Browsing by Author "Boscagli, Luca"

Now showing 1 - 17 of 17
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    Aerodynamics of a compact nacelle at take-off conditions
    (IEEE, 2023-06-08) Swarthout, Avery E.; MacManus, David G.; Tejero, Fernando; Matesanz García, Jesús; Goulos, Ioannis; Boscagli, Luca; Sheaf, Christopher
    Next generation ultra-high bypass ratio turbofans may have larger fan diameters than the previous generation of aircraft engines. This will potentially increase the nacelle diameter and may incur penalties to the weight and drag of the powerplant. To offset these penalties, a more compact nacelle may be used. Compact nacelles may be more sensitive to boundary layer separation at the end-of-runway conditions, particularly at an off-design windmilling operating point. Additionally, the flow separation on the external cowl surface is likely to be influenced by the integration between the powerplant, pylon and airframe. The publicly available NASA high lift common research model (HL-CRM) with take-off flap and slat settings was modified to accommodate an ultra-high bypass ratio powerplant. The powerplant has an intake, separate jet exhaust, external cowl and pylon. Boundary layer separation on the external cowl of the compact powerplant is assessed at end-of-runway rated take-off and take-off windmilling scenarios. Additionally, the lift curve and Cp distributions of the high lift common research model (HL-CRM) are compared for rated take-off and take-off windmilling engine mass flows. Overall, the nacelle boundary layer separates from the nacelle highlight at windmilling conditions when the engine mass flow is relatively low. The mechanism of separation at windmilling conditions is diffusion driven and is initiated on the nacelle aft-body. The pylon has a small impact on the overall mechanism of separation. However, the wing and high-lift devices of the HL-CRM introduce local separation on the external cowl. The HL-CRM wing with the installed powerplant stalls at a similar angle (αa/c = 16°) to the HL-CRM with the through flow nacelle available in the open literature. Compared with the nominal take-off condition, the maximum lift coefficient of the HL-CRM airframe was reduced by about 2% under windmilling engine mass flows.
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    Aerodynamics of a short intake in crosswind
    (Elsevier, 2022-09-05) Boscagli, Luca; Christie, Robert; MacManus, David; Piovesan, Tommaso
    The next generation of turbofan aero-engines are likely to have an increase in fan diameter to reduce the specific thrust and increase the overall propulsive efficiency. More compact nacelles with possibly shorter intakes may be used to reduce weight and drag and achieve a net reduction of fuel consumption. For these compact nacelles a key consideration is the design of the short intake at the off-design conditions such as crosswind and high incidence operations. The close coupled interaction between a short intake and the fan at these off-design conditions is one of the key challenges. Previous work focused on the impact of short intake aerodynamics on the fan but there is a similar requirement to understand the impact of the fan on the viable short intake design space. This paper addresses the influence of the fan on the separation onset of the flow within a short intake under crosswind conditions. The effect of the fan on the separation characteristics of the intake boundary layer was considered both from a steady and an unsteady point of view. A hierarchy of fan computational models was used to separately assess the different aerodynamic contributions and to evaluate a net effect of the fan on the intake critical condition. Steady computational fluid dynamics analyses showed a notable positive effect of the fan on total pressure loss at post-separation conditions relative to a configuration without the fan. However, unsteady analyses revealed that fan unsteadiness has an adverse impact on the intake separation characteristics which reduces the intake critical conditions by about 15%. The main mechanisms behind the unsteady interaction were identified. Overall this work addresses, for the first time, the role of fan unsteadiness on the separation characteristics of the boundary layer within a short intake in crosswind.
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    Characteristics of shock-induced boundary-layer separation on nacelles under windmilling diversion conditions
    (AIAA, 2023-11-02) Boscagli, Luca; MacManus, David; Tejero, Fernando; Sabnis, Kshitij; Babinsky, H.; Sheaf, Christopher
    The boundary layer on the external cowl of an aeroengine nacelle under windmilling diversion conditions is subjected to a notable adverse pressure gradient due to the interaction with a near-normal shock wave. Within the context of computational fluid dynamics (CFD) methods, the correct representation of the characteristics of the boundary layer is a major challenge in capturing the onset of the separation. This is important for the aerodynamic design of the nacelle, as it may assist in the characterization of candidate designs. This work uses experimental data obtained from a quasi-2D rig configuration to provide an assessment of the CFD methods typically used within an industrial context. A range of operating conditions are investigated to assess the sensitivity of the boundary layer to changes in inlet Mach number and mass flow through a notional windmilling engine. Fully turbulent and transitional boundary-layer computations are used to determine the characteristics of the boundary layer and the interaction with the shock on the nacelle cowl. The correlation between the onset of shock-induced boundary-layer separation and the preshock Mach number is assessed, and it was found that the CFD is able to discern the onset of boundary-layer separation.
