Scale-resolving Simulations Research Articles

Scale-Resolving Hybrid RANS-LES Simulation of a Model Kaplan Turbine on a 400-Million-Element Mesh

Double-regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different sizes and strengths. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena, like swirl, separation and strong adverse pressure gradients, and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a coarse mesh and large time step size often fail to correctly predict performance and can even lead to wrong tendencies in the overall behavior. To reveal occurring flow phenomena and physical effects, a scale-resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double-regulated five-blade model Kaplan turbine is carried out. In this paper, first, the results of the ongoing simulation are presented. The major part of the simulation domain is running in LES mode and seems to be properly resolved. The validation of the simulation results with the experimental data shows mean deviations of less than 0.8% in the global results, i.e., total head and power, and a good visual agreement with the three-dimensional PIV measurements of the velocity in the cone and both diffuser channels of the draft tube. In particular, the trend of total head and the results for the draft tube differ significantly between the scale-resolving simulation and a standard RANS simulation. The standard RANS simulation exhibits a highly unsteady behavior of flow, which is not observed in the experiments or scale-resolving simulation.

Scale-resolving simulation of a low-pressure turbine on hybrid supercomputers

The increased computing power of modern hybrid supercomputers is expanding the applicability of scale-resolving simulations in scientific and industrial applications. This paper is devoted to such a supercomputer simulation technology for turbomachinery. A heterogeneous parallel algorithm is outlined and its parallel performance is demonstrated on various hybrid supercomputers by executing a single simulation on dozens of central and graphics processing units. The scale-resolving numerical simulation of the flow in a linear cascade of T106C high-lift low-pressure turbine blades is considered. The presence of a laminar–turbulent transition on the suction side of the blade, caused by the separation of the boundary layer, leads to a significant increase in the loss of kinetic energy. The effect of increasing losses with a decrease in the Reynolds number is captured. A strong dependence of the numerical results on the incoming turbulent flow conditions is observed. The effect of imposing synthetic turbulence at the inflow is studied, as well as the required mesh resolution to capture the laminar–turbulent transition well.

On the Effectiveness of Scale-Averaged RANS and Scale-Resolved IDDES Turbulence Simulation Approaches in Predicting the Pressure Field over a NASCAR Racecar

Racecar aerodynamic development requires well-correlated simulation data for rapid and incremental development cycles. Computational Fluid Dynamics (CFD) simulations and wind tunnel testing are industry-wide tools to perform such development, and the best use of these tools can define a race team’s ability to compete. With CFD usage being limited by the sanctioning bodies, large-scale mesh and large-time-step CFD simulations based on Reynolds-Averaged Navier–Stokes (RANS) approaches are popular. In order to provide the necessary aerodynamic performance advantages sought by CFD development, increasing confidence in the validity of CFD simulations is required. A previous study on a Scale-Averaged Simulation (SAS) approach using RANS simulations of a Gen-6 NASCAR, validated against moving-ground, open-jet wind tunnel data at multiple configurations, produced a framework with good wind tunnel correlation (within 2%) in aerodynamic coefficients of lift and drag predictions, but significant error in front-to-rear downforce balance (negative lift) predictions. A subsequent author’s publication on a Scale-Resolved Simulation (SRS) approach using Improved Delayed Detached Eddy Simulation (IDDES) for the same geometry showed a good correlation in front-to-rear downforce balance, but lift and drag were overpredicted relative to wind tunnel data. The current study compares the surface pressure distribution collected from a full-scale wind tunnel test on a Gen-6 NASCAR to the SAS and SRS predictions (both utilizing SST k−ω turbulence models). CFD simulations were performed with a finite-volume commercial CFD code, Star-CCM+ by Siemens, utilizing a high-resolution CAD model of the same vehicle. A direct comparison of the surface pressure distributions from the wind tunnel and CFD data clearly showed regions of high and low correlations. The associated flow features were studied to further explore the strengths and areas of improvement needed in the CFD predictions. While RANS was seen to be more accurate in terms of lift and drag, it was a result of the cancellation of positive and negative errors. Whereas IDDES overpredicted lift and drag and requires an order of magnitude more computational resources, it was able to capture the trend of surface pressure seen in the wind tunnel measurements.

