Efficient Design Investigation of a Turbofan in Distorted Inlet Conditions

Abstract

Designing a turbofan to operate in distorted inlet conditions is an issue of growing interest. In such conditions however, fan design can be computationally challenging. Indeed, subject to neither axi-symmetrical nor periodic inlet conditions, computations must be carried out throughout the whole circumferential domain i.e. 360°. Besides, the classical CFD approach implies the use of URANS computations so as to capture the distortion transfer across the fan stage. Eventually, computations are too onerous to be used in design loops. In this context, this paper presents a methodology to effectively assess a fan blade design domain in distorted conditions. This methodology is based on a body-force source term approach formulated in order to accurately recreate deviations, loads and losses across the fan stage. It notably enables to gain two orders in terms of restitution time and thus the possibility to use optimization tools. The design domain of this study is based on variations of profile chord, blade leading and trailing edges angles applied at two different relative heights. A Latin Hypercube Sampling (LHS) associated with a meta-model based on Radial Basis Functions (RBF) enables to assess the impact of geometric variations on performance and operability. Although this study emphasizes that some modeling improvements are still necessary, it also demonstrates the potential of the body-force methodology to conduct fan design when subject to inlet distortion.

Computation of the Unsteady Loading on a Fan Blade Due to Inlet Distortion Using Body Force Methodology

“…The body force strongly overestimates the force at the trailing edge. Similar results have already been observed by Godard [15]. These discrepancies are attributed to the inability of the body force methods to capture the shocks.…”

“…Thollet [13], with his body force model based on a Lift/Drag analogy and using Kotapalli's [14] body force modeling of metallic blockage, showed in his thesis that his model correctly captures the effect of decreased intake length on flow separation delay on the intake lip. Godard [15] presented a body force methodology for fan blade design under distorted conditions. In his study, Godard showed that body force calculations have significantly smaller restitution time compared to classic U-RANS calculations, with a difference of two orders of magnitude.…”

“…In his study, Godard showed that body force calculations have significantly smaller restitution time compared to classic U-RANS calculations, with a difference of two orders of magnitude. Godard [15] applied his methodology to conduct a parametric study based on variations of profile chord, blade leading edge angle and blade trailing edge angle. Defoe [16], based on Peters' [11] work, proposed a body force method using Hall's [17] model to compute the unsteady loading on a blade for vertically and radially stratified inlet distortions.…”

A New Loss Generation Body Force Model for Fan/Compressor Blade Rows: An Artificial-Neural-Network Based Methodology

“…However, the simulations are limited to a specified range of operating conditions. New developments in parallel force models have been implemented for nonuniform inflows in fans by using a simple empirical-based correlated model for turbulent flow over a flat plate [15,16]. The model used in the two latter references does not include the momentum thickness Reynolds number which is relevant when the flow is separated on the blade.…”

Fan Design Investigation on the Airbus Nautilius Engine Integration Concept

“…However, designing a fan in BLI conditions is a real challenge. Nevertheless, several authors have already managed to draw some guidelines using both low-fidelity methods [24,25] or more advanced unsteady approaches. In particular, fan design in BLI conditions must account for non-axisymetric inflows, which can be partially addressed by non-axisymetric components (ex.…”