Reynolds-averaged Navier-Stokes Results Research Articles

Two Aerodynamic Mid-Fidelity Approaches on a Distributed Propulsion Wing

A comparison of two potential-theory based mid-fidelity approaches on the aerodynamics of a distributed propeller–wing tractor configuration is presented. The design space for aircraft configurations is enlarged by using distributed electric propulsion so a demand for investigating different variants, especially regarding the number of propellers, is present. While many lower fidelity tools are available in the literature, they are often only documented with integral results. This paper presents two different, independently implemented numerical approaches and provides a comparison of spanwise load distributions on a distributed propeller configuration under cruise conditions with existing Reynolds-averaged Navier–Stokes (RANS) results. The isolated propeller and wing calculations using both methods are verified a priori with respect to their agreement. In addition, a discretization study of both methods is presented. The detailed results of the spanwise lift and drag distributions are compared between the two methods. Two different angles of attack and two different propeller pitch settings are calculated, and the differences in the spanwise distributions and the governing integral results between both methods and the RANS results are highlighted. Finally, a comparison of the individually required computational effort is presented.

High-fidelity numerical investigation of a real gas annular cascade with experimental validation

This study aims at investigating real gas flow in the complex geometry of the Cambridge University annular turbine cascade using numerical simulations. The objectives include validating the numerical approach and understanding the loss mechanisms in this configuration. The numerical results are compared to experimental measurements obtained at various locations in the domain. Two turbulence modeling techniques, large Eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS), are employed to assess the influence of turbulence models and inlet turbulence levels. The results show good agreement between numerical simulations and experimental measurements in regions upstream of the trailing edge. However, discrepancies arise in the transition region of the suction side boundary layer, and RANS results are influenced by the choice of turbulence injection. In the wake of the blade, both RANS and LES accurately predict the stagnation pressure ratio, with some slight differences in shock positions and total pressure levels. The analysis reveals that large vortical structures at the hub contribute significantly to the overall losses in this annular configuration. The study quantifies losses due to boundary layers, the wake, and vortical structures using a loss coefficient, with RANS and LES producing slightly different results. These differences, while calling for further experimental measurements, also hint at the possible inaccuracy of the present turbulence models in the context of real gas flows for which a dedicated modeling effort is required.

Normal and knocking combustion of hydrogen: A numerical study

This work presents a numerical study of normal and knocking combustion of hydrogen in a cooperative fuel research (CFR) engine. It is noteworthy that this study is the first to simulate this problem in a CFR engine. This engine has a significant relevance to spark-ignition engines as it is used to examine knock susceptibility of different fuels and explore fuel-engine interactions under a controlled environment. Using the Reynolds Averaged Navier Stokes (RANS) framework, a single compression ratio and four different spark timings are considered to investigate the transition from normal to knocking combustion. The results are validated against the experimental pressure trace data for both normal and knocking combustion. The model has been rigorously validated without changing the model constants across all cases. It is shown that for knocking cases an initial auto-ignition hotspot appears near the exhaust valve, where the unburned temperature is higher than the rest of the domain. A pressure wave then propagates, forming a secondary auto-ignition spot and two auto-ignitive flames eventually merge. The propagation speed of the auto-ignitive flame front is found to be 6–10 times higher than that of the premixed flame. Using the resonance theory of Bradley, the auto-ignition events are found to be in the developing detonation region. Furthermore, zero-dimensional homogeneous reactor simulations are shown to be suitable to predict the occurrence of auto-ignition in such engine, while 3-D RANS results are needed to accurately predict the pressure trace and auto-ignition timing. The results of this work also demonstrate how temperature stratification impacts the auto-ignition events.

Wind Effects on Dome Structures and Evaluation of CFD Simulations through Wind Tunnel Testing

