This paper deals with an application of computational fluid dynamics (CFD) to partial admission stages in a steam turbine. The calculation of partial admission stages requires unsteady analysis and full circle modeling. Therefore, quasi-3-dimensional (Q-3D) analysis of the mean radius is conducted to reduce computational load. First, an experiment using the air turbine is carried out. The result is in good agreement with the result of CFD analysis under the same conditions as the experiment, and the application of the Q-3D method to partial admission stage analysis is validated. Using this method, 2-stage analysis of partial admission is conducted. The influence of the circumferential position of the admitted arc on stage efficiency is discussed. The efficiency difference is related to the windage loss caused by pressure distribution in the circumferential direction. It is found that there is an optimum circumferential position of the admitted arc from the point of view of turbine efficiency.
Eight hundred MWe class PWR turbine-generators operated smoothly and continuously at sudden load reduction, from full load to house load, maintaining NPSH of the feedwater booster pumps through transition even though the available NPSH never exceeded zero. NPSH of the pump at 151.3 degrees C, at which the available NPSH was minimal during transition, was evaluated as a slightly negative value, in spite of a positive value at room temperature, applying both the Ruggeri-Moore method extended to the negative area on condition of gas venting out of the system, using data of both room temperature and 95 degrees C of a model pump facility, and another restriction by gas presence at the impeller inlet. The above evaluated high temperature NPSH demonstrated successful operation of the units equipped with a low static suction head yielding zero available NPSH during transition, resulting in alteration of the design criteria of the feedwater system and thereby contributing to possible cost reduction.
We study the motion of a pair of bubbles rising in the vertical line, at intermediate Reynolds number (5 < Re < 150), both numerically and experimentally. It has been predicted, by analytical and numerical studies, that there exists a stable equilibrium distance between a pair of bubbles due to the balance between the potential repulsive and viscous atractive forces. However, no experimental results have ever confirmed the existence of an equilibrium distance between bubbles rising in a vertical line. Most experimental results indicated that a pair of bubbles collided. We solve this paradox and answer the question: "Is there an equilibrium distance?" by presenting both experimental evidence of an existence of the equilibrium distance and the detailed numerical results of a deforming-spatial-domain/space-time finite element method, taking bubble surface deformation effects into account.
The correlation of liquid-solid contact fraction in transition boiling was derived by focusing on the dimensionless wall temperature θ=(Tw-TCHF)/(TMHF-TCHF). The following correlation was obtained from experimental results for water, R-113 and LN2: Γ=1.000-0.9120θ-0.1343θ2, where qtb=qCHFΓ+qMHF(1-Γ). In the present model, considering a pseudo-liquid solid contact right after the detachment of a bubble from a liquid-vapor interface, transient heat conduction was analyzed in it three-dimensionally. Liquid-solid contact time and area were determined by the present correlation of the fractions of liquid-solid contact: τcontact=0.3Γt, Awet=15 × 15 × Γa, Γt=Γa=Γ0.5={1.000-0.9120θ-0.1343θ2}0.5. The heat transfer during the wet period was estimated using qwet=f(ΔTsat0.8). The prediction by the present model was in agreement with the present experimental data for water. Furthermore, a simulation of the rewetting was performed; the experimental results of cooling curves during the rewetting were well reproduced by the transient heat conduction model using the present correlation of transition boiling heat transfer and the present liquid-solid contact model.
Post-dryout heat transfer analysis was carried out considering droplet behavior by using the Lagrangian simulation method. Post-dryout heat transfer is an important heat transfer mechanism in many industrial appliances. Especially in recent Japanese BWR licensing, the standard for assessing the integrity of fuel that has experienced boiling transition is being examined. Although post-dryout heat transfer analysis is important when predicting wall temperature, it is difficult to accurately predict the heat transfer coefficient in the post-dryout regime because of the many heat transfer paths and non-equilibrium status between droplet and vapor. Recently, an analysis model that deals with many heat transfer paths including droplet direct contact heat transfer was developed and its results showed good agreement with experimental results. The model also showed that heat transfer by droplet could not be neglected in the low mass flux condition. However, the model deals with droplet deposition behavior by experimental droplet deposition correlation, so it cannot estimate the effect of droplet flow on turbulent flow field and heat transfer. Therefore, in this study we deal with many droplets separately by using the Lagrangian simulation method and hence estimate the effect of droplet flow on the turbulent flow field. We analyzed post-dryout experimental results and found that they correlated well with the analysis results.
We evaluated the performance of the newly developed atmospheric mesoscale model, WRF, for the simulation of urban-scale weather in the Tokyo metropolitan area during a high photochemical Oxidant event. The simulation clearly shows that WRF represents the spatial distribution of surface air temperature during the daytime, although the model temperature is lower than the observations in the late afternoon to evening in the urban area. The wind system can be well reproduced in WRF. Simulated convergence zone moves toward the inland areas located to the northwest of the coastal area during the three hours. These results are consistent with the observations of temperature and Photochemical Oxidant, indicating that WRF has enough potential to predict the ongoing Oxidant concentration.
