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Drag force and drag coefficient
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
If the engine is not buried inside fuselage, it must be in direct contact with air flow. In order to reduce the engine drag, the engine is often located inside an aerodynamic cover called nacelle. For the purpose of drag calculation, it can be considered that the nacelle is similar to the fuselage, except that its length-to-diameter ratio is lower. Thus, the nacelle zero-lift drag coefficient (CDon) will be determined in the same way as that in a fuselage. In the case where the nacelle length-to-diameter ratio is below 2, assume 2. This parameter is used in Equation 3.19. Some aero-engine manufacturers publish the engine nacelle drag in the engine catalog, when the installed drag is demonstrated. In such a case, use that manufacturer data. Determine nacelle drag only when the engine uninstalled thrust is available. The nacelle of an engine for an Airbus A330 is shown in Figure 3.15.
Improvement of aeropropulsion fuel efficiency through engine design
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Kenneth L. Suder, James D. Heidmann
NASA’s aggressive noise and fuel burn reduction goals are driving aircraft engine designs to higher bypass ratios and larger fan diameters. Aircraft engine noise and fuel burn reduction are directly correlated to fan size, fan pressure ratio and fan bypass ratio. As the fan size increases, there is a corresponding drop in fan pressure ratio and an increase in fan BPR. At some point, as the fan size continues to increase, a minimum is reached between fan size and weight and drag. The larger, heavier nacelle produces more drag during flight, and overcomes the advantages of a larger fan. Hence, a technology paradigm shift is needed to reduce the minimum point, which is produced by introducing advanced fan and core technology. A shift of this type was produced by Pratt & Whitney (P&W) with their geared-turbofan (GTF) UHB engine design. UHB engines are defined as engines with a fan BPR equal to or greater than 12. NASA in cooperation with P&W has been investigating UHB technology over the last 20 years, but the GTF is the first generation of UHB engines that will see EIS with an aircraft manufacturer. The paradigm shift produced by the GTF is achieved by operating the fan and core in such a way as to optimize the performance of both. Direct-drive turbofans necessarily operate the fan and low-pressure turbine at the same speed. At low fan speeds, the LPT is operating at faroff-design conditions, and its efficiency goes down, increasing fuel burn. P&W introduced a gearbox into their GTF engine design that allows the fan and LPT to operate at different speeds—thus more optimum, higher efficiency conditions—and so reduced fuel burn. As BPR increases, the mean radius ratio of the fan and LPT increases. Consequently, if the fan is to rotate at its optimum blade speed, the LPT will spin slowly so that additional LPT stages will be required to extract sufficient energy to drive the fan. Introducing a planetary reduction gearbox with a suitable gear ratio between the low-pressure shaft and the fan enables both the fan and LPT to operate at their optimum speeds. A geared turbofan uses a larger fan that moves more air at a lower speed, allowing the same thrust as its nongeared counterpart, but with less energy expended.
Detection of dis-bond between honeycomb and composite facesheet of an Inner Fixed Structure bond panel of a jet engine nacelle using infrared thermographic techniques
Published in Quantitative InfraRed Thermography Journal, 2022
Renil Thomas Kidangan, Chitti Venkata Krishnamurthy, Krishnan Balasubramaniam
The smooth shaped structure that surrounds the jet engine is known as the nacelle. It provides an aerodynamic shell for minimum drag [1], incorporates de-icing capability [2], noise attenuation [3], and mechanisms to reverse engine thrust for braking [4]. The core compartment of the nacelle comprises an outer casing called the Inner Fixed Structure (IFS). IFS is a sandwich-type panel with honeycomb metal core between two composite facesheets. One side of the IFS bond panel is attached with a thermal insulation layer to protect it from high-temperature exposure. Figure 1 shows the schematic of IFS bond panel used for the study. The IFS bond panel composite facesheet that is in contact with engine airflow is perforated with thousands of holes, typically in the range of 1 mm in diameter and the distance (centre to centre) between any two adjacent holes is 3.5 mm (Figure 1). A total of 20,164 holes are present on the facesheet considered for this study which comprises of 6.33% of the total area of the facesheet. The perforations help to attenuate the jet engine’s noise by damping the energy response, directing the sound into the honeycomb core, rather than hitting a hard surface that simply deflects the sound. These panels are subjected to extreme temperatures on both sides. The heat damage caused due to that on the inner bonding layer between composite facesheet and honeycomb core is of greater concern. Clip bonds and the stainless-steel (SS) thin sheet covered thermal insulation layer on one side, and perforated composite facesheet and the honeycomb core on the other side prevent access to this layer. Hence, the development of non-destructive techniques (NDT) is necessary; however, extremely challenging. In this work, active thermography inspection techniques [5] for accessing the hidden layer and identifying the defects are proposed. The active approach requires an external heat source to excite the materials for inspection. Two methods have been proposed in this paper: flash thermography and induction thermography.