Search results

The research in this paper helps to understand the difference between the Eulerian method and the Lagrangian method in describing the performance of Pelton turbine buckets, so as to improve the design level and design efficiency of the runner.

This paper used DualSPHysics to calculate the unsteady flow of the Pelton turbine runner bucket and compared it with the mesh-based method to explore the difference between mesh-based and particle-based methods in torque curves, jet flow patterns and pressure characteristics.

It is noted that the particle-based method is challenging to compare with the mesh-based method concerning accuracy. In addition to better describing the free water film, the particle method also captures many droplets near the water film, but it cannot well describe the negative pressure region on the bucket back and the resulting jet interference after cutting off the jet. Compared with the mesh-based method, the pressure measurement points obtained by the particle-based method generally have shorter periods and violent fluctuations, and the pressure value of some points is underestimated.

This paper helped to calculate the unsteady characteristics of the Pelton turbine by Fluent, CFX and DualSPHysics; exploration jet flow pattern differences between the mesh and meshfree methods; prediction of the flow interference between the bucket back and the jet and the pressure curve of SPH usually has a shorter period and violent fluctuations.

THE structural design of the BAC One‐Eleven generally follows closely that of the Vickcrs Vanguard and the VC10†—involving the use of a considerable number of integrally‐machined components. As a short‐haul aircraft the average time per flight of the BAC One‐Eleven is expected to be of the order of 45 min. during which period full cabin pressure differential will be attained, speeds of the order of its design cruising speeds will be achieved and the undercarriage and flaps will be operated for take‐off and landing. Based on current estimations this involves a design aim of a minimum crack‐free life of 40,000 flights, landings and take‐offs —a much more severe requirement than that for the long‐range subsonic jets. Critical areas of the aircraft (undercarriage, flaps, tailplane and cabin pressure skins) are thus designed on fatigue considerations related principally to the number of flights made. The accent has therefore been placed on building a rugged structure which is easy to maintain and has a long service life. Small amounts of additional weight, properly disposed, can effect large improvements in the service life, particularly necessary on a short‐haul aircraft, and although weight saving is always of prime importance it must be balanced by other factors—especially in the primary structure.

The purpose of this study is to address the issue that the traditional V-shaped ball valve profile shape is limiting the flow control characteristics in a series structure and to optimize the design profile by proposing an open-hole profile.

This paper proposes a Gaussian process regression surrogate model based on the genetic algorithm optimization of swarm intelligence, combined with the Expected Improvement point addition criterion, to optimize and correct the design profile. The flow regulation performance of the optimized V-shaped regulating ball valve is verified through a combination of numerical simulation and experiment.

The results demonstrate that the optimized V-shaped regulating ball valve has higher flow regulation accuracy and a more stable flow regulation process. After optimization, the flow characteristic curve of the spool is closer to the ideal equal percentage characteristic. The simulation results of the flow field are consistent with the experimental results.

The proposed method significantly reduces the optimization time, has higher efficiency and solves the problem that traditional optimization methods struggle with, which is ensuring optimal flow regulation performance. Compared to the traditional trial-and-error optimization method, the proposed method is more effective. The feasibility of the method is supported by experimental results.

This study aims to investigate the suitability of a multi-step prototyping strategy for producing pneumatic rotary vane actuators (RVAs) for the development of lightweight robots and actuation systems.

RVAs typically have cast aluminum housings and injection-molded seals that consist of hard thermoplastic cores and soft elastomeric overmolds. Using a combination of additive manufacturing (AM), computer numerical control (CNC) machining and elastomer molding, a conventionally manufactured standard RVA was replicated. The standard housing design was modified, and polymeric replicas were obtained by selective laser sintering (SLS) or PolyJet (PJ) printing and subsequent CNC milling. Using laser-sintered molds, actuator seals were replicated by overmolding laser-sintered polyamide cores with silicone (SIL) and polyurethane (PU) elastomers. The replica RVAs were subjected to a series of leakage, friction and durability experiments.

The AM-based prototyping strategy described is suitable for producing functional and reliable RVAs for research and product development. In a representative durability experiment, the RVAs in this study endured between 40,000 and 1,000,000 load cycles. Frictional torques were around 0.5 Nm, which is 10% of the theoretical torque at 6 bar and comparable to that of the standard RVA. Models and parameters are provided for describing the velocity-dependent frictional torque. Leakage experiments at 10,000 load cycles and 6 bar differential pressure showed that PJ housings exhibit lower leakage values (6.8 L/min) than laser-sintered housings (15.2 L/min), and PU seals exhibit lower values (8.0 l/min) than SIL seals (14.0 L/min). Combining PU seals with PJ housings led to an initial leakage of 0.4 L/min, which increased to only 1.2 L/min after 10,000 load cycles. Overall, the PU material used was more difficult to process but also more abrasion- and tear-resistant than the SIL elastomer.

More work is needed to understand individual cause–effect relationships between specific design features and system behavior.

