Multi-block Navier-Stokes Research Articles

Electroactive morphing effects on the aerodynamic performance through wobulation around an A320 wing with vibrating trailing edge at high Reynolds number

This study aims to investigate the effects of electroactive morphing on a 70cm chord A320 wing by means of near trailing edge slight deformation and vibration. Wing morphing is performed by Macro Fiber Composites (MFC) piezoelectric actuators distributed along the span of the “Reduced Scale” (RS) prototype of the H2020 European research project “Smart Morphing and Sensing for aeronautical configurations” - (SMS). The configuration studied corresponds to a low-subsonic regime (Mach number 0.063) with a 10∘ incidence and a Reynolds number of 1 Million. The numerical simulations are carried out with the Navier-Stokes Multi-Block (NSMB) solver, which takes into account the deformation of the rear part of the wing implemented experimentally with the piezoelectric actuators. A detailed physical analysis of the morphing effects on the wake dynamics and on the aerodynamic performance is conducted with a constant amplitude of 0.7mm over a wide range of actuation frequencies [10-600]Hz. Optimal vibration ranges of [180-192]Hz and [205-215]Hz were found to respectively provide a 1% drag reduction and a 2% lift-to-drag ratio increase compared to the non-morphing (static) configuration. The natural frequencies associated with the shear layer Kelvin-Helmholtz (KH) vortices and the Von-Kármán (VK) vortex shedding were found to play a central role in the modification of the wake dynamics by morphing as well as in the increase of the aerodynamic performance. Actuating at (or close to) the upper shear layer (USL) natural frequency (∼185Hz) provides an order of 1% drag reduction and 1% lift-to-drag ratio increase, while actuating at (or close to) the lower shear layer (LSL) natural frequency (∼208Hz) provides an order of 8% lift increase and 2% lift-to-drag increase. Furthermore, the linear modulation in time of the actuation frequency (wobulation) demonstrated, through an appropriate mapping, the ability to quickly and efficiently detect optimal constant actuation frequency ranges providing aerodynamic performance increase and simultaneously reducing the amplitude of the main instability modes.

Computational fluid dynamics investigations of aerodynamic control surfaces of a vertical landing configuration

The European project RETALT (Retro Propulsion Assisted Landing Technologies), funded by the Horizon 2020 framework program (Grant agreement No 821890), has as main objective to investigate critical technologies for the assisted descent and landing of re-usable first stages. Among these technologies, one can find aerodynamics, aerothermodynamics, flight dynamics, guidance navigation and control (GNC), Structures, mechanisms, thrust vector control (TVC) and thermal protection systems (TPS). The present paper focuses in particularly on the aerodynamics technology applied to a vertical landing launcher configuration, called RETALT1, including retro-propulsion. During the landing phase of the first stage of the launcher, the main devices for control and trim of the vehicle (besides the retro-propulsion) are the aerodynamic control surfaces (ACS). Three types of aerodynamic control surfaces are investigated by means of numerical computations, using the NSMB (Navier Stokes Multi Block) CFD code. The control surfaces considered are the deployable interstage segments (also named petals), grid fins and planar fins. Aerodynamic coefficients as well as forces acting on the control surfaces are extracted from the CFD computations to assess the efficiency of each type of devices and to populate the Aerodynamic Database (AEDB) for flight dynamic analysis.

Numerical investigation of frequency-amplitude effects of dynamic morphing for a high-lift configuration at high Reynolds number

PurposeThe purpose of this study illustrates the morphing effects around a large-scale high-lift configuration of the Airbus A320 with two elements airfoil-flap in the take-off position. The flow around the airfoil-flap and the near wake are analysed in the static case and under time-dependent vibration of the flap trailing-edge known as the dynamic morphing.Design/methodology/approachExperimental results obtained in the subsonic wind tunnel S1 of Institut de Mécanique des Fluides de Toulouse of a single wing are discussed with high-fidelity numerical results obtained by using the Navier–Stokes multi-block (NSMB) code with advanced turbulent modelling able to capture the predominant instabilities and coherent structure dynamics. An explanation of the dynamic time-dependent grid deformation is provided, which is used in the NSMB code to simulate the flap’s trailing-edge deformation in the morphing configuration. Finally, power spectral density is performed to reveal the coherent wake structures and their modification because of the morphing.FindingsFrequency of vibration and amplitude of deformation effects are investigated for different morphing cases. Optimal morphing regions at a specific frequency and a slight deformation were able to attenuate the predominant natural shear-layer frequency and to considerably decrease the width of the von Kármán vortices with a simultaneous increase of aerodynamic performances.Originality/valueThe new concept of future morphed wings is proposed for a large scale A320 prototype at the take-off position. The dynamic morphing of the flap’s trailing-edge is simulated for the first time for high-lift two-element configuration. In addition, the wake analysis performed helped to show the turbulent structures according to the organised eddy simulation model.

