Global Aerodynamic Coefficients Research Articles

Dynamic Structural Scaling Concept for a Delta Wing Wind Tunnel Configuration Using Additive Manufacturing

Considering aeroelastic effects plays a vital role in the aircraft design process. The construction of elastic wind tunnel models is a critical element in the investigation of occurring aeroelastic phenomena. However, the structural scaling between full-scale and reduced-scale configurations is a complex design and manufacturing task and is usually avoided in wind tunnel testing. This work proposes a numerical approach for a dynamic aeroelastic scaling technique, which is applied to a fictive delta wing configuration. This scaling methodology is designed to optimise the structural layout of wind tunnel models with an integrated rib and spar structure to meet the behaviour of a realistic full-scale equivalent. For the modelling approach of the wing structure, a beam and shell structure is utilised. The applied scaling laws for the relevant quantities and the applied procedures are described. Computational fluid dynamics (CFD) calculations are performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations for the assumption of a rigid full-scale and down-scaled wing. These calculations are used to verify the aerodynamic scaling assumptions, which are applied to the scaling procedure of the wind tunnel model. Global aerodynamic coefficients are evaluated for a variety of angles of attack. The local flow phenomena of the full-scale and the scaled model are compared in more detail for a medium and a high angle of attack. The pressure coefficient distribution shows a proper accordance for the full-scale and the scaled model. To verify the results of the structural scaling optimisation, a high-fidelity structural full-scale model is compared with the scaled model using the ELFINI FEM solver. Therefore, all structural components are modelled by 2D elements. The results for the reduced eigenfrequencies and according modes of the full-scale and the scaled model show a high level of similarity. A static deformation of the structural grids is performed by applying the aerodynamic loads from the CFD simulations. The results show that the deviation of the nondimensional deformation between the scaled and the full-scale model is negligible. Consequently, the applied scaling methodology proves to be a valuable tool for the conceptual approach of designing aeroelastically scaled wind tunnel models considering 3D-printed material.

Aerothermochemical analysis of the Orion capsule in rarefied transitional flow regime during Mars entry

It is well known that NASA developed the Orion project, besides for a rescue shuttle for the International Space Station, also for the transportation of instruments and astronauts to Moon, Mars and beyond. The forthcoming use of Orion for Mars landing stimulated Zuppardi to compute global aerodynamic coefficients in rarefied, transitional flow along a high altitude entry path. A Direct Simulation Monte Carlo (DSMC) code computed the coefficients at the altitudes of 80, 90 and 100 km, in the range of angles of attack 0–180 deg. The aim of the present paper, that can be considered as the logic follow on of the previous paper by Zuppardi, is to evaluate, in high altitude entry path, the influence of: 1) chemical reactions on the flow field and on some local quantities (temperature, pressure and heat flux) along the Orion surface, 2) typology of entry trajectory (direct and orbit) on both local quantities and drag coefficient, 3) heat flux associated to the surface recombination reactions. Computations were carried out in axisymmetric flow and in the altitudes interval 60–100 km by means of a home made code for the computation of the entry trajectories and of the powerful and advanced two-dimentional/axisymmetric DSMC code (DS2V) for the solution of the flow field around Orion.

Computer analysis of rarefied aerodynamics around a winged space-plane for Mars entry

The forthcoming use of Orion for Mars landing stimulated Zuppardi to compute global aerodynamic coefficients in rarefied flow along an entry path. Zuppardi and Mongelluzzo also studied Aerodynamics of a blunt cylinder, provided with flapped fins, as a possible alternative to Orion for Mars Entry, Descent and Landing. Computer tests were carried out, in the altitude interval 60-100 km, by three codes: i) home made code computing the entry trajectory, ii) Direct Simulation Monte Carlo code (DS2V), solving 2D/axisymmetric flow field and computing local quantities, iii) Direct Simulation Monte Carlo code (DS3V) solving 3D flow field and computing global aerodynamic coefficients. The comparison of the aerodynamic behaviour of the two capsules in axisymmetric flow field verified that heat flux and wall temperature for the finned-cylinder are higher than those of Orion. The DS3V results verified that Orion is better than the finned-cylinder to produce an aerodynamic force for slowing down the capsule. On the contrary, the results indicated that the finned-cylinder is better in terms of attitude control capability. The purpose of the present paper is to compare Aerodynamics of: Orion, finned-cylinder, a hypothetical, winged space-plane in high altitude Mars entry path. Computations were carried out by means of the two above mentioned DSMC codes, along both orbit and direct entry trajectories. While the global aerodynamic coefficients of the space-plane are comparable with those of the finned cylinder, the aerodynamic and thermal stresses (or pressure, temperature and heat flux) at the nose stagnation point are higher for the space-plane. Therefore, the finned-cylinder seems to be a valid alternative to Orion.

