An Experimental High-Temperature Turbine ( No . 1 : 26 ) • Part I . mThe Cooling Performance of a Set of Extruded Air-Cooled Turbine Blades
Cooling characteristics are given in terms of the variation of average blade temperature at mid-span with cooling-flow rate, Reynolds number, gas/cooling-air absolute temperature ratio, and, for the rotor, gas-stream incidence. Chordwise and spanwise variations of blade temperature are also presented. Measured pressure-drop characteristics indicate that in a gas-turbine engine, with the cooling-air inlet pressure equal to the turbine gas inlet total pressure, cooling flows roughly equal to 1.8 per cent and 3.0 per cent of the main gas flow could be passed through the nozzle and rotor blades respectively, giving average relative temperatures at mid-span of approximately 0.6 in each instance. Comparisons with theoretical estimates of blade temperature show that the external heat-transfer rates to the nozzle blades agreed well with those measured on similar blades in cascade tests. For the rotor blades the external heat-transfer rates appear to have been between those predicted from cascade and earlier turbine test data. From the measured effects of Reynolds number on blade temperature it seems that approximately equal areas of laminar and turbulent boundary layer existed on both nozzle and rotor blades, and that as the turbine inlet temperature was raised, the extent of the turbulent layer tended to increase.
An Examination of the Flow and Pressure Losses in Bfade Rows of Axial ' Flow ' Turbines )
~The design of axial-flo~ turbines has been hampered in the past by a lack of comprehensive data regarding pressure losses and gas deflections through rows of turbine blades. In the present report much of the available information relating to this subject is studied and analysed to determine magnitudes of gas pressure losses and deflections in a wide variety of blade rows and also to determine the separate influences of variables such as blade shape, blade spacing, gas Mach number, Reynolds number, incidence, etc. Of particular importance are the effects of secondary flows on the aerodynamic performance of a blade row and special attention is paid to ' secondary losses ', which form the difference between the total losses occurring in an actual turbine blade row and the smaller two-dimensional flow losses which are usually measured in a blade cascade tunnel. Eff&cts of blade tip clearance are also studied. Resulting from this analysis a number of empirical guiding rules and charts have been derived from which approximate values of the overall pressure losses and gas deflections in a range of blade rows can be deduced. A particularly significant feature brought to light is that the secondary losses can in many instances be large, the loss being generally found to be great when the blading has low reaction.
Three-Dimensional-Flow Theories for Axial Compressors and Turbines
It has long been known that the energy losses occurring in an axial compressor or turbine cannot be fully accounted for by the skin-friction losses on the blades and annulus walls. The difference, usually termed secondary loss, is attributed to miscellaneous secondary flows which take place in the blade row. These flows both cause losses in themselves and modify the operating conditions of the individual blade sections, to the detriment of the overall performance. This lecture analyses the three-dimensional flow in axial compressors and turbines, so that, by appreciation of the factors involved, possible methods of improving the performance can readily be investigated.The origin of secondary flow is first examined for the simple case of a straight cascade. The physical nature of the flow, and theories which enable quantitative estimates to be made, are discussed at some length. Following this, the three-dimensional flow in an annulus with a stationary blade row is examined, and, among other things, the in...