Large Eddy Simulation Research Articles

Aerodynamic and acoustic study of a small scale lightly loaded hovering rotor using large eddy simulation

The aerodynamics and acoustics of a small-scale lightly loaded hovering rotor operating at low Reynolds number is investigated using high-fidelity numerical simulation. A canonical geometry is considered, which allows for different flow topologies typical of transitional flows to develop along the span. Specifically, regions with laminar attached flow, trailing edge laminar separation with prominently 2D structures, and successive laminar separation, transition and reattachment with prominently 3D structures are identified. Furthermore, the lightly loaded configuration is conducive to significant blade-wake interaction, that in turn affects the dynamics of the boundary layer. The acoustic footprint of these phenomena are analyzed by correlating pressure fluctuations in the flow to those at the blade surface. It is found that the radiated noise is characterized by tonal peaks at the blade passing frequency and harmonics, and by a broadband hump at higher frequencies, consistent with experimental observations. The broadband hump exhibits distinct peaks that are found to originate from the separated shear layers on both pressure and suction sides. In particular, two noise generation mechanisms arising at two different frequencies in the broadband hump are identified. One is due to the interaction between an instability transported in the tip vortex of one blade and the leading edge of the following blade, and another one is found to rely on the interaction between an instability transported in the tip vortex and in the wake of one blade scattered by the trailing edge of the following blade.

A wall-modeled immersed boundary/large eddy simulation method and its application to simulating heart valve flows

In this work, a wall-modeled immersed boundary (IB)/large eddy simulation (LES) method is extended to the simulation of moving-boundary flows. The used non-equilibrium algebraic wall model is based on an assumed velocity profile, the coefficients of which are determined from physical constraints provided by the full turbulent-boundary-layer equations. To implement the wall model in an IB method named the local domain-free discretization (DFD) method, a local coordinate system fixed on the moving body is introduced. Thus, wall modeling is transformed into a local two-dimensional problem and the complexity of implementation of the wall model is reduced. In the present LES-DFD method, the tangential velocity at an exterior dependent node is determined via wall shear stress prescribed by the wall model. To reduce computational cost for simulating an internal flow with moving boundaries, the stationary boundaries are handled by the body-fitted-grid method and the moving boundaries by the local DFD method. There is no need of an auxiliary grid for solving the non-equilibrium algebraic wall model. Therefore, the inbuilt advantage of an IB method can be retained when simulating moving-boundary problems, and the economy of equilibrium wall models can also be preserved. The present method is applied to simulating the pulsatile flows through a bileaflet mechanical heart valve implanted in a model aorta. The predicted results show an acceptable agreement with the referenced experimental measurements or numerical results at much higher resolution and the applicability of the non-equilibrium wall model to LES of complex moving-boundary flows is verified.

Turbulence modeling of stratified turbulence using a constrained artificial neural network

For large eddy simulations (LES) of stratified turbulence in the strongly stratified regime, an artificial neural network (ANN) with five hidden layers is used to construct a sub-grid scale (SGS) model. The ANN is assessed by comparing it to the Smagorinsky model, the dynamic Smagorinsky model, the gradient model, and filtered direct numerical simulation data. In the a priori test, the SGS model using ANN performed better than the Smagorinsky model and the gradient model in terms of the correlation coefficient and relative error of the energy transfer rate. However, the ANN does not provide sufficient energy dissipation when it is applied to LES with a larger filter width because it overpredicts backscatter. To address this problem, we also trained a constrained ANN using a custom loss function that penalizes excessive backscatter. It is shown that the constrained ANN successfully predicts less backscatter, maintaining the high correlation coefficient without ad hoc clipping. These results show that ANN is a promising tool for realizing a highly accurate and stable SGS model for stratified turbulence.