In the study, a series of wind tunnel tests were conducted to investigate wind effects acting on dome structures (1/60 scale) induced by straight-line winds at a Reynolds number in the order of 106. Computational Fluid Dynamics (CFD) simulations were performed as well, including a Large Eddy Simulation (LES) and Reynolds-Averaged Navier–Stokes (RANS) simulation, and their performances were validated by a comparison with the wind tunnel testing data. It is concluded that wind loads generally increase with upstream wind velocities, and they are reduced over suburban terrain due to ground friction. The maximum positive pressure normally occurs near the base of the dome on the windward side caused by the stagnation area and divergence of streamlines. The minimum suction pressure occurs at the apex of the dome because of the blockage of the dome and convergence of streamlines. Suction force is the most significant among all wind loads, and special attention should be paid to the roof design for proper wind resistance. Numerical simulations also indicate that LES results match better with the wind tunnel testing in terms of the distribution pattern of the mean pressure coefficient on the dome surface and total suction force. The mean and root-mean-square errors of the meridian pressure coefficient associated with the LES are about 60% less than those associated with RANS results, and the error of suction force is about 40–70% less. Moreover, the LES is more accurate in predicting the location of boundary layer separation and reproducing the complex flow field behind the dome, and is superior in simulating vortex structures around the dome to further understand the unsteadiness and dynamics in the flow field.

Large eddy simulation of atmospheric boundary layer flow over complex terrain in comparison with RANS simulation and on-site measurements under neutral stability condition

Large eddy simulation (LES) of the atmospheric boundary layer (ABL) flow over complex terrain is presented with a validation using meteorological tower (met-tower) data through an improved neutral stability sampling approach. The proposed stability sampling procedure includes a condition based on the most-likely occurrence time-periods of the neutral ABL and reduces the variabilities of the conditional wind statistics calculated at the met-towers in comparison to our previous work. The ABL flow simulations are carried out over a potential wind site with a prominent hill based using the OpenFOAM-based simulator for on/off-shore wind farm applications by applying the Lagrangian-averaged scale-invariant dynamic sub-grid scale turbulence model. A low-dissipative scale-selective discretization scheme for the non-linear convection term in the LES governing equation is adopted implicitly to ensure both the second-order accuracy and bounded solution. The LES inflow is generated through a precursor method with a “tiling” approach based on the flow driving parameters obtained from a corresponding Reynolds-averaged Navier–Stokes (RANS) simulation. Overall, the averaged wind velocity profiles predicted by the LES approach at all met-tower locations show a similar tendency as the RANS results, which are also in reasonable agreement with the met-tower data. An obvious difference in wind speed standard deviation profiles is seen between LES and RANS, especially at regions downstream of the hill edge, where the LES shows under-predicted results at the highest measurement levels in comparison to the tower data. The computational costs of the LES are found to be about 20 times higher than the RANS simulations.

Investigation of the quasi-periodic airflow oscillation and ventilation performance of an enclosed environment with a jet air supply

Unsteady airflows lead to better mixing in ventilated enclosures, facilitating indoor pollutant dispersion and exhausting. In this study, an air jet ventilated enclosure and its flow characteristics were investigated using experimental measurements and computational fluid dynamics simulations, focusing on the quasi-periodic fluctuation of the airflow field and the advantages of such an oscillation pattern for the ventilation efficiency. Starting from a non-converged Reynolds-averaged Navier–Stokes (RANS) simulation, we then used the unsteady RANS method (URANS). As validated by sampling the high-frequency velocity data of representative positions in the jet-ventilated space, the URANS results reflected the unsteady flow characteristics more precisely than the RANS results, further confirming that the supply jet air swung up and down quasi-periodically. The ventilation performance of such an actual quasi-periodic airflow was evaluated by purging a gaseous pollutant from the enclosure, and the results were compared with those in the average steady-state airflow field to showcase the different performance of the unsteady ventilation system.

Modeling of Cube Array Roughness: RANS, Large Eddy Simulation, and Direct Numerical Simulation

AbstractFlow over arrays of cubes is an extensively studied model problem for rough wall turbulent boundary layers. While considerable research has been performed in computationally investigating these topologies using direct numerical simulation (DNS) and large eddy simulation (LES), the ability of sublayer-resolved Reynolds-averaged Navier–Stokes (RANS) to predict the bulk flow phenomena of these systems is relatively unexplored, especially at low and high packing densities. Here, RANS simulations are conducted on six different packing densities of cubes in aligned and staggered configurations. The packing densities investigated span from what would classically be defined as isolated, up to those in the d-type roughness regime, filling in the gap in the present literature. Three different sublayer-resolved turbulence closure models were tested for each case: a low Reynolds number k–ϵ model, the Menter k–ω SST model, and a full Reynolds stress model. Comparisons of the velocity fields, secondary flow features, and drag coefficients are made between the RANS results and existing LES and DNS results. There is a significant degree of variability in the performance of the various RANS models across all comparison metrics. However, the Reynolds stress model demonstrated the best accuracy in terms of the mean velocity profile as well as drag partition across the range of packing densities.

