Windage Research Articles

Initiation of epithelial wound closure by an active instability at the purse string.

The ability of biological systems to withstand and recover from various disruptions, such as spontaneous genetic mutations and environmental damage, largely relies on intricate feedback mechanisms. We theoretically study a mechanical response of an epithelial tissue facing damage in the form of a circular wound. Our model describes a feedback loop between the generation of active forces in the actomyosin and tissue mechanics, described by the vertex model. While the exact dynamics of wound closure may be influenced by several biophysical mechanisms that interplay in a non-trivial way, our findings suggest that the closure may initiate as an active instability, triggered by a reduced myosin-turnover rate at the wound's perimeter. We explore the interplay between myosin dynamics and the elastic properties of the tissue, elucidating their collective role in determining wound's loss of stability, leading to the initiation of the closure process.

Flow mechanism and back gap windage loss of a sCO2 radial inflow turbine with impeller scallops

The Internal flow mechanisms and windage loss in impeller back gap of a supercritical carbon dioxide (sCO2) radial inflow turbine with scallops are comprehensively investigated in this paper. The study emphasizes the effects of scallop depth and leakage outlet pressure. The results indicate that scallop structures lead to a degradation in overall turbine performance. Under design conditions, a turbine with a scallop depth ratio of 0.5 exhibits a 3.7% reduction in efficiency and a 3.4% decrease in total power compared to no scallop configuration. Furthermore, as scallop depth increases, the skin friction coefficient decreases in the disk gap while it increases for the seal in the impeller back gap. Increasing leakage outlet pressure reduces the leakage flow rate and skin friction coefficient. Fitted models for skin friction coefficient are proposed respectively. The conclusions providing valuable insights for designing and optimizing sCO2 radial inflow turbines with scallops.

Design and Performance Analysis of Windings Considering High Frequency Loss and Connection Mode of a Starter Generator

The starter generator is the key component of the aircraft’s starter generation system. A high power density, efficiency, and reliability are essential for an aircraft’s starter generator. The configuration of the windings is closely related to the performance of the starter generator. In this paper, the winding performance analysis and design are studied. Considering the skin effect, circulation effect, and proximity effect, a calculation model of winding loss under high-frequency operation is established. The motor performance under different winding connections is compared. Through a comprehensive comparison of starting performance, generation loss, and process performance differences, the optimum configuration of windings is identified. The performance of the starter generator including winding resistance, current, and no-load loss was tested on the prototype platform to verify the rationality and correctness of the analysis and design methods.

The impact of an open-label design on human amniotic membranes vs. silver sulfadiazine dressings for second-degree burns: a randomized controlled clinical trial

BackgroundBurn wounds require optimal medical management due to associated psycho-emotional and socioeconomic impacts and severe pain. The use of synthetic and biological dressings improves healing and reduces burn wound complications. The present study aimed to compare the outcomes of using human amniotic membrane (hAM) dressings and conventional silver sulfadiazine (SSDZ) ointment dressings in the management of second-degree burn wounds.MethodsFifty patients who participated in this clinical trial were divided into two groups via simple randomization. All the enrolled patients, who had burnt in the last 24 h, had thermal damage mechanisms and were suffering from less than 20% second-degree heat-burn wounds on the skin surface. The target group (n = 25) was treated with hAM, and the control group (n = 25) was treated with SSDZ ointment. The researcher-designed checklist was used to determine the clinical performance in the follow-up assessments on days 7, 14, and 30.ResultsNo significant differences were detected in terms of sex, age, or percentage of burn wounds (p > 0.05). Wound epithelialization at days 7, 14, and 30, scar formation, wound pigmentation, pain severity, analgesia requirements, and hospital stay length (on day 30) were significantly lower in the target group (treated with hAM) than in the control group (treated with SSDZ ointment) (p < 0.05). However, treatment costs in the target group ($170) were significantly higher than those in the control group ($71) (p < 0.001).ConclusionDespite its higher cost, hAM, as a technology-based therapy dressing, demonstrates superiority over SSDZ ointment in terms of wound healing and pain management.

Numerical Analysis of A Two-Phase Turbine: A Comparative Study Between Barotropic and Mixture Models

Abstract Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. This paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.

