Computational Evaluation of Aerodynamic Loading on Retractable Landing-Gears

This study investigates the substantial challenges that landing gear systems face due to increased aircraft speeds and traffic volumes, focusing particularly on bird strike incidents. By utilizing the Smoothed Particle Hydrodynamics (SPH) method alongside a rigid-flexible coupling finite element model, we analyzed the dynamic characteristics of bird impacts on ten typical landing gear structures. The simulations indicated that stress peaks exceeding 1200 MPa occurred in the nose landing gear pipelines, drag brace, spring, and main landing gear pipelines post-impact, leading to severe damage and loss of functionality. The aluminum drag brace displayed deformations greater than 15 mm, which poses significant safety risks. Additionally, a positive correlation was observed between peak structural deformation and bird impact speed on the main landing gear’s upper locking rod, with larger deformations inducing significant concentrated stress in the pin joints, which escalates with increased speed. Structures not directly impacted by the bird strike maintained sufficient rigidity, though certain critical areas require enhanced strength and protective measures such as reinforced panels in the design. This research provides theoretical support for designing bird strike protection in landing gear systems.

Computational fluid dynamics is employed to predict the aerodynamic properties of the prototypical trailing-edge control surfaces for a small, regional transport, commercial aircraft. The virtual experiments are performed at operational flight conditions, by resolving the mean turbulent flow field around a realistic model of the whole aircraft. The Reynolds-averaged Navier–Stokes approach is used, where the governing equations are solved with a finite volume-based numerical method. The effectiveness of the flight control system, during a hypothetical conceptual pre-design phase, is studied by conducting simulations at different angles of deflection, and examining the variation of the aerodynamic loading coefficients. The proposed computational modeling approach is verified to have good practical potential, also compared with reference industrial data provided by the Leonardo Aircraft Company.

Turbomachinery aerodynamic and aeroacoustic modelling is recognized to be one of the main areas of interest in the frame of industrial engineering, due to the large number of applications concerning the rotating fluid machines. Numerical modelling is today widely integrated in the design and development process of industrial components, as well as Computational Fluid Dynamics (CFD) is a tool well integrated into the industrial development and production life-cycles. This has been made because of two main factors: the increase in the performance of relatively cheap computing systems and the progress made by development of integrated CAE virtual environment even more oriented to design and optimization. Furthermore well established and validated CFD methodologies able to deal with the high complexity of geometries and multiphysics approaches are available and practicable within the industrial environment. Nevertheless since for many of applications such as aerodynamics, heat exchange, etc., CFD is largely used, there are still some areas where it represents a challenge, in particular for its industrial applicability. One of these areas is the Computational AeroAcoustics (CAA), whose interest is rapidly growing due to the increasing demand of quick and efficient numerical tools for the design-to-noise approach to airframe components. The major difficulty of CAA is that noise is a secondary effect of other physical phenomena, and noise prediction has to deal with highly complex topics such as turbulence modelling and transition to turbulence prediction. Moreover the sound pressure compared with the hydrodynamic pressure is several orders of magnitude smaller making its numerical prediction very difficult. The goal of the present work is to perform investigations on two rotating fluid machines: the vertical axis wind turbines (VAWT) and the high speed transonic cruise propellers. The investigations performed were focused on the aerodynamic and aeroacoustic theoretical and numerical modelling in order to achieve the numerical results that actually miss in the literature improving the know-how for two classes of problems which play a central role in the modern industry: the renewable energies and the advanced transportation systems. VAWT modelling was approached from a theoretical point of view, by the implementation of a modern unsteady aerodynamic model for non-stationary airfoil aerodynamic coefficients prediction (the Beddoes Leishman model) into a classical theory, the Double Streamtube Paraschivoiu model. The acoustic modelling of WT was approached on a general basis with the modelling of the airfoil self-generated problem. It was chosen as it is one of the most prominent noise sources for wind turbines and it represents a big challenge for CFD. The preliminary literature review pointed out how there are different airfoil self-generated noise typologies, according to the laminar/turbulent characteristics of the flow field, airfoil aerodynamic parameters and far-field flow conditions. Different CFD numerical approaches were used for the different noise generation mechanisms, including transient RANS/LES simulations with a particular focus for novel turbulence modelling methodologies, involving transitional models and Embedded LES. The acoustic pressure flow computations were performed with the Ffowcs Williams Hawkings (FW-H) acoustic analogy and pressure time signals post-processed with an in-house built acoustic tool. Deep explorations of acoustic signal noise processing, Fast Fourier Transformation techniques and noise signal corrections have been necessary in order to achieve good agreement between experimental and computational data. The reference test-case was the NACA 0012 airfoil, chosen for the wide amount of experimental data available in literature in a significant range of velocities and angles of attack. The problem of propeller aerodynamic and aeroacoustic modelling was approached with the CFD and CAA simulation of a subsonic propeller, the NACA 4-(3)(08)-03, chosen for the experimental results available in literature for the 2-bladed and 7-bladed configurations. This test-case allowed us to set up properly the numerical simulation, the CAD model and the computational grid requirements for such kind of geometries. In a second stage the attention was focused on the NASA SR2 and SR3 geometries, both in the 8-bladed configuration. Experimental data in transonic conditions for wind tunnel and flight test were available for these two geometries, and numerical simulations were performed for 5 different data sets, for asymptotic Mach numbers between 0.6 and 0.9 and rotational speeds between 6000 and 9000 rpm. Results of the simulations are compared with experiments, showing the ability of this approach to predict noise with a discrepancy within a few dB for the different simulated conditions and microphones locations. Particular attention is given to the set of corrections to be applied to acoustic experimental data in order to be consistently compared with free field CFD results. The CFD simulation strategy has been refined to perform complete aerodynamic and aeroacoustic calculations with highly competitive computational cost.

