Compressor Blade Tip Gap Gradient for Vortex Control
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Solution Overview
Problem
Conventional methods to suppress clearance flow in compressors, such as using eave-shaped tip clearance reduction plates, complicate the blade structure and may not lead to high efficiency, as they can facilitate the accumulation of low-energy fluid and the formation of vortices, resulting in losses.
Innovation Solution
A compressor design where the gap between the blade tip and the casing is smaller at the leading edge but larger downstream, allowing high-energy clearance flow to be supplied to the suction surface, reducing the accumulation of low-energy fluid and suppressing the breakdown of the blade tip leakage vortex, thereby reducing reverse flow and losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the gap between the blade tip and casing is uniformly small throughout the blade length, then clearance flow loss is reduced, but boundary layer accumulation is facilitated and vortex breakdown occurs
Solution Approach 1:
The gap size is made non-uniform along the blade span, with different gap sizes in different regions. Specifically, the gap is smaller in the root region and larger in the tip region, allowing each region to have optimal gap characteristics for its local flow conditions, thereby preventing vortex breakdown while controlling clearance flow loss.
Solution Approach 2:
The gap size varies continuously along the blade span rather than being constant, creating a dynamic gradient in clearance flow characteristics. This gradual variation allows the flow to adapt smoothly, preventing abrupt changes that would cause vortex breakdown while still controlling overall clearance flow loss.
2Object-generated harmful factors
If the gap between the blade tip and casing is increased downstream, then boundary layer accumulation is suppressed, but clearance flow increases
Solution Approach 1:
The gap expansion is applied locally in the downstream region where boundary layer accumulation occurs, rather than uniformly throughout. This targeted approach suppresses boundary layer accumulation in the critical region while minimizing the overall increase in clearance flow and associated losses.
Solution Approach 2:
The gap is increased only in the partial range downstream of the leading edge where it is most needed to prevent boundary layer accumulation and vortex breakdown, rather than increasing it uniformly along the entire blade span. This partial action achieves the necessary effect with minimal penalty in clearance flow loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses the increase in losses attributed to the blade tip leakage vortex, leading to a more efficient compressor operation by reducing the reverse flow range and occurrence, resulting in a high-efficiency centrifugal compressor.
Implementation Method 1
A boundary layer developed on the suction surface of the blade (a low-energy fluid) is accumulated in the vicinity of the tip of the blade due to the action of a centrifugal force
Implementation Method 2
a reverse flow may be generated, especially on a high-pressure operating point, as the accumulated low-energy fluid is overpowered by a pressure increase (adverse pressure gradient)
Data Source
AI summary
A compressor comprises: a rotor including a hub and a blade provided on an outer peripheral surface of the hub; and a casing surrounding the rotor so as to face a tip of the blade across a gap. Provided that the gap between the tip of the blade and the casing has a size t0 at a leading edge of the blade, the gap between the tip of the blade and the casing has a size larger than t0 in at least a partial range downstream of the leading edge in an axial direction of the rotor.