Incoming Flow Research Articles

Regular reflection to Mach reflection (RR–MR) transition in short wedges

Regular reflection (RR) to Mach reflection (MR) transitions ( ${\rm RR}\leftrightarrow {\rm MR}$ ) on long wedges in steady supersonic flows have been well studied and documented. However, in a short wedge where the wedge length is small, the transition prediction becomes really challenging owing to the interaction of the expansion fan emanating from the trailing edge of the wedge with the incident shock and the triple/reflection point. The extent of this interaction depends on the distance between the wedge trailing edge and the symmetry line (Ht). This distance is a geometric combination of the distance of the wedge leading edge from the symmetry line $(H)$ , the wedge angle ( $\theta$ ) and the wedge length $(w)$ . In the present study, we used the method of characteristics to model the complete wave interactions which accurately predicted shock curvatures and the reflection configurations for all ranges of the incoming flow Mach number. In the case of short wedges, the transition criterion strongly depends on the wedge length, which can be so adjusted even to eliminate the ${\rm RR}\rightarrow {\rm MR}$ transitions till the wedge angle reaches the no-reflection domain. Transition lines for both the detachment criterion and von Neumann criterion are also drawn to investigate the dual solution domain, and the reflection configurations were verified experimentally for the first time on short wedges. By using proper input configuration parameter ( $w/H$ ), various types of shifts in the dual solution domain for short wedges are studied and categorised into three types, namely Type I, Type II and Type III.

Novel Fluidic Oscillator Evaluation Considering Dimensional Modifications

Although flow mixing and cooling can be greatly enhanced when considering the use of fluidic oscillators (FOs), they are more commonly employed in active flow control (AFC) applications where the injected pulsating flow interacts with the boundary layer, usually in order to delay its separation. In fact, prior to any FO implementation in a given application, it is essential to study the range of frequencies and amplitudes it can generate as a function of the incoming mass flow and its dimensions. This is what is being performed in the present manuscript for a rather novel FO configuration. A numerical study of a standard three-dimensional (3D) FO configuration, and also using a two-dimensional (2D) approach, is initially presented. After comparing the 3D and the 2D results and analyzing the main differences, we modified some of the internal dimensions of the FO in order to evaluate the variation in its dynamic performance. The present results clarify which internal dimensional modifications are more effective in generating larger output frequencies and velocity field variations. Care is taken to analyze the origin of self-sustained oscillations. This paper links, for the first time, the origin of the pressure force oscillations at the feedback channel’s outlet, with the interaction of the mixing chamber central jet and the reverse feedback channel flow at the mixing chamber’s converging walls. A novel equation relating the FO outlet mass flow frequency with the time-averaged FC reverse flow is presented and discussed. In fact, the present study needs to be seen as the continuation of a former one, recently published by authors, where the effects of several Reynolds numbers as well as some different internal dimensions were considered.

The queuing system of a scientific journal

The results of the research difference of the calendar date between begining and ending editorial processes in the Journal of “Almaz – Antey” Air and Space Defence Corporation are given, and the counting of dates per month for beginning the processes (entering articles, transferring to literacy editing etc.). Based on the analysis it was concluded that the incoming article might be considered as an incoming application to queuing system, which the scientific journal is. For such incoming application can be estimate the distribution functions incoming flows, average and maximum term be in queuing system, also as the distribution functions of the service mode and another characteristics, which stay unchanged (stationary) in time for researched scientific journal.

Investigation of the Influence of Spoiler and Maintenance Track on Second-Order Heaving Vortex-Induced Vibration

To improve the guidance for the wind tunnel test, this study initially conducted thorough research on the wind environment at a coastal bridge site to ascertain the characteristics of the wind parameters varying along the bridge span. Subsequently, the measured results were utilized to steer wind tunnel test research, focusing on analyzing the influence of the spoiler and maintenance track on the second-order heaving vortex-induced vibration of the flat steel box girder. This investigation uncovered two distinct distributions in the angle of attack along the span: bimodal distribution and asymmetric unimodal distribution. The angle of attack of the incoming flow was primarily concentrated within ±5°. Both the two-side and the windward spoiler were found to exert similar effects on the second-order heaving vortex-induced vibration, primarily impacting the second lock-in region. Furthermore, the outer maintenance track could effectively suppress the vortex-induced vibration, while the spacing of the inner maintenance track significantly affected the vortex-induced vibration at high wind speeds.