Morphing of a supercritical wing by means of trailing edge deformation and vibration at high Reynolds numbers: Experimental and numerical investigation

This article examines the morphing effects of the trailing-edge deformation and vibration on the turbulent structures in the wake of a supercritical Airbus-320 wing. It is shown that the electroactive morphing has the capacity to produce an enhanced aerodynamic performance (lift increase, drag reduction) and reduce the amplitude of instability modes associated to aerodynamic noise. The appropriate actuation is achieved with piezoactuators placed in the trailing edge region. The work presented has been carried out numerically using the Navier–Stokes Multi Block (NSMB) code, as well as experimentally with measurements obtained in the S4 wind tunnel of IMFT by means of TRPIV (Time-Resolved PIV) with a sampling rate around 10 KHz. The Reynolds number is 1 Million. The study is carried out in the low subsonic regime at an incidence angle of 10°, corresponding to take-off/landing flight phases and analyses significant morphing effects obtained by optimal deformations and vibrations of the near trailing edge region. The interactions that are prompted in the wake region are analyzed by means of Proper Orthogonal Decomposition (POD), considering the near wake structure in respect of the morphing effects. The effects on the aerodynamic coefficients thanks to manipulation of specific vortex dynamics in the shear layers and the wake are discussed and optimal frequency/amplitude ranges for the vibrations are quantified.

Effects of vibrating and deformed trailing edge of a morphing supercritical airfoil in transonic regime by numerical simulation at high Reynolds number

This article examines the aerodynamic performance increase of an Airbus A320 aerofoil thanks to morphing of the near-trailing-edge region in transonic regime corresponding to cruise conditions. The study has been carried out by numerical simulation at Reynolds number Re=2.06×106 and Mach number of 0.78, by using the NSMB code (Navier–Stokes MultiBlock) including adapted turbulence modelling approaches sensitised in capturing coherent structures development. It has been shown that transonic buffet occurs at angle of incidence 1.8° and in a more pronounced way at angle of 5°. The interactions among the shock-boundary layer area, the shear layers vortices and those of the near wake have been analysed by spectral analysis and streakline dynamics. Strong feedback effects have been shown from the near trailing-edge region towards the SWBLI (Shock Wave Boundary Layer Interaction) up to the upstream of the shock area. By taking benefit from these feedback effects, it has been obtained that morphing applied as a slight upwards deflection of the near-trailing-edge region by 2° is able to practically attenuate the buffet instability and to increase lift-to-drag ratio by 10.4 percent. The trailing-edge’s area vibration at low amplitudes simulating the motion of piezo-patches of MFC type (Macro-Fibre Composites) applied experimentally in the context of the H2020 European research project www.smartwing.org/SMS/EU) has shown a lock-in effect of the buffet’s frequency. Therefore, a conditioning of the shock’s motion by means of these actuations can be reached, although a relative increase of the rms of the aerodynamic forces is produced in this case. The study of a combined upwards slight deflection and of trailing-edge area vibrations allowed obtaining decrease of drag and increase of lift-to-drag ratio with simultaneous decrease of rms. These effects have been studied for a wide frequency range from 200 to 500 Hz.

A single step ice accretion model using Level-Set method

A new approach using the Level-Set framework is developed in the NSMB (Navier–Stokes-multi-block) compressible solver for modeling the ice/air interface evolution through time during in-flight icing. Droplet distribution and impingement efficiency are computed by an Eulerian approach and the accreted ice is calculated by a PDE model. An icing velocity field is introduced and the Level-Set equations are solved on body-fitted multi-block structured grids. The whole process is parallelized with the MPI library for efficient calculations. Single step icing is simulated on NACA23012 and NACA0012 airfoils and on the ONERA-M6 and the GLC-305 swept wings. In all the studied cases, the results are in good agreement with existing and available data validating the feasibility of the approach.

