AIAA Journal

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ISSN / EISSN : 0001-1452 / 1533-385X
Total articles ≅ 26,707
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Gustavo Luiz Olichevis Halila, , Charles A. Mader, ,
AIAA Journal pp 1-14; https://doi.org/10.2514/1.j060481

Abstract:
The inclusion of transition to turbulence effects in computational fluid dynamics simulations makes it possible to design laminar flow airframes. It also increases the level of physical representations for simulations of standard airframes because laminar flow regions may be present in parts of the aircraft in multiple flight conditions. Modified Reynolds-averaged Navier–Stokes (RANS) models that consider transition effects became popular in the last decade and indicated favorable agreement with experimental data. However, these models present more difficult convergence behavior when compared with fully turbulent RANS approaches. To address this issue, an approximate Newton–Krylov solver is leveraged to solve the transitional flow over aeronautical configurations using a flow-stability-based, smooth RANS transition model. The amplification factor transport (AFT) model is modified to create a smooth variant, referred to as AFT-S. Strategies have been developed to obtain representative physical solutions that exhibit good agreement with experimental data. The convergence behavior for the transition RANS model is also addressed, and its impact on the numerical results is assessed. These results constitute the first in-depth investigation on the numerical behavior of an AFT-type transition model.
Bernhard Eisfeld, Christopher L. Rumsey, Vamshi Togiti, Sebastian Braun, Arne Stürmer
AIAA Journal pp 1-20; https://doi.org/10.2514/1.j060510

Abstract:
Numerical simulations of the NASA Juncture Flow Experiment are carried out, employing a Reynolds-stress model. A transformation of the length-scale determining variable is suggested for improving the numerical robustness of the model. Results obtained with different unstructured flow solvers on different sets of grids show very good agreement, except for velocity and Reynolds-stress profiles in the vicinity of the predicted separation region. A recently developed length-scale correction and, particularly, prescribing transition on the fuselage and wing increase the predicted size of the separation region, where the variation is on the order of the experimental uncertainty. Detailed comparison of velocity and Reynolds-stress profiles with experimental data reveal a general deficiency of the model in predicting the peak of the streamwise normal stress and the distribution of all Reynolds stresses in the vicinity of the separation region. However, all predicted sizes of the separation region are in fair agreement with the experimental data.
Marshall C. Galbraith, Carmen-Ioana Ursachi, Durgesh Chandel, Steven R. Allmaras, David L. Darmofal, Ryan S. Glasby, Douglas L. Stefanski, J. Taylor Erwin, Kevin R. Holst, Ethan A. Hereth, et al.
AIAA Journal pp 1-15; https://doi.org/10.2514/1.j060861

Abstract:
In this work, Reynolds-averaged Navier–Stokes (RANS) solutions for a multi-element airfoil computed with Massachusetts Institute of Technology Solution Adaptive Numerical Simulator (SANS), United States Department of Defense High Performance Computing Modernization Program CREATETM-AV Kestrel component Conservative Field Finite Elements (COFFE), and SU2 using output-based adapted meshes are compared with RANS solutions computed using manually generated meshes adhering to “best practices.” The adapted meshes are generated using the process implemented in SANS, which seeks to find a mesh that minimizes the error estimate of a given output functional. The manually generated meshes are the result of a systematic study of the influence of a range of meshing parameters on solution accuracy. Using the adapted meshes generally leads to a reduction of more than one order of magnitude in lift and drag error relative to the manually generated meshes of a comparable node count for all of the computational fluid dynamics solvers. Alternatively, the node counts of the adapted meshes are more than an order of magnitude smaller than the manually generated meshes for a given lift and drag error level. The improved accuracy in lift and drag computed with the adapted meshes can partially be attributed increased resolution around the stagnation points and trailing edges of the airfoil elements relative to the manually generated meshes. Notably, the adapted meshes provide accurate results despite having y+ values generally significantly larger than one.
, André V. G. Cavalieri, Maurício V. Donadon,
AIAA Journal pp 1-12; https://doi.org/10.2514/1.j060784

