Reynolds Stress Model Research Articles

Effect of void space arrangement on wind power potential and pressure coefficient distributions for high-rise void buildings

High-rise void building complexes can augment the permeation of airflows over buildings, and thereby strengthen urban wind energy harvesting for realization of the sustainable development goals (SDGs). This paper considers the wind over a typical 2×2 compact high-rise building array with the openings to analyze the wind power potential at varying void sizes, locations of voids, and direction of incoming wind. The predicted mean wind speeds and turbulence intensities are compared against the measured data with 4 generic high-rise building models having voids in an atmospheric boundary layer wind tunnel for validation of the computational model. Based on the comparative results from four common Reynolds-averaged Navier-Stokes (RANS) turbulence models including the standard, realizable, renormalization group (RNG) k-ε, and shear-stress transport (SST) k-ω models as well as the Reynolds stress model (RSM), the RSM approach can provide the most accurate predictions of streamwise mean velocity and turbulence intensity. The present study then conducts CFD simulations to explore the effects of opening configuration and wind direction on the wind field around high-rise void buildings. Considering the variations of void sizes of 10 × 10 m2, 12.5 × 12.5 m2, 15 × 15 m2, void heights of z/H = 0.25, 0.5, 0.75 and wind directions of 0°, 45°, respectively, the simulated results indicate elevated wind power densities with acceptable turbulence intensities over the upstream gap passage and void channels to achieve prospective urban wind power harvest and mitigate wind load on structures of high-rise void buildings.

TURBULENCE MODELLING OF INCIPIENT WAVE BREAKING ON A VERTICAL CYLINDER ON A SLOPED BED

The extensive use of vertical piles as basic components of coastal structures, e.g. monopile wind turbine foundations, has made the study of wave impact on vertical cylindrical structures in the breaking zone of major practical importance. To investigate the breaking wave forces on a vertical cylinder located on a sloped bed, Reynolds-averaged Navier–Stokes equations (RANS) based turbulence models have been used as closure in most recent computational fluid dynamics (CFD) studies. The present study adopts a Reynolds stress model (RSM), namely the Wilcox (2006) stress-ww model, as our primary turbulence closure model to simulate the experiment of Irschik et al. (2004). The Wilcox (2006) stress-ww model has been analysed in the recent work of Li et al. (2022) and proven to be neutrally stable in the potential flow region beneath surface waves, thus it naturally avoids any unphysical turbulence over-production in the pre-breaking zone (unlike two-equation models in their standard forms). It has also shown good accuracy in predicting surf zone breaking waves in Li et al. (2022) and deep-water wave breaking due to modulational perturbations in Li and Fuhrman (2022). For comparison purposes, the present study also conducts simulations with the stabilized LF18 kk- ww model, as well as with no turbulence model.

Тестова задача моделювання течії у ступені компресора Rotor 37

The subject of the study is the dependence of the degree of pressure increase on the airflow in the impeller of the axial compressor degree. The object of study is the Rotor 37 axial compressor. The purpose of this study was to select a turbulent viscosity model when conducting a test task in the Rotor 37 compressor. To achieve this goal, the following tasks were solved: to create a three-dimensional model of the object under study; develop a grid model of the object under study; to simulate the flow in a certain range of air flow; to compare the data of numerical and physical experience; evaluate the flow visualization in the Rotor 37 axial compressor stage for all studied turbulent viscosity models. When studying the flow in the stage of the axial compressor Rotor 37, the numerical experiment method was used. The flow simulation was carried out by solving the system of Navier-Stokes equations, which was closed by the turbulent viscosity model. The study used seven turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, and QI Reynolds Stress. For simulation, a computational grid was built with the adaptation of the boundary layer. This study presents the results of a flow simulation test problem in the Rotor 37 compressor. The results of the study show that all the tested turbulent viscosity models can be used to simulate the flow in an axial compressor. However, the flow calculation with the SSG Reynolds Stress turbulent viscosity model has the smallest error. An analysis of the visualization of streamlines in the interblade channel of the Rotor 37 compressor showed that in all cases, the flow pattern with all turbulent viscosity models is similar. Some differences are observed when modeling the flow with the BSL Reynolds Stress and SST turbulence models. An important factor that should also be taken into account when modeling is the calculation time. In this case, the shortest calculation time was observed for simulation with SST model. Scientific novelty and practical significance is that new data were obtained when testing the following turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, QI Reynolds Stress. The results obtained made it possible to choose a turbulent viscosity model for further research.

