Browsing by Author "Christie, Robert"

Now showing 1 - 17 of 17
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    Aerodynamics of aero-engine installation
    (Sage Publications, 2016-02-24) Stankowski, Tomasz P.; MacManus, David G.; Sheaf, Christopher; Christie, Robert
    This paper describes current progress in the development of methods to assess aero-engine airframe installation effects. The aerodynamic characteristics of isolated intakes, a typical transonic transport aircraft as well as a combination of a through-flow nacelle and aircraft configuration have been evaluated. The validation task for an isolated engine nacelle is carried out with concern for the accuracy in the assessment of intake performance descriptors such as mass flow capture ratio and drag rise Mach number. The necessary mesh and modelling requirements to simulate the nacelle aerodynamics are determined. Furthermore, the validation of the numerical model for the aircraft is performed as an extension of work that has been carried out under previous drag prediction research programmes. The validation of the aircraft model has been extended to include the geometry with through flow nacelles. Finally, the assessment of the mutual impact of the through flow nacelle and aircraft aerodynamics was performed. The drag and lift coefficient breakdown has been presented in order to identify the component sources of the drag associated with the engine installation. The paper concludes with an assessment of installation drag for through-flow nacelles and the determination of aerodynamic interference between the nacelle and the aircraft.
  • Thumbnail Image
    ItemOpen Access
    An automated approach for the aerodynamic design of close-coupled propulsion/airframe configurations
    (Council of European Aerospace Societies, 2020-02-28) Matesanz García, Jesús; Christie, Robert; Tejero, Fernando; MacManus, David G.; Heidebrecht, Alexander
    Reducing aircraft emissions is a key element in mitigating the environmental impact of aviation. Within this context, different novel aircraft propulsion configurations have been proposed. A common feature of many of these novel configurations is the closer integration of the propulsive system and the aircraft airframe with an expected increase of the aerodynamic coupling. Therefore, is necessary to assess the performance of the aerodynamic installation of the propulsive system of these configurations with a systematic approach. A systematic and automated methodology for the design and performance evaluation of embedded propulsion systems is defined. This methodology is demonstrated with a Boundary Layer Ingestion propulsive fuselage concept. This approach covers the geometry design of the selected configuration, an automatic aerodynamic numerical computation and a novel performance evaluation for the design. A Design Space Exploration was performed to characterize the relative importance of the individual parameters of the geometry and their correlation with the key performance metrics. Finally, a multi-objective optimization was carried to demonstrate the capabilities of this approach.
  • Thumbnail Image
    ItemOpen Access
    An automated approach to nacelle parameterization using intuitive class shape transformation curves
    (American Society of Mechanical Engineers (ASME), 2017-01-18) Christie, Robert; Heidebrecht, A.; MacManus, David G.
    A tool to create parametric aerodynamic shapes using intuitive design variables based on class shape transformation (CST) curves is presented. To enable this, a system has been developed which accepts arbitrary constraints and automatically derives the analytical expressions which describe the corresponding class shape transformation curves. Parametric geometry definitions for fan cowl and intake aero-lines were developed using the generalized method. Computational fluid dynamics (CFD) analysis of the fan cowl shows that despite the simple geometry definition, its performance characteristics are close to what would be expected of a finished design. The intake geometry was generated in a similar way and met the typical performance metrics for conventional intakes. This demonstrates the usefulness of the tool to quickly and robustly produce parametric aero-lines with good aerodynamic properties, using relatively simple intuitive design variables.
  • Thumbnail Image
    ItemOpen Access
    Coupled propulsive and aerodynamic analysis of an installed ultra-high bypass ratio powerplant at high-speed and high-lift conditions
    (AIAA, 2023-06-08) Matesanz García, Jesús Matesanz; MacManus, David G.; Tejero, Fernando; Goulos, Ioannis; Hueso Rebassa, Josep; Swarthout, Avery E.; Christie, Robert
    To achieve the targets proposed in the Flightpath 2050 for the aviation industry, more efficient propulsive systems are required. One possible solution is to increase the bypass ratio of the engines to increase the propulsive efficiency and reduce the specific fuel consumption. However, larger fan diameters are expected for these configurations, which results in an increase in the aerodynamic coupling between the powerplant and the airframe. The aim of this work is to develop and demonstrate a thrust and lift matching methodology for installed powerplants using a coupled aero-propulsive model. As a proof of concept, the aerodynamic performance of an ultra-high bypass ratio powerplant integrated with the airframe was evaluated across different flight conditions. This includes high-lift operating conditions such as end of runway; and high-speed conditions such as mid cruise. To evaluate the aerodynamic performance of the propulsion integration a combined assessment of the airframe and powerplant aerodynamics is required using computational fluid dynamics (CFD). The integration of the powerplant with the airframe has the potential to change the engine requirements across the aircraft operational envelope. To account for this the aerodynamic analysis is coupled with a turbomachinery model to adjust the engine thermodynamic conditions at a given operating point.
  • Thumbnail Image
    ItemOpen Access
    Design and analysis of non-axisymmetric installed aero-engine exhaust systems
    (Elsevier, 2020-09-17) Otter, John J.; Goulos, Ioannis; Christie, Robert; MacManus, David G.
