Wing-body Junction Research Articles

A numerical study of the wall-modeled large-eddy simulations of attached and separated flows with a semi-coupled synthetic turbulence generator

The predictive accuracy of the fluctuations inside turbulent boundary layers directly relies on the upstream turbulence synthesizer in wall-modeled large-eddy simulations (WMLESs). The conventional fully coupled synthetic turbulence generator (STG) strongly depends on the grid topology and simultaneous advancement of the unsteady Reynolds-averaged region. In this study, the two-stage semi-coupled STG, which is tolerant to the grid topology and is cost-effective due to the compatibility with precursor methods, was investigated. First, the semi-coupled STG efficiently generated artificial turbulence based on the existing benchmark data in the calculations of the fully developed channel flow. The adaptation length of the STG was less than ten boundary layer thicknesses by means of the Reynolds stresses and wall shear stresses, while the downstream turbulence was sufficiently “mature” for the predictions of more complex flows. The semi-coupled method with different wall-modeling strategies was validated for the mildly separated flow over a flat strut. The steady two-dimensional (2D) precursor data at the inlet were effectively utilized by the STG to generate turbulence and the monitored pressure fluctuations agreed well with the experimental data. Finally, the calculations of the flow around a wing–body junction showed that the algebraic wall-modeled large-eddy simulation demonstrated good accuracy in predicting the horseshoe vortex at the symmetry plane, and coherent structures rapidly developed from the artificial turbulence generated by the STG. To conclude, the WMLES with the semi-coupled STG can effectively predict the unsteady fluctuations in the attached and separated boundary layers. The compatibility of the semi-coupled STG with precursor methods and the relatively low computational cost of the WMLES can broaden the application areas of the STG method in complex flows at high Reynolds numbers.

Computations of Flow Near the Nose of Wing-body Junction

Computations of Flow Near the Nose of Wing-body Junction

Review of research on streamwise corner boundary layer

This paper is a brief review of recent research on the streamwise corner boundary layer as it affects the component performance evaluation of both the theoretical and practical aircraft design. Typical examples include aircraft wing–body junction, rectangular air intakes, and turbine-hub flow. The paper addresses the questions of what we know and do not know about the streamwise corner boundary layer. Streamwise corner flows are characterized by the presence of secondary flows in the cross-stream planes, which are driven by the normal and secondary-shear components of the Reynolds stress tensor. Extensive studies of analysis for Prandtl's second kind of secondary flows have promoted the understanding of characteristics and formation of streamwise corner boundary layer. However, compared to the flat plate boundary layer, the research on the streamwise corner boundary layer is still far from enough, especially in the similarity solution, the instability, and transition mechanism. In recent years, a significant progress has been achieved in the study on the streamwise corner boundary layer in turbulent flow through direct numerical simulation and stress−ω Reynolds stress model.

Structural aspects of the attached turbulent boundary layer flow over a hill

Three-dimensional turbulent boundary layers under strong pressure gradients and curvature are the rule in real-world flow applications but are typically not well predicted by turbulence models due to isotropic eddy viscosity or equilibrium assumptions. Validation-quality data in complex 3D flows is necessary for continued efforts to improve simulation accuracy. The Benchmark Validation Experiments for RANS/LES Investigations (BeVERLI) Hill bump model, designed specifically for validation experiments, was tested in the Virginia Tech Stability Wind Tunnel to collect validation experiment data on the three-dimensional (3D) boundary layer flow over a 3D hill. Laser Doppler velocimetry measurements on the bump model were used to study the mean flow and turbulence structure and evaluate the impact of pressure gradient and curvature upon the total shear stress in the boundary layer and evaluate the impact of pressure gradient and curvature upon the total shear stress behavior in the near-wall region. From analysis of the BeVERLI Hill flow, including the boundary layer just upstream of the hill, and comparison with the 3D flow around a wing-body junction of Ölçmen et al. (Exp Fluids 31:219–228, 2001), it is shown that none of the stations studied exhibit a constant shear stress region over any significant region of the boundary layer.Graphical abstract

Application of the Nonlinear SST Turbulence Model for Simulation of Anisotropic Flows

