Comparative Investigation of Three Highly Loaded LP Turbine Airfoils: Part II — Measured Profile and Secondary Losses at Off-Design Incidence
Bibliographic record
Abstract
The first part of the paper compared the midspan aerodynamics and the secondary flows for a family of three low-pressure turbine (LPT) airfoils at design conditions. However, since a typical engine spends much of its time operating at off-design conditions, good tolerance of LPT airfoils to off-design operation is desired. The sensitivity of the midspan flow to Reynolds number was examined for the three airfoils in a paper presented at the 2006 ASME-IGTI Turbo-Expo. The present paper examines the performance of the airfoils for three values of incidence: −5, 0, and +5 degrees relative to design. Both the profile and secondary losses are considered. Detailed loading distributions measured at midspan are used to explain the behaviour of the profile flow and the resulting change in losses as the incidence was varied. The secondary flow behaviour is determined as at the design incidence from detailed flowfield measurements made downstream of the trailing edge using a seven-hole pressure probe. The results show that in terms of profile losses the baseline airfoil (which has a Zweifel coefficient Z = 1.08) and the front-loaded one with Z = 1.37 have comparable losses over the range of incidences examined. However, the aft-loaded airfoil with Z = 1.37 had noticeably higher profile losses than the other two. On the other hand, the front-loaded one has higher secondary losses than its aft-loaded counterpart at all conditions examined. This obviously poses a dilemma for the designer in terms of the choice of loading distribution. It was also noted that the distribution of loading seems to affect the secondary losses more than the loading level (Zweifel coefficient). An interaction of the secondary flows with the suction side separation bubble might be responsible in part for this finding.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".