Mitsubishi Heavy Industries (Italy)

Abstract To mitigate the erosion issue in steam turbines, it is crucial to suppress the formation of coarse droplets spreading from the trailing edge upstream as well as from the shroud wall. The droplet size will be highly dependent on the trailing edge shapes and wettability, while the quantitative measurement under well-controlled flow conditions is limited, and hence, the theoretical prediction model including the effect of controlled trailing edge has yet established. We have developed an experimental setup, in which the shearing gas is fully developed and the liquid sheet on a wall is in uniform thickness along the transversal direction, allowing for the quantitative and general discussion from the wavy liquid sheets to the fragmenting droplet in a consistent manner. Here, we perform the visualization experiment on an acrylic pipe flow at the trailing edge thickness of 0.5 mm, 1.0 mm, and 2.0 mm, and the tapered angle of 10 deg and 30 deg, and at the wettability of hydrophobic condition. We successfully quantify the extending ligament from the trailing edge and the following droplet statistics using a high-speed imaging technique. By implementing the hydrophobic tapered wall, we clearly find that the circumferential wavelength between two ligaments on the trailing edge becomes short by minimizing the accumulated liquid on the edge stimulated by the Rayleigh-Taylor instability, leading to the formation of small droplets and suppression of coarse droplets. We finally formulate a theoretical model to predict the mean/maximum droplet sizes and distributions with considering the shape of trailing edge and wettability, which is validated by the present experimental results.

Abstract Pneumatic probes are widely used to measure flow properties in turbomachinery, including downstream of rotor blade rows. This paper investigates the aerodynamic interaction between a row of compressor blades and a downstream cylindrical probe, using unsteady, three-dimensional simulations. The study demonstrates the probe influence on rotor performance as a function of probe size and rotor proximity, identifies the physical mechanisms driving rotor-probe interactions, and quantifies the resulting probe measurement errors. A probe downstream of a rotor row causes each blade passage to deviate periodically from the steady, axi-symmetric characteristic, as they pass the probe. In this study, the largest rotor disturbance occurs for a probe of diameter 14% blade chord, located 30% axial chord downstream of the rotor trailing edges. The flow coefficient, ϕ, moving with the rotor passage, varies between −10.4% and +5.5% compared to a case with no downstream probe. The total-to-total pressure rise coefficient, ѱtt, increases by up to 7.7%. These rotor-probe interaction effects are driven by the unsteady response of the rotor passage to the potential field of the probe. In the stationary frame, measurement error occurs because the probe is exposed to the disturbed flow field and this leads to maximum average errors of Δϕ = −15.1% and Δѱtt = 8%. The magnitude of the rotor disturbance decreases as the probe is moved away from the trailing edge of the blades and when probe size is reduced. Reducing probe size close to the blade row reduces the rotor disturbance more than moving a large probe downstream. Including a stator blade row downstream of the probe does not have a large impact on the sensitivity to probe size and proximity and the physical mechanisms are unchanged.

In hot water simulating LWR coolants, the fatigue life of stainless steel depends strongly on temperature and strain rate and decreases with decreasing strain rate. On the other hand, it has been experimentally confirmed that a certain strain range on the compression side does not contribute to the reduction of fatigue life and has been reported as the insensitive strain region. Although the evaluation method of environmental effects is prescribed in the JSME Standard Environmental Fatigue Evaluation Method, it is expected that the amount of reduction in fatigue life can be predicted more rationally by considering this region.

Flexible endoscopic surgery in the field of internal medicine requires advanced technique. The master - slave robot supports insertion of a flexible endoscope. The robot allows forward and backward movement and swiveling of the endoscope, as well as vertical and lateral bending of the endoscope tip. Bidirectional haptic feedback function is realized by bilateral master-slave control. The motions and forces between master and slave device are visualized by the control system, which would be available to quantify of the operation of the endoscope and useful as a teaching tool. In this report, the visualizations of the force and motion are presented, and the potential of the system is discussed.

In typical pressurized water reactor (PWR), in case that one steam generator (SG) cannot be credited for the primary cooldown, it is necessary to homogenize primary coolant temperature among loops using at least one reactor coolant pump (RCP) for the plant cooldown. If the natural circulation condition is established due to unavailability of all the RCPs, the continuous cooldown using intact SGs causes to disturb the smooth depressurization because it leads to void generation in the top of the non-cooldown SG tube where the high temperature coolant is remained. For this purpose, W.Sakuma, et al.[1] suggested the outline of asymmetric cooldown procedure without any RCPs restart. Since the suggested procedure is based on only one secondary condition (SG dry-out) of non-cooldown SG, and hence the impact of difference of the secondary condition should be investigated. In this paper, the sensitivity analyses were performed to confirm the impact on the asymmetric cooldown procedure, and consequently, it was confirmed that the coolable range used in the procedure was expanded if the water inventory exists in non-cooldown SG. Therefore it was concluded that the coolable range which was defined with the SG dry-out condition in non-cooldown SG can be conservatively applied for the operating procedure.

Liquid inlet behavior to a heat surface in micro-bubble emission boiling (MEB) was investigated by flow measurement using particle image velocimetry (PIV). Subcooled pool boiling experiments under atmospheric pressure were carried out using a heat surface with a diameter of 10 mm. An upper end of a heater block made of copper was used as the heat surface. Working fluid was the deionized water and the subcooling was varied from 40 K to 70 K. Three K-type thermocouples were installed in the copper block to measure the temperature gradient, and the heat flux and wall superheat were estimated from these temperature data to make a boiling curve. The flow visualization around the heat surface was carried out using a high-speed video camera and a light sheet. The microbubbles generated in the MEB were used as tracer particles and the velocity field was obtained by PIV analysis of the acquired image sequence. As a result, the higher heat fluxes than the critical heat flux could be obtained in the MEB region. In addition, the distribution characteristics of the velocity in MEB region were studied using the PIV results and the location of the stagnation point in the velocity fields was discussed.