As the propulsor fan pressure ratio (FPR) is decreased for improved fuel burn, reduced emissions and noise, the fan diameter grows and innovative nacelle concepts with short inlets are required to reduce their weight and drag. This paper addresses the uncharted inlet and nacelle design space for low-FPR propulsors where fan and nacelle are more closely coupled than in current turbofan engines. The paper presents an integrated fan–nacelle design framework, combining a spline-based inlet design tool with a fast and reliable body-force-based approach for the fan rotor and stator blade rows to capture the inlet–fan and fan–exhaust interactions and flow distortion at the fan face. The new capability enables parametric studies of characteristic inlet and nacelle design parameters with a short turn-around time. The interaction of the rotor with a region of high streamwise Mach number at the fan face is identified as the key mechanism limiting the design of short inlets. The local increase in Mach number is due to flow acceleration along the inlet internal surface coupled with a reduction in effective flow area. For a candidate short-inlet design with length over diameter ratio L/D = 0.19, the streamwise Mach number at the fan face near the shroud increases by up to 0.16 at cruise and by up to 0.36 at off-design conditions relative to a long-inlet propulsor with L/D = 0.5. As a consequence, the rotor locally operates close to choke resulting in fan efficiency penalties of up to 1.6% at cruise and 3.9% at off-design. For inlets with L/D < 0.25, the benefit from reduced nacelle drag is offset by the reduction in fan efficiency, resulting in propulsive efficiency penalties. Based on a parametric inlet study, the recommended inlet L/D is suggested to be between 0.25 and 0.4. The performance of a candidate short inlet with L/D = 0.25 was assessed using full-annulus unsteady Reynolds-averaged Navier–Stokes (RANS) simulations at critical design and off-design operating conditions. The candidate design maintains the propulsive efficiency of the baseline case and fuel burn benefits are conjectured due to reductions in nacelle weight and drag compared to an aircraft powered by the baseline propulsor.

Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

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Application of Navier-Stokes Code PAB3D With k-c Turbulence Model to Attached and Separated Flows

Civil turbofan engine exhaust aerodynamics: impact of bypass nozzle after-body design

This paper describes the numerical investigation of convergent conical nozzles done in the AIAA Propulsion Aerodynamic Workshop number one Axisymmetric, three-dimensional, and unsteady computations were conducted for three main test cases These test cases were 1) axisymmetric convergent conical nozzles of 15, 25, and 40 deg half-angle as well as a reference nozzle; 2) the 25 deg half-angle nozzle with a splitter plate inserted in its plane of symmetry; and 3) the vortex shedding observed at the base of the splitter plate The effects of base drag and freestream Mach number on calculated velocity coefficient were analyzed The discharge coefficients and velocity coefficients determined from the axisymmetric solutions matched the experimental data well The wall Mach numbers and sonic line positions were also well predicted In the axisymmetric computations, the shock position was well captured by the fine grid However, when the nozzle pressure ratio was high, the three-dimensional Reynolds-averaged Navi

Performance Prediction of Conical Nozzle Using Navier-Stokes Computation

Reduction of aircraft manufacturing cost benefits aircraft direct operating cost (DOC). The degree of stringency in specifying aircraft smoothness influences cost, i.e. the tighter the tolerance, the higher is the manufacturing cost. Discrete surface roughness arising from manufacturing tolerance at the wetted surface may be seen as an ‘aerodynamic’ defect. Features such as steps, gaps, waviness and fastener flushness (termed excrescence), seen as defects, contribute to aircraft parasitic drag. The study is conducted on an isolated nacelle which is considered to be representative of an entire aircraft. Eleven key manufacturing features at the wetted surface of a generic long duct nacelle are identified, each associated with surface roughness. The influence of tolerance allocation at each of the key features is investigated to establish a relationship between aircraft aerodynamics and associated costs. The initial results offer considerable insight to a relatively complex problem in a multi-disciplinary environment. Excrescence drag arising out of these ‘aerodynamic’ defects is assessed by using CFD and semi-empirical methods. Cost versus tolerance relationships are established through in-house methods using industrial data. The aircraft unit price typically contributes from two to four times more than the fuel burn to aircraft direct operating costs. A trade-off study between manufacturing cost and aircraft drag indicates that, in general, there is scope for some relaxation of present-day tolerance allocation, to reduce aircraft acquisition cost, which would in turn reduce direct operating costs.

