Multi-Scale Parallelised CFD Modelling Towards Resolving Manufacturable Roughness

2019 ◽  
Author(s):  
Marios Kapsis ◽  
Li He ◽  
Yan Sheng Li ◽  
Roger Wells ◽  
Omar Valero ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Large Scale ◽  
Practical Interest ◽  
Design Parameters ◽  
Flow Structures ◽  
Local Flow ◽  
Multi Scale ◽  
Micro Structures ◽  
The Impact ◽  
Micro Elements

Abstract Typical turbomachinery aerothermal problems of practical interest are characterised by flow structures of wide-ranging scales, which interact with each other. Such multi-scale interactions can be observed between the flow structures produced by surface roughness and by the bulk flow patterns. Moreover, additive manufacturing may sooner or later open a new chapter in component designs by granting designers the ability to control the surface roughness patterns. As a result, surface finish, which so far has been treated largely as a stochastic trait, can be shifted to a set of design parameters that consist of repetitive, discrete micro-elements on a wall surface (‘manufacturable roughness’). Considering this prospective capability requirement, the question would arise regarding how surface micro-structures can be incorporated in computational analyses during a design phase in the future. Semi-empirical methods for predicting aerothermal characteristics and the impact of manufacturable roughness could be used to minimise computational cost. However, the lack of element-to-element resolution may lead to erroneous predictions, as the interactions among the roughness micro-elements have been shown to be significant for adequate performance predictions [1]. In this paper a new multi-scale approach based on the novel Block Spectral method is adopted. This method aims to provide efficient resolution of the detailed local flow variation in space and time of the large scale micro-structures. This resolution is provided without resorting to modelling every single ones in detail, as a conventional large scale CFD simulation would demand, but still demonstrating similar time-accurate and time-averaged flow properties. The main emphasis of the present work is to develop a parallelised solver of the method to enable tackling large problems. The work also includes a first of the kind verification and demonstration of the method for wall surfaces with a large number of micro-structured elements.

Multiscale Parallelized Computational Fluid Dynamics Modeling Toward Resolving Manufacturable Roughness

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Marios Kapsis ◽  
Li He ◽  
Yan Sheng Li ◽  
Omar Valero ◽  
Roger Wells ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Surface Roughness ◽  
Large Scale ◽  
Design Parameters ◽  
Flow Structures ◽  
Multiscale Approach ◽  
Local Flow ◽  
The Impact ◽  
Micro Elements

Abstract Typical turbomachinery aerothermal problems of practical interest are characterized by flow structures of wide-ranging scales, which interact with each other. Such multiscale interactions can be observed between the flow structures produced by surface roughness and by the bulk flow patterns. Moreover, additive manufacturing (AM) may sooner or later open a new chapter in the way components are designed by granting designers the ability to control the shape and patterns of surface roughness. As a result, surface finish, which so far has been treated largely as a stochastic trait, can be shifted to a set of design parameters that consist of repetitive, discrete micro-elements on a wall surface (“manufacturable roughness”). Considering this prospective capability, the question would arise regarding how surface microstructures can be incorporated in computational analyses during designing in the future. Semi-empirical methods for predicting aerothermal characteristics and the impact of manufacturable roughness could be used to minimize computational cost. However, the lack of element-to-element resolution may lead to erroneous predictions, as the interactions among the roughness micro-elements have been shown to be significant for adequate performance predictions (Kapsis and He, 2018, “Analysis of Aerothermal Characteristics of Surface Micro-Structures,” ASME J. Fluids Eng., 140(5), p. 051104). In this paper, a new multiscale approach based on the novel block spectral method (BSM) is adopted. This method aims to provide efficient resolution of the detailed local flow variation in space and time of the large-scale microstructures. This resolution is provided without resorting to modeling every single ones in detail, as a conventional large-scale computational fluid dynamics (CFD) simulation would demand, but still demonstrating similar time-accurate and time-averaged flow properties. The main emphasis of this work is to develop a parallelized solver of the method to enable tackling large problems. The work also includes a first of the kind verification and demonstration of the method for wall surfaces with a large number of microstructured elements.

Experimental Study of Large-Scale Flow Structures in an Aneurysm

2018 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Large Scale ◽  
Flow Structures ◽  
Pump System ◽  
Vortical Structures ◽  
Abnormal Growth ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
The Impact ◽  
Inflow Conditions ◽  
Aneurysm Model

An aneurysm is an abnormal growth in the wall of a weakened blood vessel, and can often be fatal upon rupture. Studies have shown that aneurysm shape and hemodynamics, in conjunction with other parameters, play an important role in growth and rupture. The objective of this study was to investigate the impact of varying inflow conditions on flow structures in an aneurysm. An idealized rigid sidewall aneurysm model was prepared and the Womersley number (α) and Reynolds number (Re) values were varied from 2 to 5 and 50 to 250, respectively. A ViVitro Labs pump system was used for inflow control and Particle Image Velocimetry was used for conducting velocity measurements. The results showed that the primary vortex path varied with an increase in α, while an increase in Re was correlated to the vortex strength and formation of secondary vortical structures. The evolution and decay of vortical structures were also observed to be dependent on α and Re.