Abstract:
The effect of addition of viscoelastic plies on the acoustic scattering quadrupoles near the trailing edge of laminated plates is evaluated. A numerical method is applied to compute the acoustic field scattered by finite flexible plates. For a two-dimensional problem whereby a cantilevered plate scatters sound from a point quadrupole near the free edge, results show that adding viscoelastic layers to a composite plate can modify the far-field sound. Parametric investigations show that this treatment reduces scattered noise near resonance frequencies. Discussions on the positioning and thickness of the viscoelastic layers and operating temperature are provided. The use of outer viscoelastic layers in composite plates is predicted to significantly reduce acoustic scattering near resonances due to structural damping.
Jung-Hoon Kim, , , Paruchuri Chaitanya, Phillip Joseph, S. M. Hasheminejad, Tze Pei Chong, M. F. Shahab, Mohammad Omidyeganeh, Alfredo Pinelli
AIAA Journal pp 1-12; https://doi.org/10.2514/1.j060716

Abstract:
Experimental studies of a NACA 65(12)-10 airfoil with a sinusoidal leading-edge undulation (LEU) were carried out to simultaneously optimize its aerodynamic and aeroacoustic performances by considering the attached as well as the separated flow at the effective Reynolds number of 106 , where the maximum lift was increased without sacrificing drag or overall noise at near- and poststall angles. Further aerodynamic and aeroacoustic tests indicated that a combination of LEU wavelength λ/c=30% and amplitude h/c=6% gave an optimum LEU by considering the aerodynamic performance as well as the noise reduction. Particle image velocimetry measurements of the flow over the optimized airfoil showed biperiodic velocity fluctuations downstream of the LEU peaks that were associated with unsteady stall cell structure near the trailing edge.
Monika Chauhan, Luca Massa
AIAA Journal pp 1-20; https://doi.org/10.2514/1.j060424

Abstract:
We conduct large-eddy simulations to investigate the role of thermal nonuniformity on the development of instability modes in the shear layer of supersonic M=1.5 jets. We develop an arbitrary high-order discontinuous Galerkin scheme, build meshes with over 100 million degrees of freedom, and validate the model against particle image velocimetry (PIV) and microphone data. The analysis focuses on both numerical issues (such as convergence against the polynomial order of the mesh), modeling issues (such as the choice of subgrid model), and underlying physics (such as vortex stretching and noise generation). We consider the use of wall models to capture the viscous sublayer at the nozzle. We conclude that the Vreman subgrid-scale model leads to the most accurate predictions of both the near-field velocity and the far-field noise, while the Smagorinsky model is best in the nozzle and near the lip area. Injection in the shear layer is more effective at reducing sound generation in the near field than injection in the core. The difference in effectiveness is less substantial in the far field. Injection in the shear layer creates an unstable three-dimensional structure that leads to loss of coherency and three-dimensional effects in the core. Three-dimensionality in the core supports vortex stretching leading to fast mixing.
Tim De Troyer, David Hasin, David Keisar, Srimanta Santra,
AIAA Journal pp 1-11; https://doi.org/10.2514/1.j060933

Abstract:
Quasi-static and dynamic stall control experiments, using dielectric barrier discharge plasma actuators, were performed on a square-tipped aspect-ratio-one wing, with a NACA 0015 profile, under harmonic pitching, at a Reynolds number of 3×105 . Relatively low O(1) and relatively high O(10) pulse-modulated reduced excitation frequencies were introduced at the leading edge; the former produced the largest poststall lift improvements, whereas the latter produced the highest maximum lift. A reduced frequency, based on laminar separation bubble shedding, was enlisted to explain the differences between the two results. Under conditions of dynamic pitching, evidence of a dynamic stall vortex was absent, due to its interaction with the strong tip vortices, consistent with prior experimental and numerical investigations. As a general rule, performance benefits produced by excitation under quasi-static conditions were reproduced under harmonic pitching. Low-order dynamic stall and dynamic stall control models, based on a modified version of the Goman–Khrabrov delta-wing concept, were evaluated. Model constants were obtained from quasi-static data sets, and a single baseline dynamic case was employed to determine the time constants. The model produced excellent results for both baseline and controlled cases, which was attributed to similar lift and stall mechanisms exhibited by delta and rectangular low-aspect-ratio planforms.
Takao Suzuki, , Michael Kh. Strelets, Andrey K. Travin
AIAA Journal pp 1-17; https://doi.org/10.2514/1.j060400

