Full-scale Condition Research Articles

Application of periodic boundaries in freight train aerodynamic performance simulations

The length of long marshalling freight train and the non-streamline shape of wagon lead to more difficulties in simulating the aerodynamic performances. To simplify the simulation process of long freight trains and conserve computational resources, periodic boundary conditions and the improved delayed detached eddy simulation based on the shear-stress transport k-ω turbulence model were employed in this study. To better analyze the aerodynamic coefficients of full-scale, nine-boxcar, and periodic-boundary simulations, the pressure and viscous drag were analyzed separately. Aerodynamic coefficients and surrounding flows of freight trains obtained from periodic-boundary, full-scale, and nine-boxcar simulation methods are compared in detail to investigate the feasibility of the periodic-boundary condition for numerical simulations of long freight trains. The dependence of the computational mesh was verified in the STAR-CCM + software. Simulation results show that the deviations of drag coefficient under the periodic-boundary and full-scale conditions is 7.6 %, and that of the nine-boxcar and full-scale conditions is 5.7 %. Based on the simulated flow fields, the variations of pressure and velocity fields around the test wagon are similar in these three simulations. Besides, the distribution of detached vortices around the test wagon are similar in simulations. Moreover, locomotive has no significant influence on aerodynamic performances of the fifth wagon in the simulation of one locomotive with nine boxcars. In this study, the computing time of full-scale condition is 58 hours, and that of periodic-boundary condition is one-tenth of full-scale condition. Consequently, it can be concluded that the periodic boundary is a potential choice in aerodynamic simulations of a long freight train, better balancing the simulation accuracy and efficiency.

Experimental Study on Failure Model of Tailing Dam Overtopping under Heavy Rainfall

Abstract Unusual rainfall is the primary cause of the failure of the tailing dams, and overtopping is the most representative model of the tailing dam failure. The upstream tailing dam was selected as the research object to study the whole process of breach extension and the overtopping dam-failure mechanism under the full-scale rainfall condition. The results showed that the significant size grading phenomenon in the front, middle, and end of the tailing pond was obvious due to the flow separation effect, and its average particle diameter was D50. At different moments of rainfall, the height of the infiltration line at different positions of the dam body was different; at the rainfall of 3600 s, the height of the infiltration line lagged behind the height of the tailing pond, and this phenomenon from the tail of pond to the outside of the dam slope became more obvious. After the rainfall of 3600 s, the height of the infiltration line lagging behind the water level in the pond basically disappeared, and the rate of infiltration line rise kept pace with the rate of water level. The process of overtopping dam-failure experienced dam overtopping (gully erosion), formation of a multistepped small “scarp,” breach rapid expansion, formation of large “scarp,” and burst (fan-shaped formation). The width and depth of the breach showed a positive correlation, and the widening rate of the breach was 3 to 8 times of the deepening rate, especially in the middle of the dam break, widening behavior occupied the dominant factor. The shape of the dam body after failure was parabolic, and the dam body had obvious elevation changes. These results provide the theoretical guidance and engineering application value for improving the theory and early warning model of the upstream tailing dam.

Propeller tip vortex mitigation by roughness application

In this study, the application of surface roughness on model and full scale marine propellers in order to mitigate tip vortex cavitation is evaluated. To model the turbulence, SST k−ω model along with a curvature correction is employed to simulate the flow on an appropriate grid resolution for tip vortex propagation, at least 32 cells per vortex diameter according to our previous guidelines. The effect of roughness is modelled by modified wall functions. The analysis focuses on two types of vortices appearing on marine propellers: tip vortices developing in lower advance ratio numbers and leading edge tip vortices developing in higher advance ratio numbers. It is shown that as the origin and formation of these two types of vortices differ, different roughness patterns are needed to mitigate them with respect to performance degradation of propeller performance. Our findings clarify that the combination of having roughness on the blade tip and a limited area on the leading edge is the optimum roughness pattern where a reasonable balance between tip vortex cavitation mitigation and performance degradation can be achieved. This pattern in model scale condition leads to an average TVC mitigation of 37% with an average performance degradation of 1.8% while in full scale condition an average TVC mitigation of 22% and performance degradation of 1.4% are obtained.

