Abstract
Heat transfer coefficients in the cooling cavities of turbine airfoils are greatly enhanced by the presence of discrete ribs on the cavity walls. These ribs introduce two heat transfer enhancing features: a significant increase in heat transfer coefficient by promoting turbulence and mixing, and an increase in heat transfer area. Considerable amount of data are reported in open literature for the heat transfer coefficients both on the rib surface and on the floor area between the ribs. Many airfoil cooling design software tools, however, require an overall average heat transfer coefficient on a rib-roughened wall. Dealing with a complex flow circuit in conjunction with180∘bends, numerous film holes, trailing-edge slots, tip bleeds, crossover impingement, and a conjugate heat transfer problem; these tools are not often able to handle the geometric details of the rib-roughened surfaces or local variations in heat transfer coefficient on a rib-roughened wall. On the other hand, assigning an overall area-weighted average heat transfer coefficient based on the rib and floor area and their corresponding heat transfer coefficients will have the inherent error of assuming a 100% fin efficiency for the ribs, that is, assuming that rib surface temperature is the same as the rib base temperature. Depending on the rib geometry, this error could produce an overestimation of up to 10% in the evaluated rib-roughened wall heat transfer coefficient. In this paper, a correction factor is developed that can be applied to the overall area-weighted average heat transfer coefficient that, when applied to the projected rib-roughened cooling cavity walls, the net heat removal from the airfoil is the same as that of the rib-roughened wall. To develop this correction factor, the experimental results of heat transfer coefficients on the rib and on the surface area between the ribs are combined with about 400 numerical conduction models to determine an overall equivalent heat transfer coefficient that can be used in airfoil cooling design software. A well-known group method of data handling (GMDH) scheme was then utilized to develop a correlation that encompasses most pertinent parameters including the rib geometry, rib fin efficiency, and the rib and floor heat transfer coefficients.
Highlights
Serpentine cooling channels within turbine airfoils are usually roughened with ribs
The equivalent heat transfer coefficient for a rib is defined as a heat transfer coefficient that, when applied on the base surface of the rib, will have the same thermal effects as that of the actual heat transfer coefficient applied on all rib exposed surfaces, that is, Aribhrib = Abasehequiv
The first step in this investigation was to determine which parameters were dominant in rib fin effects
Summary
Serpentine cooling channels within turbine airfoils are usually roughened with ribs. These ribs increase the level of mixing of the cooler core air with the warmer air close to the channel wall and restart the boundary layer after flow reattachment between ribs resulting in enhanced convective heat transfer coefficients. Experimental results, reported by many investigators, show as high as a five-fold enhancement in heat transfer coefficients of rib-roughened surfaces when compared with those of smooth (nonribbed) channels. International Journal of Rotating Machinery and Korotky [21], and Taslim and Lengkong [22, 23] and Webb et al [24] These studies show a considerable variation in heat transfer coefficient from the surface area between the ribs to the rib forward, top, and aft surfaces. The main objective of this investigation was to generate a correlation for the rib fin effect corrections that encompasses all common rib geometric parameters as well as the common hot and cold side flow conditions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
