scholarly journals Development of a numerical-computational methodology for the simulation of unsteady flows with heat transfer

2015 ◽  
Author(s):  
Κωνσταντίνος Στόκος
Keyword(s):  
Heat Transfer ◽  
Unsteady Flows ◽  
Test Cases ◽  
Benchmark Test ◽  
Computational Methodology ◽  
Edge Based

Σκοπός της διδακτορικής διατριβής ήταν η ανάπτυξη μιας αριθμητικής-υπολογιστικής μεθοδολογίας για την προσομοίωση γενικά μη μόνιμων ροών με ταυτόχρονη μεταφορά θερμότητας.Ο αναπτυχθείς επιλύτης είναι κατάλληλος για την προσομοίωση δισδιάστατων ή τρισδιάστατων, ασυμπίεστων, στρωτών ή τυρβωδών ροών συνεκτικού και Νευτώνειου ρευστού. Για την απαραίτητη σύζευξη των πεδίων πίεσης και ταχύτητας εφαρμόζεται η προσέγγιση της τεχνητής συμπιεστότητας. Για την πρόβλεψη ανωστικών ροών του ασυμπίεστου ρευστού, η μεταβολή της πυκνότητας λόγω θερμοκρασιακών διαφορών προσομοιώνεται σύμφωνα με την προσέγγιση Boussinesq. Για τις τυρβώδεις ροές χρησιμοποιούνται δύο ευρέως διαδεδομένα RANS μοντέλα τύρβης, το μοντέλο τύρβης k-ω SST στη χαμηλών και υψηλών αριθμών Re έκδοσή του και το υψηλών αριθμών Re k-ε μοντέλο τύρβης.Ο επιλύτης εφαρμόζει μια κεντρο-κομβική (node-centered) πεπερασμένων όγκων τεχνική διακριτοποίησης, χρησιμοποιώντας ακμο-βασική (edge-based) και διαφανή (transparent) προσέγγιση σε υβριδικά αριθμητικά πλέγματα. Για τον υπολογισμό των μη-συνεκτικών όρων αναπτύχθηκε εκ του μηδενός ο προσεγγιστικός Riemann επιλύτης του Roe. Οι συνεκτικοί όροι διακριτοποιούνται χρησιμοποιώντας ένα κεντρικό σχήμα. Η χρονική διακριτοποίηση επιτυγχάνεται μέσω ενός πλήρως πεπλεγμένου σχήματος για τη χρονοπροέλαση στον ψευδο-χρόνο και το φυσικό χρόνο.Όλες οι εξισώσεις μέσης ροής (εξισώσεις συνέχειας, ορμής και ενέργειας) επιλύονται ισχυρά συζευγμένες. Η ισχυρή σύζευξη των εξισώσεων προτιμήθηκε μετά από σύγκριση με την ασθενώς συζευγμένη επίλυση, σύγκριση την οποία δεν έχουμε βρει στη βιβλιογραφία να παρουσιάζεται για το συγκεκριμένο σύστημα εξισώσεων. Η ισχυρή σύζευξη έδειξε γρηγορότερη σύγκλιση για σημαντικά μη-συνεκτικά φαινόμενα και μας επέτρεψε τη χρήση υψηλότερων αριθμών CFL κάνοντας τη σύγκλιση ακόμα γρηγορότερη.Για τη μοντελοποίηση της θερμικής ακτινοβολίας εφαρμόστηκαν δύο μεθοδολογίες. Η πρώτη αποτελεί μια αναλυτική μεθοδολογία που βασίζεται στη χρήση γωνιακών παραγόντων και η δεύτερη αποτελεί μια πεπερασμένων όγκων μεθοδολογία.Μετά από την ανάπτυξη της αριθμητικής μεθοδολογίας σε υπολογιστικό κώδικα επιλύθηκαν αρκετές περιπτώσεις αναφοράς (benchmark test cases) για την επαλήθευση της ορθής λειτουργίας του κώδικα και την αξιολόγηση των δυνατοτήτων του. Τα αποτελέσματα είναι αρκετά ενθαρρυντικά όπως συμβαίνει και με την παραλληλοποίηση του επιλύτη, που παρουσίασε σημαντική μείωση του υπολογιστικού χρόνου.Τέλος, προχωρήσαμε στην προσομοίωση δύο σεναρίων πυρκαγιάς σε αεριζόμενη σήραγγα. Οι περιπτώσεις πυρκαγιάς προσομοιώθηκαν είτε λαμβάνοντας υπόψη την ακτινοβολία και την αγωγή στο τοίχωμα είτε όχι. Η θερμική ακτινοβολία και η αγωγή στο τοίχωμα έδειξαν ότι είναι απαραίτητες για την πρόβλεψη ρεαλιστικών αποτελεσμάτων.