Harvesting both wind energy and vibration energy by a zigzag structure with hybrid magnetic and piezoelectric effects

In practical environments, wind energy and vibration energy often coexist. Considering this, we introduce a new energy harvester designed to concurrently harness wind energy and vibration energy by integrating magnetic and piezoelectric effects. This harvester is composed of a zigzag structure and a bluff body. The bluff body is designed to execute galloping under incoming fluid flow and produce outputs, while the zigzag bi-stable structure can harness the energy of base excitation effectively. The introduction of magnetic interaction leads tothe softening-spring characteristic, which is verified by the nonlinear analysis. This softening-spring nonlinearity canenhance the working frequency range of the harvester. The results obtained from the numerical simulations indicate that the interaction of base excitation and wind flow can significantly improve the non-resonance region output. Corresponding validation experiments are carried out. The results are in good agreement with the numerical ones. Under stochastic excitations, the output power obtained from the hybrid scenario can reach 73.04 μW, representing a 16 % increase compared to the pure base excitation scenario.

Study on power characteristics of wind turbine on the Loess Plateau terrain based on wind tunnel experiment

In order to investigate the impact of the flow field on wind turbine power in northwest China’s Loess Plateau, a wind tunnel experiment was conducted using a self-designed model that simulated the actual terrain. By comparing experiments utilizing an ideal mountain model under varying incoming wind speeds, it was revealed that the Loess Plateau terrain resulted in an increased inflow wind speed for the wind turbine. This higher inflow wind speed led to an approximate 5% increase in output power but also caused about a 6.1% rise in power fluctuations. Through analysis of the power spectrum of the output, it was discovered that turbulence below the decoupling frequency strongly modulates the output power of the wind turbine. This study also provided insights into spatial scale ranges where incoming flow turbulence structures can modulate output power, ranging from approximately 0.3 times to 5 times the diameter of rotor blades.

Data generation and training of surrogate models for friction factor and Nusselt number in low Reynolds number flows through pin fin geometries

Abstract The design of various biomedical, electronics cooling, and microfluidic devices relies on geometry-specific models and empirical correlations for flow and heat transfer through microscale pin fin geometries. Machine learning techniques are being used across many branches of science to develop more generalized surrogate models that can predict such transport processes. To collapse the simulation of flow and thermal properties across many different pin fin surfaces into a single predictive tool, the present study develops machine-learning-based surrogate models for the friction factor and Nusselt number (for constant wall temperature conditions) for fully developed low Reynolds number flow across pin fin geometries of differing cross-section shape (circular, square, triangular) in aligned or staggered arrangements, oriented at any angle to the incoming flow, and for a range of transverse and longitudinal pitches, with water as the working fluid. The model training data are generated using an automated workflow that allows thousands of numerical simulations to be carried out on across different geometric and flow configurations. A total of ~14,800 distinct simulation cases, for both friction factor and Nusselt number, are generated whilst varying the Reynolds number and aforementioned geometric parameters to train and test the machine learning models. The machine learning model architecture takes inputs of both image and vector data, and then outputs a scalar friction factor or Nusselt number. The trained models yield a goodness of fit (R2) value of 0.98 on unseen data.

Computational Investigation of the Operating Mechanism of the Ranque-Hilsch Vortex Tube

Abstract The Ranque-Hilsch vortex tube is a device that splits an incoming flow into two outgoing streams, but with the peculiar property that one stream exits at a lower total temperature than the incoming flow and the other at a higher total temperature. This temperature separation is accomplished without any moving parts, electronics or external power supplied to the device. Despite the passage of nearly a century since the effect's discovery, there remains a dearth of understanding regarding the mechanism responsible for the phenomenon. In fact, the literature contains competing theories with little evidence providing support. A promising technique to discern the responsible mechanisms for the energy transfer from the ultimately cold stream to the ultimately hot stream is to computationally define a stream tube that propagates upstream from the exits such that the stream tube interface separates the hot flow from the cold flow. In this paper, we apply this method to a three-dimensional, full-volume analysis of the flow within a vortex tube using a computational simulation that was thoroughly validated against experiments on a physical replica of the computational geometry. In this novel study, the integral form of the energy equation was used to quantify all forms of the energy transfer within the vortex tube. The results demonstrate that the phenomenon of temperature separation is attributable primarily to viscous work in the radial direction due to the circumferential flow, with a lesser contribution from heat transfer in the radial direction.