Large-Eddy Simulations with remeshed Vortex methods: An assessment and calibration of subgrid-scale models

This study assesses various subgrid-scale models within the framework of Large Eddy Simulation (LES) using a remeshed Vortex method (RVM). RVM is a semi-Lagrangian method discretizing the vorticity-velocity Navier–Stokes equations that has proven to be a stable and less dissipative alternative to more classical Eulerian methods. The subgrid-scale models are first tested on the well-known Taylor–Green Vortex case at Re=5000. Notably, the Variational Multiscale (VMS) variant of the Smagorinsky model and the Spectral Vanishing Viscosity (SVV) approaches emerge as the best-suited to the RVM, as they add diffusion to only the smallest resolved vorticity scales. Then, a stochastic uncertainty quantification analysis is conducted for both selected models, and the model coefficients are calibrated against direct numerical simulation. These coefficients are then applied to additional cases (different regimes, grid resolutions and test cases), showing the robustness of the calibration within the RVM-LES framework.

Reduction of Drag Coefficient Due To Misaligned Wind‐Waves

AbstractRecent field observations suggest that the air‐sea momentum flux (or the drag coefficient) is significantly reduced when the dominant wind‐forced surface waves are misaligned from local wind. Such conditions may occur under rapidly changing strong winds (such as under tropical cyclones) or in coastal shallow waters where waves are refracted by bottom topography. A recent Large Eddy Simulation (LES) study also shows that the drag coefficient is reduced by a misaligned strongly forced wave train (with a small wave age of 1.37). In order to investigate more realistic field conditions, this study employs LES to examine the effect of a misaligned (up to 90°) surface wave train over a wide range of wave age up to 10.95. For all wave ages examined, the drag coefficient is reduced compared to the flat surface condition when the misalignment angle exceeds around 22.5°–45°. The drag reduction may occur even if the form drag of the wave train is positive.

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Research on the unsteady flow field and aerodynamic noise characteristics in the circular space of ultra-high-speed elevators

Due to the non-streamlined blunt body shape of the elevator car, intense aerodynamic loads and noise are generated in the annular space when the elevator operates at high speed in a narrow hoistway. This article uses large-eddy simulation and Curle acoustic theory to establish a numerical model of the wellbore flow field under different guiding shapes of the elevator car. First, the mechanism of action between the flow guide shape, vortex characteristics, and aerodynamic load was studied, and the influence of operating speed on aerodynamic load under different flow guide shapes was analyzed. Second, the distribution and spectral characteristics of noise in the annular space under different flow guide shapes were studied from the near field and far field scales. Finally, it can be concluded that increasing the guide surface can significantly reduce the pressure difference between the upper and lower parts of the car, weakening the separation of the tail airflow. The number of guide surfaces, installation position, and vertex offset significantly impact drag and lateral force, with the optimal reduction of 34.65% and 57.6%, respectively. The maximum sound source intensity of near-field noise is mainly concentrated at the arc transition in the upper part of the annular space, and the frequency is mainly concentrated in the range of 500–1000 Hz. The sound pressure level is linearly related to the logarithm of the longitudinal distance, and the noise attenuation speed becomes faster with the increase in the number of guiding surfaces.

Modeling the Subgrid-Scale Scalar Variance: A Priori Tests and Application to Supersaturation in Cloud Turbulence

Abstract The subgrid-scale (SGS) scalar variance represents the “unmixedness” of the unresolved small scales in large-eddy simulations (LES) of turbulent flows. Supersaturation variance can play an important role in the activation, growth, and evaporation of cloud droplets in a turbulent environment, and therefore efforts are being made to include SGS supersaturation fluctuations in microphysics models. We present results from a priori tests of SGS scalar variance models using data collected in turbulent Rayleigh–Bénard convection in the Michigan Tech Pi chamber for Rayleigh numbers Ra ∼ 108–109. Data from an array of 10 thermistors were spatially filtered and used to calculate the true SGS scalar variance, a scale-similarity model, and a gradient model for dimensionless filter widths of h/Δ = 25, 14.3, and 10 (where h is the height of the chamber and Δ is the spatial filter width). The gradient model was found to have fairly low correlations (ρ ∼ 0.2), with the most probable values departing significantly from the one-to-one line in joint probability density functions (JPDFs). However, the scale-similarity model was found to have good behavior in JPDFs and was highly correlated (ρ ∼ 0.8) with the true SGS variance. Results of the a priori tests were robust across the parameter space considered, with little dependence on Ra and h/Δ. The similarity model, which only requires an additional test filtering operation, is therefore a promising approach for modeling the SGS scalar variance in LES of cloud turbulence and other related flows.

