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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Titanium alloys have greater density than light alloys, but they have higher strength-to-weight and stiffness-to-weight ratios and they maintain these values even at elevated temperatures. Despite their inherently high cost and difficulty to manufacture, the use of titanium alloys has become common especially when weight reduction is required, or strength is required at temperatures higher than that can be sustained by aluminum alloys or polymer composites. The wide-chord fan blade, full moving stabilizer surfaces, and internal structure of combat aircraft provide good examples of titanium alloy applications. Their biggest use is in engine structures for discs, blades, shafts, high-pressure compressors, and nozzle assemblies. Titanium alloy comprises almost 10% of the Boeing 777 aircraft’s weight. Ti-6Al4V is the most general-purpose, high-strength alloy used in aerospace applications.
Noise mitigation strategies
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Modern engines also have fewer fan blades. The number of fan blades is primarily determined by the aerodynamic design and desire to lower weight and cost. However, fan noise also contributes to the selection since the number of blades and operating speed determine the BPF. Fan noise can be reduced by shifting tones away from regions of the noise spectrum that contribute to the most annoying frequencies as determined by the perceived noise level (PNL) metric. PNL is used to compute the effective perceived noise level (EPNL) for the aircraft certification process described in Chapter 1. Figure 4.2 shows a picture of a fan from a CF6 engine compared with a modern engine design. The part-span shroud shown in Figure 4.2(a) is no longer used since modern wide-chord fans (Fig. 4.2(b)) have improved aeroelastic characteristics in addition to having higher efficiencies and lower noise.
Axial Flow Compressors and Fans
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Axial compressors are those in which the air flows mainly parallel to the rotational axis. Axial flow compressors have a large mass flow capacity, high reliability, and high efficiency, but have a smaller pressure rise per stage (1.1:1–1.4:1) than centrifugal compressors (4:1–5:1). However, it is easy to link together several stages and produce a multistage axial compressor having pressure ratios up to 40:1, as in recent compressors. Integrally bladed rotors permit blade speeds significantly above conventional rotors and hence stage pressure ratios greater than 1.8 [1]. Axial compressors are widely used in gas turbines, notably jet engines, wind tunnels, air blowers, and blast furnaces. Engines using an axial compressor are known as axial flow engines. Almost all present-day jet engines use axial flow compressors, the notable exception being those used in helicopters, where the smaller size of the centrifugal compressor is useful. The fan in turbofan engines is also an axial compression module, which is treated as an axial compressor having less blades of very large height, wide chord, and large twist. These fans may be single stage, or up to three stages, in low bypass turbofan engines. Jet engines nowadays use two or three axial compressors for higher pressure ratios. Nearly all the turbojet engines are of the two-spool type, which have two compressors identified as low and high pressure. Two-spool turbofan engines have the fan as the low-pressure spool. Sometimes, this fan represents the first stage of the low-pressure compressor. The fan in this case is followed by a few stages of an axial compressor, which represents the first module of the engine core. In other turbofans the fan on its own represents the low-pressure compressor, which is followed by the high-pressure compressor. Three-spool turbofan engines have a fan, an intermediate pressure, and a high-pressure compressor. The low-pressure compressor turns at the lowest rpm while the high-pressure compressor turns at the highest speed.
Modeling and characterization of bilayer containment ring in gas turbine engine
Published in International Journal for Computational Methods in Engineering Science and Mechanics, 2020
The two effective bilayer containment systems derived from the fundamental planar impact studies are further examined here as containment rings. Figure 7 shows the finite element model used in this blade shedding analysis. The model comprises a released blade and trailing blade mounted on the rigid rotor, and a containment ring. The trailing blade is included in the model as it significantly increases released blade kinetic energy during blade shedding [6]. The wide-chord TI6Al4V blades with pretwist and dovetail joint typically used in fan blades in turbofan engines were adopted in the analysis. The bladed rotor was assumed to be rotating at 2500 rpm, and has an outer radius of 1305 mm, which are typical values of wide body engines [42,43]. The model considers clearance between the blade tip and the inner radius of the containment ring (1316 mm) to account for the elongation of the blades due to the centrifugal loading and presence of abradable coating. Abradable coating was neglected in the model, as it is relatively soft and wears away with contact. The total areal mass of the containment ring was assumed to be 50 kg/m2. In addition to the two bilayer rings, our analysis also included a traditional single TI ring to facilitate comparisons with the bilayer targets. The thickness of the TI ring and bilayer containment rings are given in Table 3.
A critical review of different works on marine propellers over the last three decades
Published in Ships and Offshore Structures, 2023
Pritam Majumder, Subhendu Maity
To reduce the fluctuation of pressure in the suction side and pressure side, Lee et al. (2010) introduced a new design propeller namely Wide Chord Tip (WCT) propeller. Since pressure fluctuation caused vibration and noise production in the marine propeller, this kind of propeller significantly helped to improve efficiency by reducing pressure fluctuation. The main fundamental characteristic of this propeller was to reduce the expanded area to optimise pitch and chamber. According to their investigation, there was around 2% efficiency improvement with the WCT propeller than the conventional propeller.