High Load Region Research Articles

Experimental study on the relationship between combustion and noise and vibration in a gasoline engine

An experimental study was conducted to clarify the relationship between engine combustion and noise and vibration, and concerning design indexing for its suppression. This study focused on the vehicle interior noise caused by combustion in which vibration transmission is the main component at high speed and high load region. A phenomenon in which both the combustion's exciting force and the structure's exciting force are combined is defined as vehicle interior noise caused by combustion. Conventionally, combustion and noise and vibration are often discussed in terms of the average cycle, but considering the nonstationary property of noise and vibration, in this paper analyzed the characteristics of both exciting force for vibration in cycle-by-cycle based on clustering analysis. The engine vibration is affected by heat release characteristics even with the same engine structure specifications. The heat release characteristics were determined as indicators for the combustion's exciting force. The engine vibration is affected by piston specifications even with the same heat release characteristics. The piston tilt and translational displacement were determined as indicators of the structure's exciting force. This paper clarifies the influence of each exciting force on vibration and discusses indexing that contributes to design.

Particulate emissions from gasoline vehicles using three different fuel injection technologies

Gasoline vehicle emission is a major source of urban particulate matter (PM), particularly ultra-fine PM (≤100 nm), exerting adverse health effects. While the PM emissions from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles have been well addressed in previous studies, few studies have reported the PM emission from the new mixed injection (MI) vehicles. Here, we employed a chassis dynamometer to investigate particle emissions under the Worldwide Harmonized Light vehicles Test Cycles (WLTC) from vehicles with three different fuel injection technologies. The PM and particle number (PN) emission factors (EFs) for MI vehicles are 129.53 μg/km and 1.0 × 1013 #/km, respectively. A trend of PFI > MI > GDI is observed for both PM and PN EFs for vehicles with same emission standard. Notably, the PM emissions of MI vehicles are greatly affected by both fuel injection methods at low and medium speeds, but are more significantly affected by PFI at high speeds. MI vehicle shows much lower PM and PN emissions than other vehicles at low-, medium-, and high-speed phases, but substantial hiher ultra-fine PM emission at extra-high speed phase. This is because the insufficient air supplied by naturally-aspirated engine of MI vehicles in the high-load region leads to incomplete combustion and generate large formation of ultra-fine particles. Besides, the gasoline particulate filter reduces 94.5% of PM emission but produces abundant nucleation-mode particles during regeneration at the extra-high speed phase for MI vehicles. Our study gives an insight to the state-of-the-art engine technology, i.e., MI vehicles, and reveals that this new technology is a feasible alternative for simultaneously reducing pollutant emissions from gasoline vehicles.

Experimental investigations on the friction behavior of partially femtosecond laser-textured journal bearing shells

Journal bearings are the most commonly used load elements in rotating systems and have a long history in tribology research. However, the relatively new surface modification technique of femtosecond laser texturing has rarely been used to increase the efficiency of journal bearings. We used a 300-fs laser to create chevron-shaped microstructures in different circumferential texture locations on half-bearing shells to investigate the effect of partial texturing on the tribological performance of journal bearings. With a customized shaft-bearing shell setup, the coefficient of friction and lubrication film thickness was tracked in two load scenarios at varying rotational speeds. In fully film conditions, the findings demonstrate that textures in the high-load region of journal bearings provide the highest lubricant film thickness and lowest friction compared to textures in the pressure build-up, divergent zone, and unstructured reference. Moreover, surface textures in the high-load area also perform better in boundary and mixed lubrication. Experimental data have also shown that asymmetric texture designs have a detrimental effect on lubrication performance. In contrast to symmetric designs, the lubrication film build-up is hindered. The research results represent a step toward transferring laboratory findings on laser surface texturing for tribological optimization in real applications.