The application of the nonlinear SST turbulence model (SST NL) for the calculation of flows with turbulence anisotropy is considered. The results of the following validation test cases are presented: the flow in a square duct, the corner flow separation at a wing-body junction (NASA Juncture Flow) and the transonic wing flow (NASA CRM). The nonlinear model has been found to significantly improve the quality of simulating the anisotropic flows as compared to models based on the Boussinesq hypothesis. It is shown that the model prevents false corner separation at the wing-body junction and thereby achieves a qualitative improvement in simulation results. The test case of the transonic wing flow revealed an upstream displacement of the shock wave on the upper side of the wing which leads to an underestimation of the lift force when using the SST NL model. In all the tests considered, the SST NL model required an increase in computational cost of at most 5 % compared to the conventional SST model.

Numerical Investigation of a Simplified Wing–body Junction Flow

The flow past a simplified wing-body junction configuration is simulated using a shear layer adaptive improved delayed detached-eddy-simulation (SLA-IDDES) approach in which an appropriate subgrid lengthscale is adopted in the boundary region, where the grid may be strongly anisotropic, to prevent the excessive generation of subgrid-scale eddy viscosity. The numerical results show overall good agreement with the experiment carried out by Ölçmen and Simpson. The self-induced chaotic switching of the horseshoe vortex between two flow modes is simulated and analysed, and its effects on the vortex legs and their inherent oscillation are also investigated. It is found that the corner vortex also exhibits an alternating formation and breakdown process with basically the same frequency as the horseshoe vortex. Corner separation is found to be affected also by the upstream horseshoe vortex and the inherent oscillation of the vortex legs.

NASA Juncture Flow Computational Fluid Dynamics Validation Experiment

The purpose of the NASA Juncture Flow experiment was to acquire high-quality flowfield details deep in the corner of a wing–body junction specifically for the purpose of computational fluid dynamics (CFD) validation. A truncated DLR F6 wing was used along with a flat-sided fuselage with windows that allowed both laser Doppler velocimetry and particle image velocimetry measurements to be made very close to the corner. This paper describes the experiment and its results. It also makes comparisons between the wind-tunnel data and Reynolds-averaged Navier–Stokes CFD results using a new version of a quadratic constitutive relation that was recently developed to improve separated corner-flow predictions. This validation experiment provides useful flowfield data that can be used to test the ability of CFD methods and models to accurately represent separated juncture flow physics.

Performance of Wall-Modeled LES with Boundary-Layer-Conforming Grids for External Aerodynamics

We investigate the error scaling and computational cost of wall-modeled large-eddy simulation (WMLES) for external aerodynamic applications. The NASA Juncture Flow is used as representative of an aircraft with trailing-edge smooth-body separation. Two gridding strategies are examined: 1) constant-size grid, in which the near-wall grid size has a constant value and 2) boundary-layer-conforming grid (BL-conforming grid), in which the grid size varies to accommodate the growth of the boundary-layer thickness. Our results are accompanied by a theoretical analysis of the cost and expected error scaling for the mean pressure coefficient and mean velocity profiles. The prediction of is within less than 5% error for all the grids studied, even when the boundary layers are marginally resolved. The high accuracy in the prediction of is attributed to the outer-layer nature of the mean pressure in attached flows. The errors in the predicted mean velocity profiles exhibit a large variability depending on the location considered, namely, fuselage, wing-body juncture, or separated trailing edge. WMLES performs as expected in regions where the flow resembles a zero-pressure-gradient turbulent boundary layer such as the fuselage ( error). However, there is a decline in accuracy of WMLES predictions of mean velocities in the vicinity of wing-body junctions and, more acutely, in separated zones. The impact of the propagation of errors from the underresolved wing leading edge is also investigated. It is shown that BL-conforming grids enable a higher accuracy in wing-body junctions and separated regions due to the more effective distribution of grid points, which in turn diminishes the streamwise propagation of errors.

