Caractérisation de l'écoulement d'air dans une maquette d'alternateur hydroélectrique par méthodes numérique et expérimentale
Bibliographic record
Abstract
RESUME Le potentiel d'augmentation de la puissance des alternateurs hydroelectriques existants est un sujet de recherche actuel a l'Institut de Recherche d'Hydro-Quebec (IREQ). Un aspect important de cette etude est l'analyse du refroidissement de l'alternateur par ventilation, qui se base en partie sur les simulations numeriques d'ecoulements fluides (CFD). En raison de la complexite des calculs numeriques, un processus de validation est necessaire et pour cette raison une maquette d'alternateur a l'echelle de 1 : 4 a ete construite a l'IREQ. L'objectif global du present projet de maitrise est d'effectuer des simulations CFD de l'ecoulement de ventilation dans la maquette d'alternateur afin de determiner les caracteristiques principales de l'ecoulement et de les comparer a des mesures experimentales. Une etude numerique preliminaire en 2D et en 3D indique qu'une interface rotor-stator de type mixing plane est plus appropriee pour les conditions de l'ecoulement dans l'entrefer de l'alternateur. En consequence, ce type d'interface est utilisee tout au long de cette etude. Les principales caracteristiques de l'ecoulement et la repartition des debits d'air dans la maquette sont decrites a partir des resultats de simulations 3D. Par ailleurs, la presence et l'orientation du jet principal sortant de l'ouverture du radiateur et du debit de retour vers le rotor sont confirmees qualitativement via des techniques de visualisation de l'ecoulement. Les simulations CFD avant et apres une modification de l'orientation des pales des ventilateurs radiaux et de la forme des capots indiquent que ce changement a entraine une augmentation substantielle des pertes de ventilation, ce qui est en bon accord avec les mesures de pertes sur la maquette. Ceci est causee par l'accroissement du debit genere par les ventilateurs suite a leur modification. Cependant, le debit utile qui atteint les ouvertures de radiateur diminue en raison d'une augmentation majeure des fuites de capots, causee par l'agrandissement du jeu entre le capot et le rotor. Les simulations realisees avec les proprietes de l'air a 25.0 C et a 46.2 C revelent une reduction uniforme des debits massiques d'air dans la maquette lorsque la temperature augmente. Ceci est principalement cause par la diminution de la densite de l'air, puisque les debits volumiques demeurent presque identiques. De plus, la reduction de debit massique occasionne une reduction equivalente des pertes de ventilation.----------ABSTRACT The possibility of increasing the power output of existing generators is currently being investigated at the Hydro-Quebec Research Institute (IREQ). An important part of this study is the analysis of generator ventilation cooling, which is achieved by CFD simulations. Due to the complexity of flow calculations, a validation process is necessary and for this reason a 1:4 scale model of a hydro-generator has been built at IREQ. The objective of the present study is to perform CFD simulations of the ventilation flow in the scale model generator in order to determine the main flow characteristics and compare them to experimental data. Preliminary 2D and 3D simulations suggest that the mixing plane rotor-stator interface type is more appropriate for the flow conditions in the generator air gap. Therefore, this interface type is used throughout the study. The main characteristics of the flow and its distribution are described based on 3D simulations results. Moreover, the presence and orientation of dominant flow features, such as the main jet exiting the radiator opening and the return flow to the rotor, are confirmed qualitatively via flow visualization techniques. Simulations of the flow before and after a slight design change of the radial fans and overhang baffles indicate an increase in windage losses, which is in good agreement with measurements on the scale model. The increase in losses is caused by the increased flow rate through the fans after the design change. However, the useful flow rate that reaches the radiator openings actually decreases, as leakage from the overhang baes is increased. Simulations performed with the properties of air at 25 C and 46.2 C reveal a linear reduction in mass flow rates in the scale model when the temperature is increased. This is mainly caused by the decrease in the density of the air as volume flow rates remain fairly constant. Furthermore, the reduction in mass flow rate is associated with an equivalent reduction in windage losses.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".