214 Test blade

As mentioned in the previous section, two test blades are used: one is the pressure blade for static pressure distribution measurement on the blade surface, and the other is the naphthalene blade for mass transfer measurement. Both blades have the same high pressure blade profile.

The pressure blade is hollow and assembled from two aluminum sheets with the high pressure blade surface profile and two caps through pins and screws. It has a height of 19.69cm (7.75 inch). There are eight rows of pressure tap holes on the blade surfaces along the span, with the first row 2.2cm (0.875 inch) away from its top tip and each row consisting of 30 taps, of which 28 are used in this study. Prom the interior of the pressure blade, pressure taps are connected to an outside pressure manometer through small-diameter plastic tubes. The pressure blade is first used for balancing the flow through blade passages by comparing the static pressure on the central blade surface with that of neighboring blades and adjusting the bleeds and the tailboards accordingly. It is also used for measuring the effect of tip clearance on the static pressure distribution on the blade surface.

The naphthalene blade made essentially of solid aluminum, consists of a top hollow cap, a thin bottom cap, and a main part with a spanwise through hole (fig. 2.3), with an overall height of 18.7cm (7.375 inch). The through hole and the hollowed cap are designed for cooling air injection from the tip for future study. The side and top surfaces of the naphthalene blade are 2.5mm deeper than the rims at top and bottom of the blade. These small gaps leave room for liquid naphthalene to cast around the blade side and top surfaces by a mold. Some grooves are cut on those deeper surfaces for holding the naphthalene cast.

A specially designed mold and modified casting procedures are employed for the naphthalene blade with tip surface. To obtain a smooth naphthalene-cast profile, inner surfaces of the mold with the high pressure blade profile are well polished. The naphthalene tip surface can be obtained between the depressed tip of the blade and a flat spacer with a smooth inner surface and a thickness of 0.95cm (0.375 inch), which also makes the total height of the blade and the spacer compatible with that of the mold. Thus, during the casting, the liquid naphthalene will first go through a inlet funnel to the bottom of the mold, then go through a small hole in the spacer to form the tip naphthalene surface, and then fill the gap between the metal surfaces of the naphthalene blade and mold to obtain smooth naphthalene surfaces, and finally exit from the top air vent holes. It is found that the temperature of the mold may have some effects on the smoothness of the casting since the mold temperature is not uniform during the solidification process.

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