Publications in turbomachinery aerodynamics and related fields

2 vols.; For the book related to this thesis titled 'Cascade Aerodynamics' please apply direct to issuing universityAvailable from British Library Document Supply Centre- DSC:DX77221 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

The relationship between energy separation and base drag in turbine blade wakes

During annular cascade testing of a highly-loaded turbine stage of aggressive design, the nozzle blading experienced a redistribution of the downstream total temperature field. In this ostensibly adiabatic arrangement, the central regions of the vane wakes exhibited a significant decrease in total temperature and their edges showed an unexpected increase. To resolve these anomalous results and obtain detailed information over the Mach number range, the mid-span section of the nozzle was tested in a large scale transonic planar cascade. At high subsonic speeds, vortex shedding created energy redistribution in the wake. This was measured using an 80 kHz bandwidth temperature probe, making it possible to investigate wake total temperature fluctuations in addition to fluctuations in total pressure, and hence entropy. 'Hot spots' of increased total temperature were found to be located at the edge of the wake and 'cold spots' of decreased total temperature were located close to the wake center line. The results from the turbine cascade were consistent with the phenomenon of energy separation behind bluff bodies. High base pressure losses were observed and were also related to the vortex shedding. The blade had a thick trailing edge and the high base pressure loss condition coincided with the peak of energy separation in the wake. The analysis indicates that in the subsonic speed range the phenomena of energy separation and of base pressure deficit are inextricably linked to, and are caused by, vortex shedding. A strategy for minimizing the related adverse impacts on performance is outlined. Copyright \ua9 2013 by ASME.Peer reviewed: YesNRC publication: Ye

The role of streamwise vorticity in flows over turbomachine blade suction surfaces

Streamwise streaks and vortices are frequently encountered in low Reynolds number flows over blading. Observations have shown that, in addition to flows over concave pressure surfaces, convex suction surfaces are also influenced by streamwise vortices. These observations are based on surface flow visualization studies and computational work with highly resolved Large Eddy Simulation. Fine scale organized streaks exist in the laminar regions of turbine and compressor blading and are predictable. For a turbine blade with a blunt leading edge, at Reynolds numbers typical of aircraft cruise conditions, the streamwise vorticity may persist, on a time-average basis, to influence the entire suction surface. Time resolution is required to capture the flow complexity that is fundamental for an understanding of the physical behavior of the laminar boundary layer and its separation and transition. Progress has been made in modeling and predicting transition and laminar separation and the new findings of interesting vortical behavior need to be incorporated. In the leading edge region spanwise vorticity may promote early transition and bubble closure; further downstream streamwise vorticity may become established. The physics of this streamwise vorticity imposes severe requirements on the temporal and spatial resolution of both experimental and computational methods. A narrow spanwise computational strip does not allow the streamwise vorticity to settle into an organized pattern; if it is to become organized, an adequate spanwise domain is required. Copyright \ua9 2010 by ASME.Peer reviewed: YesNRC publication: Ye

Measurement and Computation of Energy Separation in the Vortical Wake Flow of a Turbine Nozzle Cascade

This paper describes the observation, measurement, and computation of vortex shedding behind a cascade of turbine nozzle guide vanes that have a blunt trailing edge. At subsonic discharge speeds, periodic wake vortex shedding was observed at all times at a shedding frequency in the range 7–11 kHz. At high subsonic speeds the wake was susceptible to strong energy redistribution. The effect was greatest around an exit Mach number of 0.95 and results are presented for that condition. An unusually cold flow on the wake centerline and hot spots at the edges of the wake were measured. These were found to be a manifestation of Eckert–Weise effect energy separation in the shed vortex street. Experimental identification of these phenomena was achieved using a new stagnation temperature probe of bandwidth approaching 100 kHz. Using phase-averaging techniques, it was possible to plot contours of time-resolved entropy increase at the downstream traverse plane. Computational work has been undertaken that gives qualitative confirmation of the experimental results and provides a more detailed explanation of the fine scale structure of the vortex wake. The topology of the wake vortical structures behind blunt trailing-edged turbine blades is becoming clearer. These measurements are the first instantaneous observations of the energy separation process occurring in turbine blade wake flows. This was also the first demonstration of the use of the probe in the frequency, Mach number, and temperature ranges typical of operation behind the rotors of high-performance turbomachines such as transonic fans

Pulsating Coolant Ejection Effects Downstream of a Transonic Rounded Trailing Edge

Trailing edge blowing is used in a great variety of applications. In particular, high-pressure turbines bleed about 3% of the engine core massflow through a rear slot. At transonic conditions the coolant flow alters substantially the base region, and therefore the wake and shocks. Certain pulsating coolant frequencies give rise to exotic vortical shedding structures, not observed when the coolant is continuous. A detailed analysis of the flow field near the trailing edge region has been performed using the in-house HybFlow code. A rounded trailing edge with null and continuous blowing (at different pressure ratios) have been compared with a blunt trailing edge geometry using steady simulations. Both shock intensity, and wake loss are discussed in this paper considering pulsating coolant ejection at various frequencies and blowing ratios