On the Climate Impact of Surface Roughness Anomalies

2008 ◽  
Vol 65 (7) ◽  
pp. 2215-2234 ◽  
Author(s):  
Daniel B. Kirk-Davidoff ◽  
David W. Keith
Keyword(s):  
Surface Roughness ◽  
Large Scale ◽  
Climate Impact ◽  
Water Model ◽  
Dynamic Mechanisms ◽  
Community Atmosphere Model ◽  
Horizontal Length ◽  
Rossby Wave Response ◽  
The Mean ◽  
The Impact

Abstract Large-scale deployment of wind power may alter climate through alteration of surface roughness. Previous research using GCMs has shown large-scale impacts of surface roughness perturbations but failed to elucidate the dynamic mechanisms that drove the observed responses in surface temperature. Using the NCAR Community Atmosphere Model in both its standard and aquaplanet forms, the authors have explored the impact of isolated surface roughness anomalies on the model climate. A consistent Rossby wave response in the mean winds to roughness anomalies across a range of model implementations is found. This response generates appreciable wind, temperature, and cloudiness anomalies. The interrelationship of these responses is discussed, and it is shown that the magnitude of the responses scales with the horizontal length scale of the roughened region, as well as with the magnitude of the roughness anomaly. These results are further elucidated through comparison with results of a series of shallow-water model experiments.

Wavelet-based phase average on the multi-scale wake structures of square cylinder

2018 ◽  
Vol 16 (06) ◽  
pp. 1850055
Author(s):  
Yan Zheng ◽  
Akira Rinoshika ◽  
Jianqin Suo
Keyword(s):  
Wavelet Transform ◽  
Large Scale ◽  
Half Period ◽  
Flow Structures ◽  
Square Cylinder ◽  
Average Technique ◽  
Intermediate Scale ◽  
Multi Scale ◽  
Phase Average ◽  
Scale Structures

Phase-average technique based on wavelet multi-resolution analysis and continuous wavelet transform are used to reveal the phase-averaged features of square cylinder wake measured by high-speed PIV. The one-dimensional orthogonal wavelet analysis is first applied to decompose the measured velocity fields into large-, intermediate- and small-scale structures. Then the phase information referenced with large- and intermediate-scale flow structures are clearly identified based on Morlet wavelet transform. Finally, the data ensembles are phase-sorted to give phase-averaged representations of measured flow field. The instantaneous multi-scale structures suggest that large-scale vortices are weakened and begin to transfer into intermediate-vortices at the downstream of separation region. The intermediate-scale vortex observed at the upper boundary of shear layer is considered to be associated with the secondary vortex movement. The phase-averaged intermediate-scale structures tend to convey downstream along streamwise direction, with the rotation sense varying from the first half period to the last half period. The peaks of phase-averaged large-scale Reynolds stress tend to move back and forth in the near-wake region. These findings suggest that the proposed phase-average technique is effective in revealing multi-scale fluid dynamics of wake flow structures.

scholarly journals Examples of Monte Carlo techniques applied for nuclear data uncertainty propagation

2019 ◽  
Vol 211 ◽  
pp. 07008 ◽  
Author(s):  
Oscar Cabellos ◽  
Luca Fiorito
Keyword(s):  
Monte Carlo ◽  
Large Scale ◽  
Uncertainty Propagation ◽  
Nuclear Data ◽  
Monte Carlo Technique ◽  
Data Uncertainty ◽  
Design Parameters ◽  
Monte Carlo Techniques ◽  
Bayesian Monte Carlo ◽  
The Impact

The aim of this work is to review different Monte Carlo techniques used to propagate nuclear data uncertainties. Firstly, we introduced Monte Carlo technique applied for Uncertainty Quantification studies in safety calculations of large scale systems. As an example, the impact of nuclear data uncertainty of JEFF-3.3 235U, 238U and 239Pu is demonstrated for the main design parameters of a typical 3-loop PWR Westinghouse unit. Secondly, the Bayesian Monte Carlo technique for data adjustment is presented. An example for 235U adjustment using criticality and shielding integral benchmarks shows the importance of performing joint adjustment based on different set of integral benchmarks.