Aerodynamics of Orion in Rarefied Flow Along a Mars Entry Path

It is well known that the Orion capsule was born as a rescue shuttle for the International Space Station. NASA developed the Orion project for the transportation of instruments and astronauts to moon, Mars, and beyond. Orion is similar in shape but larger than the Apollo command module; Orion will be able to host up to six astronauts, but Apollo command module could host only three astronauts. The aerodynamics of Orion during reentry to Earth in all rarefied regimes (that is, from free molecule regime to continuum) was already studied. The forthcoming use of Orion for Mars landing stimulated the author to evaluate global aerodynamic coefficients in rarefied flow along an entry path. The study considered problems both in axisymmetric and in three-dimensional flows by means of two direct simulation Monte Carlo codes. Global aerodynamic coefficients were computed at the altitudes of 80, 90, and 100 km. Special attention was paid to longitudinal stability.

Magnus effect for roll-decoupled canards on a spinning body of revolution

PurposeSpinning slender bodies are affected by lateral Magnus forces and moments when exposed to cross-flow. The effects occurring for spinning bodies of revolution in combination with stabilising or control surfaces such as canards are not yet fully explained. Therefore the present work aims to investigate the phenomena arising from the interactions of a roll-decoupled guidance unit with a spinning rear body are investigated.Design/methodology/approachA generic tangential-ogive-cylinder projectile equipped with deflectable canards on a roll-decoupled nose is investigated by means of 3D Reynolds-averaged Navier–Stokes simulations at Mach number 2 for angles of attack up to 22 degrees. Different canard deflection angles up to 9 degrees are considered. Global aerodynamic coefficients as well as local flow fields are analysed to explain the interactions occurring between the roll-decoupled guidance unit and the spinning rear body.FindingsThe deflected canards lead to flow interactions resulting in lateral forces and moments even without a spinning motion of the rear part. Depending on the canard deflection angles, these forces act in or against the direction of the classical Magnus effect. For angles of attack smaller than 10 degrees it is possible for the current body geometry to directly superpose the lateral effects resulting from the fins for the non-spinning model with those occurring for the non-finned but spinning model to obtain the total forces and moments acting on a spinning model with canted canards. However, the lateral effects generated on the guidance unit itself are insignificant compared to the canard-induced effects on the rear body.Originality/valueA detailed analysis of the interaction effects arising from a decoupled guidance unit containing canards with a non-spinning/spinning rear body is performed and the underlying phenomena are revealed.

Towards Virtual Flight in Realistic Environments: A Hybrid Coupled Simulation Method

The vision of establishing a simulation system for virtual flight in a realistic environment is addressed by the coupling of two separate flow solvers in a bidirectional manner. In the long run, this shall enable (for example) the simulation of a flight through realistic atmospheric turbulence, including the effects on the aircraft and the rollup of trailing vortices and their further development until final decay. A compressible Reynolds-averaged Navier–Stokes (RANS) solver resolves the near field around a vortex generator (a rectangular NACA0012 wing geometry), including its boundary layer. An incompressible large-eddy simulation (LES) solver is used to model the atmosphere around the vortex generator, with its wake footprint in the LES domain being of primary interest. Two validation cases are presented. First, the method is partially validated with data from a wind-tunnel experiment. The second case is a vertical gust-wind simulation, which is compared to an already validated pure RANS approach for calculating the global aerodynamic coefficients given analytically defined atmospheric disturbances. The hybrid method proves to be powerful in cases where large-scale transient atmospheric effects and their interaction with flying aircraft are to be studied.