On the Co-existence of Transonic Buffet and Separation-Bubble Modes for the OALT25 Laminar-Flow Wing Section

Transonic buffet is an unsteady flow phenomenon that limits the safe flight envelope of modern aircraft. Scale-resolving simulations with span-periodic boundary conditions are capable of providing new insights into its flow physics. The present contribution shows the co-existence of multiple modes of flow unsteadiness over an unswept laminar-flow wing section, appearing in the following order of increasing frequency: (a) a low-frequency transonic buffet mode, (b) an intermediate-frequency separation bubble mode, and (c) high-frequency wake modes associated with vortex shedding. Simulations are run over a range of Reynolds and Mach numbers to connect the lower frequency modes from moderate to high Reynolds numbers and from pre-buffet to established buffet conditions. The intermediate frequency mode is found to be more sensitive to Reynolds-number effects compared to those of Mach number, which is the opposite trend to that observed for transonic buffet. Spectral proper orthogonal decomposition is used to extract the spatial structure of the modes. The buffet mode involves coherent oscillations of the suction-side shock structure, consistent with previous studies including global mode analysis. The laminar separation-bubble mode at intermediate frequency is fundamentally different, with a phase relationship between separation and reattachment that does not correspond to a simple ‘breathing’ mode and is not at the same Strouhal number observed for shock-induced separation bubbles. Instead, a Strouhal number based on separation bubble length and reverse flow magnitude is found to be independent of Reynolds number within the range of cases studied.

Analysis of the vortex-dominated flow field over a delta wing at transonic speed

AbstractThe present work provides an advancement in the prediction of delta wing flow and an improved understanding of various flow physical phenomena which occur over the wing in transonic conditions. Scale-resolving simulations of the vortex-dominated flow around a sharp leading-edge VFE-2 wing have been performed using the SA-based IDDES model. The complex leading-edge vortex pattern with embedded shocks and subsequent shock-vortex interaction is investigated. A promising accuracy has been achieved using the high-fidelity flow field data provided by the scale-resolving simulation results. Besides the assessment of sensitivity to spatial and temporal resolution, physical aspects are presented, which are not accessible in experimental data in such detail and require scale-resolving simulation approaches. This includes the observation of the vortex system and the shocks in the fully three-dimensional flow field data. Finally, turbulence-related quantities such as eddy viscosity and resolved Reynolds-stresses and their behaviour during the vortex formation and sustaining process are analysed.

Efficient spectral implementation of ODE wall model and the extension of integral wall model to unstructured LES solvers

While wall modeling has become an indispensable tool for scale-resolving simulation of high Reynolds numbers wall-bounded turbulent flows, discussion of efficient implementation of wall models in parallel unstructured-grid solvers is lacking. In this paper, we discuss physical and numerical improvements to two zonal wall models based on integral form of the boundary layer differential equations within an unstructured-grid cell-centered finite-volume LES solver. The first model is a novel implementation of the ODE equilibrium wall model, where the velocity profile is expressed in the integral form using the constant shear-stress layer assumption and the integral is evaluated using a spectral quadrature method, resulting in a local and algebraic (grid-free) formulation. The second model is the modified form of the integral wall model of Yang et al. (2015) [14], which is based on the vertically-integrated thin-boundary-layer PDE along with a prescribed composite velocity profile in the wall-modeled region. A modification to the inner layer velocity profile which fixes the coordinate invariance issue of the original model is proposed. Additionally, several numerical challenges unique to the implementation of these integral models in unstructured mesh environments, such as the exchange of wall quantities between wall faces and LES cells, and the computation of surface gradients, are identified and possible remedies are proposed. The computational performance of the wall models is assessed both in a priori and a posteriori settings against the traditional finite-volume based ODE equilibrium wall model, showing a comparable computational cost for the integral wall model, and superior cost scaling for the spectral implementation over the finite-volume based approach. Load imbalance among the processors in parallel simulations seems to severely degrade the parallel efficiency of finite-volume based ODE wall model, whereas the spectral implementation is remarkably agnostic to these effects. The integral wall model, however, is even more prone to parallel efficiency degradation than the finite-volume based ODE wall model due to communication overhead among processors in highly parallelized settings.