scholarly journals Multi-Scale Target-Specified Sub-Model Approach for Fast Large-Scale High-Resolution 2D Urban Flood Modelling

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 259
Author(s):  
Guohan Zhao ◽  
Thomas Balstrøm ◽  
Ole Mark ◽  
Marina B. Jensen
Keyword(s):  
High Resolution ◽  
Real Time ◽  
Large Scale ◽  
Goodness Of Fit ◽  
Significant Loss ◽  
Urban Flood ◽  
Multi Scale ◽  
The Impact ◽  
Mean Square Errors ◽  
Model Approach

The accuracy of two-dimensional hydrodynamic models (2D models) is improved when high-resolution Digital Elevation Models (DEMs) are used. However, the entailed high spatial discretisation results in excessive computational expenses, thus prohibiting their implementation in real-time forecasting especially at a large scale. This paper presents a sub-model approach that adapts 1D static models to tailor high-resolution 2D model grids relevant to specified targets, such that the tailor-made 2D hydrodynamic sub-models yield fast processing without significant loss of accuracy via a GIS-based multi-scale simulation framework. To validate the proposed approach, model experiments were first designed to separately test the impact of two outcomes (i.e., the reduced computational domains and the optimised boundary conditions) towards final 2D prediction results. Then, the robustness of the sub-model approach was evaluated by selecting four focus areas with distinct catchment terrain morphologies as well as distinct rainfall return periods of 1–100 years. The sub-model approach resulted in a 45–553 times faster processing with a 99% reduction in the number of computational cells for all four cases; the goodness of fit regarding predicted flood extents was above 0.88 of F2, flood depths yield Root Mean Square Errors (RMSE) below 1.5 cm and the discrepancies of u- and v-directional velocities at selected points were less than 0.015 ms−1. As such, this approach reduces the 2D models’ computing expenses significantly, thus paving the way for large-scale high-resolution 2D real-time forecasting.

scholarly journals Experiments and 3D simulations of flow structures in junctions and their influence on location of flowmeters

2012 ◽  
Vol 66 (6) ◽  
pp. 1325-1332 ◽  
Author(s):  
E. Mignot ◽  
H. Bonakdari ◽  
P. Knothe ◽  
G. Lipeme Kouyi ◽  
A. Bessette ◽  
...  
Keyword(s):  
Flow Rate ◽  
Open Channel ◽  
Flow Structures ◽  
Flow Rate Measurement ◽  
Flow Measurements ◽  
Local Flow ◽  
Junction Flow ◽  
Typical Error ◽  
The Impact ◽  
Sewer Networks

Open-channel junctions are common occurrences in sewer networks and flow rate measurement often occurs near these singularities. Local flow structures are 3D, impact on the representativeness of the local flow measurements and thus lead to deviations in the flow rate estimation. The present study aims (i) to measure and simulate the flow pattern in a junction flow, (ii) to analyse the impact of the junction on the velocity distribution according to the distance from the junction and thus (iii) to evaluate the typical error derived from the computation of the flow rate close to the junction.

scholarly journals When do cosmic peaks, filaments or walls merge? A theory of critical events in a multi-scale landscape.

2020 ◽  
Author(s):  
C Cadiou ◽  
C Pichon ◽  
S Codis ◽  
M Musso ◽  
D Pogosyan ◽  
...  
Keyword(s):  
Critical Points ◽  
Large Scale ◽  
Saddle Points ◽  
Cosmic Time ◽  
Gaussian Random Fields ◽  
Critical Event ◽  
Multi Scale ◽  
Merger Rate ◽  
The One ◽  
The Impact

Abstract The merging rate of cosmic structures is computed, relying on the Ansatz that they can be predicted in the initial linear density field from the coalescence of critical points with increasing smoothing scale, used here as a proxy for cosmic time. Beyond the mergers of peaks with saddle points (a proxy for halo mergers), we consider the coalescence and nucleation of all sets of critical points, including wall-saddle to filament-saddle and wall-saddle to minima (a proxy for filament and void mergers respectively), as they impact the geometry of galactic infall, and in particular filament disconnection. Analytical predictions of the one-point statistics are validated against multiscale measurements in 2D and 3D realisations of Gaussian random fields (the corresponding code being available upon request) and compared qualitatively to cosmological N-body simulations at early times (z ≥ 10) and large scales (≥ 5Mpc/h). The rate of filament coalescence is compared to the merger rate of haloes and the two-point clustering of these events is computed, along with their cross-correlations with critical points. These correlations are qualitatively consistent with the preservation of the connectivity of dark matter haloes, and the impact of the large scale structures on assembly bias. The destruction rate of haloes and voids as a function of mass and redshift is quantified down to z = 0 for a ΛCDM cosmology. The one-point statistics in higher dimensions are also presented, together with consistency relations between critical point and critical event counts.

