TAILIEUCHUNG - Turbo Machinery Dynamics Part 5

Tham khảo tài liệu 'turbo machinery dynamics part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | FAN AND COMPRESSOR AIRFOILS 143 FIGURE Fan airfoil profile for supersonic flow. consequence of shock are only a part of the problem since interaction between the boundary layer and shock waves magnifies the viscous losses Saravananamuttoo Rogers and Cohen 2001 . A damper at part span is required in long and flexible fan blades to control torsional and flexural motion and also proves advantageous in the event of ingestion of a foreign object during the takeoff roll of the aircraft. However the performance of the portion of the blade in the proximity of the damping device is diminished especially if it is located where the Mach number is high. Wide chord fan blade development has eliminated the need for dampers but improvements in manufacturing and stress analysis techniques have played no small role in bringing about this progress. A fan rotor with integral wide-chord blades machined from a single forging has been developed by some aircraft engine manufacturers. A hollow core with stiffeners helps to cut the weight of some very large fan blades. STALL AND SURGE To understand the phenomenon of surging consider a compressor operating at a constant speed. The machine is connected to a chamber. A throttle valve placed in the discharge line from the chamber is gradually opened. As the airflow rate increases air pressure also rises from the initial point as a result of the built-up energy within the chamber. Maximum efficiency is reached at some point and further flow leads to a decline in the pressure. With further opening of the valve the flow rate reaches a point beyond the compressor s capability. The airflow is not continuous and the efficiency drops off rapidly. In reality most of the pressure between the initial valve opening and the point of maximum efficiency cannot be delivered because the flow tends to surge. A sudden drop in pressure accompanied by considerable swings in the flow rapidly spreads through the compressor during the process. When the .

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