Eddy-resolving Reynolds-stress modelling of thermal mixing in cross-stream type T-junction configurations

The present work is concerned with the numerical simulation study of turbulent thermal mixing involving hot main and cold branch streams at high Reynolds numbers in two T-junction configurations that differ in flow rate ratio. This results in two topologically very different flow scenarios, classified as “wall-jet” and “impinging-jet” mixing processes. The underlying reference database originates from the well-known experimental WATLON study[16], dealing with the phenomena of thermal stripping in piping systems, and provides details on the configuration geometry and the associated boundary and operating conditions. The turbulence model used, implemented in the finite-volume-based numerical code OpenFOAM® [30], is a near-wall Reynolds stress model formulation appropriately sensitized by applying the scale-adaptive modeling strategy to enable its eddy-resolving capability [14]. The flow analysis includes the first- and second-order statistics, including both the flow and thermal fields, with the model results closely following the experimental reference. This refers to the global flow topology in terms of the flow separation pattern, both in terms of its shape and size, as well as to the individual mean velocity and temperature profiles and their fluctuating components. In addition, the spectral features of the flow are studied in detail using the proper orthogonal decomposition (POD) method to identify the low-rank structures whose frequency signatures contribute most to the phenomena of thermal stripping phenomena.

Improving Separation Prediction of Cyclone Separators with a Hybrid URANS-LES Turbulence Model

The CFD simulation of cyclone separators has remarkably evolved over the past decades. Nowadays, computational models are essential for designing, analyzing, and optimizing these devices. Due to the intrinsic anisotropy of the flow inside these separators, the Reynolds stress model (RSM) has been mostly employed. However, RSM models fail to solve most time and space scales, including those relevant to particle behavior. Consequently, the prediction of the grade collection efficiency may be hindered, particularly for low-Stokes-number particles. For example, the precessing vortex core phenomenon (PVC), a well-known phenomenon that is relevant for particle motion, is not usually captured in Reynolds-averaged Navier–Stokes (RANS) simulations. Alternatively, the large-eddy simulation (LES) has been proven to be a superior approach since it captures many time and space scales that would have been otherwise dissipated, allowing for more accurate predictions of particle collection. However, this accuracy comes at a considerable computational cost. To combine the advantages of these two models, the main objective of this research was to evaluate a new hybrid RSM-LES model applied to the cyclone’s flow. The results were compared to experimental data and with RSM model results. It showed that, compared to a RANS model given by the RSM closure model, the grade collection efficiency curve obtained by the hybrid model is closer to the experimental one, even for the coarser mesh. Beyond that, the results showed that while the improvement in results was not proportional to mesh refinement for RANS modeling, the hybrid model showed significant improvement with mesh refinement.