    In order to increase propulsive efficiency, and hence reduce fuel consumption, future aero-engines are expected to operate with higher bypass ratios and larger fan diameters relative to current in-service engines. As such, propulsion systems are likely to be more closely-coupled with the airframe which is expected to accentuate detrimental aerodynamic interference effects between the engine and airframe. It is therefore crucial that the design of future aero-engine exhaust systems is considered as part of an engine-airframe configuration in order to ensure that the expected benefits of high BPR engines are realised. This work presents the aerodynamic performance and evaluation of a set of novel exhaust systems within complete engine-airframe configurations. The introduction of non-axisymmetric exhaust systems was shown to mitigate the aerodynamic penalties associated with closely-coupled propulsion systems at cruise conditions. Relative to an axisymmetric baseline configuration, the introduction of non-axisymmetric bypass and core nozzles were found to increase the net vehicle force of the engine-airframe configuration by 0.8% and 0.6% respectively. As a result of this work, it can be concluded that non-axisymmetric exhaust systems represent a viable method for reducing aircraft cruise fuel burn.
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    Lateral jet interaction with a supersonic crossflow
    (Cranfield University, 2010-10) Christie, Robert; MacManus, David G.
    A lateral jet in a supersonic crossflow creates a highly complex three-dimensional flow field which is not easily predicted. The aim of this research was to assess the use of a RANS based CFD method to simulate a lateral jet in supersonic crossflow interaction by comparing the performance of available RANS turbulence models. Four turbulence models were trialled in increasingly complex configurations; a flat plate, a body of revolution and a body of revolution at incidence. The results of this numerical campaign were compared to existing experimental and numerical data. Overall the Spalart-Allmaras turbulence model provided the best fit to experimental data. The performance of the lateral jet as a reaction control system was assed by calculating the force and moment amplification factors. The predicted flowfield surrounding the interaction was analysed in detail and was shown to predict the accepted shock and vortical structures. The lateral jet interaction flowfield over a body of revolution was shown to be qualitatively the same as that over a flat plate. An experimental facility was designed and manufactured allowing the study of the lateral jet interaction in Cranfield University’s 2 ½” x 2 ½” supersonic windtunnel. The interaction was studied with a freestream Mach number of 1.8, 2.4 & 3.1 and over a range of pressure ratios (50≤PR≤200). Levels of unsteadiness in the interaction were measured using high bandwidth pressure transducers. The level of unsteadiness was quantified by calculating the OASPL of the pressure signal. OASPL was found to increase with increasing levels of PR or MPR and to decrease with increases of Mach number. The levels of unsteadiness found were low with the highest levels found downstream of the jet.
  • Thumbnail Image
    ItemOpen Access
    Low order models for transonic afterbody aerodynamic characteristics
    (AIAA, 2020-01-05) Zuccolo, Giovanni; Christie, Robert; MacManus, David G.; Goulos, Ioannis; Martin, Peter
    A key aspect in the preliminary design of new combat aircraft is the prediction of the afterbody and exhaust system aerodynamic drag. To meet the various operating conditions requirements for a multi-role vehicle the afterbody typically includes a variable geometry. Within the preliminary design context, this makes the aerodynamic performance prediction a difficult challenge. This research investigates reduced order models for prediction of the aerodynamic performance of axisymmetric transonic afterbody and nozzle systems for a range of aerodynamic conditions and geometric degrees of freedom. The aerodynamic performance metric of interest is afterbody drag coefficient (CD). Two reduced order models are investigated: artificial neural network and Gaussian process. The geometric variables include boattail closing angle, nozzle throat to exit area ratio and afterbody mean angle and the aerodynamic parameters are free-stream Mach number and nozzle pressure ratio. The results show that these types of reduced order models can be used for preliminary design aerodynamic performance prediction. The Gaussian process CD prediction is less accurate compared to the artificial neural network with the latter giving a prediction uncertainty of approximately ±0.01 in CD with a 2σ confidence level. The Gaussian process prediction uncertainty is approximately ±0.013 CD.
  • Thumbnail Image
    ItemOpen Access
    Methodology assessment for the design and analysis of aero-engine short intakes
    (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
  • Thumbnail Image
    ItemOpen Access
    Nacelle design for ultra-high bypass ratio engines with CFD based optimisation
    (Elsevier, 2020-09-09) Robinson, Matthew; MacManus, David G.; Christie, Robert; Sheaf, Christopher; Grech, Nicholas
    As the size of aero-engines has increased in recent years, the need for slimmer and shorter nacelles has become more pressing. A more aggressive design space must therefore be explored for nacelle designs which are expected to perform worse in the off design conditions such as spillage than current nacelle designs. In this work, a novel design space has been explored through the use of an optimisation method which evaluated nacelle aerodynamic performance based on computational fluid dynamics simulations. A multi-objective optimisation was undertaken where cruise drag, drag rise Mach number, spillage drag and two metrics based on the pressure distribution of the nacelle were optimised. Comparable optimal designs were picked from the Pareto sets of optimisations carried out at different nacelle lengths and radial offsets and some key outcomes established from their aerodynamics and geometries. It was determined that a reduction in the length of the nacelle from 3.8 highlight radii to 3.1 radii resulted in a significantly worse aerodynamic performance which included an increase in peak surface isentropic Mach number at cruise of 0.1 and up to four times as much spillage drag. It was however also established from the optimisation results that as the required drag rise Mach number was decreased the overall performance of short nacelles improved significantly.