Simulation and Validation of Cavitating Flow in a Torque Converter with Scale-Resolving Methods

The purpose of this paper is to study the mechanism and improve the prediction accuracy of transient torque converter cavitation flow by the application of scale-resolving simulation (SRS) methods with particular focus on cavitation vortex flow. Firstly, the numerical analysis of the entire internal flow field of the torque converter was carried out using different turbulence models, and the prediction accuracy of the hydraulic characteristics of the adopted models was analyzed and validated via test data. Secondly, the cavitation and turbulence behavior in the internal flow field were analyzed, and the blade surface pressure according to different turbulence models was compared and validated through test data. Finally, the transient cavitation characteristics of the flow field were studied based on the stress-blended eddy simulation (SBES) model. The prediction accuracy of the cavitation flow field simulation of the torque converter is significantly improved using the SRS model. The maximum error of capacity constant, torque ratio and efficiency are reduced to 3.1%, 2.3%, and 1.3% at stall, respectively. The stator is more prone to cavitation than pump and turbine. The SBES model has the highest prediction accuracy in multiple measurement points, and the maximum deviation can reach 13.32% under stall. Attached cavitation bubbles and periodic shedding cavitation can be found in the stator, and the evolution period is about 0.0036 s, i.e., 279 Hz. The prediction accuracy of different models was compared and analyzed, which has important guiding significance for the high-precision prediction and analysis of fluid machinery.

Aeroacoustic Simulations of an Axial Fan with Modelled Turbulent Inflow Conditions

In applications, the acoustics of fans can differ significantly from the measurements of the standalone fan. This is due to disturbed inflow conditions, for example, caused by a heat exchanger upstream of an axial fan. Resolving the complex geometry and dimensions of typical heat exchangers in aeroacoustic scale-resolving simulations leads to a very high computation effort, which is currently not economically feasible. Turbulence reconstruction tools, such as the FRPM, provide the possibility to model the turbulent inflow conditions, thereby avoiding the representation of the heat exchanger in the aeroacoustic simulations. This approach is tested on a benchmark experiment of a ducted fan with an upstream turbulence grid.

Suppression of the Spatial Hydrodynamic Instability in Scale-Resolving Simulations of Turbulent Flows Inside Lined Ducts

This paper addresses one of the major obstacles arising in the high-fidelity scale-resolving simulations of turbulent flows inside ducts with the walls covered by acoustic liners in order to attenuate the sound radiated from the duct. It consists of the development of spatial hydrodynamic (convective) instability over the treated walls at the low values of the acoustic resistance of the liner. For reasons that remain unclear, the growth rate of this instability and its effect on sound propagation through the duct is strongly overestimated by the CFD simulations using the macroscopic concept of the locally reacting acoustic impedance. A new damping volume source term (“body force”) is proposed, whose introduction into the momentum equation resolves this issue by means of artificially suppressing the instability while remaining within the framework of the computationally efficient model of the impedance wall, i.e., without trying to simulate the liner microscopically. Examples are presented of the application of the developed methodology to the flows in the grazing impedance tubes with two different liners. They suggest that the proposed form of the damping source term can be considered universal and that the suppression of the hydrodynamic instability ensured by this term is not accompanied by any significant distortion of the propagation of the sound waves and the turbulence statistics, except for a very narrow near-wall region.

Riblet Performance Beneath Transitional and Turbulent Boundary Layers at Low Reynolds Numbers

Several high-resolution scale-resolving simulations are carried out to examine the effect of riblets on the mean and turbulent statistics of a zero-pressure-gradient boundary layer. The Reynolds number is chosen such that the riblets are exposed to both the transitional and turbulent regimes of the boundary layer. This is in contrast to the turbulent channel flow or fully turbulent boundary layers studied in the literature. The boundary layer is subjected to freestream turbulence and roughness tripping. The transition process and the extent of the turbulent regime on the riblets are altered by tripping the boundary layer with an isolated hemispherical roughness element. The influence of the riblets on the transition onset and the viscous drag reduction is demonstrated through time-averaged, phase-averaged, and instantaneous flow quantities. The effect of the V-shaped riblets with both sharp and curved tips (and valleys) is also explored. With riblets, the viscous drag in the turbulent regime is reduced by 4–6% when compared to a smooth surface, and the efficacy of sharp V-shaped riblets is shown to be marginally higher than for the curved riblets. In the transitional flow regime, the coherent structures over riblets are predominantly spanwise oriented. In particular, a separated shear layer forms over the riblet leading edge as the flow encounters an abrupt surface transition from the smooth surface onto the riblets. A leading-edge ramp is shown to effectively minimize the additional spurt in the turbulent kinetic energy and the associated losses incurred due to this abrupt surface change.