Computational Fluid Dynamics (CFD) simulations play an increasingly important role in academic research and industrial product development due to the growing availability of computational resources. The accuracy of CFD results is strongly influenced by spatial discretization, i.e., the meshing of the computational domain. To ensure reliable and grid-independent results, potential discretization errors must be quantified. A commonly applied approach for estimating spatial discretization errors is Richardson extrapolation, which relies on systematically generated grids at different resolutions. In this study, the applicability and accuracy of Richardson extrapolation for estimating spatial discretization errors in CFD are analyzed. The simulations are performed using the commercial CFD solver ANSYS CFX 2024R2. The computational grids are generated with ANSYS MESHER and ANSYS TURBOGRID to ensure high-quality structured meshes. Two distinct CFD models are considered: a backward-facing step, a well-established benchmark case, and a turbomachinery blade passage, a case commonly used in engineering practice. Both models are systematically meshed using hexagonal grids, and the error estimation method is applied to various grid sizes and evaluation quantities. The derived results are comprehensively compared to assess the effectiveness and reliability of the method. Based on these findings, conclusions and recommendations for the practical application of Richardson extrapolation in CFD are provided in detail.

A nonlinear aeroelastic model for a flexible panel is expanded to consider the effect of the viscous boundary layer using a Reynolds-averaged Navier–Stokes (RANS) solver. This study presents the use of the dynamically linearized time-domain approach reduced-order model to compute the generalized aerodynamic force from a computational fluid dynamics (CFD) simulation within the nonlinear aeroelastic solver. Results obtained using the RANS approach are compared with those using an inviscid CFD solver and also the full potential flow. The flutter onset critical condition is obtained based on the limit cycle oscillation amplitudes for a range of supersonic Mach numbers. Additionally, the effect of different viscous boundary-layer thicknesses is explored. Conclusions are made based on the application of this more complete aerodynamic theory, particularly for near-transonic Mach numbers.

Steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are presented for the three-dimensional flow over a simplified tractor/trailer geometry at zero degrees yaw angle. The simulations are conducted using a multi-block, structured computational fluid dynamics (CFD) code. The turbulence closure model employed is the two-equation Menter k-ω model. The discretization error is estimated by employing two grid levels: a fine mesh of 20 million cells and a coarser mesh of 2.5 million cells. Simulation results are compared to experimental data obtained at the NASA-Ames 7×10ft wind tunnel. Quantities compared include vehicle drag, surface pressures, and time-averaged velocities in the trailer near wake. The results indicate that the RANS approach is able to accurately predict the surface pressure on the vehicle, with the exception of the base region. The pressure predictions in the base region are poor due to the inability of the RANS model to accurately capture the near-wake vortical structure. However, the gross pressure levels in the base region are in reasonable agreement with experiment, and thus the overall vehicle drag is well predicted.

In this chapter, first, basic information about the landing gear (definition, purpose, and duties, etc.) is given. Examples of different aircraft are given throughout the chapter. Systems in large aircraft such as extend-retract mechanisms are explained on Boeing 737 aircraft. As mentioned in the chapter introduction, landing gears are the elements that provide contact with the ground during the landing—takeoff phases and movements on the ground (during taxi), the friction resistance is minimized, and they best absorb the loads caused by the horizontal and vertical movements of the aircraft. Afterward, different landing gear layouts and their usage areas, advantages, and disadvantages are mentioned. Landing gear struts, which are one of the basic elements of the landing gear and provide structural strength, are mentioned. By specifying the characteristics of different strut structures, the damping structure of the energies arising from the landing is explained. After the strut structures, wheels, tires, and brake structures, which are the other basic elements of the landing gear, are explained. Since there are retractable landing gears in large aircraft, the extend-retract mechanisms of the main and nose landing gear, their controls, and indicators are mentioned. Finally, the nose wheel steering mechanism that provides guidance during movement on the ground and the tail skid structure that prevents the tail from hitting the ground directly during takeoff are mentioned.KeywordsLanding gearMain landing gearNose landing gearExtend-retract mechanismAeronautics

Computational fluid dynamics was employed to predict the early stages of the aerodynamic breakup of a cylindrical water column, due to the impact of a traveling plane shock wave. The unsteady Reynolds-averaged Navier–Stokes approach was used to simulate the mean turbulent flow in a virtual shock tube device. The compressible flow governing equations were solved by means of a finite volume-based numerical method, where the volume of fluid technique was employed to track the air–water interface on the fixed numerical mesh. The present computational modeling approach for industrial gas dynamics applications was verified by making a comparison with reference experimental and numerical results for the same flow configuration. The engineering analysis of the shock–column interaction was performed in the shear-stripping regime, where an acceptably accurate prediction of the interface deformation was achieved. Both column flattening and sheet shearing at the column equator were correctly reproduced, along with the water body drift.

Numerical Investigation of Wind Pressure Coefficients for Photovoltaic Arrays Mounted on Building Roofs

<div class="section abstract"><div class="htmlview paragraph">Advancements in additive manufacturing (AM) technology have enabled the use of Triply Periodic Minimal Surface (TPMS) lattice structures to integrate thermal and structural functions into a single component. These structures offer advantages such as weight reduction, compactness and enhanced heat dissipation, making them promising for automotive, aerospace and electronics applications. TPMS structures, characterized by zero mean curvature and periodic crystalline geometry, have recently gained significant research attention thanks to their potential in thermal management. Among various TPMS geometries, the gyroid and diamond structures stand out for their thermal and fluid dynamic performance. This study explores the influence of cell geometry, unit cell size, and wall thickness on the efficiency of TPMS-based heat exchangers, as these parameters are crucial for their technical feasibility. Using Computational Fluid Dynamics (CFD) simulations, a comparative analysis is conducted for a case study represented by a heat exchanger. The numerical approach relies on a steady-state Reynolds-Averaged Navier-Stokes (RANS) approach with the Reynolds Stress Transport (RST) Elliptic Blending model, while heat transfer is analyzed through the Conjugate Heat Transfer (CHT) technique. The results indicate that reducing the unit cell size enhances heat transfer but also increases pressure drop at a fixed flow rate. Similarly, increasing the wall thickness raises pressure losses, though its effect on heat transfer is minimal. Overall, the diamond structure outperforms the gyroid in both thermal efficiency and flow permeability, making it a more effective choice for TPMS-based heat exchangers. These findings offer valuable insights for optimizing TPMS geometries in high-performance heat transfer applications, guiding future research and industrial implementations.</div></div>

