Framework for estimation of nacelle drag on isolated aero-engines with separate jets

Typically, the evaluation of nacelle drag in preliminary design is required to find an overall optimum engine cycle and flight trajectory. This work focuses on the drag characteristics of aero-engine nacelles with separate jet exhausts. The main body of analysis comes from 3D numerical simulations. A new near-field method to compute the post-exit force of a nacelle is presented and evaluated. The effects of the engine size, Mach number, mass flow capture ratio and angle of attack are assessed. The results obtained from the numerical assessments were used to evaluate conventional reduced-order models for the estimation of nacelle drag. Within this context, the effect of the engine size is typically estimated by the scaling ratio between the maximum areas and Reynolds numbers. The effect of the angle of attack on nacelle drag is mostly a function of the nacelle geometry and angle of attack. In general, typical low-order models based on skin friction and form factor can underestimate the friction drag by up to 15% at cruise operating point. Similarly, reduced-order models based solely on Reynolds number, and Mach number can underestimate the overall nacelle drag by up to 74% for free stream Mach number larger than the drag rise Mach number.

Download Full-text

Mach Number Influence on Reduced-Order Models of Inviscid Potential Flows in Turbomachinery

Journal of Fluids Engineering ◽

10.1115/1.1511165 ◽

2002 ◽

Vol 124 (4) ◽

pp. 977-987 ◽

Cited By ~ 17

Author(s):

Bogdan I. Epureanu ◽

Earl H. Dowell ◽

Kenneth C. Hall

Keyword(s):

Mach Number ◽

Steady Flow ◽

Inviscid Flow ◽

Reduced Order Models ◽

Reduced Order ◽

Spatial Gradients ◽

Potential Flows ◽

Proper Orthogonal Decomposition Technique ◽

Flow Through ◽

Phase Angles

An unsteady inviscid flow through a cascade of oscillating airfoils is investigated. An inviscid nonlinear subsonic and transonic model is used to compute the steady flow solution. Then a small amplitude motion of the airfoils about their steady flow configuration is considered. The unsteady flow is linearized about the nonlinear steady response based on the observation that in many practical cases the unsteadiness in the flow has a substantially smaller magnitude than the steady component. Several reduced-order modal models are constructed in the frequency domain using the proper orthogonal decomposition technique. The dependency of the required number of aerodynamic modes in a reduced-order model on the far-field upstream Mach number is investigated. It is shown that the transonic reduced-order models require a larger number of modes than the subsonic models for a similar geometry, range of reduced frequencies and interblade phase angles. The increased number of modes may be due to the increased Mach number per se, or the presence of the strong spatial gradients in the region of the shock. These two possible causes are investigated. Also, the geometry of the cascade is shown to influence strongly the shape of the aerodynamic modes, but only weakly the required dimension of the reduced-order models.

Download Full-text

A Parametric Analysis of Reduced Order Models of Potential Flows in Turbomachinery Using Proper Orthogonal Decomposition

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/2001-gt-0434 ◽

2001 ◽

Cited By ~ 10

Author(s):

Bogdan I. Epureanu ◽

Earl H. Dowell ◽

Kenneth C. Hall

Keyword(s):

Mach Number ◽

Proper Orthogonal Decomposition ◽

Steady Flow ◽

Inviscid Flow ◽

Orthogonal Decomposition ◽

Reduced Order Models ◽

Reduced Order ◽

Spatial Gradients ◽

Potential Flows ◽

Proper Orthogonal

An unsteady inviscid flow through a cascade of oscillating airfoils is investigated. An inviscid nonlinear subsonic and transonic model is used to compute the steady flow solution. Then a small amplitude motion of the airfoils about their steady flow configuration is considered. The unsteady flow is linearized about the nonlinear steady response based on the observation that in many practical cases the unsteadiness in the flow has a substantially smaller magnitude than the steady component. Several reduced order modal models are constructed in the frequency domain using the proper orthogonal decomposition technique. The dependency of the required number of aerodynamic modes in a reduced order model on the far-field upstream Mach number is investigated. It is shown that the transonic reduced order models require a larger number of modes than the subsonic models for a similar geometry, range of reduced frequencies and interblade phase angles. The increased number of modes may be due to the increased Mach number per se, or the presence of the strong spatial gradients in the region of the shock. These two possible causes are investigated. Also, the geometry of the cascade is shown to influence strongly the shape of the aerodynamic modes, but only weakly the required dimension of the reduced order models.

Download Full-text

Aspects of aero-engine nacelle drag

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410018765574 ◽

2018 ◽

Vol 233 (5) ◽

pp. 1667-1682 ◽

Cited By ~ 7

Author(s):

Matthew Robinson ◽

David G MacManus ◽

Christopher Sheaf

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Mach Number ◽

Wind Tunnel ◽

Near Field ◽

Pressure Ratio ◽

Exhaust System ◽

Extraction Methods ◽

Field Method ◽

Rate Of Change

To address the need for accurate nacelle drag estimation, an assessment has been made of different nacelle configurations used for drag evaluation. These include a sting mounted nacelle, a nacelle in free flow with an idealised, freestream pressure matched, efflux and a nacelle with a full exhaust system and representative nozzle pressure ratio. An aerodynamic analysis using numerical methods has been carried out on four nacelles to assess a near field drag extraction method using computational fluid dynamics. The nacelles were modelled at a range of aerodynamic conditions and three were compared against wind tunnel data. A comparison is made between the drag extraction methods used in the wind tunnel analysis and the chosen computational fluid dynamics approach which utilised the modified near-field method for evaluation of drag coefficients and trends with Mach number and mass flow. The effect of sting mounting is quantified and its influence on the drag measured by the wind tunnel methodology determined. This highlights notable differences in the rate of change of drag with free stream Mach number, and also the flow over the nacelle. A post exit stream tube was also found to create a large additional interference term acting on the nacelle. This term typically accounts for 50% of the modified nacelle drag and its inclusion increased the drag rise Mach number by around Δ M = 0.026 from [Formula: see text] to [Formula: see text] for the examples considered.

Download Full-text

Reduced Order Models of Low Mach Number Isothermal Flows in Microchannels

ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2013-73150 ◽

2013 ◽

Cited By ~ 2

Author(s):

Leila Issa ◽

Issam Lakkis

Keyword(s):

Mach Number ◽

Analog Circuit ◽

Stokes Equations ◽

Momentum Equation ◽

Ideal Gas ◽

Reduced Order Models ◽

Two Dimensional ◽

Reduced Order ◽

Low Mach Number ◽

Circuit Components

We present reduced order models of unsteady low Mach number isothermal ideal gas flows in two-dimensional rectangular microchannels subject to first order slip boundary conditions. The Navier-Stokes equations are simplified using Low Mach Number expansions of the pressure and velocity fields. This approximation allows decoupling the density from spatial pressure variations, thus simplifying the momentum equation. The resulting diffusion equation and the subsequent pressure-flow-rate relationship enables modeling the flow using analog circuit components. The accuracy of the proposed models is investigated for steady and unsteady flows in a two-dimensional channel for different values of Reynolds and Knudsen numbers.

Download Full-text