Compressor Airfoil Tip Dihedral for Stall Margin
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Solution Overview
Problem
Conventional compressor rotor blades in gas turbine engines experience flow blockage and reduced stall margin due to tip vortex formation, leading to efficiency losses and potential stall, which existing casing treatments fail to fully address.
Innovation Solution
The compressor rotor blade features a specific airfoil design with dihedral and sweep profiles at the leading and trailing edges, which redirect weak airflow inward and delay the propagation of flow across the rotor passage, reducing tip vortex formation and improving stall margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If tip clearance is reduced to minimize tip leakage flow, then tip vortex formation is reduced, but manufacturing complexity and risk of contact with casing increase
Solution Approach 1:
The patent applies local quality by implementing dihedral angles specifically at the leading and trailing edges of the airfoil tip region, while maintaining conventional geometry in other areas. This localized modification addresses tip vortex formation without requiring complete redesign of the entire airfoil structure, thus balancing performance improvement with manufacturing feasibility.
Solution Approach 2:
The patent introduces dihedral angles in the spanwise direction (z-axis) to control tip leakage flow, adding a third dimension to the traditionally two-dimensional airfoil design. This dimensional enhancement allows flow control without reducing tip clearance, resolving the contradiction between minimizing tip vortices and maintaining simple geometry.
2Reliability
If casing treatments such as circumferential grooves are used to reduce tip leakage flow, then stall margin improves, but compressor efficiency decreases
Solution Approach 1:
The patent extracts the flow control function from the casing treatment (grooves) and relocates it to the airfoil geometry itself through dihedral angles. This removes the need for efficiency-penalty-inducing casing treatments while maintaining stall margin improvement, as the dihedral angles directly control tip leakage flow at its source without creating additional losses.
Solution Approach 2:
The dihedral angles act as an intermediary structure that modifies tip leakage flow behavior without requiring casing modifications. This intermediate geometric feature redirects flow inward before it can form harmful vortices, achieving stall margin improvement through flow management rather than flow restriction, thus preserving efficiency.
3Ease of manufacture
If tip clearance is increased to improve manufacturing tolerance, then manufacturing ease increases, but tip vortex formation and blockage increase
Solution Approach 1:
The patent applies preliminary action by using the dihedral angles to redirect tip leakage flow inward before it can propagate across the rotor passage and cause blockage. This pre-emptive flow control occurs at the leading and trailing edges where tip leakage originates, preventing downstream blockage issues even when larger tip clearances are used for manufacturing tolerance.
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 enhances the compressor's stall margin and throttle range by over 5% with no loss in design point efficiency, effectively mitigating blockage and increasing airfoil tolerance to throttling.
Implementation Method 1
The airfoil has an inner span region and an outer span region and the trailing edge has a dihedral profile such that the trailing edge dihedral angle decreases in at least a portion of the inner span region and the outer span region
Implementation Method 2
The compressor rotor blades carry a lift on the body of the airfoil that manifests itself as a higher static pressure on the pressure surface of the airfoil and a lower static pressure on the suction surface of the airfoil. The pressure difference between pressure side and suction side of the airfoil drives flow through the tip gap of the compressor rotor.
Implementation Method 3
This tip flow can roll up into a vortex, which tends to collect on the pressure side surface of the circumferentially adjacent blade, leading to high levels of loss and blockage in the compressor tip region.
Data Source
AI summary
An airfoil for a compressor is described. The airfoil has a root, an airfoil tip, a leading edge, a trailing edge, airfoil pressure and suction sides extending between the leading edge and the trailing edge. The airfoil has an inner span region and an outer span region and the trailing edge has a dihedral profile such that the trailing edge dihedral angle decreases in at least a portion of the inner span region and the outer span region.