TURBULENCE MODELS FOR ACCURATE AEROTHERMAL PREDICTION IN HYPERSONIC FLOWS

2010 ◽  
Vol 24 (13) ◽  
pp. 1345-1348 ◽  
Author(s):  
XIANG-HONG ZHANG ◽  
YI-ZAO WU ◽  
JIANG-FENG WANG
Keyword(s):  
High Performance ◽  
Turbulence Modeling ◽  
Thermal Protection ◽  
Transport Model ◽  
Integrated Design ◽  
Turbulence Models ◽  
Computational Prediction ◽  
Hypersonic Flows ◽  
Design And Optimization ◽  
Sst Model

Accurate description of the aerodynamic and aerothermal environment is crucial to the integrated design and optimization for high performance hypersonic vehicles. In the simulation of aerothermal environment, the effect of viscosity is crucial. The turbulence modeling remains a major source of uncertainty in the computational prediction of aerodynamic forces and heating. In this paper, three turbulent models were studied: the one-equation eddy viscosity transport model of Spalart-Allmaras, the Wilcox k -ω model and the Menter SST model. For the k -ω model and SST model, the compressibility correction, press dilatation and low Reynolds number correction were considered. The influence of these corrections for flow properties were discussed by comparing with the results without corrections. In this paper the emphasis is on the assessment and evaluation of the turbulence models in prediction of heat transfer as applied to a range of hypersonic flows with comparison to experimental data. This will enable establishing factor of safety for the design of thermal protection systems of hypersonic vehicle.

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart–Shur Correction Term

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Transport Model ◽  
Wide Range ◽  
Sst Model ◽  
The One

A rotation-curvature correction suggested earlier by Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) for the one-equation Spalart–Allmaras turbulence model is adapted to the shear stress transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and direct numerical simulations (DNS) data, on the one hand, and with the corresponding results of the original SST model and advanced Reynolds stress transport model (RSM), on the other hand. It is found that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Assessment of Turbulence Model Predictions for an Aero-Engine Centrifugal Compressor

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jason A. Bourgeois ◽  
Robert J. Martinuzzi ◽  
Eric Savory ◽  
Chao Zhang ◽  
Douglas A. Roberts
Keyword(s):  
Centrifugal Compressor ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Flow Fields ◽  
Reynolds Stress Model ◽  
Tip Clearance ◽  
Mean Flow ◽  
Tip Clearance Flow ◽  
Sst Model

The accurate prediction of mean flow fields with high degrees of curvature, adverse pressure gradients, and three-dimensional turbulent boundary layers typically present in centrifugal compressor stages is a significant challenge when applying Reynolds averaged Navier–Stokes turbulence modeling techniques. The current study compares the steady-state mixing plane predictions using four turbulence models for a centrifugal compressor stage with a tandem impeller and a “fish-tail” style discrete passage diffuser. The models analyzed are the k-ε model (an industry standard for many years), the shear stress transport (SST) model, a proposed modification to the SST model denoted as the SST-reattachment modification (RM), and the Speziale, Sarkar, and Gatski Reynolds stress model (RSM-SSG). Comparisons with measured performance parameters—the stage total-to-static pressure and total-to-total temperature ratios—indicate more accurate performance predictions from the RSM-SSG and SST models as compared to the k-ε and SST-RM models. Details of the different predicted flow fields are presented. Estimates of blockage, aerodynamic slip factor, and impeller exit velocity profiles indicate significant physical differences in the predictions at the impeller-diffuser interface. Topological flow field differences are observed: the separated tip clearance flow is found to reattach with the SST, SST-RM, and RSM-SSG models, while it does not with the k-ε model, a larger shroud separation at the impeller exit seen with the SST and SST-RM models, and core flow differences are in the complex curved diffuser geometry. The results are discussed in terms of the production and dissipation of k predicted by the various models due to their intrinsic modeling assumptions. These comparisons will assist aerodynamic designers in choosing appropriate turbulence models, and may benefit future modeling research.

scholarly journals Turbulence Modeling in Side-Entry Stirred Tank Mixing Time Determination

2021 ◽  
Vol 333 ◽  
pp. 02003
Author(s):  
Suci Madhania ◽  
Ni’am Nisbatul Fathonah ◽  
Kusdianto ◽  
Tantular Nurtono ◽  
Sugeng Winardi
Keyword(s):  
Turbulence Model ◽  
Turbulence Modeling ◽  
Mixing Time ◽  
Paper Industry ◽  
Turbulence Models ◽  
Computational Prediction ◽  
Operating Conditions ◽  
Stirred Tank ◽  
Critical Parameters ◽  
Working Fluid

Mixing is one of the critical processes in the industry. The stirred tank is one of the operating units commonly used in the mixing process. Several factors greatly influence the efficiency of the stirred tank, including the stirred-tank design, operating conditions, and working fluid properties. The side-entry stirred tank is widely applied in industry, among others; the processing of crude oil in the refinery industry, water-molasses mixing in the bioethanol industry, pulp stock chest in the pulp and paper industry, and anaerobic digester for biogas reactors. Mixing time is one of the critical parameters used in the design of the stirred tank. This research will model mixing time in a flat bottomed-cylindrical side-entry stirred tank with dimensions D = 40 cm and T = 40 cm using CFD ANSYS 18.2 by applying the Standard κ − ε (SKE) and Realizable κ − ε (RKE) turbulence models. The stirrer used is a three-blade marine propeller d = 4 cm which is an axial type impeller. The phenomenon of mixing in the side-entry stirred tank, qualitatively described through computational prediction results in the form of flow profiles and tracer density change contours locally. Moreover, quantitatively indicated by mixing time validated using experimental data carried out by the conductometry method. The computational prediction shows that the mixing time modeled using the SKE turbulence model shows a similarity level of 68.16%, while the RKE turbulence model shows 31.94%.