Development of a three-dimensional icing simulation code in the NSMB flow solver

An icing model is developed in the Navier-Stokes multi-block (NSMB) compressible solver. The code implemented in this study is based on an Eulerian formulation for droplets tracking solved implicitly by means of CGSTAB or SIP methods, a modified iterative Messinger model using an improved water runback scheme for ice thickness calculation and three-dimensional mesh deformation to track the ice/air interface through time. The whole process is parallelised with MPI for efficient calculations. Validation is performed on several test cases including NACA23012 and NACA00012 airfoils and ONERA-M6 swept wing. Pressure coefficients around iced 23012 airfoil are compared with experimental data. Rime icing is computed on a DLR-F6 wing/body configuration. In all studied cases, the results are in good agreement with the literature.

Temperature Measurements in an Arc-Heated Plasma Wind Tunnel by Laser-Induced Fluorescence

Laser-induced fluorescence using the A-X(0,0) band for excitation of nitric oxide is a promising approach for examining high-enthalpy flows. Spectroscopic investigations within this excitation wavelength band intend to identify appropriate transitions that maximize the fluorescence signal and minimize possible interference with other species. Special emphasis was placed on the comparison of the temperature measurements and the computational fluid dynamics calculations based on an equilibrium model. The flow simulations are conducted with a Navier–Stokes multiblock, which is a multiblock structured finite volume solver. The rotational temperatures of nitric oxide within a high-enthalpy flow, with a stagnation enthalpy of , were measured by two-line and multiline thermometry methods using laser-induced fluorescence. For the purpose of validation, the measurement and calculation method was applied to simulated excitation spectra, a test cell, and a well-characterized flat flame burner. Comparisons between spectroscopy measurements and freestream temperature calculations showed a good agreement. Additionally, the spectroscopy measurement results were consistent with the theoretical approach of thermochemical equilibrium.

Numerical simulation of the fluid–structure interaction in a tube array under cross flow at moderate and high Reynolds number

The unsteady loads in a tube bundle are studied at moderate and high Reynolds number by means of URANS and hybrid (DDES) modelling. The onset of fluid-elastic instability is analysed for different structural parameters, Scruton number and reduced velocity. The simulations have been carried out with the code NSMB (Navier–Stokes Multi Block) by using turbulence modelling methods URANS and DDES (Delayed Detached Eddy Simulation). The CEA-DIVA configuration is considered for the cylinders array for an inter-tube Reynolds number 60000. The study is carried out for a configuration of (4×5) cylinders in static conditions as well as for the vertical free motion of one of the central cylinders in one DOF (Degree Of Freedom).The inter-tube Reynolds number is 60000. It is found that this cylinder spontaneously displays an oscillatory motion which first corresponds to Vortex Induced Vibration (VIV), associated to a lock-in mechanism for low values of the reduced velocity and secondly develops Movement Induced Vibration, MIV, for higher values of the reduced velocity. The variation of the cylinder׳s oscillations frequency, of the unsteady loads and the structure׳s displacement are studied as a function of the reduced velocity for low and high values of the Scruton number. The increase of the phase-lag between the forces and the displacement is predicted and discussed for different Scruton number values and reduced velocities.

Drag Prediction Workshop 4 Results Using Different Grids Including Near-Field/Far-Field Drag Analysis

CFS Engineering and RUAG Aviation participated in the 4th Drag Prediction Workshop organized by AIAA in June 2009. Calculations were made for the Common Research Model configuration using the Navier–Stokes multiblock solver on the grids generated at CFS Engineering. After the workshop, the polars were computed on the medium multiblock structured grids provided by other workshop participants for the Common Research Model configuration with 0 deg horizontal tail deflection. All these results were processed by a far-field drag extraction tool developed jointly by RUAG Aviation and CFS Engineering. This paper first summarizes the theory behind the drag extraction tool. The results of the different calculations are presented and a detailed analysis of the drag breakdown on the different grids is given. This shows that the spread in drag coefficients obtained on different grids is much lower when using the effective drag computed by the drag extraction tool than when using the near-field drag.

