Scale-resolving Simulations Research Articles

Thermo-Hydraulic Characteristics of Micro-Scale Surface Roughness Topology of Additively Manufactured Surface Model: Modal Decomposition Perspective

As a consequence of rapid development of additive manufacturing (3D printing) methods, the academic/industrial demand has been continuously increasing. One field of application is the manufacturing of heat exchanging devices using this promising method. In this regard, understanding the underlying mechanisms from a thermo-hydraulic viewpoint becomes important. Therefore, in this study, scale-resolving large eddy simulation (LES) is applied to reveal the flow details in combination with a model of roughness topology occurring in additive manufacturing. To process the transient LES results, proper orthogonal decomposition (POD) is used to extract the coherent flow structures, and the extended POD is used to rank the flow modes based on thermal importance. The main aim of the present work is to go beyond the conventionally applied methodologies used for the evaluation of surface roughness, i.e., averaged numerical study or experimental overall performance evaluation of the flow/thermal response of additively manufactured surfaces in heat exchangers. This is necessary to reveal the underlying flow mechanisms hidden in the conventional studies. In this study, the behavior of the flow over the micro-scale surface roughness model and its effects on heat transfer are studied by assuming cone-shaped roughness elements with regular placement as the dominant surface roughness structures. The major discussions reveal the footprint of flow mechanisms on the heat transfer coefficient spatial modes on the rough surface. Moreover, comparative study on the flow/thermal behavior at different levels of roughness heights shows the key role of the height-to-base-diameter ratio of the roughness elements in thermal performance.

Scale-Resolving Simulations of a Circular Cylinder Subjected to Low Mach Number Turbulent Inflow

Inflow turbulence is relevant for many engineering applications relating to noise generation, including aircraft wings, landing gears, and non-cavitating marine propellers. While modelling of this phenomenon is well-established for higher Mach number aerospace problems, lower Mach number applications, which include marine propellers, still lack validated numerical tools. For this purpose, simplified cases for which extensive measurement data are available can be used. This paper investigates the effect of inflow turbulence on a circular cylinder at a Reynolds number of 14,700, a Mach number of 0.029, and with inflow turbulence intensities ranging between 0% and 22%. In the present work focus is put on the hydrodynamics aspect, with the aim of addressing radiated noise in a later study. The flow is simulated using the partially averaged Navier Stokes equations, with turbulence inserted using a synthetic inflow turbulence generator. Results show that the proposed method can successfully replicate nearfield pressure variations and relevant flow features in the wake of the body. In agreement with the literature, increasing inflow turbulence intensity adds broadband frequency content to all the presented fluctuating flow quantities. In addition, the applied variations in inflow turbulence intensity result in a major shift in flow dynamics around a turbulence intensity of 15%, when the dominant effect of von Kármán vortices on the dominant flow dynamics becomes superseded by freestream turbulence.

Heterogeneous CPU+GPU parallelization for high-accuracy scale-resolving simulations of compressible turbulent flows on hybrid supercomputers

A heterogeneous parallel algorithm for simulation of compressible turbulent flows and its portable software implementation are presented. The underlying numerical method is based on a family of higher accuracy edge-based reconstruction schemes on unstructured mixed-element meshes. The proposed parallel solution can engage a large number of computing devices of most of the existing computing architectures used in modern supercomputers, including manycore CPUs and GPUs. It is capable of co-execution on both CPUs and accelerators simultaneously. The multilevel parallel algorithm combines: MPI for distributing workload among hybrid cluster nodes and between devices inside nodes; OpenMP for manycore CPUs and other supporting devices, such as Intel Xeon Phi; OpenCL for massively-parallel accelerators, such as GPUs of various vendors, including NVIDIA, AMD, Intel. The main focus is on the adaptation of the numerical method and its computational algorithm to the stream processing parallel paradigm. The very limited device memory inherent in GPU computing is also taken into account. A detailed description of the parallel algorithm is presented, as well as the techniques used for its efficient parallel implementation. Special attention is paid to implicit time integration with its linear solver and calculation of convective fluxes and viscous terms. The use of mixed floating-point precision and overlapping communications and computations is also discussed. Parallel performance is demonstrated in practical applications on different kinds of supercomputers using up to 10 thousand cores and multiple GPUs of comparable overall performance.

