The Design of Aspirated Stators for Compressor Bleed

Abstract Gas turbine operation requires air to be extracted from the primary compressor flow path for a variety of purposes, including turbine cooling and off-design stage matching. This “bleed air” is typically extracted through the compressor casing using either: a continuous circumferential slot; or discrete holes, each with a diameter on the order of a blade pitch. In this article, the benefits of extracting air through an array of holes on the stator blade suction surface, each with a diameter on the order of 1% of the blade chord, are identified. Such blades are referred to as aspirated compressor blades. Using a combined experimental and computational approach, two findings are presented. First, the operating range of the aspirated compressor blade is widened through the control of corner separations. The aspiration reduces the streamline curvature of the surface limiting streamlines, inhibiting corner separation formation. This control is sensitive to air removal through aspiration holes close to the endwall where the separation is expected to occur, with increased air extraction in this region further extending the stator operating range. The second finding is that the loss of the integrated compressor passage and bleed system can be reduced by extracting air via a combined circumferential bleed slot and aspirated compressor blade approach. This article shows that using aspirated compressor blades can increase the operating range of a stator by 1.8 deg in experimental measurements, and, in simulations, increase the adiabatic efficiency of a three-stage representative industrial gas turbine compressor by 3 percentage points.