Identifying critical regions for nitrogen and phosphorus loss management in a large-scale complex basin: The Jialing River

The determination of critical management areas for nitrogen (N) and phosphorus (P) losses in large-scale basins is critical to reduce costs and improve efficiency. In this study, the spatial and temporal characteristics of the N and P losses in the Jialing River from 2000 to 2019 were calculated based on the Soil and Water Assessment Tool (SWAT) model. The trends were analyzed using the Theil-Sen median analysis and Mann–Kendall test. The Getis-Ord Gi* was used to determine significant coldspot and hotspot regions to identify critical regions and priorities for regional management. The ranges of the annual average unit load losses for N and P in the Jialing River were 1.21–54.53 kg ha−1 and 0.05–1.35 kg ha−1, respectively. The interannual variations in both N and P losses showed decreasing trends, with change rates of 0.327 and 0.003 kg ha−1·a−1 and change magnitudes of 50.96% and 41.05%, respectively. N and P losses were highest in the summer and lowest in the winter. The coldspot regions for N loss were clustered northwest of the upstream Jialing River and north of Fujiang River. The coldspot regions for P loss were clustered in the central, western, and northern areas of the upstream Jialing River. The above regions were found to be not critical for management. The hotspot regions for N loss were clustered in the south of the upstream Jialing River, the central-western and southern areas of the Fujiang River, and the central area of the Qujiang River. The hotspot regions for P loss were clustered in the south-central area of the upstream Jialing River, the southern and northern areas of the middle and downstream Jialing River, the western and southern areas of the Fujiang River, and the southern area of the Qujiang River. The above regions were found to be critical for management. There was a significant difference between the high load area for N and the hotspot regions, while the high load region for P was consistent with the hotspot regions. The coldspot and hotspot regions for N would change locally in spring and winter, and the coldspot and hotspot regions for P would change locally in summer and winter, respectively. Therefore, managers should make specific adjustments in critical regions for different pollutants according to seasonal characteristics when developing management programs.

Effect of Major Dust Events on Ambient Temperature and Solar Irradiance Components over Saudi Arabia

The Saudi government targets building eight solar plants across the country by 2030, which are expected to produce more than 3600 MW, enough to power more than 500,000 homes. However, the vast desert environment in Saudi Arabia increases dust and aerosol loading in the atmosphere, which affect the performance of photovoltaic systems due to scattering and absorption of the solar radiation by dust particles. In this work, ground-based data from weather stations located in six Saudi cities, Dammam, Hafar Al Batin, Riyadh, Jeddah, Najran, and Arar, along with data from the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to examine the effects of dust loading on aerosol optical parameters, air temperature, and solar irradiance. The effects of three major dust storms that blew over different regions in Saudi Arabia on 20 March 2017, 23 April 2018, and 15 April 2021 have been investigated. It is found that there is a strong correlation between dust loading and aerosol optical parameters. The maximum Aerosol Optical Depth (AOD) was recorded over Jeddah on 19 March 2017 (about 2), over Riyadh on 20 March 2017 (about 2.3), over Riyadh on 24 April 2018 (about 1.5), and over Najran on 15 April 2021 (about 0.9). Strong dust events are found to reduce air temperature by a few degrees in high dust loading regions. The study found that such large dust loading decreases the direct and global solar irradiance components, while it increases the diffuse component over the cities of Jeddah, Riyadh, and Najran. This could be an indication that scattering from dust particles can play a significant role in the solar irradiance intensity.

Tail Prediction for Heterogeneous Data Center Clusters

Service providers need to meet their service level objectives (SLOs) to ensure better client experiences. Predicting tail sojourn times of applications is an essential step to combat long tail latency. Therefore, as an attempt to further unravel the power of our prediction model, new study scenarios for heterogeneous environments will be introduced in this research by using either of two methods: white- or black-box solutions. This research presents several techniques for modeling clusters of inhomogeneous nodes. Those techniques are recognized as heterogeneous fork-join queuing networks (HFJQNs). Moreover, included in the research is a nested-event-based simulation model, borrowing help from multi-core technologies. This model adopts the multiprocessing technique to take part in its design to enable different architectural designs for all computing nodes. This novel implementation of the simulation model is believed to be the next logical step for research studies targeting heterogeneous clusters in addition to the several provided scenarios. Experimental results confirm that even with the existence of such heterogeneous conditions, the tail latency can be predicted at high-load regions with an approximated relative error of less than 15%.

