Hybrid LES-RANS study of an effusion cooling array with circular holes

In this paper, a multi-row effusion cooling configuration with scaled gas turbine combustor conditions is studied numerically. The distribution of the coolant film is examined by surface adiabatic cooling effectiveness (ACE). Simulation results have shown that the accuracy of cooling effectiveness prediction is closely related to the resolution of turbulent flow structures involved in hot-cold flow mixing, especially those close to the plate surface. The formation of the coolant film in the streamwise direction is investigated. It is shown that the plate surface directly downstream the coolant holes are covered well by the coolant jets, while surface regions in between the two columns of the coolant holes could not be protected until the coolant film is developed sufficiently in the spanwise direction in the downstream region. More detailed study has also been carried out to study the time-averaged and time-dependent flow field. The relation between the turbulent flow structures and coolant film distribution are also examined. The Kelvin-Helmholtz instability in the upper and lower coolant jet shear layer, is found to have the same frequency of around 8000Hz, and is independent of the coolant hole position. Additionally, it is suggested by the spectral coherence analysis that those unsteady flow structures from the lower shear layer are closely related to the near-wall flow temperature, and such effect is also independent of the coolant hole position

New Strategies for Mitigating the Gray Area in Delayed-Detached Eddy Simulation Models

This paper presents a new approach for mitigating the unphysical delay in the Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) transition, often referred to as the gray area, which is a common issue for hybrid RANS–LES turbulence models such as delayed-detached eddy simulation. An existing methodology designed for improving the LES performance in complex flows is adapted and tested. This is based on reducing the numerical diffusion in critical areas for permitting a more accurate development of turbulence. The new formulation comprises both a two-dimensional sensitive velocity gradient model and an alternative definition of the subgrid length scale, which are tested both individually and in tandem, and compared with the other formulations commonly used for addressing the gray area. Four test cases are examined, a flat plate, two variants of the incompressible backwardfacing step, and an open jet compressible case, all of which are selected to expose the adverse impact of numerical diffusion that this study seeks to address. Furthermore, the proposed changes are implemented in two different codes for the purpose of cross-validation. Encouraging results are observed, supporting the suitability of the new approach as a candidate for addressing the gray area issue in flows of this kind.This work was financially supported by the Ministerio de Economía y Competitividad, Spain (No. ENE2017-88697-R). A.P.V. was supported by an FI-DGR 2016 predoctoral contract (No. 2018FI_ B2_00072) financed by Generalitat de Catalunya, Spain. F.X.T. was supported by a Ramón y Cajal postdoctoral contract (No. RYC-2012- 11996) financed by the Ministerio de Economía y Competitividad, Spain. A.D. and A.G. were supported by Moscow Center for Fundamental and Applied Mathematics, Agreement with the Ministry of Science and Higher Education of the Russian Federation, No. 075- 15-2019-1623. The NOISEtte computations were carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University and the computing resources of the federal collective usage center Complex for Simulation and Data Processing for Mega-science Facilities at NRC “Kurchatov Institute” (http://ckp.nrcki.ru/).Peer ReviewedPostprint (published version

Enhancing respiratory comfort with fan respirators: computational analysis of carbon dioxide reduction, temperature regulation, and humidity control

Respirators provide protection from inhalation exposure to dangerous substances, such as chemicals and infectious particles, including SARS-Covid-laden droplets and aerosols. However, they are prone to exposure to stale air as the masks creat a microclimate influenced by the exhaled air. As a result, exhaled air from the lungs accumulating in the mask produce a warm and humid environment that has a high concentration of carbon dioxide (CO2), unsuitable for re-inhalation. Fans are a favourable option for respirators to ventilate the mask and remove the stale air. This study utilized computational fluid dynamics simulation consisting of a hybrid Reynolds-averaged Navier-Stokes (RANS)-large eddy simulation (LES) turbulence method to compare the inhalation flow properties for different fan locations (bottom, top, and side) with regular respirator breathing. Three mask positions, top, side, and bottom, were evaluated under two breathing cycles (approximately 9.65s of breathing time). The results demonstrated that adding a fan respirator significantly decreased internal mask temperature, humidity, and CO2 concentration. The average CO2 concentration decreased by 87%, 67% and 73% for locations bottom, top and side respectively. Whilst the top and side fan locations enhanced the removal of the exhaled gas mixture, the bottom-fan respirator was more efficient in removing the nostril jet gas mixture and therefore provided the least barrier to respiratory function. The results provide valuable insights into the benefits of fan respirators for long-term use for reducing CO2 concentration, mask temperature, and humidity, improving wearer safety and comfort in hazardous environments, especially during the COVID-19 pandemic.Comment: 23 Pages, 7 Figure

Two computational studies of a flatback airfoil using non-zonal and embedded scale-resolving turbulence modelling approaches