Aerothermal Dynamic Characteristics of Array Micro Ribs in Channel Flow

With the rising complexity of internal cooling structures in gas turbine blades, the limited cooling air volume and pressure head provided by the compressor have become significant constraints to further enhancements in the overall efficiency of gas turbines. To address this, micro-turbulators have been proposed as a viable solution in recent research. The rib turbulators, as a typical internal cooling structure, have inherent limitations in heat transfer measurements. In this study, a segmented lumped parameter method was employed to experimentally analyze the aerothermal dynamic characteristics of micro ribs under varying rib heights and Reynolds numbers in channel flow. It was found that heat transfer performance closely correlates with both rib height and the height of the incoming boundary layer. Under certain conditions of dimensionless height and dimensionless number, optimal heat transfer enhancement near the micro-rib was observed, leading to an approximately 30% increase in the overall thermal performance (OTP) compared to the results from research into traditional 90° ribs. Numerical results based on the Reynolds stress model (RSM) suggest that this improvement is primarily due to the increased turbulence intensity in the near-wall region (y+ = 20–55) of the boundary layer caused by the micro ribs. This study presents a new characteristic parameter e+/Re that offers improved representation of the heat transfer performance of micro ribs, and reveals that when this parameter is around 40, micro ribs can provide high heat transfer with low pressure loss, thereby improving the overall efficiency. These results underscore the potential applicability of micro ribs in advancing the efficiency of gas turbines and other related fields.

Eulerian–Lagrangian fluid dynamics study on the effects of inlet radial angle on the performance and flow pattern of multi-inlet cyclone separator

This paper presents a study on the influence of inlet radial angle in a multi-inlet cyclone separator using Eulerian-Lagrangian (EL) fluid dynamics approach. The investigation focuses on the behavior of air and solid particles within the cyclone. Air circulation was simulated at velocities ranging from 2 to 6 m/s, with inlet radial angles of 15°, 32°, 45°, 61°, and 72°. To model the turbulent flow, the Reynolds stress model (RSM) and renormalization group k-model (RNG) were employed, while the particle trajectories were simulated using the discrete phase model (DPM) in ANSYS Fluent. The purpose of this study was to determine how the inlet radial angle impacts various parameters: collection efficiency, pressure drop, cut-off diameter, axial velocity, and tangential velocity. The numerical data obtained from the simulations were validated and found to be consistent with the existing literature. The results revealed interesting findings. In the case of an inlet velocity of 6 m/s, the highest pressure drop of 84.5 Pa was observed for the 15° inlet radial angle, while the lowest pressure drop of 77.42 Pa was observed for the 32° inlet radial angle. It was found that the collection efficiency varied according to the radial angle of the inlet, with values of 89.00%, 91.70%, 92.50%, 94.77%, and 94.83% for 32°, 45°, 15°, 72°, and 61°, respectively. Additionally, at an inlet velocity of 2 m/s and a radial angle of 72°, 61°, 15°, 45°, and 32°, the corresponding cut-off sizes were determined to be 1.17 μm, 1.19 μm, 1.25 μm, 1.33 μm, and 1.38 μm, respectively. At an inlet velocity of 6 m/s, the peak tangential velocities were found to be approximately 1.48, 1.44, 1.44, 1.39, and 1.34 times the inlet velocity for the 15°, 72°, 61°, 45°, and 32° radial angles, respectively, within the axial location range of z = 1.5D to z = 3.4D. The peak axial velocity values for the 32°, 72°, 45°, 15°, and 61° radial angles, were reported as 0.85, 0.89, 0.92, 0.94, and 0.96 times the inlet velocity respectively.

Review of research on streamwise corner boundary layer

This paper is a brief review of recent research on the streamwise corner boundary layer as it affects the component performance evaluation of both the theoretical and practical aircraft design. Typical examples include aircraft wing–body junction, rectangular air intakes, and turbine-hub flow. The paper addresses the questions of what we know and do not know about the streamwise corner boundary layer. Streamwise corner flows are characterized by the presence of secondary flows in the cross-stream planes, which are driven by the normal and secondary-shear components of the Reynolds stress tensor. Extensive studies of analysis for Prandtl's second kind of secondary flows have promoted the understanding of characteristics and formation of streamwise corner boundary layer. However, compared to the flat plate boundary layer, the research on the streamwise corner boundary layer is still far from enough, especially in the similarity solution, the instability, and transition mechanism. In recent years, a significant progress has been achieved in the study on the streamwise corner boundary layer in turbulent flow through direct numerical simulation and stress−ω Reynolds stress model.

