Velocity Difference Research Articles

Evaluation of wind farm performance over heterogeneously rough terrain using large eddy simulation

We evaluate the effect of an abrupt change in the surface aerodynamic roughness height on a wind farm sited on it using the large eddy simulation (LES). Compared to a wind farm sited on a uniformly rough surface, the alteration in aerodynamic surface roughness from a rough to smooth value leads to substantial changes in the first-order and second-order turbulent statistics. Specifically, the rough-to-smooth surface roughness transition leads to an acceleration of the flow downstream of it, which affects the wake recovery and wind farm power production. Different velocity deficits are formulated considering different definitions of “upstream” velocity. The usual deficit, i.e., the difference between the overall wind farm upstream velocities and downstream of a turbine, attains negative values near the ground, rendering it difficult to model within the usual Gaussian radial-shape framework. An alternative definition, i.e., the difference in velocity at the same location with and without turbines on a heterogeneous surface, consistently yields positive values and is amenable to Gaussian shape-based modelling. The power generation decreases as the step change in surface roughness progressively moves into the wind farm. Maximum power is produced when all turbines are placed downstream of the surface roughness jump and minimum power is generated for a homogeneously rough surface when the entire wind farm is placed on the rough surface.

PIV experimental study on water-sediment two-phase flow in NACA0012 cascade

Abstract Sediment wear is one of the important reasons for the damage of hydraulic machinery components, and the motion characteristics of sediment are the key factors to determine the degree of wear damage. In order to reveal the mechanism of sediment wear of turbine guide vane, motion characteristics of sediment near the wall of NACA0012 cascade were studied by PIV test method. In this research, fluorescent and sediment particles were used as tracer particles respectively, and the particle images of solid and liquid phases were recorded by double-camera synchronous imaging method. Finally, the synchronous velocity field of solid and liquid phases was determined by correlation analysis of particle images. The experimental results show that the PIV test method can accurately determine the motion characteristics of the solid phase. There is velocity slip between the solid phase and the liquid phase, and the velocity deviation is related to the factors of particle characteristics and Reynolds number.

Hydraulic transient calculation by wave tracking method for pumped storage power plant with four units in a diversion system

Abstract Hydraulic transient calculations are a key issue related to the operational safety of pumped storage power plants. Based on the new calculation method, wave tracking method, this paper establishes a calculation model for the hydraulic transient of pumped storage power plant, verifies the accuracy of the calculation model through hydraulic model experiments, and calculates the transient process of Guangdong Qingyuan pumped storage power plant. The results show that the calculation error is reduced by considering the difference of wave velocity of different branch pipes by wave tracking method. The wave tracking method is convenient to establish a calculation model of pumped storage power plant with four units in a diversion system, which is suitable for the load shedding transient regime of the turbine mode and the pump outage condition, and the accuracy is good. Wave parameters visually show the connection between flow rate, pressure changes within the water transmission system, and surge fluctuations in the regulator well throughout the hydraulic transition.

Evolution of some flow-related properties of diffusive aerosols along a tube

This is the third of a series of papers dealing with the behavior of Brownian aerosol particles immersed in a laminar fluid flow. The evolution along the tube of the distributions of particle radial positions (RPD), particle residence time (RTD), and particle mean axial velocity (MAVD) were determined by Monte Carlo (MC) simulation of particles trajectories. The RPD and particle penetration was also determined by numerical solution of the advection-diffusion equation (ADE) with negligible particle axial diffusion. The fairly good agreement shown between the results obtained by these two methods justifies our confidence on the use of the MC technique to determine other particle properties, as MAVD and RTD, for which the corresponding differential equation is yet unknown. Flow-related properties of the aerosol, such as penetration and residence time, are mainly determined by its MAVD. The MAVD is intimately related to the RPD; the latter evolves in such a manner that the surviving particles tend to accumulate nearer the tube axis and farther from the wall. When the fluid local velocity depends on the spatial location, the mean particle axial velocity increases as the aerosol flows downstream the tube, and its value can be considerably larger than the mean fluid velocity, in spite that no external force is acting on the particle. A direct consequence of this counterintuitive fact is that the mean aerosol residence time in the tube can be much smaller, by a factor of ∼0.65, than that of the fluid for even moderate values of the particle diffusion coefficient. This asymptotic value of the aerosol mean residence time can be predicted using the ADE in conjunction with a simple estimation model proposed here. If the fluid velocity is constant within the tube (uniform or plug flow), the mean particle axial velocity is everywhere equal to the fluid velocity, and particles and fluid spend the same time to traverse the tube. The larger the departure of the fluid velocity profile from uniformity, the larger the difference of mean axial velocity and mean residence time between particles and fluid.

