Aerodynamic and aeroacoustic analysis of a harmonically morphing airfoil using dynamic meshing

This work explores the aerodynamic and aeroacoustic responses of an airfoil fitted with a harmonically morphing Trailing Edge Flap (TEF). An unsteady parametrization method adapted for harmonic morphing is introduced, and then coupled with dynamic meshing to drive the morphing process. The turbulence characteristics are calculated using the hybrid Stress Blended Eddy Simulation (SBES) RANS-LES model. The far-field tonal noise is predicted using the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy method with corrections to account for spanwise effects using a correlation length of half the airfoil chord. At various morphing frequencies and amplitudes, the 2D aeroacoustic tonal noise spectra are obtained for a NACA 0012 airfoil at a low angle of attack (AoA = 4°), a Reynolds number of 0.62 × 106, and a Mach number of 0.115, respectively, and the dominant tonal frequencies are predicted correctly. The aerodynamic coefficients of the un-morphed configuration show good agreement with published experimental and 3D LES data. For the harmonically morphing TEF case, results show that it is possible to achieve up to a 3% increase in aerodynamic efficiency (L/D). Furthermore, the morphing slightly shifts the predominant tonal peak to higher frequencies, possibly due to the morphing TEF causing a breakup of large-scale shed vortices into smaller, higher frequency turbulent eddies. It appears that larger morphing amplitudes induce higher sound pressure levels (SPLs), and that all the morphing cases induce the shift in the main tonal peak to a higher frequency, with a maximum 1.5 dB reduction in predicted SPL. The proposed dynamic meshing approach incorporating an SBES model provides a reasonable estimation of the NACA 0012 far-field tonal noise at an affordable computational cost. Thus, it can be used as an efficient numerical tool to predict the emitted far-field tonal noise from a morphing wing at the design stage

Effects of an unsteady morphing wing with seamless side-edge transition on aerodynamic performance

This paper presents an unsteady flow analysis of a 3D wing with a morphing trailing edge flap (TEF) and a seamless side-edge transition between the morphed and static parts of a wing by introducing an unsteady parametrization method. First, a 3D steady Reynolds-averaged Navier–Stokes (RANS) analysis of a statically morphed TEF with seamless transition is performed and the results are compared with both a baseline clean wing and a wing with a traditional hinged flap configuration at a Reynolds number of 0.7 × 106 for a range of angles of attack (AoA), from 4◦ to 15◦. This study extends some previous published work by examining the inherent unsteady 3D effects due to the presence of the seamless transition. It is found that in the pre-stall regime, the statically morphed wing produces a maximum of a 22% higher lift and a near constant drag reduction of 25% compared with the hinged flap wing, resulting in up to 40% enhancement in the aerodynamic efficiency (i.e., lift/drag ratio). Second, unsteady flow analysis of the dynamically morphing TEF with seamless flap side-edge transition is performed to provide further insights into the dynamic lift and drag forces during the flap motions at three pre-defined morphing frequencies of 4 Hz, 6 Hz, and 8 Hz, respectively. Results have shown that an initially large overshoot in the drag coefficient is observed due to unsteady flow effects induced by the dynamically morphing wing; the overshoot is proportional to the morphing frequency which indicates the need to account for dynamic morphing effects in the design phase of a morphing wing

Morphing airfoils analysis using dynamic meshing

© 2018, Emerald Publishing Limited. Purpose: The purpose of this paper is to use dynamic meshing to perform CFD analyses of a NACA 0012 airfoil fitted with a morphing trailing edge (TE) flap when it undergoes static and time-dependent morphing. The steady CFD predictions of the original and morphing airfoils are validated against published data. The study also investigates an airfoil with a hinged TE flap for aerodynamic performance comparison. The study further extends to an unsteady CFD analysis of a dynamically morphing TE flap for proof-of-concept and also to realise its potential for future applications. Design/methodology/approach: An existing parametrization method was modified and implemented in a user-defined function (UDF) to perform dynamic meshing which is essential for morphing airfoil unsteady simulations. The results from the deformed mesh were verified to ensure the validity of the adopted mesh deformation method. ANSYS Fluent software was used to perform steady and unsteady analysis and the results were compared with computational predictions. Findings: Steady computational results are in good agreement with those from OpenFOAM for a non-morphing airfoil and for a morphed airfoil with a maximum TE deflection equal to 5 per cent of the chord. The results obtained by ANSYS Fluent show that an average of 6.5 per cent increase in lift-to-drag ratio is achieved, compared with a hinged flap airfoil with the same TE deflection. By using dynamic meshing, unsteady transient simulations reveal that the local flow field is influenced by the morphing motion. Originality/value: An airfoil parametrisation method was modified to introduce time-dependent morphing and used to drive dynamic meshing through an in-house-developed UDF. The morphed airfoil’s superior aerodynamic performance was demonstrated in comparison with traditional hinged TE flap. A methodology was developed to perform unsteady transient analysis of a morphing airfoil at high angles of attack beyond stall and to compare with published data. Unsteady predictions have shown signs of rich flow features, paving the way for further research into the effects of a dynamic flap on the flow physics

Near stall unsteady flow responses to morphing flap deflections

The unsteady flow characteristics and responses of an NACA 0012 airfoil fitted with a bio-inspired morphing trailing edge flap (TEF) at near-stall angles of attack (AoA) undergoing downward deflections are investigated at a Reynolds number of 0.62 × 106 near stall. An unsteady geometric parametrization and a dynamic meshing scheme are used to drive the morphing motion. The objective is to determine the susceptibility of near-stall flow to a morphing actuation and the viability of rapid downward flap deflection as a control mechanism, including its effect on transient forces and flow field unsteadiness. The dynamic flow responses to downward deflections are studied for a range of morphing frequencies (at a fixed large amplitude), using a high-fidelity, hybrid RANS-LES model. The time histories of the lift and drag coefficient responses exhibit a proportional relationship between the morphing frequency and the slope of response at which these quantities evolve. Interestingly, an overshoot in the drag coefficient is captured, even in quasi-static conditions, however this is not seen in the lift coefficient. Qualitative analysis confirms that an airfoil in near stall conditions is receptive to morphing TEF deflections, and that some similarities triggering the stall exist between downward morphing TEFs and rapid ramp-up type pitching motions