Periodic approaching flows and pollutant dispersion of a single-sided generic building with natural ventilation

In real urban environments, wind velocities often exhibit significant time-dependent variations. However, the impact of these fluctuations on ventilation performance is not frequently addressed in the literature. To accurately predict the building ventilation performance, this paper intends to elucidate the influence of the unsteady approaching flow. Four distinct inflows, characterized by periodic sinusoidal fluctuations, are evaluated using large-eddy simulation (LES). A single-sided building model with natural ventilation is constructed and validated through a wind tunnel experiment. Four periodic inflows consist of combinations of two frequencies (f = 0.1 and 0.3 Hz) and two amplitudes (A = 0.06 and 0.09). This paper mainly compares the results of airflow patterns and ventilation performance with those of stable inflows. The results indicate that periodic inflows cause greater fluctuations in the velocity fields on the leeward side. At higher frequencies and lower amplitudes, the vertical distribution of indoor bottom vortices is relatively dispersed. It shows that periodic flows lead to noticeable changes in the ventilation rate, with a deviation between instantaneous and average Q* ranging from 13.8% to 16.5%. Compared to the stable inflow, the impacts of periodic inflows on ventilation performance vary over time; 6% and 9% variations in incoming velocities result in deviations of up to 17.5% in ventilation rates. The frequencies and amplitudes of the periodic inflows do not exhibit a linear relation with ventilation rate. Therefore, it is prudent to be cautious about adopting averaged incoming wind velocities in predicting ventilation performance. This study helps in the more accurate prediction of single-sided natural ventilation.

Modeling Lobe‐And‐Cleft Instabilities on a River Plume

AbstractThe lobe‐and‐cleft instability is a widely recognized mechanism leading to along‐front structure on density current fronts. Early studies based on laboratory and numerical simulations suggested that the lobe‐and‐cleft instability is due to convective instability in the nose of gravity currents traveling over a nonslip boundary. Horner‐Devine and Chickadel (2017, https://doi.org/10.1002/2017gl072997) reported the presence of lobe‐and‐cleft instabilities at the Merrimack River, which are generated at the river front in the absence of a no‐slip boundary. Hence, the observed lobe‐and‐cleft instabilities must be due to other mechanisms. In this study, we carried out non‐hydrostatic large eddy simulations of a riverine outflow into an idealized 3D domain. With a fine grid resolution of 0.15 × 0.31 m in two horizontal directions and about 0.125 m in the vertical direction, the model reproduced the lobe‐and‐cleft feature, with the magnitude and size of lobes consistent with the field observation. The model results revealed that instabilities start from the primary Kelvin‐Helmholtz instability, followed by the secondary instability through stretching and tilting, generating counter‐rotating streamwise vortices in the plume and at the plume head. The upwelling associated with streamwise vortex cells brings a slower flow to the plume surface, resulting in lobe‐and‐cleft patterns at the front and positive and negative vertical vorticity at the plume surface. The model also predicted a lobe width of about two to three times the plume thickness, consistent with the field observation and the lobe/cleft spacing associated with pairs of counter‐rotating streamwise vortices. Modeled turbulent dissipation rate shows a trend of exponential decay from 10−4 to 10−3 m2/s3 at the frontal head to 10−7 to 10−6 m2/s3 behind the front, similar to the findings in the previous field studies.