F/A-18 vertical tail buffeting calculation using unsteady fluid structure interaction

AbstractThe Swiss Airforce is operating F/A-18C/D Aircraft since 1997. Since the aircraft’s structural design is different from the version operated by the US Navy it was necessary to carry out a structural integrity study (ASIP) which was done by The Boeing Company in St. Louis. To validate this study a full scale fatigue test facility was build at RUAG and operated from 2003 to 2005. When operating this facility difficulties were encountered with the aerodynamic loads data provided by Boeing (insufficient, not well documented, questionable data). As a result RUAG looked for alternative methods to provide the aerodynamic loads, and a large investment was made in the development of a Computational Fluid Dynamics (CFD) tool. The Navier Stokes Multi Block (NSMB) solver, which was developed in an international collaboration, was adopted. In a first phase the code was validated by comparing results of CFD calculations with wind-tunnel results, results from literature and flight test data results. In the second phase, discussed in this paper, a Fluid Structure Interaction (FSI) tool was developed to permit unsteady aero-elastic simulations. Particular attention is focused on the vertical tail since this component of the F/A-18 fighter is very sensitive to fatigue due to unsteady loads generated by buffeting phenomena.

Sensitivity analysis based on high fidelity simulation: application to hypersonic variable-cycle engine intake design

A sensitivity analysis of a supersonic intake of a turbine-based combined cycle (TBCC) engine is presented. A multi-block Reynolds-averaged Navier-Stokes (RANS) solver was used to compute the flowfield. While RANS simulation provides more realistic performance estimate than a simplified cycle analysis, the intake design must also take into account in-flight uncertainties for robustness. In this study, we focus on the effect of geometric uncertainties on the intake performance, and propose a practical approach to simulation-based sensitivity analysis. The method begins by constructing a radial-basis function (RBF) network, trained via efficiently sampled simulations. Using the RBF network as the surrogate model, sensitivity analysis is performed using the analysis of variance (ANOVA) technique. This approach makes it possible to perform a generalised multi-input-multi-output sensitivity analysis based on high-fidelity simulation. The resulting sensitivity indices help identify dominant parameters as well as the interaction among multiple parameters, which can then be used for design refinement.

Aerodynamic analysis of flapping foils using volume grid deformation code

Nature-inspired flapping foils have attracted interest for their high thrust efficiency, but the large motions of their boundaries need to be considered. It is challenging to develop robust, efficient grid deformation algorithms appropriate for the large motions in three dimensions. In this paper, a volume grid deformation code is developed based on finite macro-element and transfinite interpolation, which successfully interfaces to a structured multi-block Navier-Stokes code. A suitable condition that generates the macro-elements with efficiency and improves the robustness of grid regularity is presented as well. As demonstrated by an airfoil with various motions related to flapping, the numerical results of aerodynamic forces by the developed method are shown to be in good agreement with those of an experimental data or a previous numerical solution.

Large-Eddy Simulation of a Round Jet in Crossflow

A numerical simulation of a round turbulent jet issuing perpendicularly into a laminar M = 0.2 boundary-layer crossflow is performed at a jet-to-crossflow momentum ratio of 3.3 and a jet Reynolds number of 6930. The mixing behavior of the jet in crossflow is investigated by computing the evolution of a passive scalar. The spatial discretization of the computational domain consists of a block-structured multiblock grid with 58 blocks and a total of 8.9 million cells. The NSMB (Navier-Stokes Multiblock) simulation code uses a finite-volume discretization with a skew-symmetric fourth-order central scheme and a four-stage Runge-Kutta method for time integration. To account for the subgrid scales, the approximate-deconvolution model is employed in a multiblock formulation. Of special interest is the mixing behavior of the jet with the crossflow connected with the complex vortex systems in the mixing region. Results are compared with incompressible large-eddy simulation data and experimental measurements at similar flow parameters. Significant findings comprise the study of the jet development along its trajectory, as well as the upstream influence of the crossflow into the nozzle. Furthermore, the three-dimensional temporal oscillation of the ejected jet body is investigated and an attempt is made to correlate it to the formation of vortices in the mixing region.

이동경계문제의 전산유체역학을 위한 체적격자변형코드

Modern multidisciplinary computational fluid dynamics often incorporates moving boundaries, as would be required in the applications such as design optimization, aeroelasticity, or forced boundary motion. It is challenging to develop robust, efficient grid deformation algorithms when large displacement of the moving boundaries is required. In this paper, a volume grid deformation code is developed based on the finite macro-element and the transfinite Interpolation, and then interfaces to a structured multi-block Navier-Stokes in-house code. As demonstrated by an airfoil with pitching motion, the hysteresis loops of lift, drag and moment coefficients of the developed method are shown to be in good agreement with those of experimental data.

