Turbofan

About: Turbofan is a research topic. Over the lifetime, 4114 publications have been published within this topic receiving 39490 citations. The topic is also known as: fanjet & turbofan engine.

Experimental Studies of Open Rotor Installation Effects

Abstract: Open rotor propulsion technologies offer an opportunity for reducing fuel burn due to the very high effective bypass ratio that results in increased propulsive efficiency. Open rotor effective bypass ratio can be 25 or higher and represents a potential advantage over even advanced ultra high bypass ratio turbofan engines. At the same time, great challenges arise from this radically different engine architecture in terms of aircraft system integration. The propulsion airframe aeroacoustic (PAA) effects of integration are one of those key challenges. Total installed noise, open rotor noise including integration effects, can be impacted by angle of attack, spacing between rotors and airframe elements, flow effects from wake ingestion or distortion from the airframe elements and several other parameters that generally depend on the aircraft configuration. In general, these effects increase noise compared to that of an isolated open rotor. This inter-relationship of the aerodynamic and aeroacoustic system integration effects is particularly important to enable future application. Furthermore, innovative integration and advanced technology may also offer the possibility of mitigating these usually negative aeroacoustic effects for a total aircraft system noise reduction. Understanding of these installation effects is essential to be able to assess the aircraft system benefits and to develop technology and approaches to achieve the best aircraft system benefits possible. An extensive model scale test campaign was conducted to investigate a broad range of these open rotor installation effects for both a conventional and an unconventional airframe. The conventional airframe was patterned after a modern twinengine aircraft configuration. The unconventional airframe was a hybrid wing body aircraft concept. The contra-rotating, eight by eight, open rotor used in this experiment was legacy technology from the 1980s flight test project. The experimental campaign was conducted in the Boeing Low Speed Aeroacoustic Facility (LSAF), shown in Figure 1. A 9 by 12 ft open jet is used to produce the forward flight simulation with a maximum Mach number of 0.25 for this experimental setup. Figure 1 shows the basic setup for this campaign with the airframe attached from the overhead structure and the open rotor rig attached on a strut from below the open jet. LSAF installed specially designed modifications for efficient positioning of the airframe relative to the open rotor. The airframe was traversed remotely relative to the fixed open rotor rig providing for the investigation of a large number of installation positions. Eight positions around the main wing of the conventional airframe and eleven positions above the hybrid wing body airframe were documented. Figure 2 shows a typical spectrum of the open rotor. In this case, the forward and aft blade rows were run intentionally at slightly different speeds. This allows the engine 3rd AIAA Atmospheric Space Environments Conference 27 30 June 2011, Honolulu, Hawaii AIAA 2011-4047

Tone Generation by Rotor-Downstream Strut Interaction

Abstract: A JT15D fan stage was acoustically tested in the NASA Lewis anechoic chamber as part of the joint Lewis/Langley Research Center investigation of flight simulation techniques and flight effects using the JT15D engine as a common test vehicle. Suspected rotor-downstream support strut interaction was confirmed through the use of simulated support struts, which were tested at three axial rotor-strut spacings. Tests were also per- formed with the struts removed. Inlet boundary layer suction in conjunction with an inflow control device was also explored. The removal of the boundary layer reduced the fan fundamental tone levels, suggesting that the mounting and mating of such a device to the nacelle requires careful attention. With the same inflow control device installed, good acoustic agreement was shown between the engine on an outdoor test stand and the fan in the anechoic chamber. HE development of effective inflow control devices (ICD's) makes it possible to study noise generation mechanisms, such as rotor-stator interaction, with reduced masking effects of inflow disturbances. Modern turbofan engines are often designed with blade/vane numbers selected to prevent propagation of the fundamental rotor-stator in- teraction tone. However, less consideration has been given to possible rotor interactions with engine support struts. These struts are either located downstream of the stator row or are integrated into the stator as large cross-section vanes.! This paper presents results for a JT15D fan stage which was acoustically tested in the NASA Lewis Research Center anechoic chamber2 as part of a joint NASA Lewis/Langley investigation of flight simulation techniques and flight effects using the JT15D-1 engine as a common test vehicle.3"7 The engines used in these studies were instrumented with blade and vane pressure transducers to assist in isolating noise generation mechanisms. Although the primary goal of this study was to evaluate inflow control techniques, the results revealed that for the JT15D-1 engine in particular speed ranges the fundamental tone was controlled by the presence of six engine support struts located downstream of the stator. Blade pressure results showing a strong six per revolution disturbance pointed to these struts as the probable noise source. The interaction between the 28-blade rotor of the JT15D and the six support struts would result in a m-22 acoustic spinning mode having 22 circumferential lobes. This mode was shown to exist in the inlet duct of a JT15D engine when the results from two pressure sensors located in the duct so as to allow spining mode identification by signal phase relationship were used.3 However, it was not possible to alter the support struts in the engine to establish the behavior of this apparent noise source. Downstream support struts were not required for the JT15D fan installation in the anechoic chamber. Six simulated support struts were fabricated and installed in the test fan stage to simulate the actual engine support strut installation. These simulated struts were located at three axial spacings from the stator trailing edge. Thus, in the present study results were obtained for the spacing effect of downstream support struts as well as for fan stage alone with no downstream struts.