Complex Interplay Between Organic and Secondary Inorganic Aerosols With Ambient Relative Humidity Implicates the Aerosol Liquid Water Content Over India During Wintertime

AbstractAerosol Liquid Water Content (ALWC), a ubiquitous component of atmospheric aerosols, modulates atmospheric chemistry through aerosol surface reactions and reduces the atmospheric visibility. However, the complex dependency of ALWC on aerosol chemistry and relative humidity (RH) in the Indian region remains poorly characterized. Here, we combine available measurements of aerosol chemical composition with thermodynamic model, ISORROPIA2.1, to reveal a comprehensive picture of ALWC in fine mode aerosols during the winter season over the Indian continental region. The factors modulating ALWC are primarily dependent on the RH, such that the effect of aerosol dry mass and hygroscopicity are significant at high RH while the effect of hygroscopicity significantly reduces with decreasing RH. ALWC is observed to display a sharp non‐linear rise, beyond a critical value of ambient RH dependent on the particle hygroscopicity. Further analysis by coupling Weather Research Forecasting‐Chem simulation with ISORROPIA2.1 revealed significant spatial heterogeneity in ALWC over India, strongly associating with regions of high aerosol mass loading and RH. The Indo‐Gangetic Plain is consequently observed to be a hotspot of higher ALWC, which explains the prevalent conditions of haze and smog during winter in this region. Our findings re‐emphasize that high aerosol mass resulting from intense pollution is vital in modulating aerosol–climate interaction under favorable meteorological conditions. Observations suggest the need for localized pollution control strategies, directed at the reduction in aerosol emissions of specific chemical composition observed to contribute to the enhancement in PM through an increase in ALWC during wintertime in the region.

2.4 MW급 4행정 주기관의 부하에 따른 배기가스 특성 분석 (어로실습선 새바다호를 중심으로)

The engines used as the main engine of a ship vary depending on the fuel, size and output. Most of the ships are currently using internal combustion engines. This study examined the exhaust gas and air pollutants emitted by SAEBADA, the fishing training ship of Gyeongsang National University. It has a 2,427 kW main engine of Nigatta Engineering that uses marine gas oil (MGO) as fuel oil. It was measured in real time for each load. According to this measurement results, the engine of the ship is operated at an optimal load to reduce the emission concentration of air pollutants in the exhaust gas. For two days from May 13th to May 14th, 2020, a real ship emission gas measurement test was conducted on SAEBADA, the fishing training ship of Gyeongsang National University while operating the ship in four modes that were mainly composed of changes in output. The gas phase materials, particulate materials, exhaust temperature, etc., were measured. As a result of the test, the nitrogen oxide (NOx) emission of SAEBADA was Tier II level. It was found that when marine gas oil (MGO) emitted relatively less air pollutants than heavy fuel oil (HFO). In addition, it was found that the nitrogen oxide (NOx) emission in the high-load region was relatively less than in the low-load region regardless of the oil type and the aging of the engine. This may be due to the combustion state. Therefore, we intend to operate SAEBADA in an efficient and eco-friendly with the results of these real ship experiments.