Power Consumption Analysis of Pulse Jet Filtration System Assisted with Pre-charger using Polyester Conductive Media

Energy consumption is a vital aspect for any industry considering the cost-effective aspect. The current study embodies the power consumption during filtration of conductive filters at different dust pre-charging levels on laboratory-based pulse jet tubular set up assisted with pre-charger. Three types of polyester conductive non-woven filter materials, viz. PTFE-coated media, stainless steel fibre blended with PET media and stainless steel scrim media, have been characterized at three different charge levels, viz. 4 kV, 8 kV, 12 kV, and without charge. The outcome revealed that there has been a significant drop in power consumption with the rise in pre-charge level. Energy utilization results have further been compared with full-scale bag house condition by calculating the energy consumed for 50 bags. The results showed that among all the materials taken for investigation the performance of PTFE-coated media is the best and role of material is most significant towards the energy consumption by the filtration system. Overall energy consumption decreases with rise in pre-charging level. It is observed that percentage contribution of energy utilized for fan has been much higher for full-scale bag house as compared to tubular-based set-up. However, in case of energy consumed by the compressor, the difference in percentage contribution is relatively less and for energy utilized due to charge, not much variation in contribution can be noted.

A Study on Onset of Liquid Entrainment in Low Pressure Depressurization System of Advanced Passive Pressurized Water Reactors

The low-pressure depressurization system (LPDS) of advanced passive pressurized water reactors (PWRs) is designed to provide depressurization of the reactor coolant system during a small break loss-of-coolant accident (LOCA). The liquid entrainment to the LPDS is important for the safety case of the advanced passive PWRs due to the significant increase of the pressure loss and the depressurization rate versus mass loss characteristics. The existing experimental researches on the liquid entrainment at LPDS have been reviewed, and the intermittent entrainment mechanism and the continuous entrainment mechanism are identified. The intermittent entrainment is closely related to the flow regime transition from the horizontal stratified flow to the intermittent flow in the hot leg where the LPDS port is located. The horizontal stratification model previously developed for the FULL SPECTRUM LOCA evaluation model has been assessed against the entrainment onset data in the available LPDS entrainment experiments, i.e., the ATLATS air–water experiment, the ADETEL air–water and steam–water experiments, and the full-scale FATE air–water experiment. The prediction matches the measure data well especially in the full-scale FATE experiments. The comparison results also confirmed the scalability of the horizontal stratification model with the applicability of the horizontal stratification criterion to the full-scale PWR condition. The uncertainty factors that impact the depressurization system entrainment onset are discussed for the future improvements. This work provides the direction to accurately model the entrainment onset for LPDS and improve the simulation of LOCA in advanced passive PWRs.

Purification of leachate from sludge treatment beds by subsurface flow constructed wetlands: effects of plants and hydraulic retention time.

Sludge treatment beds (STBs) have been used widely in many countries due to low energy consumption, low operating and maintenance costs, and better environmental compatibility. Penetration, evaporation, and transpiration are the main processes for sludge dewatering in STBs. However, the leachate quality from STBs usually cannot meet discharge limits. Moreover, such leachate has very low COD/N ratio, which makes it difficult to treat. In the present study, two subsurface flow (SSF) constructed wetlands (CWs) were investigated for the treatment of leachate from STBs under three different hydraulic retention time (HRT) (3days, 4days, 6days), aiming for evaluating the effects of plants and HRT on treatment performance, as well as the potential of SSF CWs to treat sludge leachate with low COD/N ration. The results showed that plants play an important role in leachate treatment. The best treatment performance was achieved with HRT of 4days. In this condition, the mean removal efficiencies of COD (chemical oxygen demand), NH4+-N, TN (total nitrogen), and TP (total phosphorus) in the planted and the unplanted CWs were 61.6% (unplanted - 3.7%), 76.6% (unplanted 43.5%), 70% (unplanted 41%), and 65.6% (unplanted 6%), respectively. Heavy metal concentrations were below the Chinese integrated wastewater discharge standard during the experimental period in the planted CW, and the removal efficiencies in the planted CW system were higher than in the unplanted CW system. In all, planted SSF CWs can be an effective approach in removing leachate from sludge treatment beds. Furthermore, considering to temperature and seasonal variation, the leachate from STBs needs to be further studied in pilot- and full-scale condition.