The effect of nacelle-to-rotor size on the wake of a miniature wind turbine

Wind tunnel experiments are performed to investigate the effect of nacelle-to-rotor size on the wake of a wind turbine under different Reynolds numbers. Four different turbine configurations are tested, which vary in the rotor diameter and nacelle length and diameter. The near wake region is observed to be significantly affected by the nacelle-to-rotor size of the turbine. The difference in the averaged streamwise velocity and streamwise turbulence intensity is affected more by the change in the rotor diameter than by the change in the nacelle diameter. This is likely due to the change in the nacelle length to rotor diameter ratio, and the change in the distance between the ground and rotor lower tip. The differences in the near wake characteristics are reduced by the increase in the Reynolds number. The onset of the far wake is unaffected by the nacelle-to-rotor size, and consequently, the far wake modeling can be performed with good accuracy using existing analytical models. The power coefficient values show an improvement with the increase in the Reynolds number due to the higher efficiency of the rotor and motor.

On the Roles of Stellar Rotation and Binarity in NGC 2423's Main-sequence Turnoff Region

Research has shown that many young and intermediate-age clusters (younger than ∼2 Gyr) have extended main sequences and extended main-sequence turnoffs (eMSTOs), which cannot be adequately described by a single isochrone. The reason for the extended main sequences is now known, with the most probable cause being the fast rotation of stars. However, a significant fraction of slowly rotating stars form a younger stellar population than their fast-rotating counterparts, leading to speculation that they have undergone rotational mixing processes internally. One speculation is that a considerable number of slowly rotating stars reside in close binary systems, where tidal forces from companion stars are the cause of their rotational deceleration. In this work, we report a relatively old open star cluster in the Milky Way, NGC 2423 (∼1 Gyr old), which exhibits an apparent eMSTO. As anticipated, many characteristics of NGC 2423 indicate that its eMSTO is driven by stellar rotations. Our calculations indicate that if slowly rotating stars commonly have a close companion star, they should exhibit significant differences in radial velocities observationally, and binary systems that can be tidally locked within the age of NGC 2423 should have a mass ratio close to 1. However, none of these predictions align with our observations. Interestingly, among the only two equal-mass binary systems in the observed region for which spectroscopic data could be obtained, we discovered that one of them is a tidally locked binary system. This further suggests the validity of our numerical simulation results.

Comparing Left Ventricular Structure and Functions in End-Stage Renal Disease Using Conventional Echocardiography and 2D Speckle Tracking Echocardiography.

Patients on hemodialysis (HD) are prone to various cardiovascular complications. Two-dimensional speckle tracking echocardiography (2D STE) is an innovative technique for early myocardial dysfunction detection, even with normal ejection fraction (EF). We aim to detect left ventricle (LV) dysfunction in regular hemodialysis patients using 2D STE compared to traditional echocardiography. The study comprised 30 patients with end-stage renal disease (ESRD), subdivided according to left ventricular mass index (LVMI) into group 1 with left ventricular hypertrophy (LVH) (n=19) and group 2 without LVH (n=11). Another 30 healthy control subjects were recruited as group 3. The EF, average systolic velocity (Sa), and 2D LV strain were taken as measures of LV systolic function. The indicators for diastolic function included the E/A ratio and E velocity/peak early diastolic velocity. Regarding the parameters of LV systolic and diastolic functions assessed by traditional echocardiography, we found no significant difference between groups 1 and 2. However, using 2D STE, we observed significant differences in the average Sa velocity (p=0.025), average LV strain (p=0.03), 2D global longitudinal strain (GLS) (p=0.03), E/Ea (p=0.003), and LV myocardial performance index (MPI) (p=0.006). Also, a significant positive correlation was found between LVMI and left ventricular end-diastolic diameter (LVEDD) (p<0.01, r=0.63), EF measured by 2D (p=0.034, r=0.39), mitral E/A ratio (p=0.03, r=0.49), and mitral E/Ea (p<0.01, r=0.72). There was a significantly strong negative correlation between LVMI and 2D average LV strain (p=0.034, r=-0.39). We concluded that 2D STE is more sensitive than a conventional echo in detecting early LV systolic and diastolic dysfunction even in patients with normal EF.