Ultra-High Temperature Ceramics (UHTCs) via Reactive Sintering

2007 ◽  
Vol 336-338 ◽  
pp. 1159-1163 ◽  
Author(s):  
Guo Jun Zhang ◽  
Wen Wen Wu ◽  
Yan Mei Kan ◽  
Pei Ling Wang
Keyword(s):  
Phase Composition ◽  
High Temperature ◽  
Oxidation Resistance ◽  
High Performance ◽  
Thermal Protection ◽  
Ambient Pressure ◽  
Stable Phase ◽  
Reactive Sintering ◽  
Dissociation Temperature ◽  
Monolithic Ceramics

Current high temperature ceramics, such as ZrO2, Si3N4 and SiC, cannot be used at temperatures over 1600°C due to their low melting temperature or dissociation temperature. For ultrahigh temperature applications over 1800°C, materials with high melting points, high phase composition stability, high thermal conductivity, good thermal shock and oxidation resistance are needed. The transition metal diborides, mainly include ZrB2 and HfB2, have melting temperatures of above 3000°C, and can basically meet the above demands. However, the oxidation resistance of diboride monolithic ceramics at ultra-high temperatures need to be improved for the applications in thermal protection systems for future aerospace vehicles and jet engines. On the other hand, processing science for making high performance UHTCs is another hot topic in the UHTC field. Densification of UHTCs at mild temperatures through reactive sintering is an attracting way due to the chemically stable phase composition and microstructure as well as clean grain boundaries in the obtained materials. Moreover, the stability studies of the materials in phase composition and microstructures at ultra high application temperatures is also critical for materials manufactured at relatively low temperature. Furthermore, the oxidation resistance in simulated reentry environments instead of in static or flowing air of ambient pressure should be evaluated. Here we will report the concept, advantages and some recent progress on the reactive sintering of diboride–based composites at mild temperatures.

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

scholarly journals Influence of Fabric Weave on Thermal Radiation Resistance and Water Vapor Permeability

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 525
Author(s):  
Ana Kiš ◽  
Snježana Brnada ◽  
Stana Kovačević
Keyword(s):  
High Temperatures ◽  
High Performance ◽  
Thermal Protection ◽  
Water Vapor Permeability ◽  
Radiant Heat ◽  
The Body ◽  
Vapor Permeability ◽  
Weave Structure ◽  
Fabric Structures ◽  
The Impact

In this work, aramid fibers were used to develop new, high-performance fabrics for high-temperature protective clothing. The research was based on the impact of the weave structure on fabric resistance to radiant heat. The goals of the research were primarily related to the development of new fabric structures created by the weave structure, which gives better protection of the body against high temperatures in relation to the standard weave structures that are used today. According to the results obtained it can be concluded that the fabric weave significantly affects the fabric structure, which consequently determines the effectiveness of protection against high temperatures. The justification for the use of multi-weft and strucks weave structure, which provides greater thermal protection and satisfactory breathability than commonly used weave structures, was ascertained.

Mechanism of the Transition From In-Plane Buckling to Helical Buckling for a Stiff Nanowire on an Elastomeric Substrate

2016 ◽  
Vol 83 (4) ◽  
Author(s):  
Youlong Chen ◽  
Yong Zhu ◽  
Xi Chen ◽  
Yilun Liu
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Stretchable Electronics ◽  
Buckling Mode ◽  
Design And Optimization ◽  
Out Of Plane ◽  
Plane Direction ◽  
Plane Displacement ◽  
Helical Buckling ◽  
Selection Of

In this work, the compressive buckling of a nanowire partially bonded to an elastomeric substrate is studied via finite-element method (FEM) simulations and experiments. The buckling profile of the nanowire can be divided into three regimes, i.e., the in-plane buckling, the disordered buckling in the out-of-plane direction, and the helical buckling, depending on the constraint density between the nanowire and the substrate. The selection of the buckling mode depends on the ratio d/h, where d is the distance between adjacent constraint points and h is the helical buckling spacing of a perfectly bonded nanowire. For d/h > 0.5, buckling is in-plane with wavelength λ = 2d. For 0.27 < d/h < 0.5, buckling is disordered with irregular out-of-plane displacement. While, for d/h < 0.27, buckling is helical and the buckling spacing gradually approaches to the theoretical value of a perfectly bonded nanowire. Generally, the in-plane buckling induces smaller strain in the nanowire, but consumes the largest space. Whereas the helical mode induces moderate strain in the nanowire, but takes the smallest space. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and three-dimensional complex nanostructures.

Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows

1995 ◽  
Vol 48 (4) ◽  
pp. 189-212 ◽  
Author(s):  
G. J. Brereton ◽  
R. R. Mankbadi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Unsteady Flows ◽  
Turbulence Models ◽  
Research Area ◽  
Transition To Turbulence ◽  
Measurement Technology ◽  
Internal Flows ◽  
Recent Advances ◽  
The Many

Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.

Integrated Design and Control of Active Aerodynamic Features for High Performance Electric Vehicles

2021 ◽  
Author(s):  
Alessandro Ferraris ◽  
Davide De Cupis ◽  
Henrique de Carvalho Pinheiro ◽  
Alessandro Messana ◽  
Lorenzo Sisca ◽  
...  
Keyword(s):  
Electric Vehicles ◽  
High Performance ◽  
Integrated Design ◽  
And Control
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