The prediction of the added resistance and attainable ship speed under actual weather conditions is essential to evaluate the true ship performance in operating conditions and assess environmental impact. In this study, a reliable methodology is proposed to estimate the ship speed loss of the S175 container ship in specific sea conditions of wind and waves. Firstly, the numerical simulations are performed to predict the added resistance and ship motions in regular head and oblique seas using three different methods; a 2-D and 3-D potential flow method and a Computational Fluid Dynamics (CFD) with an Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. Simulations of various wave conditions are compared with the available experimental data and these are used in a validation study. Secondly, following the validation study in regular waves, the ship speed loss is estimated using the developed methodology by calculating the resistance in calm water and the added resistance due to wind and irregular waves, taking into account relevant wave parameters and wind speed corresponding to the Beaufort scale, and results are compared with simulation results obtained by other researchers. Finally, the effect of the variation in ship speed and therefore the ship speed loss is investigated. This study shows the capabilities of the 2-D and 3-D potential methods and CFD to calculate the added resistance and ship motions in regular waves in various wave headings. It also demonstrates that the proposed methodology can estimate the impacts on the ship operating speed and the required sea margin in irregular seas.

The interaction between different components of a jet engine represents a very important aspect of the engine design process. Sudden mass flow-rate changes induced by flow separation and pressure waves, interaction of the unsteady wakes originating from the fan blades with the low-pressure compressor, high temperature streaks interacting with the first stages of the turbine are all complex unsteady phenomena that cannot be simply accounted for through boundary conditions of a single component simulation. Only simulations that integrate multiple engine components can describe these flow features accurately. Today’s use of Computational Fluid Dynamics (CFD) in gas turbine design is usually limited to component simulations. The demand on the models to represent the large variety of physical phenomena encountered in the flow path of a gas turbine mandates the use of a specialized and optimized approach for each component. The flow-field in the turbomachinery portions of the domain is characterized by both high Reynolds numbers and high Mach numbers. The prediction of the flow requires the precise description of the turbulent boundary layers around the rotor and stator blades, including tip gaps and leakage flows. A number of flow solvers that have been developed to deal with this kind of problem have been in use in industry for many years. These flow solvers are typically based on the Reynolds-Averaged Navier-Stokes (RANS) approach. Here, the unsteady flow-field is ensemble-averaged, removing all the details of the small scale turbulence; a turbulence model becomes necessary to represent the effects of turbulence on the mean flow. The flow in the combustor, on the other hand, is characterized by multi-phase flow, intense mixing, and chemical reactions. The prediction of turbulent mixing is greatly improved using flow solvers based on Large-Eddy Simulations (LES). While the use of LES increases the computational cost, LES has been the only predictive tool able to simulate consistently these complex flows. LES resolves the large-scale turbulent motions in time and space, and only the influence of the smallest scales, which are usually more universal and hence, easier to represent, has to be modeled. 2 Since the energy-containing part of the turbulent scales is resolved, a more accurate description of scalar mixing is achieved, leading to improved predictions of the combustion process,. LES flow solvers have been shown in the past to be able to model simple flames and are currently being adapted for use in gas turbine combustors. 5 In order to compute the flow in the entire jet engine, one needs to couple RANS and LES solvers. We have developed a software environment that allows a simulation of multi-component effects by executing multiple solvers simultaneously. Each of these solvers computes a portion of a given flow domain and exchanges flow data at the interfaces with its peer solvers (see Figure 1). The approach to couple two or more existing flow solvers has the distinct advantage of building upon the experience and validation that has been put