Effects of boundary layer transition on the aerodynamic analysis of high-lift systems

Transition to turbulence is known as a factor that impacts the performance of high-lift devices, but only a few numerical results that include transition are available in the literature. We use the Langtry-Menter γ−Reθ transition model to study the influence of transition to turbulence in global aerodynamic coefficients and flow topology in three-dimensional high-lift configurations. The influence of turbulence inflow variables is also addressed. Numerical results are compared with previous results obtained with the Shear Stress Transport (SST) turbulence model, which does not account for transition effects. The numerical simulations are performed using configuration “one” from the 1st AIAA CFD High-Lift Prediction Workshop. Experimental data from the NASA Langley 14 by 22-ft Subsonic Wind Tunnel provide the global aerodynamic information for the verification of our numerical results. It is observed that the inclusion of transition to turbulence impacts the flow topology, as well as the aerodynamic coefficients.

Leading-Edge Roughness Affecting Diamond-Wing Aerodynamic Characteristics

Diamond wing configurations for low signature vehicles have been studied in recent years. Yet, despite numerous research on highly swept, sharp edged wings, little research on aerodynamics of semi-slender wings with blunt leading-edges exists. This paper reports on the stall characteristics of the AVT-183 diamond wing configuration with variation of leading-edge roughness size and Reynolds number. Wind tunnel testing applying force and surface pressure measurements are conducted and the results presented and analysed. For the investigated Reynolds number range of 2.1 × 10 6 ≤ R e ≤ 2.7 × 10 6 there is no significant influence on the aerodynamic coefficients. However, leading-edge roughness height influences the vortex separation location. Trip dots produced the most downstream located vortex separation onset. Increasing the roughness size shifts the separation onset upstream. Prior to stall, global aerodynamic coefficients are little influenced by leading-edge roughness. In contrast, maximum lift and maximum angle of attack is reduced with increasing disturbance height. Surface pressure fluctuations show dominant broadband frequency peaks, distinctive for moderate sweep vortex breakdown. The experimental work presented here provides insights into the aerodynamic characteristics of diamond wings in a wide parameter space including a relevant angle of attack range up to post-stall.

Aerodynamic analysis of a C-class-like catamaran in simplified unsteady wind conditions using LES and URANS modeling

Highlights • A numerical analysis on a C-class-like geometry is performed in unsteady wind conditions at different wind frequencies. • LES and URANS models agree in predicting the global aerodynamic coefficients as well as the flow structures of the wingsail. •Stall cells appear on the wingsail in case of unsteady wind conditions and their features depend on wind frequency. •The wind frequency, affecting the stall cells, leads to a modification of the aerodynamic coefficients of the wingsail.

Methods for controlling the local spatial and temporal resolution of vortex particle simulations of bluff body aerodynamics problems

This paper presents a novel adaptive solution strategy for vortex particle methods that allows the efficient resolution of multiple scales that are characteristic of flows around bluff bodies with small structural details. The efficiency of the method arises from maintaining a sufficiently high spatial numerical discretisation near the fluid-solid interface and a progressive coarsening away from the bodies and their structural details. The control of the particle map is achieved through remeshing based on high-order interpolation kernels and ensures an accurate representation of the flow features of different scales whose resolution is critical to an accurate computation of the pressures on the immersed structure subjected to separated flows. As the required time step of the time integration is directly related to the spatial resolution, the adaptivity is further enhanced by a temporal adaptivity realized through a sub-stepping technique for controlling the frequency at which the particle convection and diffusion steps are performed. The validation of the proposed technique is performed by simulations of the impulsively started flow past a circular cylinder at Reynolds number 3000, where both the spatial and the temporal strategies are at first independently studied and then combined to full adaptivity. A substantially higher computational efficiency compared to equally accurate non-adaptive simulations is reported. Further studies of accuracy and efficiency are performed by simulating the flow past the cross section of a bridge arch geometry featuring small structural details. Solution properties studied include the resolution of local velocity profiles and global aerodynamic coefficients. These reveal how the application of the full adaptive strategy enables for the accurate and efficient prediction of the flow features. The results indicate speed-ups of up to factor 4 to 5 when comparing the new approach to the classical Vortex Particle Method.