Investigations of the Windage Losses of a High-Speed Shrouded Gear via the Lattice Boltzmann Method

Investigations of the Windage Losses of a High-Speed Shrouded Gear via the Lattice Boltzmann Method

CONTROL OF SHROUD LEAKAGE LOSS AND WINDAGE TORQUE IN A LOW-PRESSURE TURBINE STAGE

Abstract As new aeroengine architectures move to larger diameter fans and rotors, the associated increase in weight will need to be counterbalanced by lighter, more compact, and more efficient low-pressure turbines (LPT). Efficiency gains in LPTs can be achieved by reducing the losses associated with the shroud leakage flows. Flow control studies on the topic have traditionally focused on reducing the mixing loss, which constitutes a considerable proportion of the total loss. Nonetheless, increasing engine speeds are driving additional gains obtained by also targeting the reduction of windage losses. Developing a flow control solution with the dual objective of reducing over-tip cavity mixing and windage losses has not previously been attempted. This is a challenge due to conflicting flow control requirements and geometric constraints. Reducing windage loss generally requires increasing the swirl-ratio of the leakage flow, while reducing mixing loss requires reducing this ratio to match that of the main gas path. The current work proposes a novel flow control solution to successfully achieve this purpose through the emerging technology of additive manufacturing. The successful flow control concept was developed through numerical simulation, printed using an additive manufacturing process, and validated in a purpose-built rig. Experiments and computations were consistent with a cumulative reduction in cavity windage of 16%. The FCC is estimated to increase the mechanical efficiency of the turbine stage in isolation by 1%.

Analysis and Design of High Power Density Flyback Converter

ABSTRACTThis paper presents a flyback converter with high efficiency and high power density. An optimal design method for high power density planar transformers is presented. Applying the principle of flux cancellation, a matrix transformer that originally needed an independent magnetic core was integrated into a single magnetic core to reduce the volume of the core. This method effectively reduces the printed circuit board (PCB) layer number of the planar transformer and increases the possibility of the application of the planar transformer in the flyback converter. An optimized design method of the winding structure is given according to that model to further reduce the winding loss of the transformer. Meanwhile, the proposed structure is verified by finite element analysis software. Finally, a multi‐output flyback converter with a frequency of 100 kHz is designed to verify the practical performance of the proposed transformer.

Improved Reduced Switch Converter Topology for Torque Ripple Reduction in Four-Phase Switched Reluctance Motor Under Dynamic Loading

In this paper, simulation, and performance comparison of a switched reluctance motor (SRM) for a classical asymmetric bridge converter and an improved reduced switch converter topology are provided. In an improved converter, switches are shared by adjacent phases, and one diode is connected in series with each phase winding to avoid reversal of current. Double-phase magnetization is adopted for the analysis of both converter topologies. The performance of both converter topologies are demonstrated using a proportional plus integral (PI) based hysteresis current controller and dynamic load on a 7.5 kW, 8/6 pole, 4- phase SRM. Improved reduced switch converter topology uses half the number of switches as compared to the classical asymmetric bridge converter. According to the simulation results, an improved converter offers superior starting and average torque with less speed settling time. An improved converter reduces the most serious problem of torque ripple in SRM by 50% compared to the classical topology. The reduced switches lower the winding losses and improve the efficiency of the drive system.

Thermal modeling and analysis of multi-mover motors considering mover quantity and dynamic states

—Multi-mover motors are widely used in logistics transportation systems. However, the unique number of movers and variations in motion states complicate the distribution of loss and thermal characteristics, thereby increasing the difficulty of calculating temperature rise. In this paper, a winding loss calculation method that considers the multi-condition and dynamic characteristics of multi-mover motors is proposed. The convective heat transfer coefficient (CHTC) is calculated using computational fluid dynamics (CFD) and response surface methodology (RSM), with a detailed analysis of velocity distribution characteristics. The interactive effects of mover speed, acceleration, mover quantity, and the distance between adjacent movers on the CHTC are investigated. A simplified yet accurate thermal modeling is developed, reducing the required time for a single operating condition from 4 h to 0.5 h, with an error of only 4 %. Through both single variable and multivariable analyses, the thermal characteristics of multi-mover motors under different conditions are revealed. Finally, a prototype is created and tested under various operating conditions. The discrepancies between the experimental and calculated values are within 5 %, validating the accuracy of the proposed model and analysis.