Verification and Validation of Spectral Element Code for Supercritical CO2 Flow in Vertical Heated Tubes

The investigation of heat transfer in supercritical CO2 (sCO2) has garnered considerable attention in recent decades, given sCO2’s potential as a promising working fluid for advanced power conversion cycles. Despite previous research efforts, there are still gaps in our understanding of sCO2 heat transfer, particularly in conditions associated with heat transfer deterioration. To delve into sCO2 heat transfer more comprehensively, we propose employing the high-fidelity computational fluid dynamics code NekRS to simulate sCO2 flow using the large eddy simulation technique. Through graphics processing unit acceleration, NekRS achieves a higher computational speed than traditional CPU-based systems. However, before using NekRS in practical applications involving sCO2, it is imperative to perform verification and validation. This paper presents our efforts to verify and validate the NekRS code’s capability for simulating sCO2 using heated vertical tubes, where heat transfer deterioration usually happens. To accommodate the unique properties of sCO2, we have modified the NekRS code by integrating third-party property modules, such as REFPROP and PROPATH. Our simulations are compared with experimental and numerical data from the literature, instilling confidence in leveraging NekRS for future engineering applications. Our simulations also reveal that the accuracy of the property module significantly impacts the results, with REFPROP outperforming PROPATH for sCO2 properties. Additionally, we observed that, depending on the flow direction, buoyancy can either enhance or suppress turbulence in sCO2 flow. In upward flow, under certain conditions, the suppressed turbulence leads to heat transfer deterioration, resulting in elevated wall temperatures.

Noise reduction in small wind turbines with optimized serrated blades

This study employs a comprehensive combination of experimental and numerical methodologies to delve into the aeroacoustic attributes of a small horizontal axis wind turbine with optimized blades. The experimental investigation is conducted within a semi-anechoic chamber, where both original and optimized geometry models are meticulously positioned to measure the sound pressure levels across a range of rotational speeds and positions. In parallel, the numerical simulations employed the large eddy simulation, complemented by the Ffowcs Williams–Hawkings analogy, facilitating detailed examinations of both aerodynamic and acoustic aspects in the original and optimized modes. The findings reveal a subtle enhancement in aerodynamic performance with the optimized serrated blade configuration when compared to the original. Nevertheless, the reduction in noise levels within the frequency domain was remarkable, culminating in an impressive overall sound pressure reduction of about 10 dB. Furthermore, an intriguing observation emerged from noise measurement in acoustic room: the noise production experiences a marked escalation as the turbine rotational speed intensifies, particularly within the downstream domain. The lateral noise level is found to be lower compared to the axial direction and the reduced noise emission for the serrated optimized blade is more dispersed in the plane of rotation than the original blade, which was pointed out to be nearly uniform. The results provide valuable insights into the interplay of aerodynamics and aeroacoustics in the context of small wind turbines with optimized blades.

A Bayesian optimization framework for the control of combustion instability of a bluff-body stabilized combustor

Control of combustion instability for a realistic gas-turbine combustor is challenging. This work aims to establish an efficient numerical framework for optimization to improve the combustion stability of a bluff-body combustor. Large eddy simulations of the spray combustion process are conducted, and the experimental measurements are used to evaluate the numerical accuracy of the baseline case. The air preheating temperature, the Sauter mean diameter of fuel droplets, and the location of liquid fuel injection are regarded as input variables. The root mean square of pressure amplitude is regarded as an optimization objective. The Bayesian optimization framework is proposed that includes the sampling process, surrogate model, acquisition function, and genetic algorithm optimizer processes. It is found that PRMS can be reduced by 64% for the optimized case compared to the baseline case using only 17 sample evaluations. This work is promising as it provides an effective optimization framework for the development of next-generation gas-turbine combustors.

Friction Velocity Determination Techniques in Turbulent Boundary Layers with Miniature Vortex Generators

Miniature vortex generators (MVGs) have the potential to control turbulent boundary layers (TBLs). Analyzing the scaled turbulent structure of MVG TBLs in experiments typically requires indirect methods for accurate friction velocity Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document} determination. The established methods for Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document} determination need to be verified for non-generic TBLs, such as MVG TBLs, especially at near-wake stations. This study compares the performance of the five most common Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document}-determination methods when applied to MVG TBLs. The methods are tuned in terms of their free parameters and fitting ranges using direct measurements of Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document} from large eddy simulation data, and applied to a corresponding experiment to assess their accuracy. Based on the findings, an “inner” method, which is the Musker function with a drifting buffer layer incorporating a bump function, is recommended for MVG TBLs of the form investigated, as it provides a good estimation of Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document} with uncertainty <3%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$<3\\%$$\\end{document} for all streamwise stations. The method is applied to three further experimental tests with different flow conditions to study trends in Uτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$U_\ au$$\\end{document}. The error of the drag variation is <6%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$<6\\%$$\\end{document}, which indicates the method is reliable for MVG TBLs at high Reynolds numbers.