The purpose of this study was investigating the noise emission, flow-style, fan's performance regarding to cross-fan with three different rotor-skew angle (RSA) rotors. The special flow visualization setups for both vertical and parallel investigation of smoke slice were used to overcome the blind sight of a Laser-Doppler or a particle-tracking velocimeter, and the three-dimensional flow differences were confirmed with streamline images. The experimental results indicated that RSA-5, which is a rotor with a nearly a pitch skew within blade's two end shrouds, has a lower sound emission and little pressure drops relative to that of no skew angle case, RSA-0. RSA-10, two pitches twisting case, also has a better acoustics quietness than that of RSA-0, but it excited undesired noise in a high frequency components around 2 - 4 kHz. In this work, for a compromise between flow and acoustics performances, RSA-5 shows the most suitable design for cross-flow fan rotor.
In order to obtain the data on turbulent mixing rate between triangle tight lattice subchannels, which will be adopted as the next generation BWR fuel rod bundle, adiabatic experiments were conducted for single- and two-phase flows under hydrodynamic equilibrium flow conditions. The gas and liquid mixing rates measured for two-phase flows were found to be affected by the void fraction and/or flow regime, as reported in our previous study on a simulated square lattice rod bundle channel having hydraulic diameters of about four times larger than the present tight lattice channel. Comparing the present mixing rate data with those for the square lattice channel and a triangle one in other institution, we found that the mixing rate was considerably smaller in the present channel than the other ones, i.e., a channel size effect.
An efficient and scalable Balancing Domain Decomposition (BDD) type preconditioner for large scale linear systems arising from 3-dimensional heat transfer problems is presented. The new method improves parallel scalability of BDD by employing an incomplete balancing technique to approximate a coarse space problem and a diagonal scaling to precondition the local fine space problems instead of the Neumann-Neumann preconditioner. It may increase the number of iterations but reduces the computation costs of the precondition process for each iteration. Consequently, total computation time and required memory are expected to be reduced. The convergence estimates may also be independent of the number of subdomains. We have implemented this algorithm on the parallel processors and have succeeded in solving some ill-conditioned large scale heat transfer problems.
With increase in traffic volume and change in travel related characteristics, vehicular emissions and energy consumption have increased significantly since two decades in India. Current models are not capable of estimating vehicular emissions accurately due to inadequate representation of real-world driving. The focus of this paper is to understand the level of Indian Driving cycle (IDC) in representing the real-world driving and to assess the impact of real-world driving on vehicular emissions. The study has revealed that IDC does not represent the real-world driving. Irrespective of road classes, about 30% of time is spent below 20 km/hr and the speed too exceeds IDC’s maximum limit of 42 km/hr. Emissions are estimated for different driving patterns using International Vehicle Emission (IVE) model. Emission rates vary significantly from one class of road to another and the largest effect is on local streets.
In this study, passive control methods for attaching horizontal and vertical fences on the lower surface of the cylinder near a moving ground were adopted to enhance the aerodynamic characteristics with the changes in gap height. The horizontal fences increase the domain where the lower separated shear layer is interfered by viscous effect on the ground. In a moving ground, this viscous effect is only slightly observed due to elimination of shear layer induced by relative ground motion. However, vertical fences diminish the momentum provision intended to roll up to wake region by blocking the gap flow, thereby suppressing the vortex shedding irrespective of ground conditions. Therefore, the horizontal fences in a moving ground have the advantage of reducing averaged lift and drag though cannot suppress the vortex-induced oscillation. Even though vertical fences have an advantage of suppressing vortex shedding past a cylinder, the existence of the vertical fences themselves causes the averaged drag to increase above the critical gap height due to the existence of vertical fences.
In this paper, we present a digital holographic particle image velocimetry (DHPIV) technique with a spatio-temporal derivative method for velocity measurement in 3D space and the results of evaluating on its measurement accuracy. In this technique, hologram patterns are observed as digital images using an electronic camera, such as CCD or CMOS, and image reconstruction is carried out on a personal computer. Since an in-line observation system is utilized in conventional digital holography, a numerically reconstructed image is considerably enlarged in the depth direction and its depth resolution is extremely low; hence, the measurement accuracy in the depth direction is inaccurate in a digital holographic measurement. To overcome this difficulty, we apply a spatio-temporal derivative method to this technique for the detection of particle displacement along the z-axis. In a numerical simulation, measurement accuracy is evaluated for a multi particle model and a cubic cavity flow model. Furthermore, we examine the effect of noise on displacement measurement accuracy for numerically constructed noisy hologram patterns.
