GB677835A - Improvements relating to rotary compressors - Google Patents

Abstract

677,835. Centrifugal and axial-flow compressors; gas turbine plant. POWER JETS, (RESEARCH & DEVELOPMENT), Ltd. March 13, 1950 [March 1, 1949; March 14, 1949], Nos. 2792/49, and 6986/49. Classes 110(i) and 110(iii) Pre-whirl is imparted to the gas in the annular intake passage of a centrifugal compressor by means of a bladed rotor which is driven at a substantially lower rotational speed than the centrifugal impeller, and is arranged with its blading sweeping a duct area substantially greater than that at the impeller entry. An air compressor forming part of a jet propulsion plant comprises a centrifugal impeller 1, Fig. 1, driven by a gas turbine (not shown) and connected by gearing 5 to a pre-whirl rotor 3 so that the latter is rotated in the same direction but at say, 1/3 of the rotational speed of the impeller 1. Desirably, the mean diameter of the pre-whirl blading 4 is, as shown, greater than that of the impeller eye, and is at least as great as the external diameter of'the impeller eye. The blading is twisted to impart, either alone or in conjunction with the boundary layer and viscosity effects of the intake passage 9, free vortex flow. The impeller vanes are twisted at 1a to give shockless entry. The inner wall 10 of the passage 9 is either mounted for free rotation or, as shown, is attached to the rotor 3. Struts 8 support the gearing 5. In a modification, Fig. 2, the air passes radially inwards through the blading 4, which is not twisted, the free vortex flow being imposed entirely by the curvature of the passage 9. The pre-whirl rotor may be driven by a separate turbine, which may be a low pressure turbine in series with the main turbine. The centrifugal impeller may be double-sided, and there may be more than one centrifugal stage. The prewhirl may be imparted by the last set of rotating blades of an axial-flow compressor. According to the first Provisional Specification, the compressor may be of the axialflow type, and the pre-whirl may be imparted by a combination of rotor and stator means. The pre-whirl rotor may rotate at 55 to 75 per cent of the impeller speed. According to the second Provisional Specification an annular slot may be provided in the outer wall of the intake passage to remove the boundary layer of air, together with suspended foreign particles. Specifications 579,780, and 587,509 are referred to.