Income of women whose jobs were to sort eucalyptus leaves after the COVID-19 pandemic

Buru Regency is the primary hub for producing eucalyptus oil, a highly valued commodity in the region. The oil extracted from the eucalyptus epidemic plant possesses antiseptic, antibacterial, and antifungal characteristics. Amidst the Covid-19 pandemic, numerous industries require it as a fundamental component of pharmaceuticals. An essential factor in the eucalyptus oil production process is the presence of eucalyptus leaves. Therefore, leaf-sorting workers, including women, are required to ensure this availability. However, in reality, the daily lives of eucalyptus leaf massagers are characterized by challenging economic conditions and a socio-economic environment that lags behind workers in other sectors. This study aims to examine and investigate the roles and work patterns of employed women and the strategies they employ to ensure the consistent flow of household income. The research employed a qualitative methodology with a phenomenological approach. A total of 24 informants were purposefully selected based on their involvement in achieving the research objectives. The results indicate that the COVID-19 pandemic has altered the circumstances of women who collect leaves and rely heavily on eucalyptus trees as a natural resource. Physical adaptation strategies are the preferred methods used to fulfill household requirements. Implementing physical adaptations does not deter women leaf-sorters from continuing their work. Their commitment to meeting their basic needs significantly motivates them to persist in their role as leaf sorters. The income of women engaged in sorting eucalyptus leaves in their households during the COVID-19 pandemic.

Effect of plasma excitation on aerodynamic characteristics of airfoil under Martian conditions

Due to the low density and pressure of the Martian atmosphere, the aerodynamic performance of the airfoil of the Mars UAV needs to be further improved. Plasma excitation active flow control technology is used to improve the lift of the airfoil and reduce the drag of the airfoil under Martian conditions. The effects of the action position, excitation power and incoming flow angle of attack on the lift and drag of the airfoil are studied under the low Reynolds number conditions on Mars. The results show that plasma excitation increases lift in the trailing edge area of the lower surface, with a maximum lift increase rate 37%; reduces drag in the leading edge area of the lower surface, with a maximum drag reduction rate 8%; the greater the excitation power and the smaller the incoming flow angle of attack, the more obvious the improvement of the airfoil lift-to-drag ratio. Plasma excitation induces pressure waves, forming a pressurization zone and a decompression zone upstream and downstream of the excitation, respectively, resulting in the formation of a pressurization surface and a decompression surface on the airfoil surface. When the excitation position is close to the trailing edge, the pressurization surface expands, and the pressure difference between the upper and lower surfaces of the airfoil increases, thereby achieving lift increase; when the excitation position is close to the leading edge, the decompression surface expands, and the pressure difference drag of the airfoil decreases, thereby achieving drag reduction.

Effects of wall heating on wall pressure fluctuations and flow noise in a low-Reynolds-number turbulent channel flow with temperature-dependent viscosity

Wall pressure fluctuations and flow noise substantially degrade sonar detection performance and the acoustic stealth performance of underwater vehicles. This paper numerically investigates the effects of wall heating on wall pressure fluctuations in turbulent channel flow of water with temperature-dependent viscosity, exploring a novel method for controlling wall pressure fluctuations and flow noise in underwater vehicles. Large-eddy simulation (LES) is employed for the numerical calculation of the flow field, while a hybrid method combining LES with Lighthills acoustic analogy is employed to predict flow noise. The numerical results show that when the temperature difference between the wall and the incoming flow is 30 K and 50 K, the peak root-mean-square pressure fluctuations decrease by 6.76% and 8.91%, respectively. Wall heating stabilizes the pressure field near the wall, with the spectral levels of wall pressure fluctuations showing average decreases of approximately 1 dB and 2 dB. Wall heating weakens the energy-containing structures of wall pressure fluctuations and increases the overall convection velocity by 1.22% and 3.81%, respectively. Flow structure analysis reveals that the weakening of energy-containing structures results from the suppression of the vortex structures in the near-wall region. In the wall heating cases, peak turbulent kinetic energy decreases by 12.6% and 15.8%, respectively. Moreover, the sound pressure level of flow noise decreases with increasing wall temperature, with the maximum noise reduction exceeding 3 dB. Previous studies have not yet explored the effects of viscosity reduction caused by wall heating on wall pressure fluctuations and flow noise. This study demonstrates that wall heating is a promising method for reducing wall pressure fluctuations and flow noise.