scholarly journals The influence of soak temperature and forging lubricant on surface properties of steel forgings

2020 ◽  
Author(s):  
S. Hill ◽  
R. P. Turner ◽  
P. Wardle
Keyword(s):  
Surface Roughness ◽  
Surface Hardness ◽  
Lower Surface ◽  
Design Parameters ◽  
Compression Tests ◽  
Molybdenum Disulphide ◽  
Small Series ◽  
Ring Compression ◽  
Water Based ◽  
The Impact

AbstractA small series of ring compression tests were performed on BS970:708M40 alloy steel. The samples were tested using a 2-factor temperature variable, and a 4-factor lubricant variable, as the design parameters. Two differing soak temperatures were used, namely 1030 °C and 1300 °C respectively. The lubricants applied at the billet to tooling interface were synthetic water–based, graphite water–based, graphite and molybdenum disulphide viscous grease, and finally, unlubricated samples were tested. The ring compression tests were performed using a traditional drop forging hammer and induction heating to minimise any unintentional process variability. The impact that the two varying process parameters have upon the compression sample was then assessed by measuring each sample’s surface hardness and surface roughness prior to and post forging with fully calibrated equipment. It was demonstrated that the higher soak temperature of 1300 °C yielded a lower surface hardness value and higher surface roughness than the lower soak temperature, 1030 °C. The two water-based lubricants offered negligible change in results compared with the unlubricated forging, strongly suggesting that the lubricants were evaporated off the surface prior to forging. However, the results from the graphite–molybdenum disulphate grease do indicate in particular higher surface roughness than other lubricants, and a non-symmetric distortion pattern.

Challenges and Opportunities for the Turbine Performance Improvement Through Stator Clocking and Vane Bowing

2007 ◽  
Author(s):  
Antoni Smolny ◽  
Jaroslaw R. Blaszczak ◽  
Jan Krysinski ◽  
Tomasz Borzecki
Keyword(s):  
Aspect Ratio ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Flow Structures ◽  
Major Influence ◽  
Two Stage ◽  
Local Flow ◽  
Low Aspect Ratio ◽  
The Impact

The paper describes experimental and numerical investigations of turbine vane clocking effects on the flow process in a two-stage turbine with low-aspect ratio stators. The data present clocking effects that can be observed both for local flow patterns and external characteristics for the entire machine in terms of efficiency. A low-aspect ratio and high turning create a highly three-dimensional flow that is dominated by secondary flows. The aim was to reduce the impact of the secondary flows by bowing the first stator vanes by means of different vane bending and the stator clocking. Another major objective was to show how wake trajectory features can be applied in a turbine design. The changes in the secondary flow structures of the first stator were performed by leaning and bowing the airfoils to achieve load reduction near end walls. This can lead to a weaker end wall secondary flow structures and lower losses. Bowed blades are nowadays often adopted for high-pressure gas and steam turbines. The results demonstrate that incoming interacting streamwise vortices have a major influence on the secondary flows and loss generation mechanisms of the downstream airfoil rows. Using the clocking concept, the secondary flow structures are forced to interact one with another at different positions of the stators. This procedure reveals the best nature of such interactions and shows the resulting benefits. The data acquired by clocking the upstream cascade can identify the effects of incoming vortices, particularly when they entering the leading edge regions of the downstream cascade airfoil. The results for this test indicate that the size and strength of the secondary flows for the downstream cascade should be lower than those obtained without interaction. It is apparent from these investigations that incoming stream-wise vortices may have a potential effect on the flow distribution for downstream airfoil rows. The first part of the paper presents results of the stator clocking identification for different geometries of the first stator. An introduction of the vane bowing has redesigned the first stator. The cylindrical version and two combinations of the bowed vanes with low and high curvature have been considered for the first stator. The authors have found that modified vanes produce smaller and weaker secondary flow structures. The second part presents experimental and numerical results of the clocking investigations for the above-mentioned versions. The experiments have shown that clocking effects seem to be related to the stator wake and vortex structures which produce low momentum fluid areas. These areas interact with boundary layers or secondary flow regions of the second stator where the fluid momentum is already low. Clocking effects on external flow parameter are analyzed versus the low momentum area trajectories due to the first stator vane bowing. The present work focuses on the structures that are formed downstream as a result of the exit flow field of the upstream stage, and examines the implication for efficiency improvement. This paper therefore deals with an interaction of complex three-dimensional stator-rotor flow structures in the two-stage axial turbine.

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