Coupling mechanism of pressure and temperature in a co-rotating cavity with radial flow

In the secondary air system (SAS) of an aeroengine, co-rotating cavities with radial flow are in charge of extracting airflow from the compressor and providing it to the turbine. In high-speed cavities, pressure and temperature have a strong coupling correlation, which had not been investigated in previous studies. Accurate monitoring of airflow quality is a prerequisite for improving its cooling efficiency. In this study, theoretical analysis and verified numerical simulation were used to investigate the flow and heat transfer in the cavities, and a coupled prediction model (CPM) was developed to study the correlation among velocity, pressure and temperature. The results revealed that density, viscosity, and swirl ratio were important mediums for coupling pressure and temperature. Furthermore, autocorrelations existed in velocity, pressure, and temperature, and their fluctuations were rapidly transmitted through the mediums and eventually backfired. The CPM, which could be used to predict aerodynamic parameters, showed a relative average error of less than 10% compared to the Reynolds stress model (RSM).

Reynolds-stress root modeling based on a statistical theory

A new methodology of turbulence modeling is proposed by combining a statistical theory [T. Ariki, Phys. Fluids 31, 065104 (2019)] and the Reynolds-stress-root method [T. Ariki, Phys. Rev. E 92, 053010 (2015)], aiming at realizing practical turbulence model of wider applicability with the help of theoretical support. The resultant model integrates, at the same time, the following five features: coordinate covariance, realizability condition, near-wall behavior, history effect, and streamline curvature effect, which are all key ingredients to build up better turbulence model mimicking realistic behaviors. Numerical assessments of the model are conducted for homogeneous shear flow, channel flow, flow in a rotating pipe, and flow between concentric annuli, all of which show reasonable agreement with direct numerical simulations and experiments.

Experiments and modelling of biomass pulverisation in swirling and non-swirling bluff body-stabilised turbulent annular flows

Deeper insights into particle loading have practical significance in applications particularly when this affects fuel-oxidiser mixing and flame stabilisation, as occurs in pulverised fuel (biomass) combustion systems. The underlying particle flow and dispersion characteristics not only play a crucial role in controlling overall combustion performance but can also impact emissions. A fundamental understanding of particle flow dynamics and dispersion behaviour for raw pulverised biomass, under non-swirling and swirling conditions need further systematic investigation to better understand the interplay between swirling and non-swirling bluff-body stabilised recirculation zones and particles emitted from a centralised jet. This work uses Particle Image Velocimetry (PIV) with three-dimensional multi-phase simulations based on the Discrete Phase Model (DPM) and Reynolds Stress Model (RSM) to investigate the flow and dispersion characteristics in confined flows typical of many practical combustors. Raw pulverised biomass-laden is introduced through a central turbulent jet (Rej = 4500 and 7800) and also subjected to turbulent annular flows (Res = 35,500), both non-swirling (S = 0) and swirling conditions (S = 0.3). Simulations are first validated against Constant Temperature Anemometry (CTA) resolved inlet boundary conditions and flow field PIV data under similar conditions.Results show that when a pulverised biomass-laden central jet interacts with a surrounding turbulent annular flow (non-swirling, swirling) the presence of a bluff-body based recirculating zone (BB-RZ) leads to biomass particle entrainment (pick up) and their recirculation over the bluff-body before being dispersed further downstream. Under non-swirling conditions, a significant 35% decrease in the mean particle axial velocity is measured coupled with an even more substantive 177% increase in turbulent fluctuation along the centreline. These findings are indicative of intense upstream (x/D ≈ 0.64) turbulent mixing and more intense particle dispersion into a BB-RZ. For swirling annular flow conditions near the end of the BB-RZ, the interaction between a biomass-laden central jet and the annular flow is comparatively weaker in the upstream region relative to non-swirling conditions. However, swirl significantly enhances downstream particle dispersion and lateral spread as reflected by a 254% hike in the mean particle radial velocity. Numerical predictions show that for the same particle loading ratio, but different (higher and lower) Reynolds number of a central particle-laden jet (i.e., the carrier gas), the conditions at relatively lower central jet Reynolds number allow better particle recirculation in BB-RZ as well as enhancing downstream lateral particle dispersion and entrainment, compared to a higher Reynolds number in the central jet. Outcomes from this investigation may have implications on the design and operation of pulverised (solid) fuel combustors if operated on renewably sourced biomass rather than traditional fossil fuels.