Methodical approach to determining the main parameters of the evacuation system for the wounded with the use of different types of transport

The timeframe for evacuating the wounded is a critical factor that largely determines the fate of a wounded soldier. Even at the initial stage of the war waged by the russian federation against Ukraine, there were almost no frontline ambulances, and there was a critical shortage of ambulances. At present, despite significant efforts to provide the Armed Forces of Ukraine with weapons and military equipment, as well as material and technical means, including medical equipment and property, in particular through international technical assistance, the problem of the lack of the required number of specialised medical evacuation vehicles has not been fully resolved. From this point of view, the issue of correct formulation of requirements for the rational composition and specially equipped various types of vehicles (including sanitary transporters, ambulances), including general use, the system of evacuation of the wounded, and determining the possibility of its further improvement through the methodological apparatus is relevant. The purpose of the article is to present a methodological approach to determining the main parameters of the system of evacuation of the wounded of an operational group of troops with the involvement of various types of transport. The formation of a model of the casualty evacuation system as a mass service network (MSN) will minimise the time spent waiting for medical care by wounded personnel, determine the rational composition of forces and means of the tactical casualty evacuation system. To model the system and processes of evacuation of the wounded from the battlefield during hostilities, including their transportation to medical facilities located in the depths of the third logistics zone, the mathematical apparatus of the theory of mass service was used. In particular, we are talking about the devices of queuing systems (QS) and MSN. The existing system of military evacuation of the wounded and sick is a four-tier system in which all wounded with moderate and severe severity are evacuated. Based on this, the system of evacuation of the wounded can be represented as an MSN, which has a number of features. First of all, this MSN is an open queuing network (OQN), i.e. the flow of requests to enter the network is unlimited, homogeneous and comes from an external independent source. As a result of the calculations, data were obtained on the values of network parameters (average number of applications in queues – 119.47 applications/hour, average number of applications in the network – 158.53 applications/hour, average waiting time for applications in queues for service – 11.95 hours, average time of application stay in the network – 15.85 hours) and the parameters of each QS operating in the MSN – transmission coefficient, incoming flow intensity, load factor, average number of busy channels, average number of applications per QS, average queue length, average waiting time for an application in the service queue, average time for an application to stay in the QS. Analysing the calculated data, from the point of view of creating a rational OQN, the casualty evacuation system achieves maximum efficiency when its productivity in processing the incoming flow of requests is maximised, and the minimum values of such parameters as the number of requests for service in the queue and the number of service channels operating in the network are minimal.

A Research on Relationship between Tax Revenues and Social Demography: A Comparison of Bosnia and Turkey

Tax revenue is one of the common issues of both public administration and public law. The tax system is an important phenomenon that shows not only the income and cash flow of the country but also the functioning of the legal system and justice within the country. In this study, the population of Bosnia and Herzegovina and tax revenues in Turkey aimed to investigate the relationship between the demographic structure. For this purpose, the data obtained from the World Bank for the last twenty years, the gender, age ratio of the population, and some demographic variables for both countries, urban and rural population rates are associated with tax revenues. In the study, the Kolmogorov Smirnov Test was used for the normality test of data, Mann Whitney U was used for the non-normally distributed data, and the Independent Sample T-test was used for the normally distributed data. Correlation and regression analysis and Granger Causality Test were performed for both countries. According to the results of the study, changing demographic variables affect indirectly even if they are not directly influential in affecting tax revenues. Therefore, in order to ensure fairness in tax distribution and the allocation of a more effective tax distribution system, a tax system that takes into account demographic variables and evaluates regional and social differences in a better way is needed. Although Turkey to Bosnia and Herzegovina in accordance with a more comprehensive macroeconomic structure, Bosnia and Herzegovina has a more regular distribution of the tax system.