Synthetic Turbulence Generation for High-Order Scale-Resolving Simulations on Unstructured Grids

An extended version of the synthetic eddy method for generation of synthetic turbulence has been developed via a source term formulation and implemented in the open-source cross-platform solver PyFR. The method caters for the full space-dependent anisotropy of the target turbulent length scales, and it is agnostic of the space and time discretization of the underlying solver, which can be incompressible or compressible. Moreover, the method does not require each solution point to communicate with nearest neighbors; thus, it is well suited for modern, massively parallel, high-order unstructured codes which support mixed and possibly curved elements. The method has been applied to two test cases: incompressible plane channel flow at and compressible flow over an SD7003 aerofoil at , , and . The channel flow case was run on three topologically different meshes composed of hexahedra, prisms, and a combination of prisms and tetrahedra, respectively. Almost identical results have been obtained on the three meshes. Results also show that taking into account the anisotropy of the turbulent length scales can reduce the development length. For the SD7003 aerofoil case, the injection of synthetic turbulence improves agreement between numerical and experimental results.

Scale-Resolving Simulations of Steady and Pulsatile Flow Through Healthy and Stenotic Heart Valves.

Blood-flow downstream of stenotic and healthy aortic valves exhibits intermittent random fluctuations in the velocity field which are associated with turbulence. Such flows warrant the use of computationally demanding scale-resolving models. The aim of this work was to compute and quantify this turbulent flow in healthy and stenotic heart valves for steady and pulsatile flow conditions. Large eddy simulations (LESs) and Reynolds-averaged Navier-Stokes (RANS) simulations were used to compute the flow field at inlet Reynolds numbers of 2700 and 5400 for valves with an opening area of 70 mm2 and 175 mm2 and their projected orifice-plate type counterparts. Power spectra and turbulent kinetic energy were quantified on the centerline. Projected geometries exhibited an increased pressure-drop (>90%) and elevated turbulent kinetic energy levels (>147%). Turbulence production was an order of magnitude higher in stenotic heart valves compared to healthy valves. Pulsatile flow stabilizes flow in the acceleration phase, whereas onset of deceleration triggered (healthy valve) or amplified (stenotic valve) turbulence. Simplification of the aortic valve by projecting the orifice area should be avoided in computational fluid dynamics (CFD). RANS simulations may be used to predict the transvalvular pressure-drop, but scale-resolving models are recommended when detailed information of the flow field is required.

Assessment of a Discontinuous Galerkin Method for the Simulation of the Turbulent Flow around the DrivAer Car Model

The turbulent flow over the DrivAer fastback model is here investigated with an order-adaptive discontinuous Galerkin (DG) method. The growing need of high-fidelity flow simulations for the accurate determination of problems, e.g., vehicle aerodynamics, promoted research on models and methods to improve the computational efficiency and to bring the practice of Scale Resolving Simulations (SRS), like the large-eddy simulation (LES), to an industrial level. An appealing choice for SRS is the Implicit LES (ILES) via a high-order DG method, where the favourable numerical dissipation of the space discretization scheme plays directly the role of a subgrid-scale model. Implicit time integration and the p-adaptive algorithm reduce the computational cost allowing a high-fidelity description of the physical phenomenon with very coarse mesh and moderate number of degrees of freedom. Two different models have been considered: (i) a simplified DrivAer fastback model, without the rear-view mirrors and the wheels, and a smooth underbody; (ii) the DrivAer fastback model, without rear-view mirrors and a smooth underbody. The predicted results have been compared with experimental data and CFD reference results, showing a good agreement.

Scale resolving simulations of a high-temperature turbulent jet in a cold crossflow: Comparison of two approaches

A high-temperature turbulent jet in a cold crossflow is investigated with the help of two scale-resolving simulation approaches. This work aims at improving the methodologies used to predict the thermal footprint of exhaust gases issuing from helicopter engines onto the fuselage. Specific attention is brought to the capability of scale resolving simulations to correctly reproduce flow dynamics and turbulent mixing. Mean flow features, turbulent quantities and temperature fields are compared and validated against wind tunnel test measurements. In addition, the present work highlights the importance of synthetic turbulence injection at pipe inlet to obtain a fair prediction of both flow dynamics and temperature field.