Unified prediction of turbulent mixing induced by interfacial instabilities via Besnard−Harlow−Rauenzahn-2 model

Turbulent mixing induced by interfacial instabilities, such as Rayleigh–Taylor (RT), Richtmyer–Meshkov (RM), and Kelvin–Helmholtz (KH) instabilities, widely exist in natural phenomena and engineering applications. On the one hand, the Reynolds-averaged Navier–Stokes (RANS) method, mainly involving physical model and model coefficients, is still the most viable approach in application. On the other hand, predicting different mixing problems with the same physical model and model coefficients—defined as “unified prediction” in this paper—is the basis for practice because (1) different instabilities usually exist simultaneously in a flow system and are coupled to each other; (2) mixing processes involve a wide range of parameters (e.g., time-dependent density ratio and acceleration history, etc.). However, few models can achieve such a unified prediction. Recently, we proposed a RANS route to realize this unified prediction by setting model coefficients to match the given physical model. This study attempts to apply this to the widely used BHR2 model to achieve unified predictions of different turbulent mixing problems, including basic problems (i.e., classical RT, RM, and KH mixing) and complex problems (i.e., re-shocked RM, tilted-RT, and spherical implosion mixing). Good agreement between experiments, large-eddy simulations, and RANS results were obtained. The temporal evolution of mixing width and spatial profiles of important physical quantities are presented. Based on our achievements of the k – L and k−ε models for unified predictions, the success of BHR2 model further confirms that our RANS route is robust for different turbulent mixing models and may be expanded to other fields.

Experimental and Numerical Study of Swirling Diffusion Flame Provided by a Coaxial Burner: Effect of Inlet Velocity Ratio

This paper reports an experimental and numerical investigation of a methane-air diffusion flame stabilized over a swirler coaxial burner. The burner configuration consists of two tubes with a swirler placed in the annular part. The passage of the oxidant is ensured by the annular tube; however, the fuel is injected by the central jet through eight holes across the oxidizer flow. The experiments were conducted in a combustion chamber of 25 kW power and 48 × 48 × 100 cm3 dimensions. Numerical flow fields were compared with stereoscopic particle image velocimetry (stereo-PIV) fields for non-reacting and reacting cases. The turbulence was captured using the Reynolds averaged Navier-Stokes (RANS) approach, associated with the eddy dissipation combustion model (EDM) to resolve the turbulence/chemistry interaction. The simulations were performed using the Fluent CFD (Computational Fluid Dynamic) code. Comparison of the computed results and the experimental data showed that the RANS results were capable of predicting the swirling flow. The effect of the inlet velocity ratio on dynamic flow behavior, temperature distribution, species mass fraction and the pollutant emission were numerically studied. The results showed that the radial injection of fuel induces a partial premixing between reactants, which affects the flame behavior, in particular the flame stabilization. The increase in the velocity ratio (Rv) improves the turbulence and subsequently ameliorates the mixing. CO emissions caused by the temperature variation are also decreased due to the improvement of the inlet velocity ratio.

Aerothermal Optimization of Bladeless Turbines

Abstract The harnessing of mechanical power from supersonic flows is constrained by physical limitations and substantial aerodynamic losses. Bladeless axial turbines are a viable alternative to extract power in such harsh conditions without restricting the operating conditions. In this paper, we present a shape optimization of the wavy surface of bladeless turbines to maximize the power extraction, while minimizing convective heat flux and pressure losses. First, a baseline geometry was defined and an experimental campaign was carried out on the baseline wavy surface of the bladeless turbine at supersonic conditions. Pressure, heat flux, and skin friction measurements were compared with the Reynolds averaged Navier–Stokes results. Afterward, an evaluation routine which consisted of the geometry and grid generation, solving, and postprocessing was implemented within a multi-objective optimization routine to maximize the pressure force and minimize heat flux and pressure loss. Finally, a three-dimensional assessment in terms of power, heat load, and pressure drop was performed for the best performing geometry with the commercial solver cfd++ of Metacomp.