A Study on the Optimum Propeller at Full Scale Condition, Part2: Effect of the Reynolds Number on the Optimum Diameter and Optimum Efficiency of Propellers with Laminar Flow Blade Section

A Study on the Optimum Propeller at Full Scale Condition, Part2: Effect of the Reynolds Number on the Optimum Diameter and Optimum Efficiency of Propellers with Laminar Flow Blade Section

A Study on the Optimum Propeller at Full Scale Condition, Part 1: Effect of the Reynolds Number on the Open Water Characteristics of Propellers with Laminar Flow Blade Section

The Reynolds number effect on the open water characteristics of a propeller with a laminar type blade section has been studied by CFD and compared with the experiment. At a Reynolds number of model tests, the boundary layer flow over the blade is mostly laminar, while it becomes almost fully turbulent at a full scale Reynolds number. Because of this fact, the Reynolds number effect is very complicated. When the Reynolds number is increased from the model scale to the full scale, the open water efficiency first increases, and then start to decrease because of the transition of the boundary layer. As the boundary layer becomes almost fully turbulent, the open water efficiency again increases with increasing Reynolds number. It has been also shown that the transition Reynolds number of a propeller with laminar type blade section is higher than that of a propeller with MAU type blade section.

Optical fiber sensing technology for full-scale condition monitoring of pavement layers

Because of the rapidly increased traffic weight and severe service environment (i.e. temperature and humidity) in recent years, a great number of newly paved pavement structures suffer from premature distresses with different scales and degrees, which significantly affects the structural performance. To reflect the deformation characteristics and identify the random damage of long-span pavements, it is particularly important to develop smart optical fiber sensing technology to monitor the in-situ behaviors, which can provide useful suggestions for the repair and maintenance. Considering the evolution of random damage from microscopic to macroscopic, it can be noted that sensors with fixed gauge lengths cannot perceive the whole-process information of structural damage, and local sensors are not able to satisfy the requirement of full-scale condition monitoring of pavement structures. To overcome those deficiencies, various gauge-length based optical fiber/fiber Bragg grating (OF/FBG) sensing techniques have been developed. Laboratory tests on an 8-m-long cement stabilised gravel base layer embedded with the proposed technique have been implemented. The secondly updated sensors have been further applied to an urban asphalt pavement for on-site testing. Research results prove the measurement efficiency, effectiveness and feasibility of the proposed packaging measure and the selected gauge length, and validates the good performance of the OF/FBG sensing techniques for full-scale condition monitoring of asphalt pavements.

Wind-induced responses of a tall chimney by aeroelastic wind tunnel test using a continuous model

This study aims to investigate wind-induced responses of a 300 m high chimney by using wind tunnel tests on an aeroelastic model. Due to the fact that it is unrealistic to simulate wind flow with a high Reynolds number as high as 1 × 108 for a chimney model in a wind tunnel, roughness paper strips were attached to the model surface to artificially achieve effective high Reynolds number flow in the full-scale condition. An optimal thickness of the roughness paper strips was determined via a series of pressure measurement tests on a rigid model of the chimney. To examine wind-induced responses of the chimney, a continuous aeroelastic chimney model was manufactured with the DEVCON plastic steel liquid. After roughening the aeroelastic model by the paper strips with the optimal thickness, a series of wind tunnel tests were conducted on the model to directly acquire the structural responses, for three different oncoming wind flow conditions. Results show that the response of the roughened model is much smaller than that for the model without roughness element, indicating that ignoring the Reynolds number effect will overestimate the response. The across-wind acceleration response of the chimney is more considerable than that in the along-wind direction, when the reduced wind velocity Vr is larger than 4. In addition, the across-wind acceleration response is usually larger in the more turbulent wind flow, although the lock-in phenomenon is more evident in uniform flow.