COMPARISON OF RADIATIVE HEAT TRANSFER METHODS USING BENCHMARK TEST CASES

2001 ◽  
Author(s):  
Klaus-Peter Helbig ◽  
Pedro J. Coelho ◽  
Joaquim Chamico ◽  
John Marakis ◽  
Aristide Mbiock ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Test Cases ◽  
Benchmark Test

Application of RANS and LES to the Prediction of Flows in High Pressure Turbine Components

2011 ◽  
Author(s):  
Nicolas Gourdain ◽  
Laurent Y. M. Gicquel ◽  
Remy Fransen ◽  
Elena Collado ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Guide Vane ◽  
Unsteady Flows ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Boundary Layer Transition ◽  
Wall Heat Transfer ◽  
Layer Transition ◽  
Turbine Guide Vane

This paper investigates the capability of numerical simulations to estimate unsteady flows and wall heat fluxes in turbine components with both structured and unstructured flow solvers. Different numerical approaches are assessed, from steady-state methods based on the Reynolds Averaged Navier-Stokes (RANS) equations to more sophisticated methods such as the Large Eddy Simulation (LES) technique. Three test cases are investigated: the vortex shedding induced by a turbine guide vane, the wall heat transfer in another turbine guide vane and a separated flow phenomenon in an internal turbine cooling channel. Steady flow simulations usually fail to predict the mean effects of unsteady flows (such as vortex shedding) and wall heat transfer, mainly because laminar-to turbulent transition and the inlet turbulent intensity are not correctly taken into account. Actually, only the LES (partially) succeeds to accurately estimate unsteady flows and wall heat fluxes in complex configurations. The results presented in this paper indicate that this method considerably improves the level of physical description (including boundary layer transition). However, the LES still requires developments and validations for such complex flows. This study also points out the dependency of results to parameters such as the freestream turbulence intensity. When feasible solutions obtained with both structured and unstructured flow solvers are compared to experimental data.

Extended Models for Transitional Rough Wall Boundary Layers With Heat Transfer: Part I—Model Formulations

2008 ◽  
Author(s):  
M. Stripf ◽  
A. Schulz ◽  
H.-J. Bauer ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layers ◽  
Turbulence Model ◽  
Turbulence Intensity ◽  
Discrete Element ◽  
Rough Wall ◽  
Test Cases ◽  
Wall Boundary ◽  
Turbine Vane

Two extended models for the calculation of rough wall transitional boundary layers with heat transfer are presented. Both models comprise a new transition onset correlation, which accounts for the effects of roughness height and density, turbulence intensity and wall curvature. In the transition region, an intermittency equation suitable for rough wall boundary layers is used to blend between the laminar and fully turbulent state. Finally, two different submodels for the fully turbulent boundary layer complete the two models. In the first model, termed KS-TLK-T in this paper, a sand roughness approach from Durbin et al., which builds upon a two-layer k-ε-turbulence model, is used for this purpose. The second model, the so-called DEM-TLV-T model, makes use of the discrete-element roughness approach, which was recently combined with a two-layer k-ε-turbulence model by the present authors. The discrete element model will be formulated in a new way suitable for randomly rough topographies. Part I of the paper will provide detailed model formulations as well as a description of the database used for developing the new transition onset correlation. Part II contains a comprehensive validation of the two models, using a variety of test cases with transitional and fully turbulent boundary layers. The validation focuses on heat transfer calculations on both, the suction and the pressure side of modern turbine airfoils. Test cases include extensive experimental investigations on a high-pressure turbine vane with varying surface roughness and turbulence intensity, recently published by the current authors as well as new experimental data from a low-pressure turbine vane. In the majority of cases, the predictions from both models are in good agreement with the experimental data.