Reconstruction of unsteady viscous flows using data assimilation schemes

This paper investigates the use of various data assimilation (DA) approaches for the reconstruction of the unsteady flow past a cylinder in the presence of incident coherent gusts. Variational, ensemble Kalman filter-based and ensemble-based variational DA techniques are deployed along with a 2D compressible Navier–Stokes flow solver, which is also used to generate synthetic observations of a reference flow. The performance of these DA schemes is thoroughly analyzed for various types of observations ranging from the global aerodynamic coefficients of the cylinder to the full 2D flow field. Moreover, different reconstruction scenarios are investigated in order to assess the robustness of these methods for large scale DA problems with up to 105 control variables. In particular, we show how an iterative procedure can be used within the framework of ensemble-based methods to deal with both non-uniform unsteady boundary conditions and initial field reconstruction. The different methodologies developed and assessed in this work give a review of what can be done with DA schemes in computational fluid dynamics (CFD) paradigm. In the same time, this work also provides useful information which can also turn out to be rational arguments in the DA scheme choice dedicated to a specific CFD application.

Sparse grids‐based stochastic approximations with applications to aerodynamics sensitivity analysis

SummaryThis work compares sample‐based polynomial surrogates, well suited for moderately high‐dimensional stochastic problems. In particular, generalized polynomial chaos in its sparse pseudospectral form and stochastic collocation methods based on both isotropic and dimension‐adapted sparse grids are considered. Both classes of approximations are compared, and an improved version of a stochastic collocation with dimension adaptivity driven by global sensitivity analysis is proposed. The stochastic approximations efficiency is assessed on multivariate test function and airfoil aerodynamics simulations. The latter study addresses the probabilistic characterization of global aerodynamic coefficients derived from viscous subsonic steady flow about a NACA0015 airfoil in the presence of geometrical and operational uncertainties with both simplified aerodynamics model and Reynolds‐Averaged Navier‐Stokes (RANS) simulation. Sparse pseudospectral and collocation approximations exhibit similar level of performance for isotropic sparse simulation ensembles. Computational savings and accuracy gain of the proposed adaptive stochastic collocation driven by Sobol' indices are patent but remain problem‐dependent. Copyright © 2015 John Wiley & Sons, Ltd.

Aerodynamic Investigation for Prospective Aerospace Vehicle in the Transitional Regime

The basic quantitative tool for the study of hypersonic rarefied flows is the direct simulation Monte Carlo method (DSMC). The DSMC method requires a large amount of computer memory and performance and is unreasonably expensive at the first stage of spacecraft design and trajectory analysis. A possible solution to this problem is approximate engineering methods. However, the Monte Carlo method remains the most reliable approach to compare to the engineering methods that provide good results for the global aerodynamic coefficients of various geometry designs. This paper presents the calculation results of aerodynamic characteristics for spacecraft vehicles in the free molecular, the transitional and the continuum regimes using the local engineering method. Results and methods would be useful to calculate aerodynamics for new-generation hypersonic vehicle designs.

Hypersonic high altitude aerothermodynamics of a space re-entry vehicle

The analysis of the rarefaction effects in the prediction of the main aerothermal loads of a space re-entry vehicle is presented. It is well known that the Navier–Stokes equations fail in rarefied regimes and therefore other approaches must be used. In the present paper different configurations have been simulated by using the Direct Simulation Monte Carlo method. Moreover, slip flow boundary conditions have been implemented in a Navier–Stokes code in order to extend the validity of such a continuum method in the transitional flow regime. Finally, bridging-formulae for the high altitude aerodynamics of winged bodies have also been used. For the tuning of the methodologies, two simple geometries have been analysed, specifically designed to study the phenomenon of shock wave boundary layer interaction: the first one is a hollow cylinder flare, for which experimental data are also available; the second one is the geometry of a test article that was designed and tested at the Italian Aerospace Research Centre. The other two configurations that have been taken into account are an experimental winged re-entry vehicle and a capsule, for which global aerodynamic coefficients and local wall heating have been determined using different computational approaches. The Navier–Stokes code with slip flow boundary conditions has shown good predictive capabilities of the size of the recirculation bubble compared with the experimental results in the hollow cylinder flare test case; however, for the winged vehicle and capsule case, the CFD results are not fully satisfactory and the Monte Carlo method remains the most reliable approach, together with the bridging formulae, that provide good results for the global aerodynamic coefficients.