A hybrid viscous body force model for low-speed centrifugal compressors

The flow in centrifugal compressors is viscous and unsteady. Flow separation off the blades challenges the accuracy of simulations. A viscous body force model is expected to speed up numerical convergence and reduce the computational costs of unsteady simulations. In this paper, both stability and accuracy of the viscous body force model are investigated based on the case of a low-speed centrifugal compressor. First, two formulations of the viscous body forces are obtained from the expression of the viscous flux. Then, the numerical stability of two body force models is found to be related to drag coefficient and flow angle. For large negative drag coefficients, the viscous body forces would lead to divergences. Since unsteady Reynolds-averaged Navier–Stokes simulations show that two formulas have considerable accuracy, stability is considered as the main factor for modeling. With the findings, a hybrid viscous body force method is proposed. To assess the applicability of the hybrid model, two test cases are compared against the results obtained by unsteady Reynolds-averaged Navier–Stokes simulations. The first case is the capability evaluation of unsteady characteristics capture for low-speed centrifugal compressors. The simulation results show that the hybrid viscous body force model can capture main unsteady viscous characters, including wake vortexes and tip leakage flow. The other is the case in which the inlet total pressure is disturbed. It is found that fluctuations of pressure, temperature, and velocity predicted by the viscous body force method are close to unsteady Reynolds-averaged Navier–Stokes results. In addition, the time-accurate overall performance of the compressor with disturbance is also predicted satisfactorily. With the advantage in lowering computer resource requirement, the viscous body force model is a promising method for long length scale unsteady cases.

Assessment and Validation of Very-Large-Eddy Simulation Turbulence Modeling for Strongly Swirling Turbulent Flow

Strongly swirling flow is widely encountered in engineering applications. However, accurate prediction of the flow is still challenging for turbulence modeling. The present study reports the assessment and validation of a newly developed self-adaptive turbulence modeling, denoted as very-large-eddy simulation (VLES), for the prediction of turbulent strongly swirling flow through a suddenly expanding circular pipe at Reynolds number of and , and the corresponding swirl numbers are 1.16 and 1.23, which are both very strongly swirling flow. The VLES method is a unified simulation approach enabling a seamless evolution from Reynolds-Averaged Navier–Stokes (RANS) to LES and finally approaching direct numerical simulation (DNS) depending on the numerical resolution. In the present work, a new proposed VLES turbulence closure model, namely, VLES BSL , and other two models, denoted as VLES and VLES , are applied for the strong swirling flow simulation. Two meshes containing about 0.9 million and 5.1 million cells are applied, with different mesh resolutions. The simulation results are compared with available experimental data and RANS results. It is observed that the present VLES models accurately predict the time-averaged and root-mean-square (rms) velocities compared with the measurements on both of the two meshes. The significant features of the present strongly swirling flow, including vortex breakdown and the vortex core precession, large recirculation region, and shear-layer instability, are well captured by the present VLES models. Furthermore, the anisotropy of the Reynolds stresses of the strongly swirling flow is also well predicted. Satisfactory predictions can be obtained using low grid resolution with the VLES models, which confirm the validity and accuracy of the VLES modeling for strongly swirling turbulent flow.

Assessment of Turbulence Models in a Hypersonic Cold-Wall Turbulent Boundary Layer

In this study, the ability of standard one- or two-equation turbulence models to predict mean and turbulence profiles, the Reynolds stress, and the turbulent heat flux in hypersonic cold-wall boundary-layer applications is investigated. The turbulence models under investigation include the one-equation model of Spalart–Allmaras, the baseline k - ω model by Menter, as well as the shear-stress transport k - ω model by Menter. Reynolds-Averaged Navier-Stokes (RANS) simulations with the different turbulence models are conducted for a flat-plate, zero-pressure-gradient turbulent boundary layer with a nominal free-stream Mach number of 8 and wall-to-recovery temperature ratio of 0.48 , and the RANS results are compared with those of direct numerical simulations (DNS) under similar conditions. The study shows that the selected eddy-viscosity turbulence models, in combination with a constant Prandtl number model for turbulent heat flux, give good predictions of the skin friction, wall heat flux, and boundary-layer mean profiles. The Boussinesq assumption leads to essentially correct predictions of the Reynolds shear stress, but gives wrong predictions of the Reynolds normal stresses. The constant Prandtl number model gives an adequate prediction of the normal turbulent heat flux, while it fails to predict transverse turbulent heat fluxes. The discrepancy in model predictions among the three eddy-viscosity models under investigation is small.