Cavitation phase change phenomenon appears in many engineering applications, often eroding and damaging surfaces, so deteriorating the performance of devices. Therefore, it is a phenomenon of great interest for the research and industry communities. In this work, three different cavitation models, the Homogeneous Relaxation Model (HRM), the Schnerr and Sauer, and the Kunz, are implemented in a Eulerian multiphase homogeneous flow Computational Fluid Dynamics (CFD) solver previously developed for simulating fully atomized sprays. The improved solver can be used then to study not only cases with cavitation, such a hydrofoil, but also situations where cavitation occurs together with liquid atomization, such as high pressure injection systems. Validation of this solver is carried out for three different cases under diverse operating conditions: a two-dimmensional throttle, a hydrofoil and a single-hole fuel injector. The Reynolds-Averaged Navier-Stokes (RANS) approach is employed for taking into account the turbulence effects. Simulation results are compared to experimental data available in the literature. Among the tested cavitation models, the HRM is the one that provides the best accuracy in the three validation cases. Nevertheless, the onset of cavitation and the area occupied by the vapor cavities are always underpredicted, by all cavitation models in all validation cases. This can be associated to the unsteady and turbulent nature of the cavitation phenomenon. Even so, the computational prediction of several parameters, such as mass flow rate through the nozzles or spray spreading angle, has an error below 5-10%, which proves the capabilities of the solver.

In this work, several computational-fluid-dynamics-based approaches are employed to validate the airloads, trim angles, blade elastic motions, vortex positions, and structural loads of a rotor in low-speed, descending flight. To this end, two different comprehensive codes, CAMRAD II and DYMORE, are coupled with a computational fluid dynamics code, KFLOW, using a loose coupling methodology. A computational fluid dynamics approach using the measured blade motions is also carried out for the validation. For both clarity and consistency required in the relative comparison between different methods, an identical computational fluid dynamics grid system is used for the study. A fuselage effect is considered in the analysis. The predicted results are correlated against the measured data. CAMRAD II coupling shows good prediction for low-frequency loadings, elastic motions, and structural lag bending and torsion moments. DYMORE coupling demonstrates good matches on trim control angles, blade vortex interaction airloads, and structural flap bending but less satisfactory for lag motions. Initial results indicate poor correlation on aeropitching moments. This discrepancy is seen to be fixed when considering the actual pressure sensor locations used in the test. The blade–vortex miss distance at a desired instant is also evaluated. About 25% larger miss distance is obtained with a higher harmonic control input.

The determination of wind‐induced fatigue load in large structures and buildings with complex geometries, which do not fall in typical cases of building codes and standards, represents a consuming task, and it is usually evaluated through the aid of wind tunnel tests, while computational approaches do not yet have a large application.The practical use of computational fluid dynamics (CFD) techniques in civil engineering applications has in fact been rare outside the framework of steady‐state analyses, because of the limitations of RANS approaches and of the higher cost of LES, but with the increase in computing resources and with the introduction of new and more efficient turbulence models, the practical use of CFD to evaluate fluctuating features of wind flow is much more feasible now. With it, it is possible to foresee the possibility for the evaluation of wind‐induced fatigue loads in steel structures by using CFD. This paper has the purpose to discuss the feasibility of a procedure that uses CFD as the first step in a chain of numerical simulations that leads to the fatigue calculation of a large, complex structure.The state of the art of turbulence models for CFD is here shown by performing literature review, with particular attention to their application to case studies related to large steel structures. A special focus in this paper lies in the use of PANS models, which reduce computational cost and grid sensitivity compared with LES, while providing comparable accuracy.