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    A comparative assessment of multi-objective optimisation methodologies for aero-engine nacelles
    (ICAS, 2022-09-09) Swarthout, Avery; MacManus, David; Tejero, Fernando; Matesanz García, Jesús; Boscagli, Luca; Sheaf, Christopher
    There are significant environmental and economic drivers for the development of more fuel-efficient commercial aircraft engines. The propulsive efficiency benefits of ultra-high bypass ratio turbofans may be counteracted by the drag and weight penalty associated with larger nacelles. A more compact nacelle design may therefore be necessary to reduce these penalties. However, increasing compactness also increases the sensitivity of the nacelle to boundary layer separation under off-design windmilling conditions. This paper investigates methods for incorporating windmilling considerations alongside design point requirements within a multi-objective, multi-point optimisation. Windmilling under aircraft diversion and at the end-of-runway (EoR) condition are considered. The windmilling conditions are assessed through a combination of regression and classification type criteria. The transonic aerodynamics of the nacelle at the design point are notably different from the transonic characteristics at the diversion windmilling conditions. Meanwhile, the aerodynamics, and separation mechanisms, at the end-of-runway condition are dominated by subsonic diffusion. Overall, a combination of regression and classification mechanisms are found to be most suitable for the nacelle optimization as it delivers a design population which is favorably balanced between robustness against boundary layer separation as well as delivering nacelle drag benefits.
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    Deep-learning for flow-field prediction of 3D non-axisymmetric aero-engine nacelles
    (AIAA, 2023-06-08) Tejero, Fernando; MacManus, David; Matesanz García, Jesús; Boscagli, Luca; Hueso Rebassa, Josep; Sheaf, Christopher
    Computational fluid dynamics (CFD) methods have been widely used for the design and optimisation of complex non-linear systems. Within this context, the overall process can typically have a large computational overhead. For preliminary design studies, it is important to establish design capabilities that meet the usually conflicting requirements of rapid evaluations and accuracy. Of particular interest is the aerodynamic design of components or subsystems within the transonic range. This can pose notable challenges due to the non-linearity of this flow regime. There is a need to develop low order models for future civil aero-engine nacelle applications. The aerodynamics of compact nacelles can be sensitive to changes in geometry and operating conditions. For example, within the cruise segment different flow-field characteristics may be encountered such as shock-wave boundary layer interaction or shock induced separation. As such, an important step in the successful design of these new architectures is to develop methods for fast and accurate flow-field prediction. This work studies two different metamodelling approaches for flow-field prediction of 3D non-axisymmetric nacelles. Firstly, a reduced order model based on an artificial neural network (ANN) is considered. Secondly, a low order model that combines singular value decomposition and an artificial neural network (SVD+ANN) is investigated. Across a wide geometric design space, the ANN and SVD+ANN methods have an overall uncertainty in the isentropic Mach number prediction of about 0.02. However, the ANN approach has better capabilities to predict pre-shock Mach numbers and shock-wave locations.
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    Design of a new test rig to investigate transonic external fan cowl separation
    (Association Aeronautique Astronautique de France, 2022-03-28) Sabnis, Kshitij; Boscagli, Luca; Swarthout, Avery; Babinsky, Holger; MacManus, David; Sheaf, Christopher T.
    Ultra high-bypass ratio engines, which show considerable promise in reducing the environmental impact of commercial aviation, generally adopt slim fan cowl profiles. These geometries can be more sensitive to separation on the external surfaces in engine windmilling conditions during take-off climb out or during cruise. This paper describes the development of a two-dimensional wind tunnel rig which can accurately replicate the separation mechanisms experienced by real aero-engine nacelles. This design process highlights the importance of considering factors such as Reynolds-number effects, tunnel-wall effects, the two-dimensional nature of the rig, and the tunnel boundary layers.
