Turbomachine Airfoil Surface Roughness for Laminar Separation Control
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Solution Overview
Problem
Gas turbine engine fan blades experience unfavorable aerodynamic phenomena, such as local flow separation and unsteady aerodynamic loadings, leading to undesirable laminar separation and increased pressure loss when interacting with shocks, which reduces engine efficiency.
Innovation Solution
The method involves forming an airfoil with a majority of the suction and pressure side surfaces finished to promote laminar flow, and leaving a portion unfinished to introduce turbulence upstream of the shock, thereby reducing laminar separation and pressure loss. This is achieved by sanding or treating the surfaces and strategically leaving areas unfinished to create a second roughness that transitions the flow from laminar to turbulent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the entire surface is finished to promote laminar flow, then laminar flow efficiency is improved, but laminar separation occurs at shocks causing increased pressure loss
Solution Approach 1:
The patent applies different surface qualities to different regions of the airfoil: a finished smooth surface on the majority of the suction and pressure sides to promote laminar flow, and an unfinished rough surface at specific locations (such as the leading edge or upstream regions) to trigger early transition to turbulent flow. This local differentiation allows the flow to transition before encountering shocks, preventing laminar separation and reducing pressure loss while maintaining overall flow efficiency.
2Reliability
If the surface is left unfinished to introduce turbulence, then laminar separation is reduced, but manufacturing precision is compromised
Solution Approach 1:
The patent specifies that only certain portions of the airfoil surface need to be left unfinished (such as the leading edge region or specific chordwise locations upstream of the shock), while the majority of the surface (particularly regions downstream and critical for overall aerodynamic performance) maintains a finished smooth surface. This selective approach achieves the turbulence-triggering benefit while preserving manufacturing precision where it matters most for aerodynamic efficiency.
3Loss of energy
If the majority of the surface is finished, then laminar flow is maintained, but additional machining steps and cost increase
Solution Approach 1:
The patent reduces manufacturing complexity by specifying that only the majority portion of the surface (as opposed to the entire surface) requires finishing operations. Specific regions are intentionally left unfinished to serve as turbulence triggers, eliminating the need for additional complex machining steps or surface treatments on those areas. This approach maintains pressure loss benefits while simplifying the manufacturing process and reducing costs.
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 approach reduces laminar separation and associated pressure drops, enhancing the efficiency of the turbomachine by introducing turbulence at the right locations, thus improving engine performance without the need for additional machining steps or increased complexity and cost.
Implementation Method 1
the boundary layer will transition from a laminar or approximately laminar flow at an upstream portion of the fan blade
Implementation Method 2
to a turbulent flow at a downstream portion of the fan blade
Implementation Method 3
laminar separation when interacting with a shock
Data Source
AI summary
A method of controlling a transition from a laminar flow to a turbulent flow for an airfoil of a turbomachine includes forming an airfoil. The airfoil defines a span extending between a root and a tip and a chord extending between a leading edge and a trailing edge. The airfoil includes a suction side surface and a pressure side surface, opposite the suction side surface, each extending between the leading edge, the trailing edge, the root, and the tip. The method also includes finishing a majority of the suction and pressure side surfaces in order to form a finished surface. The finished surface defines a first roughness. The method additionally includes leaving at least a portion of the suction side surface and/or pressure side surface unfinished in order to form an unfinished surface. Furthermore, the unfinished surface defines a second roughness greater than the first roughness.