Surges in compressor-and-duct systems are said to show several manners of behaviors, called deep surge, mild surge, classic surge, and stagnation stall. The situations of the different appearances, however, have not been made fully clear. This analytical study on a single-stage axial flow fan has found that the behaviors are governed by the following three factors: (1) stage characteristics configuration (post-stall behavior of the stage characteristics), (2) stage working condition of the stage (e.g., valve throttling), and (3) the position relative to the stall-stagnation boundary. (e.g., Greitzer's B parameter).

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Cavitation erosion tests were carried out on glass fiber reinforced plastics (GFRP) for repair. The erosion is evaluated based on the maximum depth of erosion (MaxDE) obtained from the surface profiles. The MaxDE increases with the 0.3th power of exposure time. The rapid erosion rate was not observed after reaching the glass mat layer. Moreover, the accuracy of replica measurement is examined. The average MaxDE of the replica specimen is lower by 120μm than that of the original specimen, but the coefficient of variation (standard deviation/average) is very small as 7.4%.

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A multi-objective optimization technique is applied for the design of a low solidity cascade diffuser in centrifugal blowers. The two kinds of static pressure coefficient are applied for the objective functions, the one is in the design flow condition, and the other is in a small flow condition. The lift coefficient of the LSD blade was analyzed in several flow conditions. The slope of the lift coefficient curve as a function of the flow rate was applied as constraints of optimization process. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. It is found that the optimized shape of the LSD blade shows good improvement of the blade loading in whole flow rate range, and flow separation of the LSD blade is successfully suppressed by the secondary flow effect at small flow rate condition. Operating flow rate range is extended 14% to small flow rate condition without deteriorating the diffuser pressure recovery at design flow condition.

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In liquid-propellant rockets, POGO instability can occur through the fluctuation of propellant supply to the engine, the thrust fluctuation, and structural vibration. For the prediction of this instability, it is required to provide unsteady characteristics of the pump represented as the transfer matrices correlating the upstream and downstream pressure and flow rate fluctuations. In the present study, the flow rate fluctuation is evaluated from the fluctuation of pressure difference at different locations assuming that the fluctuation is caused by the inertia of the flow rate fluctuation. The present paper describes the results of experiments performed in some conditions. For the validation, transfer functions obtained by experiments are compared with Rubin's results. It was shown that the tendencies of unsteady characteristics are related to excitation frequencies, cavitation numbers and flow rate coefficients.

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The “Dual Pressure Radial Turbine” has been studied on relation between the characteristics and the flow downstream of the HPT and LPT intersection. Based on the comparison between measurement and CFD on velocity and temperature distributions at downstream of the turbine wheel and based on the analysis of the flow downstream of the intersection using CFD, the relation between the flows of HPT and LPT downstream of the intersection is well estimated. It was found that the imaginary radius of HPT and LPT boundary is affected by the balance of those pressure ratios as well as the flows downstream of the intersection flow almost independently. And HPT and LPT flow rates are affected by the imaginary radius of the boundary between HPT and LPT as well as indirectly by the turbine wheel rotational speed. And the turbine characteristics is able to be well estimated using one dimensional performance estimation tool comprising relation between imaginary radius of HPT and LPT at turbine wheel throat and balance of those pressure ratios.

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