Assessment of RANS models for flow in a loosely spaced bare rod bundle with heat transfer in low Prandtl number fluid

In the present study, a wide range of steady-state and unsteady Reynolds Averaged Navier Stokes (RANS) simulations have been performed to reproduce the turbulent flow and heat transfer in a fuel assembly of the ALFRED reactor. The considered fuel assembly consists of a loosely spaced bare rod bundle with pitch to rod diameter ratio of P/D = 1.32. It is cooled by liquid lead, hence the Prandtl number of the working fluid is very low, i.e. Pr = 0.016. The obtained results are extensively compared with the available Large Eddy Simulation (LES) results. This article is divided in two main parts. In the first part, a thorough assessment of eddy viscosity (i.e. linear and non-linear) and Reynolds stress turbulence models have been performed against the reference LES results. Flow and thermal fields have been qualitatively and quantitatively analysed. In general, RANS results are in a good agreement with the LES, however, most of the models severely overpredict wall shear stress and the corresponding pressure drop in the rod bundle. In the second part, URANS simulations have been performed to reproduce a gap vortex street in the considered loosely spaced bare rod bundle. For this purpose, two turbulence models, that gave the best steady-state RANS predictions, i.e. the k-ε cubic and the elliptic blending Reynolds-stress model, are tested as well. However, the gap vortex street in this particular loosely spaced bare rod bundle turned out to be too weak to be predicted by the URANS approach.

Prediction of Turbulent Temperature Fluctuations in Hot Jets

Large-eddy simulations were used to investigate turbulent temperature fluctuations and turbulent heat flux in hot jets. A high-resolution finite difference Navier–Stokes solver was used to compute the flow from a 2 in. round nozzle. Three different flow conditions of varying jet Mach numbers and temperature ratios were examined. The large-eddy simulation results showed that the temperature field behaved similarly to the velocity field but with a more rapidly spreading mixing layer. Predictions of the mean and fluctuating velocities were compared to particle image velocimetry data. Predictions of the mean and fluctuating temperatures were compared to data obtained using Rayleigh scattering and Raman spectroscopy. Very good agreement with experimental data was demonstrated for the mean and fluctuating velocities. The large-eddy simulation correctly predicted the behavior of the turbulent temperature field but overpredicted the levels of the fluctuations. The turbulent heat flux was examined and compared to the Reynolds-averaged Navier–Stokes results. The large-eddy simulation and Reynolds-averaged Navier–Stokes simulations produced very similar results for the radial heat flux. However, the axial heat flux obtained from the large-eddy simulation differed significantly from the Reynolds-averaged Navier–Stokes result in both structure and magnitude, indicating that the Reynolds-averaged Navier–Stokes model was inadequate. Finally, the large-eddy simulation data were used to compute the turbulent Prandtl number and verify that a constant value of 0.7, which is typically used in the Reynolds-averaged Navier–Stokes models, was a reasonable assumption.

Efficient Optimization of Ringlets for Drag Reduction over the Complete Mission Profile

Use of microsurface features such as riblets within turbulent boundary layers has proved to be an effective means of friction drag reduction. This paper proposes an effective and efficient methodology for riblet optimization for the complete mission profile with varying speed and altitude. An altitude-correction method was first developed that provided an efficient method for the prediction of drag-reduction ratios for different altitude with much fewer computational fluid dynamics solutions. The method built on data obtained from a Reynolds-averaged Navier–Stokes simulation with the turbulence model. The Reynolds-averaged Navier–Stokes results have been validated against experimental data for a flat plate with V-shaped grooves. Such a procedure was combined with a genetic algorithm and response surface models to obtain a riblet configuration with optimal drag reduction for the complete mission profile. Compared to traditional single-point optimization, an additional improvement of 1.53% (increasing by 20.8 from 7.38%) in drag-reduction ratio could be achieved with this method. The results presented here could provide significant practical engineering value for the riblet design for flight vehicles with a wide range of varying operating conditions.

Second-Law Analysis: A Powerful Tool for Analyzing Computational Fluid Dynamics (CFD) Results

Second-law analysis (SLA) is an important concept in thermodynamics, which basically assesses energy by its value in terms of its convertibility from one form to another.[...]