Statistical Error Estimation Methods for Engineering-Relevant Quantities From Scale-Resolving Simulations

Abstract Scale-resolving simulations, such as large eddy simulations, have become affordable tools to investigate the flow in turbomachinery components. The resulting time-resolved flow field is typically analyzed using first- and second-order statistical moments. However, two sources of uncertainty are present when statistical moments from scale-resolving simulations are computed: the influence of initial transients and statistical errors due to the finite number of samples. In this paper, both are systematically analyzed for several quantities of engineering interest using time series from a long-time large eddy simulation of the low-pressure turbine cascade T106C. A set of statistical tools to either remove or quantify these sources of uncertainty is assessed. First, the Marginal Standard Error Rule is used to detect the end of the initial transient. The method is validated for integral and local quantities and guidelines on how to handle spatially varying initial transients are formulated. With the initial transient reliably removed, the statistical error is estimated based on standard error relations considering correlations in the time series. The resulting confidence intervals are carefully verified for quantities of engineering interest utilizing cumulative and simple moving averages. Furthermore, the influence of periodic content from large scale vortex shedding on the error estimation is studied. Based on the confidence intervals, the required averaging interval to reduce the statistical uncertainty to a specific level is indicated for each considered quantity.

Transient simulation of an atmospheric boundary layer flow past a heliostat using the Scale-Adaptive Simulation turbulence model

Heliostat fields are exposed to changing climatic conditions as they are mostly erected in open environments where the wind naturally features a high unsteadiness at low altitude due to the ground effects. Much of the computational fluid dynamics (CFD) content in the open literature is focused on Reynolds–averaged-Navier–Stokes (RANS) simulations, which can only predict mean loads. This paper considers an isolated heliostat in worst-case orientation. The drag force is numerically modelled by means of a Scale-Resolving Simulation (SRS) in ANSYS v19. This paper firstly deals with two different methods that generate perturbations at the inlet boundary: the spectral synthesiser and the vortex method. In an empty domain, an atmospheric boundary layer (ABL) profile is modelled based on a wind tunnel experiment. Secondly, the wind tunnel test of a single heliostat model in upright orientation is replicated, aiming to model the mean and peak drag forces. Applicable for highly separated flows, the Scale-Adaptive Simulation (SAS) turbulence model is employed as it is computationally more affordable than a Detached Eddy Simulation (DES) approach. The latter would require a higher grid resolution and a reduced time step size. The SAS showed little but acceptable decay of the inlet profiles whilst achieving lateral homogeneity. The mean and root-mean-square error of the drag force signal showed a deviation with the experiment of 0.04% and 5.8%, respectively, whereas the error on the peak drag forces was around 18%, possibly mostly due to the under-prediction of the turbulent integral length scale at the model location.

Comparison of Turbulence Modeling for a Compressor Rotor at Different Tip Clearances

Due to the high Reynolds numbers together with the complex turbulent motions in turbomachinery, selecting a proper turbulence-modeling method is of vital significance in interpreting the real flow physics. In this paper, shear stress transport (SST) as a Reynolds-averaged Navier–Stokes model and scale-adaptive simulation (SAS) and zonal large eddy simulation (ZLES) as two scale-resolving simulation approaches were chosen to simulate the flow in a low-speed axial compressor rotor at three different blade tip clearances (1.3, 2.6, and 4.3% of chord length). Results of unsteady simulations at the design point were compared to the experimental data. The results prove that the ZLES model performs best in characterizing the experimental data regardless of the blade tip clearance size. The performance of the SST model in capturing the tip flow is close to the measurement data when the blade tip clearance is small, while the deviation from the experimental results increases with the clearance size enlarged. In contrast, the use of the SAS model does not result in any benefits over the SST model for the small tip clearance but demonstrates similar performance with the ZLES model for the configurations with middle and large tip clearance sizes.

Estimating parameter and discretization uncertainties using a laminar–turbulent transition model

For computational fluid dynamic (CFD) simulations at intermediate Reynolds numbers, laminar-to-turbulent transition plays an important role in the flow physics. While this phenomenon is difficult to simulate, current state-of-the-art transition models provide viable means to do so without resorting to expensive scale-resolving simulations. Previous studies of these methods show that, as in reality, the results are sensitive to the inlet turbulence characteristics and their decay upstream of the studied body. The lack of understanding of the exact effect of these boundary condition values may contribute, together with the discretization uncertainties, to an increase of uncertainty in the output quantities of interest, such as force or torque values. Using the γ−R̃eθt transition model, this work estimates the parameter and discretization uncertainties and combines them into a single value. Three input uncertainties related to turbulence are chosen: turbulence intensity, eddy viscosity, and a parameter used to define a turbulence decay-free zone upstream. Sobol indices are also obtained in order to quantify the relative importance of input and discretization uncertainties. Two cases are tested: a flat plate, focusing on the local skin friction; and a practical case of the Duisburg Propeller Test Case (DPTC), where surface-integral quantities of thrust and torque coefficients are assessed. Both cases show that the turbulence intensity and eddy viscosity have significant values of total-effect Sobol indices, showing a considerable contribution of these factors to the output variation of quantity of interests, making them key factors affecting the sensitivity of the final result. Results suggest that performing grid refinement studies alone is not sufficient to estimate the numerical uncertainties for this category of problems. It is therefore recommended to assess parameter and discretization uncertainties together for the presented and other similar applications with epistemic uncertainties related to turbulent kinetic energy.