Optimization study of a Z-type airflow cooling system of a lithium-ion battery pack

The present study aims to optimize the structural design of a Z-type flow lithium-ion battery pack with a forced air-cooling system known as BTMS (battery thermal management system). The main goal is to minimize Tmax (maximum temperature) and ΔTmax (maximum temperature difference) while ensuring an even airflow distribution within the battery module. The present study thoroughly investigates critical factors, such as the inlet air velocity, tapered inlet manifold, and the number of secondary outlets, to evaluate their impact on thermal performance and airflow uniformity within the battery module. Increasing the inlet air velocity from 3 to 4.5 m/s significantly improves the thermal cooling performance of the BTMS, resulting in a decrease of 4.57 °C (10.05%) in Tmax and 0.29 °C (9.79%) in ΔTmax compared to the original 3 m/s velocity. Further, the study assesses the significance of a tapered inlet manifold as a critical factor, revealing its substantial impact on cooling performance and temperature reductions in battery cells 3–9. It also facilitates a more uniform airflow distribution, decreasing the velocity difference between channel 9 and channel 1 from 3.32 to 2.50 m/s. Incorporating seven secondary outlets significantly improves the heat dissipation ability of the BTMS, resulting in a decrease of 0.894 °C (2.18%) in Tmax and 2.23 °C (72.84%) in ΔTmax compared to the configuration with 0 secondary outlets. By optimizing these parameters, the aim is to enhance BTMS's capabilities, improving LIB (lithium-ion battery) packs' performance and reliability. The optimized structural design parameters proposed in this study yield practical applications that extend beyond theoretical insights, impacting diverse fields reliant on lithium-ion battery technology. Through enhanced thermal management systems, applications in electric vehicles and portable electronics are poised to experience improved performance and longevity. Furthermore, these advancements inform the development of next-generation battery packs, promising reduced overheating risks and extended battery life. Such innovations are critical in energy storage systems for renewable energy applications and electric vehicle technology, facilitating faster charging times and increased driving range. Moreover, the implications extend to aerospace applications, ensuring the reliability of batteries in extreme environmental conditions.

A particle-resolved direct numerical simulation method for the compressible gas flow and arbitrary shape solid moving with a uniform framework

Compressible particle-resolved direct numerical simulations (PR-DNS) are widely used in explosion-driven dispersion of particles simulations, multiphase turbulence modelling, and stage separation for two-stage-to-orbit vehicles. The direct forcing immersed boundary method (IBM) is a promising method and widely applied in low speed flow while there is few research regarding compressible flows. We developed a novel IBM to resolve supersonic and hypersonic gas flows interacting with irregularly shaped multi-body particle. The main innovation is that current method can solve the interaction of particles and high-speed fluids, particle translation and rotation, and collision among complex-shaped particles within a uniform framework. Specially, high conservation and computation consumption are strictly satisfied, which is critical for resolving the high speed compressible flow feature. To avoid the non-physical flow penetration around particle surface, an special iterative algorithm is specially derived to handle the coupling force between the gas and particles. The magnitude of the velocity difference error could be reduced by 6–8 orders compared to that of a previous method. Additionally, aerodynamic force integration was achieved using the momentum equation to ensure momentum conservation for two-phase coupling. A high-efficiency cell-type identification method for each step was proposed, and mapping among LPs and cells was used again to select the immersed cells. As for the collision force calculation, the complex shape of a particle was represented by a cloud of LPs and the mapping of LPs and cells was used to reduce the complexity of the algorithm for contact searching. The repetitive use of the mapping relationship could reduce the internal memory and improve the efficiency of the proposed algorithm. Moreover, various verification cases were conducted to evaluate the simulation performance of the proposed algorithm, including two- and three-dimensional moving and motionless particles with regular and complex shapes interacting with high-speed flow. Specifically, an experiment involving a shock passing through a sphere was designed and conducted to provide high-precision data. The corresponding results of the large-scale numerical simulation agree well with those obtained experimentally. The current method supports flow simulations at a particle-resolved scale in engineering.

