplishing this goal. Consequently, the addition of pin fin arrays comes at the expense of increased pressure drop. Therefore the pin fin geometry must be judiciously chosen to achieve the required heat transfer rate while minimizing the associated pressure drop.
This project culminates in the measurement of both pin fin force and array pressure drop as they related to changes in the array geometry. Specifically, the effects of Reynolds number, spanwise pin spacing, streamwise pin spacing, pin aspect ratio, and flow incidence angle. Direct two-component force measurement is achieved with a cantilever beam force sensor that uses highly sensitive piezoresistive strain gauges, relating the strain at the base of the beam to the applied force. With proper characterization, forces as small as one-tenth the weight of a paper clip are successfully measured. Additionally, array pressure drop measurements are achieved using static pressure taps.
Experiments were conducted over a range of Reynolds numbers between 7,500 and 35,000. Changes in the spanwise pin spacing were shown to substantially alter the pin fin drag and array pressure drop, while changes in the streamwise pin spacing were less influential. The experimental results also showed a dramatic reduction in the pin fin drag and array pressure drop for an inline flow incidence angle. Finally, changes in the pin aspect ratio were shown to have little effect on the array pressure drop.