Wind effects on rough-walled and smooth-walled large cooling towers

Adding vertical ribs is recognized as a useful practice for reducing wind effects on cooling towers. However, ribs are rarely used on cooling towers in China since Chinese Codes are insufficient to support the design of rough-walled cooling towers, and an “understanding” hampers the use of ribs, which thinks that increased surface roughness has limited effects on the maximum internal forces that control the structural design. To this end, wind tunnel model tests in both uniform flow field with negligible free-stream turbulence and atmospheric boundary layer (ABL) turbulent flow field are carried out in this article to meticulously study and quantify the surface roughness effects on both static and dynamic wind loads for the purpose of improving Chinese Codes first. Subsequently, a further step is taken to obtain wind effects on a full-scale large cooling tower at a high Re, which are employed to validate the results obtained in the wind tunnel. Finally, the veracity of the model test results is discussed by investigating the Reynolds number (Re) effects on them. It has been proved that the model test results for atmospheric boundary layer flow field are all obtained in the range of Re-independence and the conclusions drawn from model tests and full-scale measurements basically agree, so most model test results presented in this article can be directly applied to the full-scale condition without corrections.

Methodology for Wind/Wave Basin Testing of Floating Offshore Wind Turbines

Scale-model wave basin testing is often employed in the development and validation of large-scale offshore vessels and structures by the oil and gas, military, and marine industries. A basin-model test requires less time, resources, and risk than a full-scale test, while providing real and accurate data for numerical simulator validation. As the development of floating wind turbine technology progresses in order to capture the vast deep-water wind energy resource, it is clear that model testing will be essential for the economical and efficient advancement of this technology. However, the scale model testing of floating wind turbines requires accurate simulation of the wind and wave environments, structural flexibility, and wind turbine aerodynamics and thus requires a comprehensive scaling methodology. This paper presents a unified methodology for Froude scale model testing of floating wind turbines under combined wind and wave loading. First, an overview of the scaling relationships employed for the environment, floater, and wind turbine are presented. Afterward, a discussion is presented concerning suggested methods for manufacturing a high-quality, low-turbulence Froude scale wind environment in a wave basin to facilitate simultaneous application of wind and waves to the model. Subsequently, the difficulties of scaling the highly Reynolds number–dependent wind turbine aerodynamics is presented in addition to methods for tailoring the turbine and wind characteristics to best emulate the full-scale condition. Lastly, the scaling methodology is demonstrated using results from 1/50th-scale floating wind turbine testing performed at the Maritime Research Institute Netherlands (MARIN) Offshore Basin. The model test campaign investigated the response of the 126 -m rotor diameter National Renewable Energy Lab (NREL) horizontal axis wind turbine atop three floating platforms: a tension-leg platform, a spar-buoy, and a semisubmersible. The results highlight the methodology's strengths and weaknesses for simulating full-scale global response of floating wind turbine systems.