Optimising Flywheel Energy Storage Systems: The Critical Role of Taylor–Couette Flow in Reducing Windage Losses and Enhancing Heat Transfer

Amidst the growing demand for efficient and sustainable energy storage solutions, Flywheel Energy Storage Systems (FESSs) have garnered attention for their potential to meet modern energy needs. This study uses Computational Fluid Dynamics (CFD) simulations to investigate and optimise the aerodynamic performance of FESSs. Key parameters such as radius ratio, aspect ratio, and rotational velocity were analysed to understand their impact on windage losses and heat transfer. This study reveals the critical role of Taylor–Couette flow on the aerodynamic performance of FESSs. The formation of Taylor vortices within the airgap was examined, demonstrating their effect on temperature distribution and overall system performance. Through a detailed examination of the skin friction coefficient and Nusselt number under different conditions, this study identified a nonlinear relationship between rotor temperature and rotational speed, highlighting the accelerated temperature rise at higher speeds. The findings indicate that optimising these parameters can significantly enhance the efficiency of FESSs, reducing windage losses and improving heat transfer. This research provides valuable insights into the aerodynamic and thermal optimisation of FESSs, offering pathways to improve their design and performance. The results contribute to advancing guidelines for the effective implementation of FESSs in the energy sector, promoting more sustainable energy storage solutions.

AC loss analysis on an HTS field winding of the generator with T-A formulation

In this study, we proposed a coupling model utilizing finite element software to estimate AC loss on the high-temperature superconducting (HTS) field winding of a 1 MW generator. The model comprises three distinct physical modules: rotating machinery and magnetic (RMM), electrical circuit (CE) and partial differential equation (PDE). These modules collaborate to resolve the generator's magnetic field distribution, rated output parameters and degree of current magnetization on the HTS field winding, employing Maxwell equations and T-A formulation. Given the placement of the HTS field winding on the rotor core, accurately calculating its loss in an electromagnetic field that varies both temporally and spatially presents a considerable challenge. To address this issue, we adjust the coordinate system within the PDE module to vary with the material rather than space. Our analysis reveals that the instantaneous AC loss of an HTS field winding comprises two primary components: the attenuation envelope and the oscillatory variation, resulting from the charging process and external harmonic magnetic fields. Additionally, we comprehensively discuss and analyze the influence of current excitation speed on instantaneous AC loss. Accurately estimating AC loss in HTS field windings is a critical and meaningful aspect of preliminary machine design. This study provides an essential reference for addressing this issue.

The incidence and prevalence of chronic wounds from a major plastic surgery service from a metropolitan city in south western Nigeria: A sixteen-year retrospective review

IntroductionChronic wound presents a burden to the patient due to the effect on their quality of life and cost of care. The exact prevalence is difficult to assess due to insufficient data, different study designs, and deferent study definitions of chronic wounds. There is limited data on the prevalence and the burden of chronic wound in our subregion. This study was therefore carried out to establish the burden of chronic wound in order to document a baseline data for monitoring progress, as well as provide information for advocacy on equitable distribution of resources for wound care. MethodThis was a retrospective review between January 2007 and December 2022. Data was analysed using SPSS. ResultA total of 866 patients with new chronic wounds were seen at an average of 54 cases per year. An average of 330 old and new chronic wounds are seen yearly. Chronic ulcers are developing at a rate of 1.2/1000 population, and the prevalence of chronic ulcer is 3.3/1000 population. Most patients were males (57.2 %), with a mean age of 41.7years ± 20.6. Post traumatic wound is the leading aetiology. Age correlates positively with aetiology, p=<0.001. Sickle cell and venous wounds are predominantly on the legs, p=<0.001. There is a correlation between increasing age and occurrence of chronic wound in the leg, p=<0.001. ConclusionPost traumatic wound is the leading cause of chronic wound in our subregion. There is a need to improve care of acute wounds to reduce the burden of chronic wounds.