A wall-adapted zonal URANS/LES methodology for the scale-resolving simulation of engine flows

In the present paper, a comprehensive, wall-adapted zonal URANS/LES methodology is shown for the multidimensional simulation of modern direct-injection engines. This work is the latest update of a zonal hybrid turbulence modeling approach, specifically developed by the authors for a flexible description of in-cylinder turbulent flow features with an optimal balance between computational costs and accuracy. Compared to the previous developments, a specific near-wall treatment is added, in order to preserve full-URANS behavior in the first near-wall cells, having in mind typically available mesh resolution in this part of the fluid domain. The updated methodology is applied to the multi-cycle simulation of a reference single-cylinder optical engine, which features a twin-cam, overhead-valve pent-roof cylinder head, and is representative of the current generation of spark-ignited direct-injection thermal power units. Results based on phase-specific flow field statistics and synthetic quality indices demonstrate the consistency and effectiveness of the proposed methodology, which is then qualified as a suitable candidate for affordable scale-resolving analyses of cycle to cycle variability (CCV) phenomena in direct-injection engines.

Assessment of improved delayed detached eddy simulation in predicting unsteady flows and sound around a circular cylinder

Unsteady flows in the field of engineering are usually calculated by the Unsteady Reynolds-Averaged Navier–Stokes (URANS) owing to the low requirements for computational efforts. However, the numerical resolution of URANS, especially in predicting the unsteady wake flows and sound, is still questionable. In this work, unsteady flow and sound calculations of a circular cylinder are carried out using Improved Delayed Detached Eddy Simulation (IDDES) and the Ffowcs Williams–Hawkings (FW-H) analogy. The predicted results of this calculation are compared with those from the previous studies in the literature in terms of the mean and RMS of the velocity components as well as the sound pressure. The results show that IDDES retains much of the numerical accuracy of the Large Eddy Simulation (LES) approach in predicting unsteady flows and noise while requiring a reduced computational resources in comparison to LES. It is believed that the IDDES can be applied to calculate the complex unsteady flows and flow generated sound with reasonable accuracy in engineering field, which can be used as a promising method for scale-resolving simulations to avoid the expensive computational requirements of LES.

Benchmark for scale-resolving simulation with curved walls: the Taylor Couette flow

Flow between rotating concentric cylinders, or the Taylor Couette flow, has been studied extensively because of its rich physics, ranging from axisymmetric steady laminar flow, to fully developed turbulent flow. In the present study, we advocate the use of this problem as a benchmark case for scale-resolving simulation, such as large eddy simulation (LES) and direct numerical simulation (DNS). The problem is attractive because of its simple geometry, simple boundary conditions, and complex physics involving wall-shear induced and centrifugal instability. Unlike the well-known fully developed channel flow, this problem has a curved wall boundary, and it is unnecessary to add a source term to the governing equations to sustain the fully developed turbulent flow. A p-refinement study for Re = 4000 is performed first to establish DNS data, including the time history of enstrophy, which can be used as an accuracy and resolution indicator to evaluate numerical methods, and is orders of magnitude faster than using the mean flow quantities and Reynolds stresses to evaluate solution quality. Finally, an hp-refinement study is performed to establish the relative accuracy and efficiency of high-order schemes of various accuracy.