Improved Delayed Detached Eddy Simulation with Reynolds-stress background modelling

A novel variant of Improved Delayed Detached-Eddy Simulation based on a differential Reynolds-stress background model is presented. The approach aims to combine the advantages of anisotropy-resolving Reynolds-stress closures in the modelled RANS regions with consistent LES and wall-modelled LES behaviour in the resolved flow regions. In computations of decaying isotropic turbulence with a low-dissipative flow solver it is shown that a straightforward hybridised Reynolds-stress model provides insufficient turbulent dissipation as sub-grid closure in the LES regions and is therefore locally replaced by scalar viscosity modelling. Simulations of periodic channel flows at different Reynolds numbers and grid resolutions are used to calibrate and validate the wall-modelled LES branch of the new model. A final application in embedded wall-modelled LES of a flat-plate boundary layer is widely consistent with results using the SST-RANS background model, but shows some deviations from the Coles–Fernholz skin-friction correlation. In this regard, initial sensitivity studies indicate possible adverse effects due to the synthetic-turbulence approach used in these simulations.

Modeling of Ammonia MILD Combustion in Systems with Internal Recirculation

ABSTRACT The present work focuses on the combustion of alternative renewable fuels, ammonia in this case, in a system, such as the Laboratory Unit CYclonic (LUCY) burner. This reactor can operate under Moderate or Intense Low-oxygen Dilution (MILD) combustion conditions thanks to a strong internal recirculation of flue gases. Experimental data, including in-flame temperatures and exhaust gas composition, are available. Numerical simulations based on Computational Fluid Dynamics (CFD) techniques are performed and compared to the experiments to analyze the suitability of existing numerical sub-models. More specifically, a sensitivity analysis is carried out both for the turbulence closure models, i.e., RNG k-ϵ, BSL k-ω and Reynolds Stress Model, and for the combustion models, i.e. Flamelet Generated Manifold, Eddy Dissipation Concept and Partially Stirred Reactor, incorporating seven different kinetic schemes.

Data-driven Reynolds stress models based on the frozen treatment of Reynolds stress tensor and Reynolds force vector

For developing a reliable data-driven Reynold stress tensor (RST) model, successful reconstruction of the mean velocity field based on high-fidelity information (i.e., direct numerical simulations or large-eddy simulations) is crucial and challenging, considering the ill-conditioning problem of Reynolds-averaged Navier–Stokes (RANS) equations. It is shown that the frozen treatment of the Reynolds force vector (RFV) reduced the ill-conditioning problem even for the cases with a very high Reynolds number; therefore, it has a better potential to be used in the data-driven development of the RANS models. In this study, we compare the algebraic RST correction models that are trained based on the frozen treatment of both RFV and RST for the aforementioned potential. We derive a vector-based framework for the RFV similar to the tensor-based framework for the RST. Regarding the complexity of the models, we compare sparse regression on a set of candidate functions and a multi-layer perceptron network. The training process is applied to the high-fidelity data of three cases, including square-duct secondary flow, roughness-induced secondary flow, and periodic hills flow. The results showed that using the RFV discrepancy values, instead of the RST discrepancy values, generally does not improve the reconstruction of the mean velocity field despite the fact that the propagation of the RFV discrepancy data shows lower errors in the propagation process of all three cases. Regarding the complexity, using multi-layer perceptron improves the prediction of the cases with secondary flows, but it shows similar performance in the case of periodic hills.