  • Thumbnail Image
    ItemOpen Access
    Non-axisymmetric aero-engine nacelle design by surrogate-based methods
    (Elsevier, 2021-06-15) Tejero, Fernando; Christie, Robert; MacManus, David G.; Sheaf, Christopher
    For many aerodynamic design tasks, a key challenge is the balance between the non-linearity of the transonic flow, the inherent 3D nature of the geometry and flow field, the computational cost and the level of accuracy. Within an optimisation process this is further compounded by the high degrees of freedom to define the geometry and the requirement for 3D computations at both design and off-design conditions. An example of this is the design of compact nacelles for future civil aero-engines which will have larger bypass ratios than current in-service architectures. This paper presents an approach for the design and optimisation of 3D drooped and scarfed non-axisymmetric nacelles. To reduce the computational expense, a range of surrogate-based adapted methods are investigated. Relative to the conventional approach of full numerical simulations in the optimisation loop, the adapted method identifies an acceptable design space with a 65% reduction in the total computational cost. Overall, this demonstrates a useful approach for reducing the time and cost of high-dimensional, aerodynamic design problems.
  • Thumbnail Image
    ItemOpen Access
    Parametric design of non-axisymmetric separate-jet aero-engine exhaust systems
    (Elsevier, 2019-07-16) Otter, John J.; Christie, Robert; Goulos, Ioannis; MacManus, David G.; Grech, Nicholas
    Future civil air vehicles are likely to feature propulsion systems which are more closely integrated with the airframe. For a podded underwing configuration, this close coupling is expected to require non-axisymmetric design capabilities for the aero-engine exhaust system. This work presents the development of a novel parametric representation of non-axisymmetric aero-engine exhaust system geometries based on Intuitive Class Shape Transformation (iCST) curves. An exhaust design method was established and aerodynamic analyses of a range of non-axisymmetric configurations was demonstrated. At typical flight conditions, the introduction of non-axisymmetric separate jet nozzles was shown to increase the engine net propulsive force by 0.12% relative to an axisymmetric nozzle.
  • Thumbnail Image
    ItemOpen Access
    Propulsion system integration and modelling synthesis
    (Cranfield University, 2016-07) Christie, Robert; MacManus, David G.
    Concerns over fuel costs, along with the ever increasing requirement to reduce the impact of emissions, means that the world's airlines continue to introduce low-noise and more fuel-efficient aircraft into their fleet. Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, historically an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. For example, although the typical increase in fan diameter is generally beneficial to the uninstalled engine specific fuel consumption, the increase in the nacelle drag and weight are detrimental to the aircraft performance. There is also likely to be a stronger aerodynamic coupling between the engine and the airframe. Overall there is a risk that the gains in uninstalled engine performance are wholly or partly lost due to adverse engine-airframe installation and interference effects as well as additional nacelle weight. It is clear that the quantification of the elements of installation drag is a key aspect in the assessment of the likely developments in engine design as well as on the installation requirements for future airframe architectures. The overall aim of this research is to determine the effect of nacelle size, weight, geometry and installation on flight efficiency. This aim has been addressed through the development of a framework which combines the engine thermodynamic model, aircraft performance, engine installation aspects and a flight trajectory approach. This framework has been developed to assess the relative importance of various engine installation aspects on the overall flight fuel burn for a range of short-haul and long-haul configurations.
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    The use of hybrid intuitive class shape transformation curves in aerodynamic design
    (Elsevier, 2019-10-23) Christie, Robert; Robinson, Matthew; Tejero, Fernando; MacManus, David G.
    The inherent mathematical smoothness of intuitive class shape transformation (iCST) curves has been shown to be suitable for the design of aerodynamic shapes. However, this property means that any changes to a constraint are not local but will result in a modification to the whole curve. This poses a problem to the aerodynamic designer when different parts of the curve are required to fulfil particular design requirements. A Hybrid iCST (HiCST) parameterisation approach is proposed which allows two sections of a single aero-line curve to be decoupled, without geometric discontinuity, whilst maintaining the dimensionality of a design problem. The HiCST approach has been tested on two key aerodynamic components of an aero-engine. Firstly, a design space exploration and optimisation were carried out for an aero-engine fan cowl. A comparison of Pareto fronts showed a 3.9% reduction in the minimum achievable nacelle drag from the iCST to the HiCST parameterisation. Secondly, aero-engine intakes were designed with both the iCST and HiCST parameterisations. The HiCST intake showed improved aerodynamic performance in terms of DC60 and IPR and proved more insensitive to changes in massflow and incidence. This development of the method for an aero-engine fan cowl and intake highlights the potential aerodynamic benefit from the proposed HiCST method.