A cross-platform, high-performance SPH toolkit for image-based flow simulations on the pore scale of porous media

Efficient numerical simulations of fluid flow on the pore scale allow for the numerical estimation of effective material properties of porous media like effective permeability or tortuosity, among others. In contrast to time-consuming and often expensive laboratory tests, pore scale-resolved numerical simulations further enable the computational quantification of anisotropy of inherent material properties and the estimation of representative sample domains. Numerically calculated quantities are valuable in several fields, such as carbon dioxide sequestration, geothermal energy production and groundwater contamination remediation. Our specific pore scale-resolved simulation method directly based on images obtained from Micro X-Ray Computed Tomography (μXRCT) is based on the weakly compressible Smoothed Particle Hydrodynamics (SPH) approach. SPH is a meshless Lagrangian method, highly suitable for modeling complex geometries and flow at moderate Reynolds numbers. Low Reynolds number flow, also denoted as creeping flow, is a typical scenario present in the above mentioned applications. However, SPH is computationally demanding, especially in simulations of large domains. To overcome these difficulties, we have designed a specific SPH module for the highly optimized HOOMD-blue Molecular Dynamics software. Our implementation supports single-phase flow, and targets both CPU and GPU clusters. Due to the high computational demands, scalability is essential to make the software practically usable, and our tests indicate that our implementation can scale almost ideally. We study a wide variety of test cases, which are not only representative for XRCT-based geometries, but for pore scale-resolved flow simulations in general. Additionally, we present a large-scale simulation investigating an unconventional high porous volcanic rock sample (Reticulite). Program summaryProgram title:: HOOMD-Blue.sphCPC Library link to program files::https://doi.org/10.17632/zdnj8zsrf9.1Licensing provisions:: BSD 3-Clause licenseProgramming language:: C++, CUDA, PythonNature of problem:: Fluid flow simulation in XRCT imaged porous media for digital rock physics applicationsSolution method:: Smoothed Particle Hydrodynamics

Numerical Simulation of the Streamwise Transport of a Delta Wing Leading-Edge Vortex

Longitudinal vortices are a common flow phenomenon in the flow around aircraft. They emerge wherever sharp edges are encountered and affect the stability of the boundary layers with which they interact. Hence, for an optimal aircraft design, it is necessary to accurately predict not only the formation of these vortices, but also their downstream evolution. This paper presents a numerical simulation approach for the formation and downstream transport of longitudinal vortices. The approach consists in a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation (RANS/LES) method with synthetic turbulence forcing for which different RANS/LES interface locations are investigated. To provide a quantitative analysis, an isolated sharp-edged delta wing configuration is adopted that allows to get rid of unwanted uncertainties. The presented RANS/LES approach is validated against particle image velocimetry data and compared with a wall-modeled LES and to a differential Reynolds stress model simulation. The results show that the RANS simulation is able to accurately predict the formation of the bulk vortical structure. However, its downstream transport can be accurately predicted only by a scale-resolving simulation. The hybrid RANS/LES approach allows to achieve this while saving computational resources by modeling the roll-up of the vortex. Nevertheless, its predictive accuracy highly depends on the appropriate placement of the RANS/LES interface.

Assessment of turbulence models for the prediction of Bénard-Von Kármán vortex shedding behind a truncated hydrofoil in cavitation conditions

The transient cavitating flow in the wake of a hydrofoil at zero incidence angle has been simulated using a homogeneous mixture cavitation mass transfer model combined with both Reynolds Average Navier-Stokes (RANS) and Scale Resolving Simulation (SRS) turbulence models. The hydrofoil geometry corresponds to a 2D NACA 0009 with a truncated trailing edge which has already been extensively investigated in the High-Speed Cavitation Tunnel of the EPFL. The hydrodynamic conditions of interest correspond to a free stream velocity of 20 m/s (Re = 2 · 106) without cavitation and with two different degrees of cavitation. To improve the prediction of the vortex shedding behing the hydrofoil, the γ − Rθt transitional boundary layer model has been coupled with the turbulence models. At cavitation-free regime, all the turbulence models with the exception of the SST and LES WALE ones have the ability to predict the experimentally measured vortex shedding frequency. Nevertheless, the results indicate that, neither the SST nor the DES-SST γ − Rθt , can predict the vortex shedding frequency increase which has been experimentally observed when cavitation occurs. In contrast, the numerical results provided by the SST γ − Rθt and the SSTCC γ − Rθt show the capability to predict the expected shedding frequencies for both non cavitation and cavitation conditions. Beyond all expectation, the results provided by the LES WALE seem not only to overestimate the vortex shedding frequency at cavitation free conditions but also to underestimate the frequency when the cavitation number is significantly reduced.