CFD simulations of the refueling of long horizontal H2 tanks with tilted injector

With the recent development of Hydrogen Refueling Stations (HRS), the refueling of hydrogen composite tanks is an important issue for the safe handling of hydrogen. In particular, an appropriate protocol is needed to avoid tank overheating during refueling. To model the temperature distribution everywhere inside the tank during these processes, CFD (Computational Fluid Dynamics) simulations have been performed under cases where thermal stratification occurs. The performances of several CFD turbulence models are benchmarked through a comparison with experimental data. Two injector configurations are considered in this work: a straight one and another tilted upwards. The U-RANS (Unsteady-Reynolds Averaged Navier-Stokes) - Reynolds Stress Model (RSM) is found to be the most reliable turbulence model for both configurations.

A Review of the Computational Studies on the Separated Subsonic Flow in Asymmetric Diffusers Focused on Turbulence Modeling Assessment

Separated turbulent diffuser flows have long been an object of experimental and computational investigations due to their wide use in engineering applications and fundamental importance for understanding turbulent effects. The accuracy of simulating such flows depends mainly on turbulence modeling subtleties, numerical method, and the correspondence between the boundary conditions and the experimental set-up. The current review of selected articles focuses on revealing some of the computational challenges that may occur while modeling asymmetric subsonic diffuser flows. These challenges include the influence of sidewalls on the separation, issues with grid convergence, and the definition of boundary conditions. Several known experimental test cases and attempts at simulating them are studied. The novelty of this paper is in the fact that it is focused on a specific type of diffusers (asymmetric and subsonic) and based on relatively recent data. It is concluded that for all the test cases considered, Reynolds stress models and hybrid eddy-resolving methods are the most appropriate tools for obtaining reasonable results.

The hydrodynamic characteristics of autonomous underwater vehicles in rotating flow fields

In this article, the hydrodynamic characteristics of Autonomous Underwater Vehicles (AUVs) are investigated and analyzed under the influence of rotating flow fields, which were generated in a recirculating water tank via a rotating propeller. Initially, experiments were carried out to measure flow field variables and quantities of Interest across the AUV in the presence of the rotating propeller while varying the rotational speed and the extent of rotational flow strength. The flow field across the AUV was measured using an Acoustic Doppler Velocimeter (ADV). These measured turbulent flow statistics were used to validate the Reynolds Stress Model (RSM) based numerical predictions in a commercial CFD solver. After preliminary validation of the turbulent flow statistics with the numerical predictions, a series of numerical simulations were performed to investigate the effect of the rotational flow field of the propeller on the drag, skin friction, and pressure coefficients of the AUV. The operating speed and location of the propeller were also varied to check their effects on the hydrodynamic performance of the AUV. The results provided in this article will be useful for the design optimization of AUVs cruising in shallow water where the flow is highly rotational because of wave-current interactions. Additionally, the results and analysis are relevant to study the design and operation of AUVs that have to operate in a group of unmanned underwater vehicles or near submarines and ships where the flow field is highly complex and such rotational effects are present.

Assessment of advanced RANS turbulence models for prediction of complex flows in compressors

Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) has been widely used in compressor design and analysis. However, reasonable prediction of compressor flow and its impact on compressor performance remains challenging. In this study, Menter’s Shear Stress Transport (SST) model and its variants, as well as the ω-based Reynolds stress model (Stress-BSL) are assessed. For a single rotor (Rotor 67), under the peak efficiency operating condition, all studied turbulence models predict its performance with reasonable accuracy; under the off-design conditions, SST with Helicity correction (SST-Helicity) shows superiority in predicting the effect of flow on the spanwise distribution of aerodynamic parameters. For Darmstadt’s 1.5-stage transonic axial compressor, SST-Helicity outperforms SST, SST with the Quadratic Constitutive Relation (SST-QCR) and Stress-BSL in predicting the performance as well as the spanwise distribution of aerodynamic parameters. At the design rotating speed, the stall margin given by SST-Helicity (20.90%) is the closest to the experimental measurement (24.81%), which is more than twice that by SST (8.71%) and 1.5 times that by SST-QCR (14.14%). This paper demonstrates that SST-Helicity model, together with a good quality and sufficiently refined grid, can capture the compressor flow features with reasonable accuracy, which results in a credible prediction of compressor performance and stage matching.