Deneb: An open-source high-performance multi-physical flow solver based on high-order DRM-DG method

High-order methods are being recognized as powerful tools for handling scale-resolving simulations over complex geometry. However, several obstacles still block their complete applications to practical engineering problems: a compromise between accuracy and efficiency on mixed-curved meshes, inherent vulnerability to numerical oscillations, and lack of open-source high-performance solvers for researchers. To address these issues, we present Deneb, an open-source high-order accurate numerical solver that enables high-performance scale-resolving simulations on PDE-based flow systems. Deneb uses the physical domain-based modal discontinuous Galerkin (DG) method; thus, it can provide an arbitrary high-order accurate solution on mixed-curved meshes and has the potential for handling polyhedral meshes as well. The direct reconstruction method (DRM) efficiently executes the numerical integration of DG volume and surface integrals without accuracy loss on non-affine elements where mapping functions are high-degree. The resulting DRM-DG method eliminates the severe cost of a quadrature-based approach on mixed-curved meshes. Deneb offers explicit and implicit Runge–Kutta methods as well to achieve high-order accuracy in time. In addition, Krylov subspace methods and preconditioners are available for high-performance linear system solving in parallel. Deneb possesses a strong capability to resolve multi-physical shocks without numerical instabilities with the aid of multi-dimensional limiting and artificial viscosity methods. In particular, the hierarchical multi-dimensional limiting process enables efficient computations of supersonic flows without time-step restriction. The current release of Deneb covers the simulations of hypersonic equilibrium and magneto-hydrodynamic flows as well as compressible Navier–Stokes equations, but it has the potential to solve any PDE-based multi-physical flow systems. Several benchmark problems are presented to highlight Deneb's capability to perform scale-resolving and multi-physical flow simulations. A scalability test is also presented to verify the scaling characteristics of Deneb for high-performance computing. Program summaryProgram title: DenebCPC library link to program files:https://doi.org/10.17632/723n5r797n.1Developer's repository link:https://github.com/HojunYouKr/DenebLicensing provisions: BSD-3-ClauseProgramming language: C++17Nature of problem: The physical domain-based modal DG method can achieve the expected order of accuracy with the optimal number of polynomial bases even on non-affine elements. However, the DG method becomes significantly expensive on high-order curved elements when using quadrature rules, blocking its applicability to practical engineering problems. The numerical integration should be much more efficient without compromising accuracy. In addition, the less diffusive nature of high-order methods makes them susceptible to producing spurious numerical oscillations near flow discontinuities, potentially leading to numerical instabilities. Thus, an accurate and robust shock-capturing method is essential to simulate multi-physical flows under compressible regimes. Finally, the solver needs high scalability to perform large-scale computations in parallel.Solution method: DRM is applied to the DG volume and surface integrals to perform efficient numerical integration on non-affine elements without accuracy loss. The resulting method, DRM-DG, provides arbitrary high-order accurate solutions to various PDE-based flow problems on mixed-curved meshes. The solution is also high-order accurate in time due to high-order explicit and implicit Runge–Kutta methods implemented. The external library enables high-performance linear system solving with various preconditioners in parallel. Both multi-dimensional limiting and artificial viscosity methods suppress unwanted subcell oscillations across physical discontinuities. In particular, the limiting methods simulate complex supersonic flows efficiently without time-step restriction. The solver is highly scalable on parallel computing with the aid of non-blocking communications and latency hiding.

A unified understanding of scale-resolving simulations and near-wall modelling of turbulent flows using optimal finite-element projections

The main objective of this work is to develop a unified framework that can be used as a lens to quantitatively assess and augment a wide range of coarse-grained models of turbulence, namely large eddy simulations (LES), hybrid Reynolds-averaged/LES methods and wall-modelled (WM)LES. Taking a turbulent channel flow as an example, optimality is assessed in the wall-resolved limit, the hybrid RANS–LES limit and the WMLES limit, via projections at different resolutions suitable for these approaches. These optimal a priori estimates are shown to have similar characteristics to existing a posteriori solutions reported in the literature. Consistent accuracy metrics are developed for scale-resolving methods using the optimal solution as a reference, and evaluations are performed. We further characterise the slip velocity in WMLES in terms of the near-wall under-resolution and develop a universal scaling relationship. Insights from the a priori tests are used to augment existing slip-based wall models. Various a posteriori tests reveal superior performance over the dynamic slip wall model. Guidance for the development of improved slip-wall models is provided, including a target for the dynamic procedure.