Critical radius prediction for small radius curved section of two-lane secondary highways based on speed characteristics

Small radius curved sections of two-lane secondary highways have low technical indicators, complex alignments, and frequent accidents. In order to improve the safety of traffic operation, the article investigates the curved sections of two-lane secondary highways with different radii and obtains the travelling speeds of different vehicle types at different section locations. By studying the trajectory characteristics and speed characteristics of vehicles travelling in curves, the velocity difference ratio, which responds to the continuity of driving speed, was defined. Then, based on this, this paper investigates the vehicle motion law of small radius curved road sections. The results show that the speed change of large cars in small radius curves is similar to a “U" shape, while the speed change of small cars is similar to a “V" shape. The speed adjustments of the larger cars occur mainly within the range of gentle curves, whereas the speed changes of the smaller cars are large throughout the range of curves. There is a significant exponential function relationship between curve radius and 85 % percentile speed, from which the curve radius threshold can be predicted. This provides a basis for engineering construction of curved road sections and optimization of curve design indicators, which greatly improves the traffic safety level of curved road sections.

Biomechanical improvements in gait following medial pivot knee implant surgery

BackgroundTotal knee replacements are used to improve function and reduce pain in patients with advanced osteoarthritis. The medially stabilising implant is designed to mimic a healthy knee. This study aims to provide a comprehensive analysis of the kinematics and kinetics of a medially stabilising knee implant, comparing it to a healthy control group, as well as to its pre-operative state and the contralateral limb. MethodsSixteen total knee replacement patients and ten healthy participants were recruited. Patients underwent testing 4–6 weeks before surgery and repeated the same tests 12 months after surgery. Healthy participants completed the same tests at a single time point. All participants completed three walking trials: kinematics was captured with eight cameras; kinetics with in-ground force plates. Subject-specific musculoskeletal models were developed in OpenSim. Inverse kinematics and inverse dynamics were used to determine gait parameters. Joint angles and joint moments were evaluated using Statistical Parametric Mapping. Patient-reported outcome measures were also collected at both time points. FindingsSpatiotemporal results indicate significant differences in velocity and step length between pre-operative patients and control participants. Differences are observed in the adduction angles between the contralateral and ipsilateral limbs pre-operatively. Postoperatively, there was an increase in the 1st peak flexion moment, reduced adduction moment and reduced internal rotation moment. In PROMs, patients all report improvements in pain levels and high satisfaction levels following surgery. InterpretationsFollowing medial stabilising total knee arthroplasty, patients displayed improved clinical parameters and joint moments reflecting a shift towards more normal, healthy gait.

Impact of Daily Growth Hormone Adherence on Height Velocity Among Children With Growth Hormone Deficiency (GHD)

ObjectiveTo describe adherence to daily somatropin treatment and impact on height velocity within 1 year of treatment start among patients with pediatric growth hormone deficiency in a real-world US population. MethodsThis retrospective cohort study included pediatric patients aged ≥3 years to <16 years with pediatric growth hormone deficiency prescribed somatropin by a pediatric endocrinologist at a US-based center of excellence between January 1, 2015 and December 31, 2020. Patient data were collected using hospital electronic health records linked to a specialty pharmacy patient prescription records. Adherence, evaluated over 12 months, was measured using the proportion of days covered metric and patients were categorized as adherent if their proportion of days covered ≥80%. Height velocity was annualized to compare across adherent and nonadherent patients. ResultsOne hundred eighty-one patients were identified and included in this study, of which 70.2% were male,73.5% were white, and mean age (standard deviation [SD]) at index was 12.1 (2.8). In the height velocity analysis, 174 patients were included and the mean (SD) annualized change in height was 10.2 (5.7) cm/y in the adherent group (n = 108) and 9.8 (7.6) in the nonadherent group (n = 66). The difference in height velocity between the groups was not statistically significant. ConclusionsMinor improvements in average height velocity were observed in the patient group who were adherent to somatropin therapy, although not statistically significant. Lack of observed significance may be due to small sample sizes, short observation period, a likely heterogenous population in terms of growth hormone prescribing, data bias due to single-center origin, or potential patient misclassification.