Large eddy simulation of a homogeneously charged turbulent jet ignition system

Transient jet ignition of a homogeneous methane air mixture in a turbulent jet ignition system is studied computationally using a large eddy simulation turbulence model. The jet discharges from a prechamber into a main combustion chamber via one or more orifice(s) and provides a distributed ignition source in turbulent jet ignition. The effect of orifice size and stoichiometry is studied numerically using the Converge computational fluid dynamics code. A reduced kinetic mechanism is used for combustion along with a Smagorinsky sub-model for turbulence modeling. The computed pressure traces are compared with experimental measurements through rapid compression machine tests. Computational fluid dynamics results are in acceptable agreement with the experimental data during compression and the early stage of combustion; however, an over-prediction of peak pressure was reported. Peak pressure error is in the range of 0.1%–4% for Reynolds-averaged Navier–Stokes simulation estimation compared to the experimental measurements. This error is a function of mixture stoichiometry and unburned gas temperature. The error calculation showed that with the large eddy simulation model, 1% and 12% improvements in peak pressure and burn rate estimations, respectively, were achieved compared to Reynolds-averaged Navier–Stokes results. The reduced large eddy simulation error relative to the Reynolds-averaged Navier–Stokes simulations were considered to be in the acceptable range; however, further improvements could be achieved through validation and testing of additional turbulence models. In addition, computational fluid dynamics temperature contours for various nozzle orifices and air–fuel ratios are compared to achieve deeper insight into the turbulent jet ignition combustion process in the rapid compression machine combustion cylinder. The numerical iso-surface temperature contours were obtained which enabled three-dimensional views of the flame propagation, the jet discharge, ignition and extinction events. The heat release process and regeneration of mid-range temperature iso-surfaces (1200 K) were not visible through the experimental images.

Entropy Analysis of the Interaction between the Corner Separation and Wakes in a Compressor Cascade

The corner separation in the high-loaded compressors deteriorates the aerodynamics and reduces the stable operating range. The flow pattern is further complicated with the interaction between the aperiodic corner separation and the periodically wake-shedding vortices. Accurate prediction of the corner separation is a challenge for the Reynolds-Averaged Navier–Stokes (RANS) method, which is based on the linear eddy-viscosity formulation. In the current work, the corner separation is investigated with the Delayed Detached Eddy Simulation (DDES) approach. DDES results agree well with the experiment and are systematically better than the RANS results, especially in the corner region where massive separation occurs. The accurate results from DDES provide a solid foundation for mechanism study. The flow structures and the distribution of Reynolds stress help reveal the process of corner separation and its interaction with the wake vortices. Before massive corner separation occurs, the hairpin-like vortex develops. The appearance of the hairpin-like vortex could be a signal of large-scale corner separation. The strong interaction between corner separation and wake vortices significantly enhances the turbulence intensity. Based on these analyses, entropy analysis is conducted from two aspects to study the losses. One aspect is the time-averaged entropy analysis, and the other is the instantaneous entropy analysis. It is found that the interaction between the passage vortex and wake vortex yields remarkable viscous losses over the 0–12% span when the corner separation has not yet been triggered; however, when the corner separation occurs, an enlarged region covering the 0–30% span is affected, and it is due to the interaction between the corner separation and wake vortices. The detailed coherent structures, local losses information and turbulence characteristics presented can provide guidance for the corner separation control and better design.

Methodology for Characterizing Representativeness Uncertainty in Orifice Plate Mass Flow Rate Measurements Using CFD Simulations

The measurement of the steam generator feedwater mass flow rate is a dominant source of uncertainty in the nominal thermal power calculation of a plant. In this paper, mass flow rate measurement by means of an orifice plate is considered. Reynolds-averaged Navier-Stokes (RANS) simulation was performed using the computational fluid dynamics code STAR-CCM+ to quantify the representativeness uncertainty of mass flow rate measured in a dedicated experimental configuration. The representativeness uncertainty arises from applying the tolerance values prescribed by the International Organization for Standardization (ISO) standard in non-straight piping geometries. The simulation results were compared with the test results and the uncertainty bounds prescribed by the ISO standard, demonstrating the feasibility of applying RANS in an industrial setting for sub-1% uncertainty applications. The RANS results were also used to identify the variability in the measurement result with respect to the angular location of the pressure tap used in the flow rate measurement. Second, a large eddy simulation (LES) was performed on a straight piping configuration to simulate unsteady coherent flow shedding at the orifice plate. The spectral results of LES were compared with data from a test. The time-averaged LES results are within 0.1% of the value prescribed by the ISO standard. Direct comparison of the temporal spectrum of the LES result to the test data is not possible due to the measurement technique. This work is a part of a wider effort to develop a methodology to characterize, assess, and quantify representativeness uncertainty in performance indicator measurements of plants. Spatial, temporal, and modeling representativeness uncertainties are presented in this current work.