Dynamics and energy harvesting of a flow-induced snapping sheet with nonuniform stiffness distribution

Energy harvesting through periodic snap-through of a buckled sheet has recently gained considerable attention because of its potential applications in energy harvesting in low incoming flow. Although the snapping dynamics of uniform buckled sheets has been extensively studied, the present work focuses on the energy harvesting and dynamics of a nonuniform snapping sheet with both of its ends clamped in a channel flow. The analysis reveals that the sheet undergoes periodic snap-through oscillations, with its rear half consistently serving as the main contributor to effective energy harvesting, and the potential energy contributing significantly more than the kinetic energy. Varying the stiffness difference ΔEI* shows that increasing the stiffness of the rear part and decreasing that of the fore part shifts the deformation wave toward upstream and enhances the snapping amplitude of the fore part, optimizing energy extraction. At a length compression ratio ΔL* = 0.3, the maximum potential energy is observed for ΔEI* = 1, and the total energy peaks at ΔEI* = 2. The study also identifies an optimal ΔL* = 0.4 that maximizes both total and potential energies, and triples the potential energy in comparison with ΔL* = 0.1. However, the enhancement of nonuniformity disappears at ΔL* > 0.3 for the total energy and ΔL* > 0.2 for the potential energy. These findings provide insights to aid optimization of the design and performance of snapping sheet energy harvesters.

Pengaruh Persepsi Dan Pemahaman Tentang Laporan Keuangan Terhadap Kualitas Laporan Keuangan Pelaku UMKM

This research attempts to ascertain how business actors' attitudes and comprehension impact the quality of financial reports in Kecamatan Johan Pahlawan, West Aceh Regency. While presenting comprehensive financial reports is challenging for them because not all business owners have studied accounting in-depth, some MSME actors in Johan Pahlawan District believe that accounting is not that important. All they know is that it records incoming and outgoing cash flows. tief. The general public has very little knowledge of accounting, but businesses of a reasonably big size may afford to hire an accountant or purchase software to make it easier to prepare financial reports that comply with current laws. A quantitative technique was used in this investigation. Primary data from a research sample of ninety-three MSME actors in Kecamatan Johan Pahlawan, West Aceh Regency, was directly gathered via the use of questionnaires by the researchers for the objectives of this study. Multiple linear regression data analysis is the technique employed. Based on the study's findings, Kecamatan Johan Pahlawan, West Aceh Regency's MSME financial reports' quality is significantly influenced by business actors' attitudes and knowledge, with a significant value of 0.000. The quality of MSME financial reports in Johan Pahlawan District, West Aceh Regency, is thus determined by the perception and comprehension of business players, leading to the conclusion that the alternative hypothesis statement (Ha3) is accepted.

Analysis of Processes Accompanying Cylindrical Cumulation

Flow contraction within cylindrical samples causes instability in motion, leading to the formation of circumferential compression stress. This then results in perturbations in the form of Mach three-shock configurations (protrusions) at the shock front. The area at the front of the perturbed shock wave increases due to these protrusions. Furthermore, the protrusions are amplified as a consequence of the absorption of smaller perturbations, which are continuously generated at the shock front. The shock front undergoes sharp growth at the final stage, giving rise to several large protrusions that divide it into separate sectors. These sectors undergo oscillatory movements. As the counter configurations collide, a high-pressure zone is generated, which propels some of the compressed material forward. The protrusions reach their maximum height when they become equal to the distance of the front to the axis. The near-axis region is taken up by the frontal protrusions, and the consequent rarefaction shock wave decelerates the incoming flow.