Zebrafish dspb -/- tert +/- mutant as model for arrhythmogenic cardiomyopathy. Impact of aging in the development of the disease

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Instituto de Salud Carlos III Background/Objectives Zebrafish has been reported as model to study the Arrythmogenic Cardiomyopathy, which is generally associated with desmosomal gene mutations. We have identified a founder non-sense human variant in patients from our region (DSP p.Q447*) associated with left ventricle Arrythmogenic Cardiomyopathy and we have selected it for modelling in zebra fish by CRISPR/Cas9 method, choosing exon 10 as the region of homology to be mutated and obtaining the p.T449fs* variant that determines a premature stop codon. On the other hand, tert gene enables telomerase activity and telomere maintenance and mutations in this gene have been used for studying aging effects. After multiple crossings of our dspb model with tert mutants we have obtained dspb-/-tert+/- model line. Purpose Our aim was the characterization of dspb-/-tert+/- mutants, studying the impact of aging in the development of the disease. Methods The model was obtained by crossing dspb-/- and tert-/- mutants, crossing the heterozygous mutants and genotyping for the selection of the dspb-/-tert+/- mutants. The characterization of the phenotype was performed through viability assays, cardiac function measurements and gene expression assays in larvae (3 days post fertilization) young adult (8 months old) and old adult (3 years old) individuals. Results Viability assays showed that dspb-/-tert+/- mutants suffer a premature death, with much lower survival rates than the dspb-/- group (survival dspb-/- 61.3% vs dspb-/-tert+/- 35.6%, p&amp;lt;0.01). Larvae heart rate analysis showed no significant differences. Echocardiography in young adults showed no significant differences between dspb-/-tert+/- and dspb-/- mutants. In old adults, echocardiography showed differences in heart rate (dspb-/- 142.5 ± 15.5 vs dspb-/-tert+/ -97.5 ± 3.5, p&amp;lt;0.01), respiratory frequency (dspb-/- 288.7 ± 36.1 vs dspb-/-tert+/- 95 ± 49.4, p&amp;lt;0.01) and atrial contraction velocity (dspb-/-155.7 ± 26.09 vs dspb-/-tert+/ -227.2 ± 17.6, p&amp;lt;0.05). Gene expression analysis in larvae showed that dspb expression drastically decreased (dspb-/- 0.3 ± 0.1 vs dspb-/-tert+/ -0.01 ± 0.008, p&amp;lt;0.01). In adults, dspb expression drastically decreased in heart tissue (dspb-/- 0.4 ± 0.01 vs dspb-/-tert+/- 0.06 ± 0.004, p&amp;lt;0.01) and skin (dspb-/ -0.34 ± 0.02 vs dspb-/-tert+/- 0.25 ± 0.01, p&amp;lt;0.01). Conclusion The dspb-/-tert+/- zebrafish presented worse survival rates, lower dspb gene expression levels and worse pathological cardiac phenotype at adult stages than dspb-/- mutants, proving that age is an important factor in the development of the disease and proving that dspb-/-tert+/- zebrafish is an appropriate model to study the impact of aging.

Development and experimental evaluation of an instrumented constant-force bodybuilding machine. Application to the bench press exercise

In weightlifting exercise, inertial forces result in the force exerted by the athlete being variable throughout the exercise. Many new machines and training methods are intended to maintain a more constant force value. This work aims at developing and evaluating a novel type of bodybuilding machine based on a constant-force mechanism. First, the mechanical design of the proposed constant-force bodybuilding machine (CFBM) is described and its characteristic force curves are obtained by experiments. Then, the performance of an athlete in a lifting exercise carried out in a CFBM is compared to the traditional free weight (FW) exercise in a bench press session. The results demonstrate significantly smaller variations in the force curves for the CFBM than for FW, as well as the disappearance of the braking phase shown by the FW at the end of the concentric phase. Major force differences are identified for a load of 40% of the one repetition maximum (1RM), where the maximum variation in the force curve for the FW is two times higher than for FW. Differences in velocity and power curves are also reported and analized. For the 80% of 1RM the peak and mean powers are found to be 27% and 34% higher, respectively, for CFBM than for FW.