Model and full scale CFD analysis of propeller boss cap fins (PBCF)

Computational fluid dynamics (CFD) analyses of propeller boss cap fins (PBCF) were carried out for two different propellers at model and full scale Reynolds numbers with two different inflow conditions. Computations corresponding to the reverse propeller open test (POT) experiment were confirmed to be in a good agreement with the measurement. The results of computations at different conditions have shown that increased Reynolds number and presence of hull wake both positively influence the effects of PBCF. Due to the combined effect of the Reynolds number and the wake, the gain in the propeller efficiency at the full scale condition was found to be significantly larger than that at the model test condition. The detailed investigation of the results suggested that the fin drag becomes smaller and the reduction of the boss drag becomes larger at the full scale condition. However, the predicted gain is still smaller than the values reported in the sea trial and logbook analysis. The remaining gap may be attributed to the difference in the estimated and actual wake distribution or to other factors such as interactions with hull and rudder, surface roughness, unsteadiness and hub vortex cavitation.

Towards the Design of Synthetic-jet Actuators for Full-scale Flight Conditions

Despite the proven capability of synthetic-jet actuators in delaying boundary-layer separation in laboratory experiments, a capability that allows the geometry and operating conditions of these devices to be designed and selected for maximum flow-control effectiveness in full-scale flight conditions has yet to be developed. In this two-part paper, the key results obtained during a 3-year research programme aiming at establishing such a capability based on a better understanding of the fluid mechanics of synthetic jets and an improved modelling capacity are reported. In Part 1 of this paper, the experimental studies of the behaviour of synthetic jets in both quiescent flow and a boundary layer are described. The work has led to an improved understanding of the dimensionless parameters that determine the formation and development of vortex rollup and how the strength of rollup can be enhanced by optimizing the geometry and operating condition. Based on the study of the nature of vortical structures produced as the result of the interaction with a boundary layer and their impact in the near-wall region where flow control is desired, the conditions for producing effective vortical structures for delaying flow separation were established. The finding from this work forms the basis of a number of criteria used for designing synthetic jet actuators for full-scale flight condition to be presented in Part 2.

Analysis of Wave Energy Converting Characteristics of Wave Power Generating System Installed in Breakwater (1st Report, Estimation and Evaluation for Characteristics of Turbine-Geserator in Real Sea Field Test)

The wave power generating system using the Wells turbine is installed in the breakwater in Sakata port, Japan, and consists of the air chamber, turbine, generator and safety devices. The purposes of this paper are to reveal the characteristics of each component in this system with the experimental data in the real sea, and to evaluate the accuracy of numerical models used in the simulation. The performance of Wells turbine is examined in detail for the unsteady and full-scale condition, comparing the data of the 1/4 scale model with the steady full-scale one. It is found that the performance of the system for the wave can be evaluated accurately with the steady characteristics of the turbine, in the condition that stall does not happen on the rotor. The angle of attack for the stall depends on the wave characteristics such as the magnitude of unsteadiness, requiring many trials to get the stall angle used by the calculations.

Simplified Rapid Assessment Approach to Road Network Management

A simplified approach, using limited network-specific data and the recently developed World Bank HDM Manager, was applied to the highway network of Peru to provide interim guidelines on appropriate standards and policies to be implemented, pending the results of a more elaborate study involving a full-scale road condition and traffic inventory. The design of the methodology is described, as is its application to define the best maintenance strategies for paved and unpaved road networks. The order of magnitude of the level of expenditures required is determined, and a tentative prioritization scheme for road activities is developed.

Simplified Rapid Assessment Approach to Road Network Management

A simplified approach, using limited network-specific data and the recently developed World Bank HDM Manager, was applied to the highway network of Peru to provide interim guidelines on appropriate standards and policies to be implemented, pending the results of a more elaborate study involving a full-scale road condition and traffic inventory. The design of the methodology is described, as is its application to define the best maintenance strategies for paved and unpaved road networks. The order of magnitude of the level of expenditures required is determined, and a tentative prioritization scheme for road activities is developed.

Full-scale nuclear faulted condition test

Primary Heat Transport (PHT) pumps play a major role in the safe shut-down of a nuclear reactor following a Loss-of-Coolant Accident. They have to operate under very harsh conditions for at least 17 minutes. Sulzer Bingham Pumps Inc. has qualified the PHT pumps for the new reactors at Wolsong in South Korea by means of full-scale testing.