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    Design of a quasi-2D rig configuration to assess nacelle aerodynamics under windmilling conditions
    (AIAA, 2023-06-08) Boscagli, Luca; Tejero, Fernando; Swarthout, Avery; MacManus, David G.; Sabnis, Kshitij; Babinsky, Holger; Sheaf, Christopher
    Aero-engine nacelles are typically designed to fulfil both design and off-design aircraft manoeuvres. Under-off design conditions one of the objective is to avoid large flow separation either on the external cowl or within the intake that can influence aircraft and engine operability. One particular scenario is represented by a low engine mass flow regime associated with one inoperative engine, also known as a windmilling condition. Under windmilling, the boundary layer on the external cowl of the nacelle can separate either due to the interaction with shockwaves or due to notable adverse pressure gradient towards the trailing edge. Both mechanisms are computationally difficult to model and there is a need for more validation of computational fluid dynamics (CFD) methods. The aim of this work is to develop a rig configuration which will provide CFD validation data for the aerodynamics of a nacelle under representative windmilling conditions. Two flight regimes are considered, namely windmilling diversion and end-of-runway. CFD simulations of a 3D nacelle are used to determine primary aerodynamic mechanisms associated with boundary layer separation. Two rig configurations are developed and both 2D and 3D CFD analyses are used to achieve the design objectives. Overall, this work presents the design philosophy and methods that were pursued to develop a quasi-2D rig configuration representative of the aerodynamics of 3D-annular aero-engine nacelles under windmilling conditions.
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    Effect of unsteady fan-intake interaction on short intake design
    (American Society of Mechanical Engineers, 2023-10-13) Boscagli, Luca; MacManus, David G.; Christie, Robert; Sheaf, Christopher
    The next generation of ultra-high bypass ratio civil aero-engines promises notable engine cycle benefits. However, these benefits can be significantly eroded by a possible increase in nacelle weight and drag due to the typical larger fan diameters. More compact nacelles, with shorter intakes, may be required to enable a net reduction in aero-engine fuel burn. The aim of this paper is to assess the influence of the design style of short intakes on the unsteady interaction under crosswind conditions between fan and intake, with a focus on the separation onset and characteristics of the boundary layer within the intake. Three intake designs were assessed and a hierarchical computational fluid dynamics approach was used to determine and quantify primary aerodynamic interactions between the fan and the intake design. Similar to previous findings for a specific intake configuration, both intake flow unsteadiness and the unsteady upstream perturbations from the fan have a detrimental effect on the separation onset for the range of intake designs. The separation of the boundary layer within the intake was shock driven for the three different design styles. The simulations also quantified the unsteady intake flows with an emphasis on the spectral characteristics and engine-order signatures of the flow distortion. Overall, this work showed that is beneficial for the intake boundary layer to delay the diffusion closer to the fan and reduce the pre-shock Mach number to mitigate the adverse unsteady interaction between the fan and the shock.
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    Experimental investigation of transonic external fan cowl separation
    (Association Aeronautique Astronautique de France, 2023-03-29) Sabnis, Kshitij; Boscagli, Luca; Babinsky, Holger; MacManus, David; Sheaf, Christopher T.
    When a civil aircraft engine is shut down during the cruise phase of flight and thus begins to windmill, a supersonic region forms on the external surface of the fan cowl. The terminating normal shock can separate the turbulent boundary layer developing on this external surface. A series of experiments are performed in a quasitwo-dimensional wind tunnel rig to investigate the influence of various parameters on this flow problem. As the engine mass-flow rate is reduced, an increase in normal shock strength results in the onset of flow separation which thickens the boundary layer developing on the external fan cowl surface by a factor of three. A reduction in incoming Mach number from the nominal value of 0.65 to 0.60 weakens the shock wave and thus delays flow separation. If the incoming boundary layer is laminar rather than turbulent, the normal shock Mach number is observed to increased by 10%. Despite the stronger shock, no significant flow separation can be detected even for the lowest engine mass-flow rates studied and the external nacelle surface boundary layer is measured to be thinner than for the turbulent case.
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    Fan-intake aerodynamic interactions under crosswind conditions
    (European Turbomachinery Society, 2023-04-28) Boscagli, Luca; MacManus, David; Christie, Robert
    The aerodynamics of an aero-engine intake under off-design conditions is characterized by a range of steady and unsteady mechanisms that can adversely affect the fan operability. A hierarchical computational fluid dynamics approach was used for an initial assessment of the primary aerodynamic interactions between the fan and the intake design. These approaches included steady computations with a lower order fan model as well as full unsteady computations. For a powered intake in crosswind, the direction of the wind determines the direction of rotation of the ground vortex relative to the fan. For the full unsteady analyses, the threshold crosswind speed reduced by 12kts and 22kts relative to the steady analysis for the counter-rotating and co-rotating configuration respectively. Overall, this work identified and assessed for the first time a fan-intake unsteady aerodynamic interactions that may affect the design of short intakes in association with fan systems.
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    Methodology assessment for the design and analysis of aero-engine short intakes
    (Council of European Aerospace Societies (CEAS) , 2020-02-28) Boscagli, Luca; Christie, Robert; MacManus, David G.