A non‐intrusive method for friction and windage losses estimation in induction motors

AbstractIn the in‐service induction motors (IMs), friction and windage losses (FWL) value should be determined non‐intrusively. Hence, in the in‐service IMs, instead of measuring FWL, empirical equations are used to estimate FWL value. A novel technique is proposed for estimating the FWL value in low‐voltage three‐phase IMs based on obtained data from applying the no‐load test on 425 simulated IMs in the MATLAB software. The simulated IMs are 380 V, 50 Hz, with different numbers of poles in the power range of 0.37–400 kW. The FWL value for simulated IMs is calculated based on the IEEE 112 standard and by applying the no‐load test. Then, based on the dispersion of the obtained data from the no‐load test and using non‐linear regression, according to the number of IM poles for each number of poles, a third‐degree equation for FWL estimation is fitted to the test data. The proposed method to estimate the FWL value only needs the nominal output power listed on the IM nameplate. Also, unlike existing empirical relationships, the proposed approach estimates the FWL value for IMs with high accuracy and non‐intrusively. The effectiveness of the suggested technique is confirmed by simulation and practical results.

Analysis and Optimization of the Winding Loss of Flat-Wire Motors

The flat-wire motor has the characteristics of small size, low noise, high slot fill factor and good thermal conductivity in the slot. It can significantly improve the power density of the motor and is widely used in electric vehicles. The skin effect and proximity effect of the flat wire under high-speed conditions lead to high loss. Based on the established finite element model of a two-dimensional flat-wire motor, this paper first studies the high-frequency loss of different winding layers and the conductor sizes of each layer. Secondly, the influence of the magnetic field on AC loss is reduced by optimizing the tooth-tip height and tooth-tip width. Finally, it is verified that the high-frequency loss is reduced by 16% with the optimized layers, conductor sizes and tooth-tip sizes under the drive condition of the CLTC-P (China Light-duty Test Cycle—Passenger).

Treatment of bacterially contaminated lower extremity ulcers with a fatty acid-containing wound matrix: a case series.

The aim was to evaluate the effectiveness of a marine omega fatty acid-containing multimodal wound matrix (MWM) in reducing bacterial contamination and supporting wound area reduction (WAR) in patients with hard-to-heal wounds of varying aetiologies. A prospective, single-site, pilot case series of patients with hard-to-heal wounds. All wounds were considered non-healing prior to inclusion as they had failed to achieve at least 50% WAR after at least four weeks of standard of care (SoC) treatments. Patients were seen once weekly for wound assessments, matrix application and dressing changes. Baseline and weekly fluorescence images, standard wound images and wound measurements were obtained. A total of three patients, two with venous leg ulcers (VLUs) and one with a diabetic foot ulcer (DFU) were enrolled in this pilot study. The mean baseline wound age prior to study enrolment was 24 weeks, with a mean baseline wound size of 8.61cm2. The two VLUs went on to complete closure. The DFU displayed a total WAR of 53% by six weeks, when the patient was lost to follow-up due to a geographical relocation. The mean percentage area reduction of all wounds combined was 82% upon study completion. The use of MWM proved to be effective and safe in this patient cohort. The wounds included in this case series failed to enter a healing trajectory with SoC wound therapies. The MWM supported wound closure and reduced bacterial loads in this patient cohort.

Utility of synthetic electrospun fiber matrix in general surgery: From head to toe

