Design of Combustor Cooling Slots for High Film Effectiveness: Part II—Film Initial Region

Abstract

A heuristically based geometric grouping has been used to relate the geometry of practical film cooling slots of gas turbine engine combustors to the circumferential uniformity of axial velocity in the film and the average film effectiveness. To be satisfactory, the cooling performance of a slot has been shown to require a low value of this group. A study of film development has been extended to the initial region of the film where cooling performance is at its maximum. It is demonstrated that such a region exists for both practical slots and idealized two-dimensional slots, but that the character of the initial region flow is completely different for practical slots and cannot be described by the same methods as can be used for two-dimensional slots.

Film Cooling Effectiveness Downstream of Trailing Edge Slots Including Cutback Surface Protuberances

“…Their data for MIX N = 0.04 and H lip /H slot = 0.4, the closest available to the current study, is plotted in Figure 11, showing a maximum x p /H of 6.2 for M = 1.05. When compared with the Sturgess and Pfeifer [8] data, x p /H is greater for all M, which may be due to the lower MIX N . The current study does demonstrate the non-linear relationship between M and x p /H, but there is insufficient data for a detailed comparison and the range of M in the current study did not show a peak value in x p /H.…”

“…Mukherjee [6] performed a literature survey to form a number of correlations for predicting film effectiveness and the length of the initial "potential core" region of unity effectiveness. Sturgess [7] and Sturgess and Pfeifer [8] investigated the film cooling of practical combustor slots. They formed a geometric parameter, MIX N , for characterising practical combustor slot geometries and reported the relationship between potential core length, blowing ratio, and MIX N .…”

“…Sturgess and Pfeifer [8] found that the potential core length to slot height ratio x p /H, increased with M to a peak value before reducing to a plateau value at very high M. x p /H was also found to increase with a reduction in the MIX N parameter (where MIX N = 0 corresponds to a clean slot with realistically thick lip) and H lip /H slot for the same M. No relationship between the optimum M with the largest x p /H and MIX N or H lip /H slot was found. The MIX N parameter is specific to combustor slot geometries, so not all the terms have a direct equivalent in a trailing edge slot.…”

Experimental investigation on heat transfer characteristics of film cooling using parallel-inlet holes

“…As for the third region, convective coefficient is decreased along flow direction. Sturgess [18,19] studied the influence of blowing ratio and geometrical parameters of one-row film hole on the cooling effectiveness of cooled plate. They found that the geometrical parameters have a great influence on the cooling effectiveness of film cooling and the cooling effectiveness is decreased with increasing of blowing ratio.…”

Improvement of film cooling effectiveness with a small downstream block body

“…Na and Shih [11] proposed placing a ramp with a backward step upstream of the film cooling holes. Sturgess [12,13] studied the influence of the blowing ratio and geometrical parameters of a one-row film hole on cooling effectiveness. Goldstein et al [14], Schmidt and Bogard [15], and Schmidt et al [16] studied the effects of surface roughness on adiabatic effectiveness using a flat plate and saw little degradation in the adiabatic effectiveness.…”