The contribution presents results from two computational studies conducted by Upstream CFD and ENERCON, which aim to evaluate their respective CFD methodologies for the aerodynamics and aeroacoustics prediction of a flatback airfoil with 35% relative thickness. The CFD is validated against data from two comprehensive experimental campaigns conducted in the NWB facility operated by the German-Dutch Wind Tunnels Foundation (DNW), which include measurements of mean force coefficients, static and total pressure distributions in the wake region, unsteady surface pressures and farfield sound emission. In both numerical studies, scale-resolving approaches based on detached-eddy simulation are utilised, where a comparison is drawn between a purely non-zonal use of the model in which attached boundary layers are fully modelled via RANS and a zonal use with synthetic turbulence being injected into the boundary layers upstream of the trailing edge. First, the aerodynamic flow fields are analysed, showing good agreement with the reference measurements. Farfield noise is then predicted from solid and permeable Ffowcs-Williams and Hawkings surfaces, where both the dominant shedding tone as well as broadband levels compare well with microphone array data

Numerical Characterization and Modeling of Adiabatic Slot Film Cooling

Film cooling is a technique used to protect critical surfaces in combustors, thrust chambers, turbines and nozzles from hot, chemically reacting gases. Accurately predicting the film's performance is especially challenging in the vicinity of the wall and the film injection plane due to the complex interactions of two highly turbulent, shearing, boundary layer flows. Properly characterizing the streams at the inlet of a numerical simulation and the choice of turbulence model are crucial to accurately predicting the decay of the film. To address these issues, this study employs a RANS solver that is used to model a film cooled wall. Menter's baseline model, and shear-stress transport model and the Spalart-Allmaras model are employed to determine the effect on film cooling predictions. Several methods for prescribing the inlet planes are explored. These numerical studies are compared with experimental data obtained in a UMD film cooling wind tunnel

Detached-Eddy Simulation of the Vortical Flowfield about the VFE-2 DeltaWing

The numerical simulation of the flow around a 65° delta wing configuration with rounded leading edges is presented. For the numerical simulation the Cobalt Code uses a cell-centered unstructured hybrid mesh approach. Several numerical results are presented for the steady RANS equations as well as for DES and DDES hybrid approaches. The simulations are done as part of the NATO RTO/AVT 113 working group focusing on experimental and numerical research on delta wing configurations with rounded leading edges. Within this paper the focus is related to the dual primary vortex flow topology, especially the sensitivity of the flow to angle of attack and Reynolds number effects. Reasonable results are obtained with both steady RANS and SA-DDES simulations. The results are compared and verified by experimental data, including surface pressure and pressure sensitive paint results. The impact of transition is assessed, and recommendations for improving future simulations are made

Heat Transfer Mechanism In Particle-Laden Turbulent Shearless Flows

Particle-laden turbulent flows are one of the complex flow regimes involved in a wide range of environmental, industrial, biomedical and aeronautical applications. Recently the interest has included also the interaction between scalars and particles, and the complex scenario which arises from the interaction of particle finite inertia, temperature transport, and momentum and heat feedback of particles on the flow leads to a multi-scale and multi-physics phenomenon which is not yet fully understood. The present work aims to investigate the fluid-particle thermal interaction in turbulent mixing under one-way and two-way coupling regimes. A recent novel numerical framework has been used to investigate the impact of suspended sub-Kolmogorov inertial particles on heat transfer within the mixing layer which develops at the interface of two regions with different temperature in an isotropic turbulent flow. Temperature has been considered a passive scalar, advected by the solenoidal velocity field, and subject to the particle thermal feedback in the two-way regime. A self-similar stage always develops where all single-point statistics of the carrier fluid and the suspended particles collapse when properly re-scaled. We quantify the effect of particle inertial, parametrized through the Stokes and thermal Stokes numbers, on the heat transfer through the Nusselt number, defined as the ratio of the heat transfer to the thermal diffusion. A scale analysis will be presented. We show how the modulation of fluid temperature gradients due to the statistical alignments of the particle velocity and the local carrier flow temperature gradient field, impacts the overall heat transfer in the two-way coupling regime

Numerical Simulations of a Landing Gear with Flow Through Fairings for Noise Mitigation

This study presents a numerical investigation of the noise mitigation effect provided by several fairings placed upstream of a simplified two-wheel landing gear. The chosen configuration is equipped with detachable elements that mimic realistic components, e.g. brakes and torque link, to include representative landing gear noise sources. Several numerical simulations of the flow developing around this landing gear have been carried out, with or without an additional upstream fairing to control the noise generation processes. The chosen configurations match those from related experiments performed at the Delft University of Technology. Both the numerical and the experimental studies are conducted in the framework of the European Union Horizon 2020 research project INVENTOR (INnoVative dEsign of iNstalled airframe componenTs for aircraft nOise Reduction). The numerical method is based on the Zonal Detached Eddy Simulation approach, applied on a set of Cartesian octree grids with a specific immersed boundary wall treatment. Both solid and wire mesh fairings are considered, the latter being accounted for thanks to a specific wire mesh numerical model. Overall, the simulations show a nice agreement with the measurements and allow a thorough analysis of the flow modifications responsible for noise mitigation when the fairings are introduced. Previous Chapte