Beam-induced surface modifications as a critical source of heat loads in the Large Hadron Collider

Beam-induced heat loads on the cryogenic regions of the Large Hadron Collider (LHC) exhibit a wide and unexpected dispersion along the accelerator, with potential impact on the performance of its High-Luminosity upgrade. Studies related the heat load source to the avalanche multiplication of electrons at the surface of the beam vacuum chamber, a phenomenon known as electron could build-up. Here, we demonstrate that the topmost copper surface of beam pipes extracted from a low heat load region of the LHC consists of native Cu2O, while the pipe surface from a high heat load region had been oxidized to CuO during LHC operation and maintenance cycles. Experiments show that this process increases the secondary electron yield and inhibits efficient surface conditioning, thus enhancing the electron cloud intensity during LHC operation. This study relates the abnormal LHC heat loads to beam-induced surface modifications of its beam pipes, enabling the development of curative solutions to overcome this critical limitation.

A simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines in the high pressure-high gas loading region

Hydrogen sulfide is essentially removed from the raw natural gas to meet the process, health, safety and environmental standards. Alkanolamine based absorption process remains the prevalent technique for hydrogen sulfide removal due to ease of operation and economic considerations. The design of such gas separation systems is a critical factor in meeting the stringent process requirements and optimizing operations. To achieve precise design, determination of vapor–liqid equilibrium for the system is indispensable while maintaining efficacy and simplicity. This study presents a simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines and their blends in the high pressure-high gas loading region. The model equation is developed by considering and combining amine protonation and bi-sulfide formation reactions, assuming ideal liquid properties. Satisfactory correlated values of hydrogen sulfide loadings (0.21–3.15 mol gas/mole solvent) are obtained over a wide range of temperature (298.15–393.15 K), pressure (60–7027 kPa) and alkanolamine concentration (1.12–14.27 molal). Parameters are given for the hydrogen sulfide solubility in aqueous solutions of monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol, piperazine, diglycolamine, di-isopropylamine, 1-amino-2-propanol and their selected blends. The model shall be useful for the design of alkanolamine based natural gas sweetening systems, operating at high pressure and high hydrogen sulfide gas loadings.

A Modification to Enhance the Survival of the Island FDMA Flap by Adding a Skin Bridge.

Background:Distal thumb injuries are common in high construction load regions, and it is a challenging task for the plastic surgeon to find the optimum choice that preserves thumb length and provides a sensory substitute to the lost tissue. Introducing first dorsal metacarpal artery flap has solved the dilemma. One drawback is that the flap is susceptible to distal necrosis, which can happen because of tight tunneling or insufficient venous drainage. We combined Foucher and Holevich characteristics to design a flap that promises to solve the problem.Methods:This is a case series that includes 9 patients where we describe a technique that has the potential to enhance the survival of the first dorsal metacarpal artery (FDMA) flap and decreases the rate of distal necrosis via addition of a 5-mm skin bridge to the pedicle and by avoiding tunneling. Distal necrosis of the patients in this study patients was compared with that in a control of 10 patients in whom we did the conventional FDMA flap. Patients were followed for 6 weeks to trace early postoperative complications (infection, dehiscence, and necrosis) and the establishment of protective sensation (pain and temperature).Results:None of our patients had distal necrosis, infection, or dehiscence, and all had protective sensation in the flap. In comparison, 4 patients in the control group developed distal necrosis.Conclusion:FDMA is one of the best choices when it comes to distal thumb reconstruction, but it has the disadvantage of distal necrosis, which might be avoided when using the technique mentioned in this study.

Tip leakage flow, tip aerodynamic loading and rotating instability in a subsonic high-speed axial flow compressor rotor