Intermittency in the not-so-smooth elastic turbulence.

Elastic turbulence is the chaotic fluid motion resulting from elastic instabilities due to the addition of polymers in small concentrations at very small Reynolds ( ) numbers. Our direct numerical simulations show that elastic turbulence, though a low phenomenon, has more in common with classical, Newtonian turbulence than previously thought. In particular, we find power-law spectra for kinetic energy E(k) ~ k-4 and polymeric energy Ep(k) ~ k-3/2, independent of the Deborah (De) number. This is further supported by calculation of scale-by-scale energy budget which shows a balance between the viscous term and the polymeric term in the momentum equation. In real space, as expected, the velocity field is smooth, i.e., the velocity difference across a length scale r, δu ~ r but, crucially, with a non-trivial sub-leading contribution r3/2 which we extract by using the second difference of velocity. The structure functions of second difference of velocity up to order 6 show clear evidence of intermittency/multifractality. We provide additional evidence in support of this intermittent nature by calculating moments of rate of dissipation of kinetic energy averaged over a ball of radius r, εr, from which we compute the multifractal spectrum.

Characterizing the 2D single atom solutions to capture CO2 by the digital twin model

The digital twin model is developed to characterize the CO2 capture by the Cu and B 2D single atom solution (2DSAS). The key digital functions distributions f[], g[] and h[] characterize the physical 2DSAS system with the digital code 1 and 0. The thermoelectrical effect of the 2DSAS is analyzed. The digital code combinations of Cu atoms sorting from 1111 to 11,111 with B atoms sorting from 00 to 000 were identified as more suitable for CO2 capture. The effects of velocity difference of Cu and B atoms, temperature and CO2 loading were discussed. CO2 desorption efficiency was increased by an average 4.2 % and the energy consumption of desorption was reduced by 35.4 % at h[] of 3.5 × 10-6 m/s to 5 × 10-6 m/s. The 2DSAS of Cu and C, Cu and N and Cu and Si were suggested for CO2 capture.

Rotation curves in protoplanetary disks with thermal stratification

Context. In recent years, the gas kinematics probed by molecular lines detected with ALMA has opened a new window into the of study protoplanetary disks. High spatial and spectral resolution observations have revealed the complexity of protoplanetary disk structure. Drawing accurate interpretations of these data allows us to better comprehend planet formation. Aims. We investigate the impact of thermal stratification on the azimuthal velocity of protoplanetary disks. High-resolution gas observations reveal velocity differences between CO isotopologues, which cannot be adequately explained with vertically isothermal models. The aim of this work is to determine whether a stratified model can explain this discrepancy. Methods. We analytically solved the hydrostatic equilibrium for a stratified disk and we derived the azimuthal velocity. We tested the model with SPH numerical simulations and then we used it to fit for the star mass, disk mass, and scale radius of the sources in the MAPS sample. In particular, we used 12CO and 13CO datacubes. Results. When thermal stratification is taken into account, it is possible to reconcile most of the inconsistencies between rotation curves of different isotopologues. A more accurate description of the CO rotation curves offers a deeper understanding of the disk structure. The best-fit values of star mass, disk mass, and scale radius become more realistic and more in line with previous studies. In particular, the quality of the scale radius estimate significantly increases when adopting a stratified model. In light of our results, we computed the gas-to-dust ratio and the Toomre Q parameter. Within our hypothesis, for all the sources, the gas-to-dust ratio appears higher but still close to the standard value of 100 (within a factor of 2). The Toomre Q parameter suggests that the disks are gravitationally stable (Q &gt; 1). However, the systems that show spirals presence are closer to the conditions of gravitational instability (Q ~ 5).

