Centrifugal compressor blade geometry: If the outlet relative flow angle from the rotor exceeds 90°, the impeller blades are termed “forward-curved.”

Difficulty: Easy

Correct Answer: forward curved

Explanation:


Introduction / Context:
Impeller blade exit geometry strongly affects compressor head, efficiency, and stability. Classifying blades as backward-, radial-, or forward-curved depends on the outlet angle relative to the tangent.



Given Data / Assumptions:

  • Outlet (blade) angle measured from the tangent at the impeller tip.
  • Typical classifications: backward-curved (β2 < 90°), radial (β2 = 90°), forward-curved (β2 > 90°).


Concept / Approach:
Forward-curved blades turn the flow more in the direction of impeller rotation, increasing theoretical head but often at the cost of efficiency and surge margin compared to backward-curved designs used in modern compressors.



Step-by-Step Solution:

Given β2 > 90° from tangent → classification is forward-curved.Backward-curved corresponds to β2 < 90°; radial is exactly 90°.Therefore, “forward-curved” is correct.


Verification / Alternative check:
Velocity triangles demonstrate that forward-curved blades yield larger whirl at exit, consistent with higher theoretical head.



Why Other Options Are Wrong:
They contradict the standard angle-based definitions.



Common Pitfalls:
Confusing blade metal angle definition with flow angles referenced to absolute vs. relative frames; here the conventional metal/relative angle convention is implied.



Final Answer:
forward curved

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