On numerical uncertainties in scale-resolving simulations of canonical wall turbulence

The present study focuses on applying different metrics to assess accuracy, robustness and sensitivity of scale-resolving simulations of turbulent channel flow, when the numerical parameters are systematically varied. Derived by combining well-established uncertainty quantification techniques and computer experiments, the metrics act as powerful tools for understanding the behavior of flow solvers and exploring the impact of their numerical parameters as well as systematically comparing different solvers. A few examples for uncertain behavior of the solvers, i.e. the behaviors that are unexpected or not fully explainable with our a-priori knowledge, is provided. Two open-source software, Nek5000 and OpenFOAM, are considered with the focus on grid resolution and filtering in Nek5000, and grid resolution and numerical dissipation in OpenFOAM. Considering all metrics as well as the computational efficiency, Nek5000 is shown to outperform OpenFOAM. The propagated uncertainty (a measure of robustness) in the profiles of channel flow quantities of interest (QoIs), together with corresponding Sobol sensitivity indices quantitatively measure the impact and relative contribution of different numerical parameters at different wall-distances. The locations with larger confidence intervals indicate where a QoI is more sensitive to the variation of the numerical parameters. In OpenFOAM, increasing the numerical dissipation at all considered grid resolutions leads to decreasing the uncertainties at the price of losing accuracy. In contrast, the influence of filtering in Nek5000 is found to be more complicated and relying on the grid resolution. In particular, the filter cutoff is found to be more influential than the filter weight, and at high number of Gauss–Lobatto–Legendre (GLL) points per element, it is shown that there exist optimal values for the filter cutoff which result in more accurate QoIs. From the same analysis, it is also concluded that considering the number of GLL points as an indicator of resolution and accuracy in the context of Nek5000 may require additional consideration. The analyses and metrics presented in this study are general and can be applied to any type of flow simulation. They facilitate not only the validation-and-verification process, but also the selection of adequate numerical parameters to achieve accurate and reliable results.

Lateral migration of peptides in transversely sheared flows in water: An atomistic-scale-resolving simulation

For atomistic scale-resolving simulations of peptide diffusion, which are representative of molecular sorting in micro-fluidic device, a hybrid Fluctuating Hydrodynamics - Molecular Dynamics (FH/MD) model is implemented based on the two-phase flow analogy framework. Thanks to the used framework, in comparison with existing simulations in the literature, the suggested model captures inter-atomic forces between the peptides and the surrounding shell of water atoms at atomistic resolution while concurrently taking into account the non-uniform flow effect. In comparison with previous applications of the hybrid two-phase flow analogy method, multiple moving atomic-resolution zones are implemented for the first time here. The moving zones comprise one and two peptides solvated in water with a Poiseuille flow applied, where each diffusing peptide and the surrounding water shell are dynamically resolved. The models are validated in comparison with the pure all-atom molecular dynamics simulations for the no flow case and then used to investigate how the flow rate and the starting location of peptides in the parabolic flow profile affect their lateral migration over a range of flow Reynolds numbers. It is estimated that for the Poiseuille flows considered, the FH/MD model is 2–20 times faster in comparison with the conventional all-atom non-equilibrium molecular dynamics simulations.

High-order accurate direct numerical simulation of flow over a MTU-T161 low pressure turbine blade

Reynolds Averaged Navier-Stokes (RANS) simulations and wind tunnel testing have become the go-to tools for industrial design of Low-Pressure Turbine (LPT) blades. However, there is also an emerging interest in use of scale-resolving simulations, including Direct Numerical Simulations (DNS). These could generate insight and data to underpin development of improved RANS models for LPT design. Additionally, they could underpin a virtual LPT wind tunnel capability, that is cheaper, quicker, and more data-rich than experiments. The current study applies PyFR, a Python based Computational Fluid Dynamics (CFD) solver, to fifth-order accurate petascale DNS of compressible flow over a three-dimensional MTU-T161 LPT blade with diverging end walls at a Reynolds number of 200,000 on an unstructured mesh with over 11 billion degrees-of-freedom per equation. Various flow metrics, including isentropic Mach number distribution at mid-span, surface shear, and wake pressure losses are compared with available experimental data and found to be in agreement. Subsequently, a more detailed analysis of various flow features is presented. These include the separation/transition processes on both the suction and pressure sides of the blade, end-wall vortices, and wake evolution at various span-wise locations. The results, which constitute one of the largest and highest-fidelity CFD simulations ever conducted, demonstrate the potential of high-order accurate GPU-accelerated CFD as a tool for delivering industrial DNS of LPT blades.