Unsteady Interaction Between Purge Flow and Secondary Flow in High-Lift Low Pressure Turbine

Abstract The coupling effect between the complex vortex system and the rim purge flow in the endwall region of a high-lift low pressure turbine (LPT) will significantly influence the evolution of secondary flow and the corresponding losses. This paper focused on the unsteady interaction mechanism between the rim purge flow and the secondary flow inside the high-lift LPT under the periodic wake passing. The large eddy simulation (LES) method was used to reveal the influence mechanism of rim purge flow, rotor-stator cavity interaction and unsteady wakes on the secondary flow. Detailed experimental measurement was carried out for the flow field of high-lift LPT under the influences of static purge flow. The results showed that the rim purge flow significantly increased the overturning and underturning downstream of the endwall region, resulting in aggravating secondary loss. The rotating-rim increased the difference of the circumferential velocity between the mainstream and the purge flow, aggravating the Kelvin-Helmholtz (K-H) instability, inducing the K-H vortex structure with stronger energy amplitude, and further increasing the endwall flow loss. The incoming wakes weakened the energy amplitude of the K-H vortex at the rim purge outlet, thinned the thickness of the low-energy fluid at the blade leading edge. Additionally, the interaction between the wakes and the secondary vortices further suppressed the development of the secondary flow. Nevertheless, the incoming wakes caused additional mixing losses and made a negative impact on the overall aerodynamic performance of the high-lift LPT.

Design and optimization of heat pump with infrared drying for Glycyrrhiza uralensis (Licorice) processing.

A new dryer, integrating infrared and heat pump drying technologies, was designed to enhance licorice processing standardization, aiming at improved drying efficiency and product quality. Numerical simulation using COMSOL software validated the air distribution model through prototype data comparison. To address uneven air distribution, a spoiler was strategically placed based on CFD simulation to optimize its size and position using the velocity deviation ratio and non-uniformity coefficient as indices. Post-optimization, the average velocity deviation ratio decreased from 0.5124 to 0.2565%, and the non-uniformity coefficient dropped from 0.5913 to 0.3152, achieving a more uniform flow field in the drying chamber. Testing the optimized dryer on licorice demonstrated significant improvements in flow field uniformity, reducing licorice drying time by 23.8%. Additionally, optimized drying enhanced licorice color (higher L* value) and increased retention rates of total phenol, total flavone, and vitamin C. This research holds substantial importance for advancing licorice primary processing, fostering efficiency, and improving product quality.

The effect of open-end ignition at different positions on the explosion behaviors of H2/CO/Air in variable cross-section pipe

This work is focused on the explosion performance of syngas/air premixed gas in a self-designed variable cross-section pipe under varying ignition positions (IP1, IP2) and hydrogen volume fraction (α(H2)). Results show that α(H2) has a great influence on the propagation of the flame as well as the maximum flame front velocity (FFVmax) and the maximum overpressure (Pmax). As α(H2) in the syngas increases, the time the flame stays in the pipe is gradually reduced, the FFVmax as well as the Pmax increase regardless of the ignition position. Differently, when α(H2) < 50%, the tclosed at IP1 is shorter than that at IP2. The opposite is true when α(H2) ≥ 50%. This is attributed to the difference in flame velocity and the effect of film breakage. Both α(H2) and variable cross-section chamber structure all affect the evolution of the flame morphology. When ignition at IP2, a “M” flame is observed for the first time at α(H2) = 20%, and a flame resembling a “T” shape appears at α(H2) = 70%. Ignition positions have a great influence on overpressure oscillation. In the case of α(H2) = 15%, the Fourier transform is performed for the pressure curve. When ignited at IP1, secondary unstable oscillations occur during the later stage of flame propagation. However, when ignition at IP2, primary instability oscillations occur in both the early and late stages of flame propagation. The variable cross-section chamber structure plays a role in the flame front velocity (FFV) and overpressure. After the flame front enters the variable section chamber, the FFV reduces, and when the flame front leaves the variable section chamber, due to the sudden decrease of the cross-sectional area, the FFV increases significantly, and FFVmax and Pmax are obtained at this moment.