Scale-resolving simulations of the flow in a nuclear fuel bundle with a channel spacer grid using partially averaged Navier–Stokes and large-eddy simulation

The objective of this study is to evaluate the capabilities of the Partially Averaged Navier–Stokes (PANS) method in simulations of the flow through a rod bundle representative of a nuclear fuel assembly with a channel-type spacer grid. In the PANS bridging turbulence model, filters can be applied to obtain any level of resolution from Reynolds Averaged Navier–Stokes (RANS) to Direct Numerical Simulation (DNS). The closure model is sensitive to the length-scale cutoff by means of unresolved to total kinetic energy ratio (fk) and unresolved to total dissipation ratio (fε). Simulations are conducted to study the effect of the cutoff of length scale on the results obtained for flow statistics at selected locations in the domain. The results obtained with different PANS filters are compared with Unsteady RANS (URANS), Large Eddy Simulation (LES), and experiments. The mean and fluctuating flow components are computed at a representative plane located at the inter-channel between rods. Other flow quantities analyzed include the pressure drop upstream and downstream of the spacer grid, the turbulent kinetic energy, and the unresolved eddy viscosity. Additionally, we use the Lumley triangle to study turbulence anisotropy and to compare the nature of the energy content captured with LES and one of the PANS models. It is shown that the PANS model with fk=0.4, which resolves 60% of the turbulent kinetic energy content, captures the most relevant flow physics and is a suitable modeling approach for this application.

A machine learning approach for calibrating ABL profiles in large-eddy simulations

Atmospheric boundary layer (ABL) inhomogeneity is a common problem encountered in computational wind engineering (CWE) where inflow profiles experience unintended flow adaptation while travelling from the inlet boundary to the location of interest inside the domain. This causes the region of interest to experience flow conditions different from those intended by the modeller thereby introducing error in the simulation. Solutions to ABL inhomogeneity have been proposed for RANS models but this issue remains problematic in scale-resolving simulations. In this study, a machine learning (ML) approach is proposed for calibrating ABL profiles to achieve target flow properties in large-eddy simulations (LES). The proposed method is demonstrated for ABL flow over a suburban terrain based on AS 1170.2, leading to a considerable reduction of inhomogeneity error from 49.6% to 4.6%. Sensitivity studies are also presented to investigate the influence of numerical parameters on profile calibration. While the proposed approach does not resolve underlying theoretical limitations resulting in ABL inhomogeneity, it provides a practical solution for achieving target ABL profiles which can help improve confidence in the reliability of LES for wind engineering applications.

Field inversion for transitional flows using continuous adjoint methods

Transition modeling represents one of the key challenges in computational fluid dynamics. While numerical efforts were traditionally devoted to either improving Reynolds-averaged Navier–Stokes-based turbulence modeling or developing scale-resolving simulations, cautious attention has been recently given to field inversion and machine learning techniques. This paper discusses an updated development of field inversion model for transitional flows based on k–ω shear stress transport model using the continuous adjoint approach, instead of the typical discrete adjoint method. The original model is modified by multiplying the production term of the turbulent kinetic energy equation by a spatially varying discrepancy function η(x). The adjoint equations and the relevant boundary conditions are specifically derived and integrated in OpenFOAM. The present model is validated using two zero pressure-gradient and four non-zero pressure-gradient from flow-over-flat-plate T3-series test cases. The gradient descent method is employed in the optimization process to minimize the discrepancy in the calculated shear stress. The inferred solution indicates a smooth transition to turbulence at the reported critical Reynolds numbers. The optimized model significantly improves the predictions of skin-friction coefficients, originally incorporated in the objective function. To demonstrate the usefulness of the present approach, the investigation is further extended to determine both velocity and shear Reynolds-stress profiles, which to our knowledge has not been reported before. Furthermore, a reduction in the percentage error from 50.2% to 7.3% is well observed in the predicted boundary layer thickness considering the laminar regime in the T3C5 test case.