Effect of aircraft surface smoothness requirements on cost

CFD-based 3D turbofan nacelle design system

The recently developed three-dimensional code is able to perform a computational investigation of complex aircraft aerodynamic components. This code was developed for solving the simplified Reynolds-averaged NavierStokes equations in a three-dimensional multiblock/mul tizone structured mesh domain. The present analysis was applied to commercial turbofan exhaust flow systems. Solution sensitivity to grid density is presented. Laminar flow solutions were developed for all grids, and two-equation k-£ solutions were developed for selected grids. Static pressure distributions, mass flow, and thrust quantities were calculated for on-design engine operating conditions. Good agreement between predicted surface static pressures and experimental data was observed at different locations. Mass flow was predicted within 0.2% of experimental data. Thrust forces were typically within 0.6% of experimental data.

Commercial turbofan engine exhaust nozzle flow analyses

A three-dimensional turbofan exhaust nozzle analysis system based on computational fluid dynamics (CFD) has been developed. This system has been established to aid exhaust designers in the efficient assessment and screening of their design concepts, with the prospects of a reduction in both design cycle time and wind-tunnel test costs. A reliable CFD flow solver, user-friendly grid generator, and postprocessing software are included in the system. The system is easy to use for exhaust designers who are not particularly familiar with the inner workings of CFD. Validation and applicability studies have been performed using different exhaust nozzle configurations at on-design and off-design engine operating conditions. This work demonstrates that a CFD code integrated with automatic grid generation and postprocessing can be a useful analytical tool in the practical exhaust nozzle design process. Nomenclature M = Mach number P = static pressure PA = atmospheric static pressure R = radius X — axial station XREF = reference length Subscript 00 = freestream conditions

CFD-Based Three-Dimensional Turbofan Exhaust Nozzle Analysis System

A three-dimensional turbofan inlet/fan cowl analysis system based on computational fluid dynamics (CFD) has been developed. This system was established to aid nacelle designers in the efficient assessment of their design concepts by providing for immediate evaluation of design changes without extensive reliance on wind tunnel testing. A reliable CFD flow solver, user-friendly grid generator, and postprocessing software are included in the system. The system is easy to use by designers who are not particularly familiar with CFD. Validation and applicability studies have been performed using several different inlet/fan cowl configurations at on-design and off-design engine operating conditions. This work demonstrates that an Euler-based CFD code integrated with automatic grid generation and postprocessing can reduce the development cycle time in the inlet/fan cowl design process.

Computational fluid dynamics based three-dimensional turbofan inlet/fan cowl analysis system

Recent developments of a three-dimensional (PAB3D) code have paved the way for a computational investigation of complex aircraft aerodynamic components. The PAB3D code was developed for solving the simplified Reynolds Averaged Navier-Stokes equations in a three-dimensional multiblock/multizone structured mesh domain. The present analysis was applied to commercial turbofan exhaust flow systems. Solution sensitivity to grid density is presented. Laminar flow solutions were developed for all grids and two-equation k-epsilon solutions were developed for selected grids. Static pressure distributions, mass flow and thrust quantities were calculated for on-design engine operating conditions. Good agreement between predicted surface static pressures and experimental data was observed at different locations. Mass flow was predicted within 0.2 percent of experimental data. Thrust forces were typically within 0.4 percent of experimental data.

K. Uenishi

Papers

CFD-based 3D turbofan nacelle design system

Commercial turbofan engine exhaust nozzle flow analyses

CFD-Based Three-Dimensional Turbofan Exhaust Nozzle Analysis System

Computational fluid dynamics based three-dimensional turbofan inlet/fan cowl analysis system

Commercial turbofan engine exhaust nozzle flow analyses using PAB3D