Nested Parallelization with OpenMP

OpenMP is widely accepted as a de facto standard for shared memory parallel programming in Fortran, C and C++. Nested parallelization has been included in the first OpenMP specification, but it took a few years until the first commercially available compilers supported this optional part of the specification. We employed nested parallelization using OpenMP in three production codes: a C++ code for content-based image retrieval, a C++ code for the computation of critical points in multi-block CFD datasets, and a multi-block Navier-Stokes solver written in Fortran90. In this paper we discuss the opportunities as well as the deficiencies of the nested parallelization support in OpenMP.

Prediction of Flutter of Turbine Blades in a Transonic Annular Cascade

A parallel multiblock Navier-Stokes solver with the k‐ω turbulence model is used to solve the unsteady flow through an annular turbine cascade, the transonic Standard Test Case 4, Test 628. Computations are performed on a two- and three-dimensional model of the blade row with either the Euler or the Navier-Stokes flow models. Results are compared to the experimental measurements. Comparisons of the unsteady surface pressure and the aerodynamic damping are made between the three-dimensional, two-dimensional, inviscid, viscous simulations, and experimental data. Differences are found between the stability predictions by the two- and three-dimensional computations, and the Euler and Navier-Stokes computations due to three-dimensionality of the cascade model and the presence of a boundary layer separation, respectively.

Parallel Large Scale High Accuracy Navier-Stokes Computations on Distributed Memory Clusters

We present a highly scalable parallelization of a high-accuracy 3D serial multiblock Navier-Stokes solver. The code solves the full Navier-Stokes equations and is capable of performing large-scale computations for practical configurations in an industrial enviroment. The parallelization strategy is based on the geometrical domain decomposition principle, and on the overlapped communication and computation concept. The important advantage of the strategy is that the suggested type of message-passing ensures a very high scalability of the algorithm from the network point of view, because, on the average, the communication work per processor is not increased if the number of processors is increased. The parallel multiblock-structured Navier-Stokes solver based on the parallel virtual machine (PVM) routines was implemented on 106-processors distributed memory cluster managed by the MOSIX software package. Analysis of the results demonstrated a high level of parallel efficiency (speed up) of the computational algorithm. This allowed the reduction of the execution time for large-scale computations employing 10 million of grid points, from an estimated 46 days on the SGI ORIGIN 2000 computer (in the serial single-user mode) to 5–6 hours on 106-processors cluster. Thus, the parallel multiblock full Navier-Stokes code can be successfully used for large-scale practical aerodynamic simulations of a complete aircraft on millions-points grids on a daily basis, as needed in industry.

Accurate Multiblock Navier-Stokes Solver for Complex Aerodynamic Configurations

A computational-fluid-dynamics tool capable to simulate accurately viscous flows around complex aerodynamic configurations is described. The method combines a multiblock technique with a low-dissipation numerical method incorporated into a multigrid framework. Structured subdomains (blocks) are united in multigrid/multiblock structures, and the blocks are treated independently at each stage of the numerical procedure, maintaining a regular information exchange between the neighboring blocks. In the numerical procedure the convection part of the equations is approximated by a low-order upwind-biased scheme employed for multigrid relaxation in combination with a higher-order essentially nonoscillatory scheme used to supply a defect to the right-hand side of the discrete equations on the finest multigrid level in a way ensuring the overall high accuracy of the scheme. Computational examples demonstrate the ability of the resulting method to perform accurate large-scale computations of complex three-dimensional turbulent flows around realistic aerodynamic configurations

Flow Analyses around Downwind-Sail System of an IACC Sailing Boat by a Multi-Block NS/RaNS Method

The present study concerns analyses of flows around downwind-sail system of an International America's Cup Class (IACC) sailing boat. The numerical method is a multi-block Navier-Stokes and Reynolds-averaged Navier-Stokes equation solver (hereafter, referred to as multi-block NS/RaNS method) recently developed by the present author. The main objectives of the present work are two folds: (1) an initial capability evaluation of the present multi-block NS/RaNS method in analyses of large-scale-separation flow; and (2) application of the present method to flow analyses around downwind-sail system of IACC sailing boat, on which very few studies have been so far reported. In the present study, the mainsail/spinnaker configuration is particularly considered, where focuses are placed on the aerodynamic interactions between the mainsail and spinnaker as well as the influences of sail trimming on flow and aerodynamic forces. The present numerical method is based on an extension of the RaNS method for ship flow analyses for applications to more general fluid dynamic problems, which was successfully demonstrated through the present work.