To date, pneumatic RVAs have been manufactured by large-scale production technologies. The absence of suitable prototyping strategies has limited the available range to fixed sizes and has thus complicated the use of RVAs in research and product development. This paper proves that functional pneumatic RVAs can be produced by using more accessible manufacturing technologies and provides the tools for prototyping of application-specific RVAs.

This study investigates the aerodynamics of the airflow over low-rise houses subjected to turbulent cyclonic winds along the South-eastern peninsular India, routinely afflicted by tropical cyclones. The purpose of this paper is to demonstrate how the power of modern computational fluid dynamics (CFD) and its engineering application accentuate decision-making at the planning stage of house designing in vulnerable areas.

The Weather Research and Forecasting (WRF) model was used for first simulating the landfall of cyclone Hudhud, a real storm, and its effect in extant and new house designs. Results from the WRF model were utilized to configure further CFD simulations of airflow around house designs. The analyses yielded deep insights, often non-intuitive, into airflow patterns around these houses with disparate roof forms indicating new possibilities in redesigning houses along Indian coastal areas.

This study shows that storm-induced high TKE values warranted a fuller CFD-based study. The second major finding showed that for a 90° angle of attack, arguably the most destructive attack angle, a pitched roof (with a pitch angle of 10°) worked best – this is about half the recommended angle sourced from earlier empirical estimates dating back to the British Raj period. There is a thin layer of padded air cushion shielding the roof's vulnerable surface from the storm's most energetic parts.

The originality of this research lies in its discourse to systematically resolve the TKE distribution of a cyclone impacting a standalone house. In particular, the study presents a lucid demonstration of all the probable scenarios connecting cyclonic stresses with a roof response, inferred from a careful combination of results garnered from cyclonic storm modelling coupled with CFD analysis. Additionally, the paper also shows a graphic visual representation of the forces induced on different roof designs, presented as a checklist for the first time. This should serve as a ready reckoner for civic authorities involved in disaster management over cyclone-ravaged areas.

The air data system of an aircraft includes, amongst other items, the airspeed indicator, altimeter and machmeter all of which derive their readings from measurement of air pressures. The instruments are designed on the assumption that they will be fed with pressures from the undisturbed free‐stream in which the aircraft is flying; this is not generally the case. In flight the aircraft disturbs the air mass and in doing so causes a pressure field around itself which produces the forces necessary for lift and control. The pressure sensors which detect the airstream pressures may be located within the aircraft pressure field and the pressures transmitted to the instruments may not correspond to the free‐stream pressures; if this is so then the instrument indications will be in error.

ON August 10, 1949, the Avro C102 jet transport, now better known as the Jet‐liner, made its first flight.

The sensitivity of orifice plate metering to poorly conditioned and swirling flows are subjects of concerns to flow meter users and manufacturers. The distortions caused by pipe fittings and pipe installations upstream of the orifice plate are major sources of this type of non‐standard flows. These distortions will alter the accuracy of metering up to an unacceptable degree.Design/methodology/approach – The design of orifice plate meters that are independent of the initial flow conditions of the upstream is a major object of flow metering. Either using a long straight pipe or a flow conditioner upstream of an orifice plate usually achieves this goal. The effect of cone swirler flow conditioner for both standard and non‐standard flow conditions has been carried out in the experimental rig. The measuring of mass flow rate under different conditions and different Reynolds numbers were used to establish a change in discharge coefficient relative to a standard one.Findings – The experimental results using the cone swirler flow conditioner showed that the combination of an orifice plate and cone swirler flow conditioner is broadly insensitive to upstream disturbances. The results clearly show that this flow conditioner can attenuate the effect of both swirling and asymmetric flows on metering to an acceptable level.Originality/value – Previous work on the orifice plate has shown that the concept has promise. The results of using a combination of a cone swirler and orifice plate for non‐standard flow conditions including swirling flow and asymmetric flow show this package can preserve the accuracy of metering up to the level required in the standards, providing that a new discharge coefficient is used for the combined swirler and orifice plate.

Reports on an automated apparatus and test procedure to determine the convective and diffusive gas and vapor transport properties of small pieces of woven and nonwoven fabrics, membranes, and foams. The apparatus allows measurement of these properties in the very small quantities typical of material development programs, where the largest sample available may only be 1‐10cm² in area. The convection/diffusion test method is useful for determining the gas flow resistance property and water vapor diffusion properties from a single experimental run. This eliminates the need for two separate tests, which is the usual procedure. The apparatus may also be used to perform separate tests for the diffusion property or the air permeability property, which may have some advantages when materials exhibit strongly concentration‐dependent transport properties. The convection/diffusion test method is well‐suited for rapid screening and comparison of the properties of a large number of materials with widely‐varying transport properties.

In an aircraft having a sustaining rotor incorporating a hub and a blade, the latter being connected with the hub by means of a flapping pivot, a pitch change mounting for the blade, and mechanism for controlling the blade pitch including cooperating worm and worm wheel elements, the latter of which is connected with the blade and moves therewith in the pitch change and flapping senses, the worm element being mounted to move with the blade in the flapping sense, and actuating means for the worm constructed and arranged to effect pitch change movement of the blade in predetermined relation and in response to flapping movement of the blade.