Rotating instability as an unsteady flow phenomenon is closely related to rotating stall in the compressor. In this paper, dynamic pressure measurements and full-annular URANS simulations were conducted in a subsonic axial flow compressor rotor to enhance the understanding of the flow mechanism of RI. RI characterized by a frequency band in the spectrum is detected at a narrow stable operating range in the experiments. The monitoring results from simulations show that RI characterized by a frequency hump in the spectrum appears near stall condition which is consistent with the observation in the experiments. RI shifts to lower frequency band in the rotating frame with the decrease of mass flow rate. Details of the numerical flow field indicate that RI develops synchronously with the oscillation of the tip leakage flow (TLF). The tip leakage vortex (TLV) forms a low static pressure near the pressure surface side of neighboring blade through an induced vortex. It varies the tip aerodynamic loading. Both the tip aerodynamic loading and TLF get strong with the decrease of mass flow rate. The stronger TLV will form a stronger induced vortex near the pressure surface side of the neighboring blade and propel the induced vortex toward the leading edge of blade. When a high tip aerodynamic loading region is influenced by the induced vortex near the pressure surface side, the intensity of TLF in the next passage will be weakened. Then, TLF fluctuates and leads to the oscillation of neighboring blade tip aerodynamic loading as well as the oscillation of TLF issuing from the neighboring blade. The circumferential propagation of this influence process results in RI.

Experimental Measurement of Carbon Dioxide Solubility in Aqueous N-Methyldiethanolamine + 2-(2-Aminoethylamino) Ethanol + Sulfolane and Diethanolamine + 2-(2-Aminoethylamino) Ethanol + Sulfolane Hybrid Solvents at Various Temperatures and High Pressure

The sets of vapor–liquid equilibrium (VLE) data for CO2 solubility in a combination of (N-methyldiethanolamine (MDEA) + 2-(2-aminoethylamino) ethanol (AEEA)) and (diethanolamine (DEA) + AEEA) as a chemical solvent blended with sulfolane as a physical solvent are acquired at 313.15–343.15 K within the CO2 partial pressure range up to 5600 kPa. The measurements are fulfilled for two different hybrid solvents of MDEA + AEEA + sulfolane with the weight compositions of (20–10–10) wt % and (20–10–20) wt % and a mixed solvent of DEA + AEEA + sulfolane with (20–10–10) wt %. It is deduced that CO2 loading was enhanced by substituting the MDEA with DEA, diminishing the temperature, and raising the pressure. Besides, increasing the sulfolane concentration in the aqueous system of MDEA + AEEA + sulfolane leads to enrichment in the effectiveness of the solution in CO2 absorption in the high loading region. In contrast, at low pressures, it adversely affects the acid gas loading. Moreover, it was displayed that at the same total mole of alkanolamines and sulfolane, the CO2 solubilities of AEEA + sulfolane and AEEA + MDEA + sulfolane are higher than those of AEEA + MDEA + sulfolane and MDEA + sulfolane, respectively. Therefore, it could be claimed that AEEA presents a better performance in CO2 capturing than MDEA. Besides, it was demonstrated that AEEA + sulfolane represents a higher capability in CO2 elimination than DEA + AEEA + sulfolane. Thus, the ability of DEA to remove CO2 is lesser than AEEA. Altogether, the degree of alkanolamines’ selectivity toward CO2 is found as AEEA > MDEA > DEA.

Experimental validation of inventory simulations on molybdenum and its isotopes for fusion applications

Molybdenum is a potential material for future nuclear fusion experiments and power plants. It has good thermo-mechanical properties and can be readily fabricated, making it attractive as an alternative material to tungsten (the current leading candidate) for high neutron flux and high thermal load regions of fusion devices. Unfortunately, exposure to fusion neutrons is predicted to cause significant radioactivity in elemental Mo for decades and centuries after exposure, which would be a problem during maintenance and decommissioning operations. Simulation predictions indicate that Mo activation could be reduced by isotopic adjustment (biasing). If these predictions are proven and validated, and if isotopic adjustment is technically and economically feasible, then Mo could be used in future demonstration and commercial reactors without significantly increasing the amount of long-term, higher-level radioactive waste.Transmutation (inventory) simulations used to predict activation rely on nuclear reaction data. The quality of these data impact on the confidence and uncertainty associated with predictions. Recently, UKAEA has developed benchmarks to test and validate the FISPACT-II inventory code and the input nuclear data libraries. Verification of molybdenum inventory simulations is performed against experimental decay-heat measurements from JAEA’s fusion neutron source (FNS) facility and using new data acquired from γ-spectroscopy measurements of Mo irradiated in the ASP 14 MeV facility in the UK.Results demonstrate that FISPACT-II predictions (with TENDL-2019 nuclear data) for Mo are accurate on the short-timescales (minutes, hours of irradiation and minutes, days, weeks of cooling) of these laboratory experiments. However, these kinds of experiments are limited in their coverage of the important radionuclides for decay radiation from Mo on the years, decades and beyond timescales. Further experiments with fusion relevant conditions and timescales, potentially with alternative measurement techniques, are still needed.