Downstream evolution of junction flow three-component velocity fluctuations through the lens of the diagnostic plot

Experimental measurements of the streamwise and transverse velocity components have been acquired in three spanwise/wall-normal planes in the wakes of both a streamlined ‘wing’ and a bluff ‘wing’ junction. The ‘extended’ diagnostic plot introduced by Alfredsson et al. (2011) (see figure 3 therein) is used as a benchmark to locally evaluate the departure of turbulent wing-body junction flow wakes from ‘equilibrium’ boundary layers. Both obstacles produce a secondary flow of Prandtl’s first kind, which disrupts the equilibrium implied by the universality of the extended diagnostic plot. The plane wake of the obstacle itself (away from the junction) also disrupts this equilibrium. It is found that with downstream development the boundary layer eventually recovers to the base zero-pressure-gradient ‘equilibrium’, and that this recovery process emanates from the near-wall region. The transverse velocity components are also examined in “extended diagnostic” form, revealing that the wall-normal fluctuations recover to the zero-pressure-gradient case near the wall more rapidly than the wall-parallel components.

Study on Cruise Drag Characteristics of Low Drag Normal Layout Civil Aircraft

This paper focus on the wing shape related drag reduction measures of normal layout civil aircraft, through the drag reduction to improve the aircraft performance. Mainly by the laminar flow wing to reduce skin drag and weak shock wave wing to reduce shock drag, to keep a section of laminar zone on the wing leading edge to reduce skin drag, the wing profile's pressure distribution transit from the middle part's tonsure pressure zone to the trailing edge's inverse pressure gradient zone gentle to reduce the shock drag. The wing body junction plus the body belly fairing to increase the junction flow velocity, through increase flow velocity to weak the boundary layer stacked at the junction, improve the drag performance. The blended winglet to reduce the wing tip induced drag, study the shape parameters impact on the drag reduction, longitudinal moment and directional moment, attain the winglet model with drag reduction effect, suitable pitching moment and directional moment. For the wing body fairing have significant impact on the wing shape lower surface pressure distribution, the winglet have important impact on the wing tip flow, so the single part drag reduction measure is not feasible, need to carry out integrated drag reduction study on the wing related three drag reduction measures, and study the drag reduction measure's drag reduction decrement, put a reference for the normal layout civil aircraft's drag reduction. Through the above drag reduction measure's assessment attain the effect of drag reduction and rising the normal layout civil aircraft's cruise ratio, improving the cruise performance.

Wing body junctions in ship hydrodynamics

Starting with the 1st of January 2013, all ships greater than 400 gross tons have to comply with design or operational energy efficiency index, in order to reduce the greenhouse emissions. From the naval architect’s point of view, the emission reduction measures can be hydrodynamic, structural, technological and operational. The hydrodynamic measures, which are the first that can be taken into consideration in order to reduce the EEDI, are materialized through the optimization of the hull. The Naval Architect may interfere on the bulbous bow, hydrodynamic shoulders, bulb stern, transom or appendages, the drag being then modified by reducing the wave, viscous pressure or frictional resistance components. Another way to improve the hydrodynamics of a ship is the use of Energy Saving Devices (ESD). These are appendages, mounted on the ship hull, developed to improve the flow near the propeller, which operate in the non-uniform wake field of the ship. The flow mechanism around ESDs comes down to wing-body juncture flow problems and, due to their application to the ship appendage flow, they have recently received much attention in ship hydrodynamics. Despite its simple geometric configuration, the wing-body junction flow is a very complicate flow due to the so-called horseshoe vortex system determined by the adverse pressure gradient induced by the presence of the obstacle and the three-dimensional boundary layer separations around the junction. The horseshoe vortex flow affects the drag, lift and causes a persistent lack of uniformity in the wake and is also considered as one source of the noises, vibration and unsteady inflow for the propeller.

A hybrid RANS model of wing-body junction flow

Abstract The three-dimensional flow separation over the Rood wing-body junction is an exemplar application of separation affecting many important flows in turbomachinery and aerodynamics. Conventional Reynolds Averaged Navier Stokes (RANS) methods struggle to reproduce the complexity of this flow. In this paper, an unconventional use is made of a hybrid Reynolds Averaged Navier Stokes (RANS) model to tackle this challenge. The hybridization technique combines the Menter k − ω − S S T model with the one equation sub-grid-scale (SGS) model by Yoshizawa through a blending function, based on the wall-normal distance. The hybrid RANS turbulence closure captured most of the flow features reported in past experiments with reasonable accuracy. The model captured also small secondary vortices at the corner ahead of the wing nose and at the wing trailing edge. This feature is scarcely documented in the literature. The study highlights the importance of the spatial resolution near the wing leading edge, where this localized secondary recirculation was observed by the hybrid RANS model. It also provides evidence on the applicability of the hybrid Menter and Yoshizawa turbulence closure to the wing-body junction flows in aircraft and turbomachines, where these flows are characterized by a substantially time-invariant three-dimensional separation.