Geared turbofan with three turbines all counter-rotating

Abstract: A gas turbine engine has a fan rotor, a first compressor rotor and a second compressor rotor. The second compressor rotor compresses air to a higher pressure than the first compressor rotor. A first turbine rotor drives the second compressor rotor and a second turbine rotor. The second turbine drives the compressor rotor. A fan drive turbine is positioned downstream of the second turbine rotor. The fan drive turbine drives the fan through a gear reduction. The first compressor rotor and second turbine rotor rotate as an intermediate speed spool. The second compressor rotor and first turbine rotor together as a high speed spool. The high speed spool and the fan drive turbine configured to rotate in the same first direction. The intermediate speed spool rotates in an opposed, second direction.

Wind tunnel measurements of blade/vane ratio and spacing effects on fan noise

Abstract: Introduction R turbofan engine designs aimed at increasing the structural rigidity and reducing the weight of the engine frame lead to a reduced number of stator vanes and an abandonment of vane-blade ratios greater than required for fundamental tone cutoff.' These designs, which consider stator solidity aerodynamic constraints, consist of a relatively few longer chord, larger thickness stator vanes which are load-carrying members of an integrated vane-frame. Basic acoustic data on the effects of vane-blade ratio and spacing under conditions which simulate flight are needed to determine the acoustic consequences of adopting alternate designs such as the integrated vane-frame. Expected noise consequences of varying fan stage design parameters, such as vane-blade ratio and rotor-stator spacing have often been masked in static testing. This is largely due to the fact that the fundamental blade passing tone level and, to a lesser extent, the tone harmonics levels are controlled by rotor-inflow interaction mechanisms,' which mask the rotor-stator interaction noise. The blade passing tone level of a fan designed for fundamental tone cutoff is greatly reduced with forward velocity. Noise studies performed in an anechoic wind tunnel' have shown results similar to those obtained in flight tests. In the present study the noise of a 50.8-cm-diam research turbofan simulator was measured in the anechoic wind tunnel described in Refs. 6 and 7. Both vane-blade ratio and rotorstator spacing were varied. Specifically, two stator vane numbers were chosen to achieve a cuton and cutoff condition with respect to propagation of the fundamental rotor-stator interaction tone as predicted by the theory of Ref. 8. The noise associated with each of these stator configurations was measured at three rotor-stator spacings ranging from 0.5 to 2.0 rotor chords.

Application of 3-signal coherence to core noise transmission

Abstract: A method for determining transfer functions across turbofan engine components and from the engine to the far-field is developed. The method is based on the three-signal coherence technique used previously to obtain far-field core noise levels. This method eliminates the bias error in transfer function measurements due to contamination of measured pressures by nonpropagating pressure fluctuations. Measured transfer functions from the engine to the far-field, across the tailpipe, and across the turbine are presented for three turbofan engines.