    A key aspect for the design of an aero-engine intake is that it must operate at off-design conditions such as high incidence. For short intake design the interaction with the fan cannot be neglected. This work establishes how different modelling strategies can affect the intake design boundaries and the analysis of an aero-engine short-intake. Unsteady simulations showed high levels of total pressure and swirl fluctuations while steady computations showed some limitations whenever extreme operating conditions are modelled. The analysis of a short intake showed that the fan is able to extend the incidence limit to avoid separation by about 0.6°. Overall, this work proposes a robust methodology for short-intake analysis
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    Numerical and experimental investigations of diffusion-induced boundary layer separation on aero-engine nacelles
    (Elsevier, 2024-10) Boscagli, Luca; Sabnis, Kshitij; MacManus, David G.; Babinsky, Holger; Tejero, Fernando; Sheaf, Christopher
    Aero-engine nacelles have to fulfill design requirements at both cruise and off-design conditions. Under engine windmilling conditions the ingested streamtube massflow is relatively low. A key off-design condition is take-off, which, in conjunction with an engine windmilling scenario, results in the stagnation point of the ingested streamtube being located significantly inside the intake. The combination of high angle of attack and low engine massflow rates leads to a strong flow acceleration and subsequent diffusion of the boundary layer on the upper quadrants of the external nacelle cowl, which can terminate with subsonic separation from the leading-edge. Under this condition, Reynolds number effects can play a dominant role on the separation onset and characteristics and 3D-annular wind tunnel tests cannot always achieve Reynolds’ number equivalent to full scale. A novel quasi-2D rig configuration representative of the aerodynamics of a full-size aero-engine nacelle under windmilling end of runway conditions examined in detail the characteristics of the boundary layer on the external cowl of a nacelle prior to diffusion-induced separation. Separation of the boundary layer was independently promoted through changes to represent different engine massflow rates and freestream Mach number on the rig to determine the limits of steady Reynolds Averaged Navier Stokes (RANS) methods to discern the onset of boundary layer separation. For the conditions and geometry investigated, the combined experimental and computational results showed that there was laminar to turbulent transition of the boundary layer ahead of the subsonic diffusion. The work showed that steady RANS can predict the onset of boundary layer separation with an uncertainty of approximately 10% on notional engine massflow rate and 0.05 on freestream Mach number relative to a nominal operating freestream Mach number of 0.25. This provides guidance for the industrial design and optimization of future windmilling-tolerant nacelles for large ultra-high bypass ratio turbofan engines.
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    Point-enhanced convolutional neural network: a novel deep learning method for transonic wall-bounded flows
    (Elsevier, 2024-12) Tejero, Fernando; Sureshbabu, Sanjeeth; Boscagli, Luca; MacManus, David
    Low order models can be used to accelerate engineering design processes. Ideally, these surrogates should meet the conflicting requirements of large design space coverage, high accuracy and fast evaluation. Within the context of aerospace applications at transonic conditions, this can be challenging due to the associated non-linearity of the flow regime. Different methods have been investigated in the past to predict the flow-field around shapes such as airfoils or cylinders. However, they usually have reduced spatial resolution, limiting the prediction capabilities within the boundary layer which is of interest for transonic wall-bounded flows. This work proposes a novel Point-Enhanced Convolutional Neural Network (PCNN) method that combines the advantages of the well-established PointNet and convolutional neural network approaches. The PCNN model has relatively low memory requirements in the training process, preserves the spatial correlation in the domain and has the same resolution as a traditional computational method. The architecture is used for the flow-field prediction of civil aero-engine nacelles in which it is demonstrated that the flow features of peak isentropic Mach number (Mis), pre-shock isentropic Mach number and shock location (X/Lnac) are captured within ^Mis = 0.02, ^Mis=0.04, ^X/Lnac=0.007, respectively. The PCNN model successfully predicts the integral parameters of the boundary layer, in which the incompressible displacement thickness, momentum thickness and shape factor are typically within 5% of the CFD. Overall, the PCNN method is demonstrated for transonic wall-bounded flows for a range of flow physics that include shock waves and shock-induced separation.
