The Axial Turbobrake (Patent applied for) is a novel turbomachine which can be used to absorb power generated by test turbines. Unlike a compressor there is no pressure recovery through the turbobrake. This simplifies the aerodynamic design and enables high stage loadings to be achieved. The blades used have high turning two dimensional profiles. This paper describes a single stage axial turbobrake, which is driven by the exhaust gas of the test turbine and is isolated from the turbine by a choked throat. In this configuration no fast acting controls are necessary as the turbobrake operates automatically with the turbine flow. Tests on a 0.17 scale model, show that the performance is close to that predicted by a simple two-dimensional theory, and demonstrate that the turbobrake power absorption can be controlled and hence matched to that typically produced by the first stage of a modern highly loaded transonic turbine. A full size axial turbobrake will be used in a short duration rotating turbine experiment in an Isentropic Light Piston Tunnel at RAE Pyestock.
A high rim speed turbine, incorporating some 3-D features has been designed and tested at RAE Pyestock. There has been cold flow turbine testing, with overall performance measurements, rotor exit traversing as well as surface static pressure measurements on the vane and rotor. The vane has also been tested in annular cascade on the Isentropic Light Piston Cascade giving surface heat transfer measurements on the vanes and endwalls as well as aerodynamic information. The data have been used to compare with design predictions and the reasons for the differences observed, particularly on the rotor blade, are explored.
The “Axial Turbobrake” (patent applied for) is a novel turbomachine that can be used to absorb power generated by test turbines. Unlike a compressor, there is no pressure recovery through the turbobrake. This simplifies the aerodynamic design and enables high-stage loadings to be achieved. The blades used have high-turning two-dimensional profiles. This paper describes a single-stage axial turbobrake, which is driven by the exhaust gas of the test turbine and is isolated from the turbine by a choked throat. In this configuration no fast-acting controls are necessary as the turbobrake operates automatically with the turbine flow. Tests on a 0.17 scale model show that the performance is close to that predicted by a simple two-dimensional theory, and demonstrate that the turbobrake power absorption can be controlled and hence matched to that typically produced by the first stage of a modern highly loaded transonic turbine. A full-size axial turbobrake will be used in a short-duration rotating turbine experiment in an Isentropic Light Piston Tunnel at RAE Pyestock.
In shroudless axial turbines the flow over the tips of the rotor blades is complex and accounts for significant loss of efficiency. In order to investigate the structure of this overtip flow, a row of high frequency response miniature pressure transducers was mounted in the casing of a cold flow turbine rig in the region swept by the rotor tips. The data acquisition system is described, which includes equipment for digitally sampling and storing the data synchronously with passage of the rotor blades, leading to derivation of the periodic and random elements of the pressure variation. The results are presented and compared with those from other researchers.The present study at RAE Pyestock uses high frequency response miniature pressure transducers, installed in the casing over the rotor blades, to measure the overtip pressure
An engine design study is presented in which the target is a 15 percent reduction in installed specific fuel consumption over the large engines currently in service while still meeting anticipated noise and emissions regulations. The fuel saving is achieved with a low specific thrust (bypass ratio 10) and a high overall cycle pressure ratio (42 at cruise). A three-shaft design is proposed, employing highly loaded components in order to reduce the number of turbomachinery stages and hence keep down cost and weight. It is argued that this approach is the one most compatible with projected technological advances. The engine configuration is given and the key features explained, highlighting areas where further research would be of particular advantage. Finally, the predicted engine performance is given, together with an estimate of the savings in direct operating cost.
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