Abstract:
This study investigates the instabilities of the interstage flow between a rotor and a stator in turbomachinery and evaluates their impact on the fan noise. By viewing the interstage flow as the so-called spiral-Poiseuille flow, linear stability analysis of the incompressible Navier–Stokes equations reveals two distinct instability regimes at the Reynolds numbers up to ReO(105) : The first mode excites disturbances over wide frequencies, including the rotor speed, and forms wavepacket-like structures above the outer-wall boundary layer. The second mode evolves inside the outer-wall boundary layer with slower velocity and possesses much smaller axial wavenumbers. We extract these modes using an approach analogous to dynamic mode decomposition from a database of our improved–delayed–detached eddy simulation solving NASA’s turbofan-rig test at low speed. The dynamic mode decomposition technique successfully visualizes these two instability modes even at Re4×106 , and their dispersion relations approximately agree with the characteristics predicted by the linear stability analysis. These analyses suggest that the instabilities amplify coherent disturbances in the rotor wakes and vortices near the tip until they interact with the stator; moreover, coherent structures associated with the second instability may act as stationary objects, possibly resulting in an additional fan-noise source.
Li Tian, Haitao Zhao, Guannan Wang, Yongtao Yao, Mingqing Yuan, Yahui Peng, Ji’An Chen
AIAA Journal pp 1-10; https://doi.org/10.2514/1.j060925

Abstract:
Linerless composite cryogenic tank is significant for weight reducing in launch vehicles, and a microscopic-to-macroscopic model is presented in this paper to capture the burst behaviors of the carbon-fiber-reinforced-composite cryotank. The hierarchical framework starts from the material components (carbon fiber and matrix) at microlevel, filament winding layups at mesolevel, and pressure tank at macrolevel. The locally exact homogenization theory is first introduced to generate stiffness degeneration coefficients with matrix crack and fiber fracture failure, which is compared with previous literature and good agreements are obtained. And 1° finite element representative model is then established considering spiral filament winding, and progressive damage analysis is finally conducted based on Hashin and Maximum stress criteria complied with ANSYS Parametric Design Language. In addition, the thermodynamic analysis is demonstrated by considering the integrated design structure with a corrugated sandwich cylindrical shell under multiple physical fields. The proposed multiscale model provides references for fuel cryotank design from a microscopic perspective to predict the burst pressure.
Luke Bowen, Alper Celik, Mahdi Azarpeyvand, Carlos R. Ilário da Silva
AIAA Journal pp 1-15; https://doi.org/10.2514/1.j060851

Abstract:
A preliminary version of this paper was presented at the AIAA Aviation 2020 forum (Paper 2020-2525).This paper provides an insight into the grid generated turbulence for aeroacoustic studies. Several passive grids of square bars were tested in the open-jet aeroacoustic facility at the University of Bristol. The geometric properties of the grids and their position within the tunnel contraction nozzle were varied to quantify their influence on the average and statistical flow properties as well as the generated self-noise. Moreover, case studies involving turbulence interaction noise generation with a NACA0012 airfoil and cylinder were conducted. Turbulence intensity, integral length scale, and the anisotropy of the flow generated by each grid were characterized by hot-wire measurements, and the associated far-field noise was measured by a far-field microphone array. The grid turbulence results show that the downstream evolution of the turbulence intensity and integral length scale was comparable to results of closed test-section wind-tunnel studies for the first hydraulic diameter downstream of the contraction nozzle exit. However, beyond the first hydraulic diameter, the turbulence intensity plateaus and the integral length scales show rapid growth. Moreover, the results show that grids positioned closest to the contraction nozzle exit produced turbulence closest to isotropy with high levels of turbulence intensity, but the measured noise spectra suffered from the contamination from the grids self-noise. The grids located farthest from the contraction nozzle exit performed best in terms of noise contamination and could generate almost the same level of turbulence properties as the grids closest to the contraction nozzle exit.
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