Compressor rotor blade tip winglet technology has been confirmed to be a passive flow control method that is effective in increasing the operating stability of compressors. As revealed by extensive research, the structural parameters of tip winglets are capable of affecting their stability expansion effect, whereas their mechanism and influence law of the compressor stage remains unclear. In this study, the effect exerted by the chordwise distribution of tip winglets on the stability of a high-load compressor stage was investigated. As indicated by the result of this study, the tip winglet exhibiting a proper widest position and an adequate chordwise length can effectively increase the stall margin. To be specific, the widest position was located at 25% chord, and the stall margin was increased by up to 25.39%. A winglet exhibiting a chordwise length of 50% achieved the stability expansion ability equivalent to winglet with a full chordwise length, which can be increased by 22.58%. The tip leakage flow turned out to be weakened as the axial momentum was increased, and the circumferential momentum of the flow that arose from the tip winglet was reduced. The result of this study also suggested that tip winglets can play a certain role in combing the inflow of the stator, such that the blockage of the stator channel can be reduced.

Due to the increasingly stringent emission regulations and the growing concern about energy hazard, natural gas (NG) has emerged as an alternative fuel with abundant reserves, low cost, high combustion performance and low pollutant emissions. In this study, a NG high pressure direct injection (HPDI) model is embedded in a Cummins ISX marine medium-speed four-stroke natural gas-diesel dual fuel (NGDDF) engine model. The strategies with different injection overlap of NG and pilot diesel oil (PDO) and different exhaust gas recirculation (EGR) were investigated, the following conclusions are drawn. At the same EGR rate, the injection start point of NG (SOI_NG) has impact on the compression end pressure to some extent, while the injection end point of the pilot diesel oil (EOI_PDO) makes little difference to the compression end pressure. With the increase of SOI_NG, the maximum pressure (P_Max) rises gradually. When the SOI_NG remains unchanged, the longer the pilot diesel oil (PDO) injection lasts, the higher the P_Max. The heat release rate (HRR) of HPDI engine has two peaks. The first one decreases as the EGR rate rises, while the other is inversely proportional only to the EGR rate. As the EGR rate increasing, the position of the second peak of HRR is increasingly delayed, irrespective of the injection strategy used. At the same EGR rate, the overlapping injection strategy has only a limited impact on the maximum in-cylinder temperature (about 42 K) and the soot emission (about 0.003 g/kwh). The first stage of nitrogen oxides (NO_X) generation is closely related to the EGR rate. The higher the EGR rate, the longer the interval between the first and second stage of NO_X generation. Though both reasonable injection overlap and delay of EOI_PDO are conducive to reduce pollutant emissions, it remains necessary to delay the position of the overlap angle as much as possible, and the emission reduction effect of injection overlap will diminish as the EGR rate increasing. Either the injection overlap formed by delaying EOI_PDO or advancing SOI_NG has a positive impact on indicated mean effective pressure (IMEP). The introduction of EGR will increase indicated specific fuel consumption (ISFC) of the engine, while the injection overlap strategy can be used to reduce it by 5.35 g/kwh. In order to meet the Tier III standard, the combination of injection strategy B and 18% EGR can be considered as the most effective solution for soot, ISFC and IMEP factors.

To investigate the influence of tip winglets on the tip leakage flow in a compressor cascade with different incidences, the experimental measurement combined with numerical simulation are used to study the conventional cascade and cascades with three different pressure surface tip winglets at five incidences of −6°, −3°, 0°, +3° and +6°. The results indicate that three different tip winglets at five incidences all restrain the occurrence of leakage flow, delay the mixing of leakage flow and the mainstream, change the formation path of leakage vortex and weaken its intensity, reduce the flow loss and improve the uniformity of flow field. The sensitivity of the flow field to variable incidences is reduced. The optimization degree of the flow field is proportional to the width of the blade tip winglet. The improvements are more obvious at positive angles. When the incidence reaches +6°, the flow loss is reduced by 12.4%.

Nowadays, high aerodynamic load has made blade separation an issue for compact axial compressors under high-altitude low-Reynolds-number conditions. In this study, herringbone grooves inspired by bird feathers were applied to suppress the suction side separation and reduce loss. To study the effect of bio-inspired herringbone grooves on the aerodynamic performance of compressor cascades, a high subsonic compressor cascade was taken as the research object. Under the conditions of different Reynolds numbers, the effects of herringbone grooves of different depths on the flow separation were numerically studied. The research results show that at a high-Reynolds-number condition (Re = 5.6 × 10⁵), the sawtooth-shaped wake induced by herringbone grooves increases the turbulent mixing loss near the suction surface, and the blade performance deteriorates. At a low-Reynolds-number condition (Re = 1.3 × 10⁵), the span-wise secondary flow and micro-vortex structure induced by the herringbone grooves effectively suppress the laminar separation on the suction surface of the blade, and there is an optimal depth for the herringbone grooves that reduces the profile loss by 8.33% and increases the static pressure ratio by 0.55%. The selection principle of the optimal groove depth with the Re is discussed based on the research results under six low-Reynolds-number conditions.