HEAT TRANSFER AND FRICTION FACTOR AUGMENTATION IN RIB TURBULATED FLOW

Open Access
Author:
Neely, Gaelyn L
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 17, 2009
Committee Members:
  • Karen Ann Thole, Thesis Advisor
Keywords:
  • heat transfer
  • friction factor
  • internal flow
  • ribs
Abstract:
Current gas turbine airfoils must survive in an environment where operating conditions are approaching extreme levels. Increasing the temperature of the combustion gases entering the turbine improves engine efficiency and power output; consequently, the turbine inlet temperatures have reached levels exceeding the melting point of the blade materials. Internal cooling of the turbine blades is vital to maintaining turbine blade longevity and durability. Rib-roughened channels in the blade core are commonly used to increase turbulence and secondary flows that aid the transport of energy. In addition, the ribs increase the convective heat transfer surface area. Past research has focused on two ribbed wall configurations, and worked to identify the most favorable rib design that will produce maximum heat transfer with minimal pressure loss. This paper presents an analysis of various rib configurations for a one ribbed wall configuration, by comparing the effect of pitch, aspect ratio, and rib orientation on both heat transfer and friction augmentation. Heat transfer measurements were made using infared camera thermography in the fully developed region of the channel. Additionally, the effect of total wetted area versus planform area was investigated. Experimental measurements were taken in a closed-loop recirculating channel with a parallel-plate channel test section. The channel had varying aspect ratios of 2.86 or 5 with a constant blockage ratio of 0.2. All ribs were rounded, discontinuous V-shape, at 45° to the flow with pitch-to-rib height ratios of 5 or 10. Results indicate heat transfer augmentation was higher with a pitch-to-rib height ratio of 5 compared to 10. Similarly, the pitch-to-rib height ratio of 5 caused higher friction factor augmentation. The results also indicate aspect ratio did not affect the ribbed side heat transfer augmentation; however, the 2.86:1 aspect ratio cases had higher augmentation on the unribbed side compared to the 5:1 case. An increase in aspect ratio caused an increase in friction factor augmentation; thus the 5:1 aspect ratio case had the highest friction factor augmentation.