| Micro turbine engine (MTE) has advantages of light weight, large power and high energy density. It can be used in the fields of both military and civil. MTE has been paid close attention to and developed very fast these years. The scale of MTE decreases obviously and it makes the working Reynolds number very low and tip clearance larger, which block the performance improvement of MTE. But there is little research results published on these aspects, so in this paper some research on low Reynolds number and tip clearance which influences the blade performance of MTE was done. The main works are described as follows:(1) The new non-contact pressure measurement technology based on pressure sensitive paint (PSP) was used in the millimeter scale flow field. Some subsystems of PSP were developed independently, including excitation light system based on array light emitting diode (LED), microscope system, spraying and heattreatment instruments. Calibration system of PSP was designed and typical paint calibration was done using this system. One integrated PSP system for millimeter scale flow field was established. The research of low Reynolds number and tip clearance of millimeter scale micro turbine cascade on the pressure of suction surface was finished using this PSP measurement system.(2) The flow character of millimeter scale micro turbine cascade in low Reynolds number was studied using numerical and experimental methods. The numerical results show the formation, development and interaction of the main second flow in micro cascade passage. Besides, the total pressure loss in the center of passage vortex in low Reynolds number of micro cascade is higher than it of tranditional cascade, and the influence of passage vortex on the pitch direction flow grows when it flows downstream. Compared to tranditional cascade, the average total pressure loss of S3 surface after 10% axial chord of micro cascade grows. Especially after 60% axial chord, the average total pressure loss grows quickly, far larger than it of tranditional one.(3) The influence of blade tip clearance on micro cascade flow was investigated. The results show that the exit flow in tip clearance near suction side has mixed in the fore part of blade tip. However, in the rear part of blade tip, the exit flow near suction side hasn't mixed completely. The velocity here is not the same. As the tip clearance increases, the mass of leakage flow grows proportionally and blade circumferential load decreases. When inlet Mach number is 0.1, if the tip clearance increases 1%, the mass of leakage flow grows by 17.5% and circumferential load decreases by 2%, respectively. The PSP results show the pressure on blade suction surface in the case of 5% tip clearance (which means the ratio of tip clearance and blade span is 5%) differs from the cases of 10% and 15% tip clearance. In the rear part of suction surface and near blade tip, there is high pressure area in the case of 5% tip clearance. Oppositely, low pressure exists in the same position in the cases of 10% and 15% tip clearance.(4) A kind of method for reducing tip leakage was presented using backward vortex generators (BVGs). In order to reduce leakage flow and turbine loss, the gas is guided to flow into BVGs from pressure side and flow out of balde tip at high speed in the inverse-direction of leakage flow, based on the pressure difference between pressre surface and blade tip. The key factors of BVG which affect the leakage flow was studied including the diameter ratio of inflow and outflow holes, position of BVGs, density of arrangement and outflow angle. The results show that increasing the diameter ratio of inflow and outflow holes, arranging BVGs in rear part of blade tip, decreasing outflow angle suitably can increase mass of BVGs and reduce leakage flow, consequently increase blade circumferential load.(5) Experimental study was done to verify the effect of BVGs on reducing leakage flow. After improving the working process of Micro Electrical Discharge Machining (M-EDM) and designing a whole electrode of comb shape, the BVGs whose holes diameters of 0.1 and 0.2 millimeter were made successfully. The experimental result shows that compared to the case of no BVGs, the blade circumferential load improves obviously in the case of BVGs. As inlet Mach number grows, the influence of BVGs on blade circumferential load increases. When inlet Mach number is 0.18, the blade circumferential load improves by 21.6% in the case of BVGs, comparing with the case of no BVGs. This method of reducing leakage flow using BVGs provides a positive and reserve technology for improving MTE performance in the future.
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