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    Shock-induced fan cowl separation during aeroengine windmilling at diversion from cruise
    (American Institute of Aeronautics and Astronautics (AIAA), 2024-11-13) Sabnis, Kshitij; Babinsky, Holger; Boscagli, Luca; MacManus, David; Sheaf, Christopher
    When a civil aircraft engine is operated at windmill during the cruise flight phase, there is supersonic flow acceleration around the leading edge of the fan cowl toward the external surface. The terminating normal shock wave can separate the turbulent boundary layer developing on this external surface. A series of experiments at a flight-relevant Reynolds number (1.2 million based on lip thickness) are performed in a quasi-two-dimensional wind tunnel rig to investigate the underlying flow physics. At a nominal inflow Mach number of 0.65 and a nacelle incidence angle of 4.5 deg, as the equivalent engine mass-flow rate is reduced, an increase in shock strength results in flow separation when the shock exceeds Mach 1.4. Over a 10% range in the notional engine mass-flow rate, the boundary layer developing on the external fan cowl thickens by a factor of three on the onset of separation. A reduction in the incoming Mach number from 0.65 to 0.60 weakens the shock wave and thus delays separation. An increase in surface roughness has no significant effect in situations where the boundary layer remains attached. However, for separated cases, an increased local roughness height causes a greater separation extent and a thicker boundary layer downstream of the shock wave.
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    Towards real-time CFD: novel deep learning architecture for transonic wall-bounded flows
    (2024-03-27) Tejero, Fernando; Sureshbabu, Sanjeeth; Boscagli, Luca; MacManus, David
    Low order models can be used to accelerate engineering design processes. These surrogates should meet the conflicting requirements of large design space coverage, high accuracy and fast evaluation. Within the context of aerospace applications at transonic conditions, this can be challenging due to the associated non-linearity of the flow regime. This work develops a deep learning based method for flow-field prediction. It preserves the spatial resolution of the underlying data, which enables the resolution of the boundary layer. This is an advance relative to current state-of-the-art for transonic flows. The architecture is demonstrated for a complex problem of aero-engine nacelles. The prediction of the primitive flow variables is within a root mean square error of 6×10−5. The model is used to extract the nacelle drag, and its accuracy is about 6.8% relative to CFD computations. The overall method is an enabling and fast preliminary design capability with self-consistent data for multidisciplinary design studies.
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    Unsteady aerodynamics of a coupled compact intake-fan in crosswind
    (International Council of the Aeronautical Sciences (ICAS), 2024-10-08) Lobuono, Luca; MacManus, David; Christie, Robert; Boscagli, Luca
    The design of aero-engine intakes for compact nacelles can be an important contributor in achieving cruise fuel burn reductions. A key aspect for the design of viable compact intakes is considerations of the off-design crosswind and high incidence conditions. The aerodynamics of compact intakes is also notably dependent on the flow interaction with the fan. This work analyses the unsteady intake-fan interactions under crosswind conditions. The effect of crosswind velocity is evaluated together with the intake ground plane interaction and the unsteady aerodynamic coupling between the intake and fan. The overall aim of the research is to identify the flow structures and the unsteady mechanisms involved in the separation of the intake flow. The work uses an unsteady fully coupled time resolved Reynolds averaged Navier-Stokes computational method to identify the unsteady features of intake-fan flow separation in crosswind operations. The unsteady intake flow distortion is assessed as well as the spectral signatures and engine-order perturbations due to the unsteady flow distortion. Local separated regions were identified in the diffuser. These are associated with the characteristics of the boundary layer and are phase-locked with the local pressure pulses from the fan. This aspect should be considered in the design of compact intakes with relatively high diffusion. Additional assessments of the previously reported unsteady lip separation is provided with the identification of the frequencies of the flow features in post-separation conditions and the axial and azimuthal movement of the separation due to the interaction with the ground vortex.
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    A wind tunnel rig to study the external fan cowl separation experienced by compact nacelles in windmilling scenarios
    (AIAA, 2023-01-19) Sabnis, Kshitij; Babinsky, Holger; Boscagli, Luca; Swarthout, Avery; Tejero, Fernando; MacManus, David; Sheaf, Christopher
    Ultra high-bypass ratio aircraft engines adopt slim fan cowl profiles which are sensitive to separation on their external surfaces under diversion windmilling conditions, when engine shutdown occurs during cruise. A two-dimensional wind tunnel rig is developed to investigate the separation mechanisms experienced by aero-engine nacelles in such scenarios to establish the detailed aerodynamics. The tunnel flow field with entry Mach number 0.65 broadly replicates the expected diversion windmilling flow behaviour for a full-scale nacelle, featuring a supersonic region which terminates in a normal shock wave on the external fan cowl surface. For the three conditions investigated, which relate to different engine mass-flow rates, the response of the boundary layer in this region progresses from remaining fully attached through to well-established separation. However, the rig Reynolds number based on nacelle lip thickness is about 1.2 million, roughly one-third of full scale, resulting in a transitional rather than turbulent shock-boundary-layer interaction. Nevertheless, simple simulations correctly predict the wind tunnel flow field, except for the precise boundary-layer response to normal shock waves, and so experimental data from the rig can be used to validate relevant computational methods.