Vortex flow on the wing of aircraft and flow control to improve lift properties

A high-lift configuration of the civil aircraft including body, wing in high-lift configuration, nacelle with pylon and empennage is considered in the present work. Numerical simulations of the flow have been carried out in the framework of Reynolds averaged Navier-Stokes (RANS) equations for low subsonic Mach number. The active flow control method, which is capable to improve maximal lift of the aircraft, has been considered. The influence of jet blowing near wing-body junction on aerodynamic characteristics has been investigated.

Unsteadiness control of laminar junction flows on pressure fluctuations

Smoke-wire flow visualization is conducted carefully in a laminar junction to explore the physical behavior of laminar junction flows. The two-dimensional (2D) velocity fields in the 30° plane of a laminar junction flow are acquired by a time-resolved particle image velocimetry (PIV) system at a frame rate of 1 kHz, based on which the unsteady fluctuating pressure fields can be calculated by the multi-path integration method proposed in the literature (GAND, F., DECK, S., BRUNET,V., and SAGAUT, P. Flow dynamics past a simplified wing body junction. Physics of Fluids, 22(11), 115111 (2010)). A novel control strategy is utilized to attenuate the unsteadiness of the horseshoe vortices of the laminar junction flow, and the consequent effect on pressure fields is analyzed.

Data-Driven, Physics-Based Feature Extraction from Fluid Flow Fields Using Convolutional Neural Networks

Feature identification is an important task in many fluid dynamics applications and diverse methods have been developed for this purpose. These methods are based on a physical understanding of the underlying behavior of the flow in the vicinity of the feature. Particularly, they rely on definition of suitable criteria (i.e. point-based or neighborhood-based derived properties) and proper selection of thresholds. For instance, among other techniques, vortex identification can be done through computing the Q-criterion or by considering the center of looping streamlines. However, these methods rely on creative visualization of physical idiosyncrasies of specific features and flow regimes, making them non-universal and requiring significant effort to develop. Here we present a physics-based, data-driven method capable of identifying any flow feature it is trained to. We use convolutional neural networks, a machine learning approach developed for image recognition, and adapt it to the problem of identifying flow features. The method was tested using mean flow fields from numerical simulations, where the recirculation region and boundary layer were identified in a two-dimensional flow through a convergent-divergent channel, and the horseshoe vortex was identified in three-dimensional flow over a wing-body junction. The novelty of the method is its ability to identify any type of feature, even distinguish between similar ones, without the need to explicitly define the physics (i.e. through development of suitable criterion and tunning of threshold). This provides a general method and removes the large burden placed on identifying new features. We expect this method can supplement existing techniques and allow for more automatic and discerning feature detection. The method can be easily extended to time-dependent flows, where it could be particularly impactful.

Non-linear correction for the k-ω SST turbulence model

Non-linear correction for the k-ω SST model based on the WJ-BSL-EARSM model was developed and tested for a wide range of flows. For the basic turbulence flows the corrected model (SST-NL) results are close to those of the linear SST model and surpass WJ-BSL-EARSM ones. At the same time non-linear correction is capable to predict secondary motion in rectangle channels and prevents false corner separation for flows around a wing-body junction as well as the WJ-BSL-EARSM model.

Aerodynamic Shape Optimization Design of Wing-Body Configuration Using a Hybrid FFD-RBF Parameterization Approach

Aerodynamic shape optimization design aiming at improving the efficiency of an aircraft has always been a challenging task, especially when the configuration is complex. In this paper, a hybrid FFD-RBF surface parameterization approach has been proposed for designing a civil transport wing-body configuration. This approach is simple and efficient, with the FFD technique used for parameterizing the wing shape and the RBF interpolation approach used for handling the wing body junction part updating. Furthermore, combined with Cuckoo Search algorithm and Kriging surrogate model with expected improvement adaptive sampling criterion, an aerodynamic shape optimization design system has been established. Finally, the aerodynamic shape optimization design on DLR F4 wing-body configuration has been carried out as a study case, and the result has shown that the approach proposed in this paper is of good effectiveness.