Numerical investigation on cavitation and induced noise reduction mechanisms of a three-dimensional hydrofoil with leading-edge protuberances

In this work, a National Advisory Committee for Aeronautics 66 hydrofoil with leading-edge protuberances is designed. The large eddy simulation combined with the Schnerr–Sauer cavitation model is used to obtain a satisfactory result as compared with the experimental measurement, integrating the permeable Ffowcs Williams–Hawkings equation for cavitation-induced noise analysis. It is found that the special leading-edge geometric structure deflects the incoming flow, creating two counter-rotating streamwise vortices at the peak shoulders. These lead to upwash and downwash effects and alter the pressure distribution on the suction side. The low pressure localized in the trough facilitates the advancement of the leading-edge cavitation while severely limiting the spanwise development of the cloud cavity, shortening the cavitation evolution by about 20% and reducing the maximum cavitation volume by about 35%. Analysis using the vorticity transport equation indicates that different vorticity transport equation splitting terms play dominant roles at different stages of cavitation evolution. Although the cavitation induces disturbances in the primary vortex, the effect is limited. Acoustic simulation shows that the bionic structure can reduce the total sound pressure level by 7.8–8.3 dB. The spherical noise reduction is not as effective as expected due to the similar cavitation volume acceleration processes of the two hydrofoils. However, the pressure fluctuation caused by the collapse of the cloud cavity is reduced by cavitation suppression, which reduces the linear noise. In addition, the protuberances suppress the generation of large-scale vortex systems and transform them into smaller ones, resulting in reduced spanwise correlation and coherence of the shedding vortices. This is a critical factor in noise reduction. Finally, we hypothesize that the unstable noise reduction is related to the streamwise vortices in the trough regions. These vortices increase the momentum exchange within the boundary layer, affecting its stability and weakening the acoustic feedback loop.

Study of hydrodynamic stress in cell culture bioreactors via lattice-Boltzmann CFD simulations supported by micro-probe shear stress method

Mammalian cell cultivation in pharmaceutical industry can last up to units of weeks and requires proper transport of nutrients and oxygen for cell growth and production. Given the long time period, cells experience flow fields from all bioreactor’s zones, where the energy dissipation rate (ε) varies substantially. Shear sensitive micro-probes with size comparable to cells and Kolmogorov eddies are used for the determination of the maximum hydrodynamic stress (τmax) in bioreactors. For the very first time, the micro-probe method is applied successfully not only to laboratory (3L) and pilot scale (80L and 200L), but also to industrial production scale bioreactor (12,500L) with Rushton turbine and pitched-blade (RT-PB) impeller configuration. Experimentally obtained data are used for the validation of comprehensive CFD scale-up study, using the Lattice-Boltzmann large eddy simulation (LB-LES) method. Besides τmax, this work also focuses on the study of mixing time and flow field attributes.

