Velocity Measurements in the Vicinity of the Exit and Inlet of a Spiral Bevel Gear Shroud

In many aeroengines the accessory power offtake is achieved using a spiral bevel gear set running off one of the main shafts. The crown and bevel gears are housed in an internal gearbox. Over the past few years the Nottingham University Technology Centre (UTC) in Gas Turbine Transmission Systems has researched flow near spiral bevel gears both computationally and experimentally using a purpose-built test rig. In the current investigation the rig was configured with a Trent crown gear and slightly modified shroud covering the full 360° of the gear. No external containment chamber was fitted and all testing was conducted single-phase (air only) at 5,000 rpm. Laser Doppler Anemometry (LDA) was used to obtain the three components of flow velocity at a shroud exit slot and at shroud inlet. A 2D system was utilised and thus two measurements were required at each point to give the 3 velocity components. The LDA technique enabled detailed mapping of flow features over the chosen regions, which included areas very near the shroud surfaces. Data was obtained over two measurement regions: 1) a volume mapping the air “jet” exiting the shroud exit slot at top dead centre (TDC) and 2) an area capturing the flow structures local to the shroud inlet. Combined the results form an excellent set of high quality, detailed, 3-component flow data for direct use in validating CFD models and/or to define CFD boundary conditions. At the shroud exit slot the maximum velocity measured was 46.2 m/s with the jet velocity dispersing over the measurement volume such that by 26 mm from slot plane the maximum velocity was less than 20 m/s. The jet angle was found to be only 16° off perpendicular azimuthally and 22° down from perpendicular. Data from the top 5 slots shows good similarity indicating the detailed data for the TDC slot is probably applicable to all slots. Air entering the shroud comes down the shroud face and up the rotating end face of the gear shaft. The azimuthal velocity component at shroud inlet was around 20 m/s; this is of the order of 50% of the maximum linear shaft surface speed. Within 3 mm of the rotating gear face the azimuthal velocity is less than 1 m/s. Detailed measurements were obtained only at one angular location but sufficient additional measurements were obtained to determine that for the purposes of CFD validation the results can be considered representative.

A New Class of Synthetic Jet Actuators—Part I: Design, Fabrication and Bench Top Characterization

Although the potential of synthetic jets as flow separation control actuators has been demonstrated in the existing literature, there is a large gap between the synthetic jet actuators (SJA) used in laboratory demonstrations and the SJAs needed in realistic, full-scale applications, in terms of compactness, weight, efficiency, control authority and power density. In most cases, the SJAs used in demonstrations are either too large or too weak for realistic applications. In this work, we present the development of a new class of high-power synthetic jet actuators for realistic flow control applications. The operating principle of the actuator is the same as that of crankshaft driven piston engines, which makes a significant part of the technology necessary for the actuator development available off-the-shelf. The design of the actuator is modular and scalable. Several “building block” units can be stacked in series to create the actuator of the desired size. Moreover, active exit slot reconfiguration, in the form of variable exit slot width, decouples the actuator frequency from the actuator jet momentum coefficient and allows the user to set the two independently (within limits). Part I of this paper presents the design, fabrication and bench top characterization of the actuator. Several versions of the actuator were designed, built and tested, leading up to the development of a six-piston compact actuator that has a maximum power consumption of 1200 W (1.6 hp) and can produce (for the tested conditions) peak exit velocities as high as 124 m/s. In Part II, the actuator was housed in the interior of a NACA0015 profiled wing with a chord of 0.375 m (14.75 inches). The assembly’s performance in controlling flow separation was studied in the wind tunnel.

Convective Heat Transfer in a Triple-Cavity Structure Near Turbine Blade Trailing Edge

The present study explores the internal heat transfer in a triple-cavity cooling structure with a ribbed lip for a turbine blade trailing edge. The design consists of two impingement cavities, two sets of crossover holes, a third cavity and an exit slot with eleven ribs attached to it. Local heat transfer in each subregion is determined. Results indicate that the highest heat transfer occurs in the second impingement cavity. The exit slot area between the ribs is identified as a region of low heat transfer in the overall design. A comparison with enhancement induced by arrays of pin fins and fins of other geometries reveals that the triple-cavity design represents a lesser quality cooling scheme in the range of Reynolds numbers tested. Further improvement of the convective heat transfer at the exit slot with either film cooling, or different rib geometries appears to be essential to make the triple-cavity strategy superior to those of the traditional approaches for cooling of blade trailing edge.

A frictional–kinetic model for the flow of granular materials through a wedge-shaped hopper

A quasi-one-dimensional model is used to examine the steady flow of granular materials through a wedge-shaped hopper with smooth, steep walls. Hybrid frictional–kinetic equations are used in an attempt to overcome some of the dificulties faced by earlier works, which were based on frictional equations. Owing to computational difficulties, two different solution procedures are used: (i) in the upper region, where frictional effects dominate, and (ii) the lower region which includes the exit slot and a part of the particle jet below the hopper, where kinetic and frictional effects are expected to be comparable. The equations are integrated numerically in (i). In (ii), they are linearized, and a semi-analytical solution is constructed. In contrast to the works of Kaza & Jackson (1982a) and Prakash & Rao (1991), the density varies smoothly across the exit slot. The density profile is qualitatively similar to the data of Fickie, Mehrabi & Jackson (1989). However, the range of density variation is much smaller than that observed. Owing to the approximations used, and perhaps also to the form of the kinetic constitutive equations, kinetic effects are dominated by frictional effects, except close to the downstream boundary.