BackgroundTo highlight the role of a novel synthetic electrospun fiber matrix in the treatment of high-risk wounds across a range of etiologies. MethodsThis was a retrospective study of patients at a single institution who underwent complex wound care treatment with at least 1 application of the electrospun fiber matrix from January 2021 to December 2022. Information regarding patient demographics, wound size and etiologies, pertinent medical history, and treatment outcomes was collected. ResultsTwenty-one patients with 24 complex wounds who received synthetic electrospun fiber matrix treatment were identified. Nineteen patients (22 wounds) met the inclusion criteria for analysis. Patient mean age was 63.58 ± 15.20 (range 34–90) years. A wide range of wound etiologies was represented, including transmetatarsal amputation secondary to frostbite (n = 1), post-Mohs defect (n = 2), acute trauma (n = 3), surgical dehiscence (n = 3), infected implanted medical device (n = 2), chronic ulcers (n = 3), partial ray resection (n = 1), pilonidal cyst (n = 1), rattlesnake bite (n = 1), necrotizing soft-tissue infection (n = 1), and others (n = 2). A total of 17 of 19 (89.5%) patients were observed to meet their individual clinical goals after application of the wound matrix. Wound ages ranged from 1 to 429 days before initial synthetic electrospun fiber matrix application. ConclusionThe synthetic nature of the matrix limits the risk of inflammatory response and is well tolerated, which demonstrates initial proof of concept of synthetic electrospun fiber matrix treatment in a variety of complex wounds. The positive results observed across this mixed etiology surgical analysis should be replicated in future controlled, single-etiology studies to further confirm the utility of the electrospun fiber matrix in the surgical setting.

Windage loss characterisation for flywheel energy storage system: Model and experimental validation

In this paper, a windage loss characterisation strategy for Flywheel Energy Storage Systems (FESS) is presented. An effective windage loss modelling in FESS is essential for feasible and competitive design. Unlike generic aerodynamic loss models, FESS require particular attention to their unique characteristics i.e., vacuum, small airgaps, high angular speed, and presence of low friction rotor supports.The proposed model is based on several analytical and semi-empirical windage loss solutions for cylindrical and planar surface interactions, harmonised to manage the transition between laminar and turbulent flows. Also, the model is enriched by introducing corrections for rarefied gasses, using kinetic gas theory formulation. Therefore, it is possible the reduce the windage overestimation occurring with Navier–Stokes equation solutions for laminar flow. The model is compared to case studies from the literature featuring different boundary and operating conditions, to check consistency of all the harmonised models. A dedicated experimental test-rig is developed to validate the corrections to the model for rarefied gas at different vacuum levels. Then, a non-invasive characterisation approach for FESS windage losses in self-discharge phase is proposed and validated on the test-rig.

Study on Thermal Characteristics of Winding under Inter-Turn Fault of Oil-Immersed Transformer

The inter-turn fault is a common fault of oil-immersed transformers. Due to the deterioration of inter-turn insulation, its resistance decreases, which leads to an increase in the winding coil current and loss, causing the winding temperature to rise. Therefore, analyzing the electrothermal characteristics of inter-turn short circuit faults in oil-immersed transformers can provide a theoretical basis for the diagnosis of inter-turn faults in transformers. This paper studies the equivalent circuit under inter-turn faults and establishes a field–circuit coupling model to calculate the current characteristics under different inter-turn short circuit faults of transformers. The distribution of coil losses under faults is calculated as thermal source excitations, and a thermal–fluid-coupled calculation model for oil-immersed transformers is established. After the experimental verification, it is found that both the errors between the winding and tank surface temperatures do not exceed the acceptable limits, validating the effectiveness of this model. Using this model to calculate the temperature distribution for various inter-turn short circuit faults in transformers reveals their hot-spot characteristics. The results indicate that under inter-turn fault conditions, the temperature at faulty turns will gradually increase towards a limit, eventually leading to coil damage. This research provides theoretical support for enhancing transformer detection and diagnostic capabilities.

A non-intrusive technique for estimating the efficiency of low voltage three-phase induction motors

This paper introduces a non-intrusive technique based on the air–gap torque (AGT) method to estimate the efficiency of induction motors (IMs). The technique uses a 3rd-degree equation to calculate the sum of windage and friction losses (FWL) and rotor stray load losses (SLLr), considering the number of IM poles. IM speed is estimated using motor current signature analysis, and a new procedure to estimate stator resistance is presented. Efficiency is then determined by applying the estimated rotor speed, stator resistance, and the sum of FWL and SLLr in the AGT equations. This method requires only nameplate information, IM line voltages, and currents. Simulations and experimental tests for balanced, unbalanced, and harmonic feeding modes show the proposed technique’s estimated efficiency values are very close to measured values, unlike the AGT method. This demonstrates the proposed technique’s high accuracy, making it suitable for non-intrusive efficiency estimation of in-service IMs in industrial programs.