Line-by-Line Random-Number Database for Monte Carlo Simulations of Radiation in Combustion System

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Tao Ren ◽  
Michael F. Modest
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
Monte Carlo Method ◽  
Radiative Heat ◽  
Random Number ◽  
Test Cases ◽  
Combustion System ◽  
Absorption Coefficients ◽  
One Dimensional ◽  
The Monte Carlo Method

With today's computational capabilities, it has become possible to conduct line-by-line (LBL) accurate radiative heat transfer calculations in spectrally highly nongray combustion systems using the Monte Carlo method. In these calculations, wavenumbers carried by photon bundles must be determined in a statistically meaningful way. The wavenumbers for the emitting photons are found from a database, which tabulates wavenumber–random number relations for each species. In order to cover most conditions found in industrial practices, a database tabulating these relations for CO2, H2O, CO, CH4, C2H4, and soot is constructed to determine emission wavenumbers and absorption coefficients for mixtures at temperatures up to 3000 K and total pressures up to 80 bar. The accuracy of the database is tested by reconstructing absorption coefficient spectra from the tabulated database. One-dimensional test cases are used to validate the database against analytical LBL solutions. Sample calculations are also conducted for a luminous flame and a gas turbine combustion burner. The database is available from the author's website upon request.

Benchmark test cases for the National Combustion Code

1998 ◽  
Author(s):  
K.-H. Chen ◽  
A. Norris ◽  
A. Quealy ◽  
N.-S. Liu
Keyword(s):  
Test Cases ◽  
Benchmark Test

Modifying a meshless method to solving κ−ε turbulent natural convection heat transfer

2019 ◽  
Vol 31 (01) ◽  
pp. 2050014
Author(s):  
Nasrin Sheikhi ◽  
Mohammad Najafi ◽  
Vali Enjilela
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Numerical Methods ◽  
Turbulent Flow ◽  
Turbulent Viscosity ◽  
Convection Heat Transfer ◽  
New Technique ◽  
Test Cases ◽  
Convection Heat ◽  
Transfer Problems

The conventional meshless local Petrov–Galerkin method is modified to enable the method to solve turbulent convection heat transfer problems. The modifications include developing a new computer code which empowers the method to adopt nonlinear equations. A source term expressed in terms of turbulent viscosity gradients is appended to the code to optimize the accuracy for turbulent flow domains. The standard [Formula: see text] transport equations, one of the most applicable two equation turbulent viscosity models, is incorporated, appropriately, into the developed code to bring about both versibility and stability for turbulent natural heat transfer applications. The amenability of the new developed technique is tested by applying the modified method to two conventional turbulent fluid flow test cases. Upon the obtained acceptable results, the modified technique is, next, applied to two conventional natural heat transfer test cases for their turbulent domain. Based on comparing the results of the new technique with those of the available experimental or conventional numerical methods, the proposed method shows good adaptability and accuracy for both the fluid flow and convection heat transfer applications in turbulent domains. The new technique, now, furthers the applicability of the mesh-free local Petrov-Galerkin (MLPG) method to turbulent flow and heat transfer problems and provides much closer results to those of the available experimental or conventional numerical methods.

Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver

2003 ◽  
Vol 125 (1) ◽  
pp. 25-32 ◽  
Author(s):  
W. Ning ◽  
Y. S. Li ◽  
R. G. Wells
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Test Data ◽  
Computational Efficiency ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Flow Solver ◽  
Time Marching

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.

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