A comparison of RANS models used for CFD prediction of turbulent flow and heat transfer in rough and smooth channels

CFD of convective heat transfer remains a challenge, especially in channels with irregular rough walls due to the complex fluid dynamics over and between these roughness elements. This study investigates the performance of four commonly utilised RANS CFD models, namely Spalart-Allmaras (SA), Realisable k-ε, SST k-ω, and Reynolds Stress Model (RSM) in estimating the velocity and temperature profile as well as the skin friction coefficient and Nusselt number in smooth and rough channels. The CFD results were compared with DNS and experimental data in the literature. The roughness-resolving approach was used for all models to resolve the realistic geometry of irregular roughness in channel flows. The smooth-channel flow study was conducted at Reτ = 500, 1000, 2000, and 5000 and Pr = 0.71. Over this range, compared to smooth-wall DNS data from literature, the RSM showed consistent and satisfactory performance in estimating the velocity and temperature profiles within 2.54% and 4.21%, respectively; leading to the skin friction coefficient and Nusselt number in the smooth channels being predicted very well within 1.94% and 2.03%, respectively. The rough-channel flow study was performed at Reτ = 240, 360, 540, 720, 1000 and Pr = 1, with computational cells 7.8 times that of the smooth channel to resolve the irregular roughness geometry. Over this range, the Realisable k-ε showed the best performance in estimating the roughness function within 6.85%, while the results of the other models were wider at uncertainty levels of up to 36.9%. Similarly, the Realisable k-ε demonstrated the best performance in estimating the skin friction and Nusselt number in rough channels within 2.76% and 9.50%, respectively, while the performance of the other models was to a wider latitude ranging between 15.62% to 26.34%. In the present study, the Realisable k-ε with enhanced wall treatment showed the best capabilities in capturing the mean flow characteristics of both smooth and rough channels; however, its usage should be approached with caution in flows at higher Reynolds numbers. RANS models are also discussed for forced convection heat transfer at high Reynolds numbers. The results of this study should be useful in CFD studies on the effects of roughness in complex geometries without the need for LES and DNS.

Magnetic Resonance Velocimetry Measurements of Internal Blade Cooling Flow and Computational Fluid Dynamic Validation by Data Matching With the Experimental Data

Abstract The optimal Reynolds-averaged Navier–Stokes (RANS) turbulence model to be used in a Computational Fluid Dynamics (CFD) simulation varies depending on the application. Conventionally, the model is selected from benchmark tests and experience, but its performance is difficult to predict. For this reason, this study presents a cost-effective CFD validation routine, which uses three-dimensional experimental velocity data obtained in replicas of the specific flow system. Magnetic Resonance Velocimetry is used as the measurement technique. Since the objective is only the validation of the turbulence model, the experiment and the simulation are performed with simplified flow conditions, hence stationary isothermal isovolumetric flow without inertial forces. The routine applies a data-matching routine to align the two three-dimensional data sets before they are interpolated on a common grid. Various error metrics are presented, which provide the degree of the CFD modeling error and indicate its source. For demonstration, the validation routine is used to evaluate RANS-CFD results of a three-pass internal cooling system of a high-pressure turbine airfoil used in a small industrial gas turbine. The simulations are performed with the eddy-viscosity-based turbulence model k–ω shear stress transport (SST), the Reynolds-stress Speziale, Sarkar and Gatski (SSG), and baseline-Explicit algebraic Reynolds stress model turbulence (BSL-EARSM) models. The results indicate strong local errors in the examined turbulence models. None of the models performed well enough, underlining that every RANS-CFD application needs to be validated.