Design optimisation of separate-jet exhausts with CFD in-the-loop and dimensionality reduction techniques

For Ultra-High Bypass Ratio aero-engines, the exhaust system is likely to play a significant role on the aerodynamics and performance of the aircraft. For this reason, relatively rapid methods for the aerodynamic design and optimisation of exhaust systems are required to inform design decisions at early stages of the design process. Previous exhaust optimisation works encompassed Response Surface Model (RSM) based optimisations of nozzle configurations that were parametrised with a significant number of design variables. The RSM were constructed with a large database of designs that were assessed with fine computational meshes and well resolved boundary layers. However, the large number of design variables and the computational cost required to evaluate each exhaust design limited the optimisation capabilities. This work develops a relatively more rapid exhaust optimisation method based on CFD in-the-loop and dimensionality reduction. The methodology is based on coarse meshes and wall functions to guide the optimisation process and is coupled with methods for the identification of the dominant design variables. For an UHBR aero-engine exhaust design space of 16 design variables, it was found that the velocity coefficient could be characterised with only seven parameters. Based on these results, various optimisation methods were developed and applied. These targeted the maximisation of the velocity coefficient by optimising just the 7 dominant design variables. With these approaches, a similar benefit in exhaust performance relative to the baseline optimisation method was obtained approximately 4 times faster

Heat exchanger integration with an aero-engine bypass duct

The development of aero engines with geared fans may require the use of a heat exchanger system embedded within the bypass duct to dissipate heat due to the losses within the power gearbox of the fan. It is pertinent that the naturally ventilated heat exchanger system (HEX) is designed and installed to minimise detrimental impacts on the performance of the engine while meeting the HEX heat transfer requirements. This paper demonstrates the capabilities of a coupled mixed fidelity method to model a ventilated HEX embedded within the bypass duct. A systematic approach is presented to quantify the sensitivity of HEX heat transfer, HEX volume and engine net thrust to perturbation in HEX overall size and integration. A method to explore and quantify the trade-offs in HEX performance and bypass performance is detailed. The method can be used to allow rapid assessment of the integration of the HEX with the bypass duct

Dynamic mesh framework for morphing wings CFD

In this work, a framework to perform high fidelity Computational Fluid Dynamics (CFD) analysis of dynamically morphing airfoils and wings is presented. An unsteady parametric method to model the deforming motion is proposed and then implemented in a User-Defined Function (UDF). The UDF is used for driving dynamic mesh in ANSYS Fluent.First, the framework is applied to a 2D airfoil equipped with a morphing Trailing-Edge Flap (TEF). A numerical validation of the steady and unsteady predictions is then performed against published data. Furthermore, the aerodynamic efficiency of the morphing concept is compared to an airfoil with a hinged TEF. It is found that an average of 6.5% increase in lift-to-drag ratio can be achieved with the morphed flap. The framework is then used to study the flow response to a 2D downward flap deflection at various morphing frequencies. The slope of time histories of lift and drag coefficients were found to be proportional to the morphing frequency during the morphing phase. Contrary to the lift, however, the drag experiences an overshoot in its instantaneous values, resulting in efficiency loss for all frequencies before settling to a steady. This finding indicates the presence of unsteady effects that need to be taken into account during the design phase. Qualitative analysis reveals some similarities between rapid morphing and ramp-type pitching motion.The framework is developed further to study continuous active flow control using a harmonically morphing TEF and its effect on the aerodynamic performance and acoustic spectra. The parametric method is modified to model the low amplitude (0.1 and 0.01% of the chord) harmonic morphing (combined upward and downward motion) in the TEF and the Ffowcs-Williams and Hawkings acoustic analogy was used for noise prediction. For this part of the work, a hybrid Reynolds-averaged Navier–Stokes–Large Eddy Simulation (RANS-LES) model, Stress-Blended Eddy Simulation (SBES), is used. It is shown that the 0.1% morphing amplitude induces higher sound pressure levels around the morphing frequency, and that all the morphing cases induce a shift in the main tone to a higher frequency, with a 1.5 dB reduction in the sound pressure levels. Apart from noise abatement, it is found that for a morphing frequency of 800 Hz and 0.01% amplitude it is possible to achieve up to 3% increase in aerodynamic efficiency.Finally, a framework extension from 2D to 3D is proposed, by extending the parametrization method to model both the morphed TEF and the seamless flap side-edge transition between the morphing and static parts. A comparative study between a wing with a statically morphed flap and one with a hinged flap reveals that the morphed flap produces higher lift and lower drag resulting in an enhanced aerodynamic efficiency (CL/CD) of up to 40%. This enhanced efficiency is mainly due to the absence of gaps and the contribution of the seamless transition to lift generation. The unsteady analysis of the 3D dynamically morphed wing shows the presence of the drag overshoot, which is consistent with the 2D results. Finally, when comparing 2D and 3D CFD results, it is observed that 2D results tend to over-predict both the lift and drag. This is because 2D analysis assumes that the entire span is deflecting whereas the 3D wing would only have a portion of the flap deflecting.The framework established in this thesis can be easily applied to other types of airfoils, leading-edge morphing, as well as wind and tidal turbine blades