Abstract
Helicopters often operate in dusty sites, ingesting huge amounts of contaminants during landing, take-off, hover-taxi, and ground operations. In specific locations, the downwash of the rotor may spread soil particles from the ground into the environment and, once ingested by the engine, may stick to the compressor airfoils. In the present work, the Allison 250 C18 engine’s multistage axial-flow compressor is employed to study the fouling rate on rotor blades and stator vanes from both numerical and experimental standpoints. The compressor is operated in a typical ground-idle operation, in terms of the rotational regime and contaminant concentration, in laboratory-controlled conditions. The mass of deposits is collected from the airfoil surfaces at the end of the test and compared to that estimated through the numerical model. The experimental test shows that the airfoils collect almost 1.6% of the engine’s total mass ingested during a ground-idle operation. The capability of numerical methods to predict the fouling rate on the rotating and stationary airfoils of a multistage compressor is tested through the implementation of literature based deposition models. Sticking models show a good agreement in terms of the relative results; nevertheless, an overestimation of the deposited mass predicted is observed.
Highlights
Helicopter employment in civil and military operations is widespread and often essential for critical tasks such as search and rescue missions, firefighting, or medical evacuations
According to the procedure reported in Section 2.1.2, the mass collected on each filter is divided for the respective number of airfoils of each row
The trend of the mass deposited on the single airfoil is in line with the results reported in [36,37,38]
Summary
Helicopter employment in civil and military operations is widespread and often essential for critical tasks such as search and rescue missions, firefighting, or medical evacuations. Lands characterized by dusty floor conditions or poorly aggregated soil (such as arid locations and deserts) are considered the worst scenarios for helicopter operations to be successfully carried out [1]. In such locations, dust cloud raising events (named brownouts) are extremely likely and potentially harmful for the helicopter’s operability. The compressor deterioration caused by the material removal (erosion) was documented for the first time during the U.S Army’s rotorcraft operations in Southeast Asia (during the 1960s) [4] and has been mitigated through the implementation of cyclone separator systems (i.e., Donaldson strata-tubeTM) capable of avoiding the entering of coarser particle into the engine flow path [5]. The macroscopic effects of micro-sized solid particle adhesion are the decrease in the engine shaft power at constant turbine inlet temperature, the increase in the specific fuel consumption at constant power, the decrease in the engine surge margin, and the reduced transient stability of the engine [7]
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