Local Laser Particle Fusion: Fusing of Hard Particles for the Reduction of High Contact Pressures in MMC Tool Surfaces

Lubrication-free deep drawing with metal matrix composite (MMC) tool surfaces leads to scores and grooves due to particle penetration into the formed sheet metal, and results in high local contact pressure in the radius of the deep drawing tool. To improve on this, the ratio of contacting area to total area must locally be increased in high-load regions of the tool surface. Multi-stage laser melt injection (LMI) and local laser particle fusion (LLPF) were carried out to increase the hard particle content of the MMC tool surfaces. LLPF is a novel two-step LMI process whereby hard particles are locally fused together under additional powder feeding after a regular LMI. The resulting nugget was shown to grow in height and width with an increase in the pulse duration. The substrate temperature prior to the particle fusion had an influence on the defect-free nugget growth. Whilst the chemical composition of the fused tungsten carbide (FTC) nuggets was similar to FTC particles, their hardness was slightly reduced compared to literature values for tungsten carbide. For the first time, FTC nuggets could be successfully applied on MMC tool surfaces to realize an increased hard coating area.

Enhanced Light‐Absorption of Black Carbon in Rainwater Compared With Aerosols Over the Northern Indian Ocean

AbstractBlack carbon (BC) aerosols affect climate, especially in high aerosol loading regions such as South Asia. A key uncertainty for the climate effects of BC is the evolution of light‐absorbing properties in the atmosphere. Here, we present a year‐round comparison of the mass absorption cross section (MAC; 678 nm) of BC in air (PM10) and rain, for samples collected at the Maldives Climate Observatory at Hanimaadhoo. We develop a filter‐loading correction scheme for estimating BC absorption on filters used in high‐volume samplers. The year‐round average MAC678 of BC in the rain is almost twice (13.3 ± 4.2 m2/g) compared to the PM10 aerosol (7.2 ± 2.6 m2/g). A possible explanation is the elevated ratio of organic carbon (OC) to BC observed in rain particulate matter (9.4 ± 6.3) compared to in the aerosols (OC/BC 2.6 ± 1.4 and water‐insoluble organic carbon/BC 1.2 ± 0.8), indicating a coating‐enhancement effect. In addition to BC, we also investigated the MAC365 of water‐soluble brown carbon in PM10 (0.4 ± 0.4 m2/g, at 365 nm). In contrast to BC, MAC365brown carbon relates to air mass history, showing higher values for samples from air originating over the South Asian landmass. Furthermore, calculated washout ratios are much lower for BC compared to OC and inorganic ions such as sulfate, implying a longer atmospheric lifetime for BC. The wet deposition flux for BC during the high loading winter was 3 times higher than during the wet summer, despite much less precipitation in the winter.

In Situ Joint Stiffness Increases During Skeletal Growth but Decreases Following Partial and Complete Anterior Cruciate Ligament Injury.