Investigation of low-dissipation low-dispersion schemes for incompressible and compressible flows in scale-resolving simulations

A comprehensive study is conducted on a second-order low-dissipation low-dispersion (LD2) scheme in scale-resolving simulations of both incompressible and compressible flows, using a node-based unstructured CFD solver. The scheme deploys a higher order central reconstruction of the face values (up to fourth-order on structured meshes) and a matrix dissipation formulation to reduce the dispersive and dissipative numerical errors. The LD2 scheme is examined for compressible flow cases involving shock discontinuities, LD2-Compressible (LD2C), and is verified in a classical shock-tube problem. The scheme is then further verified in Large-Eddy Simulations (LES) of decaying isotropic turbulence (DIT) in comparison with available experimental data. It is shown that in scale-resolving simulations, the LD2C scheme is able to significantly improve the prediction as compared to a conventional second-order central scheme. The scheme is then further assessed and verified in hybrid Reynolds-Averaged Navier–Stokes (RANS)-LES computations for the subsonic and supersonic turbulent channel flow, where excellent agreement with reference DNS and correlations are observed. Moreover, a supersonic base flow is simulated using hybrid RANS-LES, where improved predictions are observed. The LD2C scheme exploits a shock sensor incorporating vorticity and is shown to improve the prediction of the resolved shear stress in the shear layer of compression.

Adapting a Scientific CFD Code to Industrial Applications on Hybrid Supercomputers

The NOISEtte heterogeneous parallel code for simulating turbulent flow and aerodynamic noise is considered. In our previous works, high acceleration and parallel efficiency in scientific scale-resolving simulations using GPUs were reported. For parallelization, the MPI, OpenMP and OpenCL standards are used, the latter allows using GPUs from different vendors. However, the further transition to industrial-oriented applications brought more trouble. Instead of discussing the parallel algorithm, this work will focus on the problems that are not so obvious at first glance, which arise when developing a heterogeneous simulation code. How to deal with numerous simulation algorithm components, all those bells and whistles like wall functions, mixing plane and sliding interfaces, synthetic turbulence generators, a variety of boundary conditions, etc., that either need to be ported to the GPU side or incorporated directly from the CPU side? How to maintain and modify the OpenCL code in a growing number of source files? How to arrange the modularity of a complex heterogeneous software package? How to preserve reliability and fault tolerance, especially in the case of numerical schemes of increased accuracy, but reduced social responsibility? These issues are discussed here and some solutions will be proposed.

Evaluation of Enhanced Gray Area Mitigation Approaches Based on Jet Aeroacoustics

An investigation of various eddy viscosity models for accurate scale-resolving simulation of aerodynamics and aeroacoustics of a turbulent jet is presented. The models are considered from the perspective of solving the so-called gray area problem. This problem is related to nonphysical delay in the transition from Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) in hybrid RANS–LES approaches such as detached eddy simulation (DES) when applied to shear-layer flows. The performance of recently developed dynamic adapting subgrid length scales (, , and ) and subgrid LES models ( and S3QR) separately and together is demonstrated. The object of the investigation is an immersed subsonic turbulent jet. The simulations are carried out on a set of refining meshes using two different scale-resolving numerical algorithms with basic and higher-accuracy schemes on unstructured meshes. The evaluation of various eddy-viscosity models within the DES approach is mostly focused on the analysis of far-field noise. The study has clearly demonstrated the importance of both a numerical scheme and a subgrid turbulence model. The results show that some of the considered techniques provide the necessary accuracy to predict the noise generated by a turbulent jet. The features of the considered approaches are identified and discussed. Recommendations are formulated for the choice of the LES model and subgrid length scale for this kind of problem.

High-order scale-resolving simulations of extreme wind loads on a model high-rise building

Building facade systems can be subject to severe and highly localized wind suction pressures. Such pressures need to be accurately assessed in order to estimate the maximum loads on a typical cladding panel. Wind tunnel experiments studying turbulent flow over a model high-rise building have shown space–time localized peaks of extremely low pressure (Cp<−8) on the model building facade. Such low pressure values are unexpected and the potential implications for the cost and carbon intensity of cladding systems are significant. In this work, we use the open-source solver PyFR to carry out high-order Implicit Large Eddy Simulations (ILES) of this test case. The simulations capture, for the first time, the observed space–time localized peaks of extreme low pressure, replicating the experimental findings. The corresponding fluid structures are shown in detail. They are found to be relatively thin and long vortices spinning with an angular velocity approximately normal to the building wall.

Numerical Analysis and Experimental Investigation of Cavitating Flows Considering Thermal and Compressibility Effects

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical simulations were validated by means of already published experiments or compared with experiments conducted by the authors, and with good agreement.