The PS (Pressure Side) and SS (Suction Side) of a blade can be distinguished based on airflow characteristics, cross-sectional shape, mold and structural details, and wear patterns, as follows:
Airflow Characteristics: The PS is the pressure side-the windward side during rotation-which directly withstands airflow impact and experiences higher surface pressure. The SS is the suction side, where airflow accelerates during rotation, resulting in lower pressure. Consider an aircraft wing: the upper surface forms a low-pressure zone due to airflow acceleration, corresponding to the SS; the lower surface forms a high-pressure zone due to airflow obstruction, corresponding to the PS. This principle applies equally to wind turbine blades and turbine blades.
Cross-sectional Shape: Observing the blade's cross-section, the SS typically exhibits more pronounced convexity or curvature, whereas the PS is relatively flatter. For instance, the SS of a water turbine blade has greater curvature to accelerate water flow, while the PS is more streamlined to minimize drag. This shape difference arises because the SS requires optimized airflow separation, whereas the PS requires balanced pressure distribution.
Mold and Structure: During blade manufacturing, the PS corresponds to the female mold (concave), while the SS corresponds to the male mold (convex). Structurally, the trailing edge of the SS is usually thicker than that of the PS, resulting in greater weight. Regarding internal web connections, the PS auxiliary spar bonds tightly with the outer skin and tends to separate cleanly from the shell upon fracture, whereas the SS trailing-edge auxiliary spar may snap at specific locations (e.g., the 6-meter mark). These characteristics are particularly evident in composite blades.
Wear Patterns: After prolonged operation, wear on the PS-subjected to high-pressure airflow-often manifests as surface material spalling or indentation marks. The SS, being a low-pressure zone, is prone to cavitation or marks from particle impact. On wind turbine blades, for example, the PS commonly shows pits caused by sand and dust impact, while the SS may exhibit streaky wear patterns caused by rain erosion.
In practical applications, a combination of these methods is used for assessment. One might, for instance, make a preliminary distinction based on cross-sectional shape, verify this through airflow characteristics, and finally confirm the identification by examining wear patterns. Understanding the differences between the PS and SS is crucial for optimizing blade design and conducting failure analysis.