Graphics processing unit/artificial neural network-accelerated large-eddy simulation of swirling premixed flames

Within the scope of reacting flow simulations, the real-time direct integration (DI) of stiff ordinary differential equations for the computation of chemical kinetics stands as the primary demand on computational resources. Meanwhile, as the number of transport equations that need to be solved increases, the computational cost grows more substantially, particularly for those combustion models involving direct coupling of chemistry and flow such as the transported probability density function model. In the current study, an integrated graphics processing unit-artificial neural network (GPU-ANN) framework is introduced to comply with heavy computational costs while maintaining high fidelity. Within this framework, a GPU-based solver is employed to solve partial differential equations and compute thermal and transport properties, and an ANN is utilized to replace the calculation of reaction rates. Large eddy simulations of two swirling flames provide a robust validation, affirming and extending the GPU-ANN approach's applicability to challenging scenarios. The simulation results demonstrate a strong correlation in the macro flame structure and statistical characteristics between the GPU-ANN approach and the traditional central processing unit (CPU)-based solver with DI. This comparison indicates that the GPU-ANN approach is capable of attaining the same degree of precision as the conventional CPU-DI solver, even in more complex scenarios. In addition, the overall speed-up factor for the GPU-ANN approach is over two orders of magnitude. This study establishes the potential groundwork for widespread application of the proposed GPU-ANN approach in combustion simulations, addressing various and complex scenarios based on detailed chemistry, while significantly reducing computational costs.

A finite element framework for fluid–structure interaction of turbulent cavitating flows with flexible structures

We present a finite element framework for the numerical prediction of cavitating turbulent flows interacting with flexible structures. The vapor-fluid phases are captured through a homogeneous mixture model, with a scalar transport equation governing the spatio-temporal evolution of cavitation dynamics. High-density gradients in the two-phase cavitating flow motivate the use of a positivity-preserving Petrov–Galerkin stabilization method in the variational framework. A mass transfer source term introduces local compressibility effects arising as a consequence of phase change. The turbulent fluid flow is modeled through a dynamic subgrid-scale method for large eddy simulations. The flexible structure is represented by a set of eigenmodes, obtained through a modal decomposition of the linear elasticity equations. While a partitioned iterative approach is adopted to couple the structural dynamics and cavitating fluid flow, the deforming flow domain is described by an arbitrary Lagrangian-Eulerian frame of reference. We establish the fidelity of the proposed framework by comparing it against experimental and numerical studies for both rigid and flexible hydrofoils in cavitating flows. Under unstable partial cavitating conditions, we identify specific vortical structures leading to cloud cavity collapse. We further explore features of cavitating flow past a rigid body such as re-entrant jet and turbulence-cavity interactions during cloud cavity collapse. Based on the validation study conducted over a flexible NACA66 rectangular hydrofoil, we elucidate the role of cavity and vortex shedding in governing the structural dynamics. Subsequently, we identify a broad spectrum frequency band whose central peak does not correlate to the frequency content of the cavitation dynamics or the natural frequencies of the structure, indicating the induction of unsteady flow patterns around the hydrofoil. Finally, we discuss the coupled fluid–structure dynamics during a cavitation cycle and the underlying mechanism associated with the promotion and mitigation of cavitation.

Large-eddy simulation for indoor flow in a multizone environment

Large-eddy simulation for indoor flow in a multizone environment

Large-Eddy Simulation and Aeroacoustic Prediction of Supercritical Airfoil Side-Edge Noise

Airfoil self-noise is investigated on a cantilever wing with a supercritical profile with a compressible wall-resolved large-eddy simulation. The Reynolds number based on the chord is 620,000, and the angle of attack is 5°. The aerodynamic results reveal the development of a complex vortex system at the side edge, including primary, secondary, and tertiary vortices that govern aerodynamic noise production. The wall-pressure coefficient and root-mean-square pressure coefficient contours highlight the side-edge shear layer and flow impingement of the primary vortex at the pressure-side edge as important noise-generation mechanisms. Dynamic mode decomposition shows that the dominant pressure modes on the airfoil exist along primary and secondary vortex impingement lines. Far-field acoustic predictions based on both solid and porous Ffowcs-Willliams and Hawkings’ analogies demonstrate good agreement with experimental results between 1.5 and 9 kHz. Low-frequency tonal humps observed in the spectra result from duct acoustic modes excited by airfoil self-noise, a consequence of the installation effect. For this configuration, airfoil side-edge noise did not dominate over airfoil surface noise levels, suggesting that at low to moderate angles of attack, airfoil side-edge noise is not a significant contributor to the overall acoustic emissions.