Effects of an upstream triangular plate on the wing-body junction flow

The use of a short triangular leading-edge plate at the base of a wing-body junction is experimentally evaluated as a passive control method to eliminate the horseshoe vortices or at least to subdue their strength. The impact of the plate geometry on the efficacy of the control is assessed by considering triangular plates that have a length of 1T, 2T, and 3T, a width of 0.1T and 0.2T, and a height of 1.5T, where T is the maximum thickness of the wing. The wing model is a NACA 0020 airfoil. The Reynolds number based on the chord length is varied from Rec = 25 000 to 75 000. The incoming boundary layer is laminar in all experiments. Particle Image Velocimetry is utilized to characterize the temporal behavior and circulation strength of horseshoe vortices. The λ2-criterion is used as the vortex identification method. All the triangular leading-edge plates investigated in this study are found to decrease the circulation strength of the horseshoe vortices in the symmetry plane, although by varying degrees, compared to the baseline configuration that has no plate control. An increase in the upstream reach of the leading-edge plate significantly mitigates the vortical organization, vorticity, size, and circulation strength of horseshoe vortices. Although all plate lengths in question achieve a regression in the horseshoe vortex regime and, at the lowest Reynolds number considered, they all reduce the number of horseshoe vortices compared to the uncontrolled case, as the Reynolds number increases, longer plates are needed for such an effect. On the other hand, an increase in the thickness of the leading-edge plate deteriorates the desired control by increasing the vortical organization, vorticity magnitude, size, and circulation strength of horseshoe vortices. At higher Reynolds numbers, a thicker plate performs even poorer, resulting in extra horseshoe vortices, which can be unsteady depending on the Reynolds number. Nevertheless, all the triangular plates considered in this investigation, including the thickest one, outperform the baseline case. Overall, the proposed method is found to be an effective way for the mitigation of horseshoe vortices at the wing-body junction. The longer and thinner the plate, the better the vortex mitigation.

Wing-body junction optimisation with CAD-based parametrisation including a moving intersection

Over the past decades significant progress has been made with adjoint computational fluid dynamics solvers, which are an essential part of efficient high-fidelity aerodynamic shape optimisation. Shape parametrisation is much less mature, in particular the field is lacking efficient and automatic CAD-based parametrisation methods. The paper proposes a novel CAD-based parametrisation with CAD in the design loop such that the CAD shape can ultimately serve as a datum surface in multi-disciplinary optimisation. Wing and fuselage are modelled with B-spline surfaces. The intersection line is calculated using an in-house implementation of a B-spline surface modeller and its derivative is efficiently calculated via finite differences. The proposed parametrisation method is applied to the redesign of the wing–fuselage junction of the DLR-F6 model using an adjoint solver based on Reynolds-averaged Navier–Stokes equations. The moving intersection line capability enables the fuselage surface to be deformed and the resulting intersection line to move along the fixed wing during optimisation. The flow separation in the wing–body junction is substantially suppressed by an improved fuselage shape, at the cost of O(10) steady-state flow and adjoint solutions. The proposed parametrisation method represents an important step towards automated CAD-based optimisation for fully-featured aircraft characterised by complex intersecting surfaces.

Efficient suction control of unsteadiness of turbulent wing-plate junction flows

A wing-body junction flow of a navigating underwater vehicle is considered to be a crucial source of the flow radiating acoustic noise, which attracts much research interest. In this paper, wing-plate junction flows are experimentally investigated in a low-speed wind tunnel by smoke-wire flow visualizations and time-resolved PIV measurements. To reveal the physical behavior of such flows, smoke-wire flow visualizations are conducted for a laminar wing-plate junction. A novel control strategy is proposed, to accurately locate the suction openings where the streamline is about to roll up to form a vortex in the turbulent junction flows. The control effect is discussed in perspectives of both the time-averaged and instantaneous flow fields.