An Experimental Investigation on the Overall Cooling Performances of Two Turbine End-Wall Structures

This paper presents an experimental investigation on the overall cooling performances of two endwall specimens, one is a simple film cooling, the other is a laminated structure with pin-fins and impingement holes, but has the same cover board of the simple film cooling endwall. The two specimens are made of stainless steel with a real size of a gas turbine endwall. The experiments were carried out in a large temperature ratio (TR) of mainstream to cooling air (TR = 2.47), which is close to real operation conditions of modern gas turbines. The surface temperatures were measured by an infrared thermal imaging system (ITIS) at three blowing ratios (BRs = 0.63, 1.02, 2.04). The overall effectiveness of the two specimens was analyzed and compared. Through the analysis and comparisons, some interesting phenomena are discovered: 1) In general, as like as the previous studies of endwall cooling, the laminated endwall specimen can provide a higher cooling effectiveness averaged over the entire area than the simple film cooling specimen; 2) However, if we want to get more exact designs, the combination of the two structures may be better. Because of at low BR = 0.63, the simple endwall specimen can locally demonstrate a better cooling effect in an elliptic region of the endwall; 3) At high BR = 2.04, the design strategy of the simple endwall specimen can also locally be used in a triangle region. The exact designs can not only increase overall cooling effect, but also reduce the weight of whole endwalls.

Precision of full polynomial response surface designs on models with missing coefficients

The precision of using full polynomial response surface designs on models with missing coefficients (reduced models) is studied using efficiency measures. The loss in D- and G-efficiency of constructed first-order exact designs is minimized for the model with missing interaction coefficient. However, higher losses in D- and G-efficiency are recorded when constructed second-order exact designs are used on the model with missing interaction coefficient with few exceptions showing preferences for using the designs on the reduced model. Lower condition numbers are observed for the designs under the first-order reduced models thus indicating that the N-point exact designs are closer to being orthogonal for the reduced model than for the full model. Perfect orthoganality is achieved at design sizes 4 and 8. In fact, N-point exact designs of multiples of N=4 show perfect orthoganality when defined either for the full or reduced first-order models. In comparison to a design with perfect orthoganality, the second-order designs are far from being orthogonal.

Alternative Second-Order N-Point Spherical Response Surface Methodology Design and Their Efficiencies

The equiradial designs are studied as alternative second-order N-point spherical Response Surface Methodology designs in two variables, for design radius ρ = 1.0. These designs are seen comparable with the standard second-order response surface methodology designs, namely the Central Composite Designs. The D-efficiencies of the equiradial designs are evaluated with respect to the spherical Central Composite Designs. Furthermore, D-efficiencies of the equiradial designs are evaluated with respect to the D-optimal exact designs defined on the design regions of the Circumscribed Central Composite Design, the Inscribed Central Composite Design and the Face-centered Central Composite Design. The D-efficiency values reveal that the alternative second-order N-point spherical equiradial designs are better than the Inscribed Central Composite Design though inferior to the Circumscribed Central Composite Design with efficiency values less than 50% in all cases studied. Also, D-efficiency values reveal that the alternative second-order N-point spherical equiradial designs are better than the N-point D-optimal exact designs defined on the design region supported by the design points of the Inscribed Central Composite Design. However, the N-point spherical equiradial designs are inferior to the N-point D-optimal exact designs defined on the design region supported by the design points of the Circumscribed Central Composite Design and those of the Face-centered Central Composite Design, with worse cases with respect to the design region of the Circumscribed Central Composite Design.