Partial and complete anterior cruciate ligament (ACL) injuries occur in both pediatric and adult populations and can result in loss of joint stability and function. The sigmoidal shape of knee joint function (load-translation curve) under applied loads includes a low-load region (described by slack length) followed by a high-load region (described by stiffness). However, the impact of age and injury on these parameters is not fully understood. The current objective was to measure the effects of age and injury on the shape of joint function in a porcine model. In response to an applied anterior-posterior tibial load, in situ slack did not change (p > 0.05), despite sevenfold increases in joint size with increasing age. Joint stiffness increased from an average of 10 N/mm in early youth to 47 N/mm in late adolescence (p < 0.05). In situ ACL stiffness increased similarly, and changes in in situ joint stiffness and ACL stiffness were highly correlated across ages. With complete ACL injury, in situ slack length increased by twofold to fourfold and in situ stiffness decreased threefold to fourfold across ages (p < 0.05). Partial ACL injury resulted in less dramatic, but statistically significant, increases in joint slack and significant decreases in in situ joint stiffness in the adolescent age groups (p < 0.05). This work furthers our understanding of the interaction between joint biomechanics and ACL function throughout growth and the impact of ACL injury in the skeletally immature joint.

A Novel Magnetic Field Active Shim Method for Air-Core High-Temperature Superconducting Quadruple Magnet

An air-core high-temperature superconducting quadruple magnet (AHQM) is composed of high-temperature superconductor (HTS) coils without an iron yoke. An AHQM exhibits magnetic field characteristics that vary linearly with respect to changes in the operating current. Further, the AHQM is more suitable for use in high heat load regions. A conventional iron-core quadruple magnet (IQM) contains an iron yoke to achieve the specific shape and magnitude of the magnetic field. In the case of IQMs, the iron yoke generates most of the magnetic field. In the case of AHQMs, the magnetic fields are generated solely by HTS coils. Thus, an AHQM requires a larger number of coils to generate a magnetic field, because the iron yoke has been removed. Consequently, the influence of manufacturing errors in the AHQM is high; these errors deteriorate the designed magnetic field. Therefore, magnetic field correction is required to reduce the deterioration in the magnetic field of an AHQM. This paper, proposes a novel active shim method to compensate for the deteriorated magnetic field of an AHQM. This method improves the uniformity, but does not affect the gradient and effective length of the quadruple magnet. The effectiveness of this method is verified by simulation.

Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5×106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward-facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely, Nusselt number, was derived. This paper also presents a comparison with computational fluid dynamics (CFD) predictions performed by solving the steady-state Reynolds-averaged Navier–Stokes with Reynolds stress model using the commercial CFD solver ansysfluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25% to 0% span), and five backward-facing, upstream step geometries (step heights from 0% to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient (HTC) level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the HTC (by ∼10% to 40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3–1.3%) because of the forward-facing upstream step geometry but is slightly reduced (by 0.1–0.3%) by the presence of the backward upstream step geometry.

The Dodge City Tornadoes on 24 May 2016: Damage Survey, Photogrammetric Analysis Combined with Mobile Polarimetric Radar Data

AbstractPolarimetric measurements recorded by a mobile X-band radar are combined with photographs of the Dodge City, Kansas, tornado to quantitatively document the evolving debris cloud. An inner annulus or tube of high radar reflectivity encircled the tornado at low levels. A column of low cross-correlation coefficient ρhv was centered on the funnel cloud during the early stage of the tornado’s life cycle. In addition, two areas of low ρhv were located near the inner annulus of high radar reflectivity and were hypothesized to be regions of high debris loading that have been reproduced in simulations of lofted debris. Another column of low ρhv was a result of strong wind speeds that were progressively lofting small debris and dust as inflow rotated around and within the weak echo notch of the hook echo. A column of negative differential reflectivity ZDR was also centered on the tornado and was hypothesized to result from common debris alignment. The polarimetric structure undergoes a dramatic transition when the debris cloud was prominent and enveloped most of the funnel cloud. The weak echo column (WEC) began to fill at lower levels as large amounts of debris were lofted into the circulation. The axis of minimum ρhv shifted to a radius just beyond the funnel cloud. A column of positive ZDR was collocated with the funnel surrounded by negative ZDR. The negative ZDR and low ρhv within the debris cloud were likely the result of some common debris alignment from wheat stems. The positive ZDR within the funnel signified the presence of a few hydrometeors.