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The multihole pressure probes are widely used to determine flow velocity vectors and pressures in the fluid machinery fields due to their robustness, convenience, and economy in flow measurement. Accuracy and fast calibration of a multihole pressure probe is very important. In this article, a multihole pressure probe automatic calibration system is developed. The hardware device mainly consists of computer, motion control equipment and data acquisition (DAQ) equipment, and the software program is developed using the Glanguage based on LabVIEW platform. The fundamental theory and method of multihole pressure probes is reviewed, as well as about how to take into account the compressibility effect of the fluid. The developed system can be easily integrated by engineers in research institutes or industries, without requiring more expertise in programming or multihole probe measurement method. Furthermore, the system is used for a five-hole probe's calibration and measurement, satisfactory results are obtained. 0.5 • is the maximum uncertainty for the flow angles and 1.7% is for the velocity magnitude. The measurement biases being caused by the effect of Reynolds number are investigated. In the Reynolds number range of 1.06 × 10 4 to 4.29 × 10 4 , the measurement biases of velocity vector are presented.

In the paper the effect of negative pre-swirl on the performance and the flow in a centrifugal compressor stage are investigated by both the experimental and numerical methods. The results show that, at a negative pre-swirl, whether the pressure ratio of compressor is increased or not is determined by the contest between the increased energy transfer and flow losses. At a large negative pre-swirl, the flow losses in the IGV and the impeller are increased obviously, which makes the pressure ratio and efficiency reduced dramatically. The further flow analysis show that, the enhanced separation area in the IGV and the depravation of the inlet flow condition of the impeller are the main sources of the losses, while there is almost no influence of the pre-swirl on the diffuser losses. Additionally, at a large negative pre-swirl there exist vortexes shedding from the separation region at impeller leading edge, which causes severe excited force on the impeller leading edge.

This paper studies a novel vaned diffuser with inclined leading edge to reduce the fan noise. The aerodynamic performances and sound pressure level (SPL) of the centrifugal fan with five different diffusers were measured in an anechoic chamber, and the inclined angles of the five diffusers are 45°, 60°, 120°, 135° and 150°, respectively. The flow coefficient of the fan varies from 0.037 to 0.14, the rotational speed ranges from 20000rpm to 35000rpm. The test results show that, by using diffuser vanes with inclined leading edge, the overall noise of the fan is reduced in the experimental conditions, and it has the minimum value at the flow rate coefficient of 0.084. The overall noise reduction of 5.3dB was made with the diffuser leading edge inclined angle of 150°.

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