The flow through the single-plate lock-up clutch in an automotive torque converter with a 250-mm nominal diameter was numerically investigated using a CFD code. The flow was computed under various clearances between the lock-up piston and the torque converter cover. The stable location of the lock-up piston was determined so that the thrust acting on it became zero. The computation results showed that the fluid flowed outwards in the narrow channel between the lock-up clutch facing and the converter cover, whereas the flow reversed inwards near the lock-up piston surface upstream and downstream of the narrow channel in most cases. Along the outer surface of the axial flow channel near the exit, the flow also reversed far upstream of the channel. The computation results well predicted the stable position of the lock-up piston. It is noteworthy that the sharp increase in clearance in the coupling range can be clearly captured with this method.
A plane submerged turbulent water jet discharged parallel to the offset bottom wall in a channel with a finite water depth was investigated experimentally. Depending on the depth of the nozzle and its height from the bottom, the jet deflects towards either of two boundaries, the free surface or the solid wall. Detailed data on the velocity field measured by the Particle Image Velocimetry (PIV) method are obtained to examine the effect of the opposite boundary on the deflecting jet and the difference in the jet development between the deflection to the free boundary and that to the solid boundary. The mean velocity profiles and the spread rates of the jet are compared with those of a conventional plane free jet by applying a curved coordinate system along the jet centerline.
Reduction in NOx and soot in light and medium duty diesel engines and meeting the U.S. emission standards is an important challenge. This paper shows how injection rate shaping should be performed to reduce NOx while engine performance and soot formation remain almost constant. Effects of intercooler with and without rate shaping on NOx reduction will be investigated. Results indicated that the rate shaping and pilot/split injection was an effective technique to reduce NOx at some operating condition. Combined effects of intercooler and rate shaping have shown a reduction of NOx by 50% for some operating conditions. At idle condition, a split injection was found to be a good solution for NOx reduction. A combustion simulation computer program was used in this analysis for six different operating conditions.
The total space and weight of the feedwater heaters in a nuclear power plant (NPP) can be reduced by replacing low-pressure feedwater heaters with high-efficiency steam injectors (SIs). The SI works as a direct heat exchanger between feedwater from condensers and steam extracted from turbines. It can attain pressures higher than the supplied steam pressure. The maintenance cost is lower than that of the current feedwater heater because of its simplified system without movable parts. In this paper, we explain the observed mechanisms of the SI experimentally and the analysis of the computational fluid dynamics (CFD). We then describe mainly the analysis of the heat balance and plant efficiency of the innovative-simplified NPP, which adapted to the boiling water reactor (BWR) with the high-efficiency SI. The plant efficiencies of this innovative-simplified BWR with SI are compared with those of a 1 106 MWe-class BWR. The SI model is adopted in the heat balance simulator as a simplified model. The results show that the plant efficiencies of the innovate-simplified BWR with SI are almost equal to those of the original BWR. They show that the plant efficiency would be slightly higher if the low-pressure steam, which is extracted from the low-pressure turbine, is used because the first-stage of the SI uses very low pressure.
Heat pumps using CO(2) as a natural refrigerant have been developed and are expected to contribute to energy saving in hot water supply. In residential applications. CO(2) heat pumps are used in combination with hot water storage tanks. The objective of this series of papers is to analyze the overall performance of a hot water supply system composed of a CO(2) heat pump and a hot water storage tank by numerical simulation. In the 1st report. a simulation model of a CO(2) heat pump is created based on thermodynamic equations and measured data for an existing CO(2) heat pump. In addition, the performance of a CO(2) heat pump is clarified in relation to the air temperature as well as the inlet and Outlet water temperatures.
Flow around a living tree was investigated as basic research of a windbreak forest. A type of conifer, which is named "goldcrest, " was used as the test piece in a wind tunnel experiment. The drag coefficient of the living tree was measured in the range of a mean flow velocity of 5∼15m/s. The drag coefficient of the living tree was less than that of a two-dimensional circular cylinder. Because flow passes through the tree's crown which has the permeability of branches and leaves, the drag coefficient was decreased as the flow velocity was increased. Moreover, the flexibility is that the bole of a living tree also plays an important role in drag reduction, bending itself so as to decrease the projected area. In the wake behind the living tree, reverse flow was found at further downstream region than the case of a circular cylinder.
The paper gives some personal observations on various aspects of enhanced condensation heat transfer. The topics discussed are external condensation (horizontal low-finned tubes and wire-wrapped tubes), internal condensation (microfin tubes and microchannels) and Marangoni condensation of binary mixtures.
A wavelet multi-resolution technique is applied to analyze the three vorticity components obtained simultaneously using an eight-wire probe in the far wake of a circular cylinder at a Reynolds number of 6 000. Using this technique, the vorticity is decomposed into a number of orthogonal wavelet components based on different central frequencies, which correspond to the scales of turbulent structures. The vortical structure of each wavelet component is examined in terms of vorticity variance. The present result shows a relatively large contribution to the longitudinal vorticity variance from the large-scale structures than both to the transverse and to the, spanwise vorticity components. The dominant contributions to the vorticity variances are from the intermediate and relatively small-scale structures.