Numerical simulation and experimental study on guidance performance of hypersonic seeker under aerodynamic optical transmission effects

When a hypersonic seeker flies at high speed within the atmosphere, intense interaction with the incoming flow gradually develops into a complex turbulent flow field. This interaction results in complex thermal responses at the seeker window, causing aerodynamic optical effects such as image shift, jitter, and blur of the target image, thereby restricting the seeker's detection capability and accuracy. This paper uses a numerical simulation model for the guidance performance of a hypersonic seeker under aerodynamic optical transmission effects. The study focuses on an ellipsoidal seeker, with its supersonic flight simulation on the basis of the Reynolds-Averaged Navier-Stokes (RANS) equations to get a non-uniform gradient flow field. The correctness of the flow filed results can be verified by wind tunnel experiments. The transient temperature field of the seeker is solved using an unsteady thermal conduction-radiation coupled fluid-solid heat transfer method. Finally, the guidance performance of the hypersonic seeker under aerodynamic optical effects is predicted using the ray tracing method, which employs wavefront aberration, point spread function, degraded images, and image shift.

The influence of vortex structures on the aerothermodynamics of aerospace vehicles

Numerical simulation of supersonic flow around sequentially arranged wings, which include a vortex generator wing and a downstream main wing, have been conducted. Aerodynamic configurations of this type can be found on various re-entry spacecraft. This study investigates the influence of vortex structures on the magnitude and distribution of pressure, temperature, and heat fluxes on the surface of the main wing. The supersonic incoming flow at Mach number M∞ = 3 and Reynolds number ReL = 1∗107 with different attack angles (10° - 20°) of the generator wing and the main wing is considered. It has been established that under certain parameter values, there is a reduction in the drag experienced by the main wing and a decrease in temperature on its surface.

Influence of the shock wave-turbulence interaction on the swirl distortion in hypersonic inlet

This study uses the Large Eddy Simulation (LES) technique to conduct an exhaustive analysis of the flow characteristics within the Rectangular-to-Elliptical shape Transition (REST) inlet under Mach 6 conditions. It mainly focuses on investigating the influence of the shock wave-turbulence interaction on the swirl distortion at the inlet exit. At the design condition, characterized by 0° Attack and 0° Sideslip, the incident shock wave at the inlet lip undergoes multiple reflections within the boundary layer of the domain wall, culminating in the formation of turbulent structures. The first reflected shock wave has the highest energy, exerting a significant impact on the boundary layer and the exit swirl distortion. On the contrary, the energy of the incident shock wave is progressively reduced due to repeated reflections, which results in reducing the exit swirl distortion. Under off-design conditions, characterized by 6° Attack and 0° Sideslip as well as 6° Attack with 6° Sideslip, variations in the incoming flow make the incident shock wave move inward, decreasing the frequency of shock wave reflections and even significantly reducing the reflected shock waves under conditions of 6° Attack and 6° Sideslip. However, this results in significantly increasing the exit swirl angle and distortion intensity. The obtained results demonstrate that changes in the incoming flow conditions significantly affect the level of exit swirl distortion by modulating the shock wave-turbulence interaction, especially in terms of the positioning of the incident shock wave and the quantity of reflected shock waves. In addition, this paper studies the wall heat transfer coefficient of the inlet. The obtained results show that the interaction between shock waves and the boundary layer significantly affects the heat transfer coefficient. This study provides a foundation for the comprehension and prediction of the performance of hypersonic inlets across a spectrum of flight conditions, and for the guidance of the design and optimization of such inlets.

Redundancy Design of FADS System for Complex Leading- Edge Aircraft Based on Neural Network

The flush airdata sensing system (FADS) calculates flight parameters such as angle of attack, sideslip angle, Mach number, incoming flow pressure and static pressure based on the pressure measurement of the aircraft surface. It can effectively solve the problem that the leading edge of the pitot tube protruding from the fuselage cannot adapt to the severe aerodynamic heating faced by hypersonic aircraft during the cruise phase, and at the same time meet the aircraft's demand for stealth performance. At present, there is little analysis and research on the use of neural network methods and FADS systems for complex leading edge aircraft. In view of the subsonic/transonic conditions of hypersonic aircraft returning autonomously during the landing phase, the redundancy design and verification of the head FADS system of complex leading edge aircraft are carried out considering the influence of thin leading edge and inlet components. 15 pressure measuring holes are opened in the head of the complex leading edge aircraft. Through a large number of refined numerical simulations, the pressure database of the aircraft under different incoming flow conditions is established, and the typical working conditions are verified by wind tunnel tests. For the complex leading edge aircraft, 4 sets of neural network algorithms are established based on pressure data and redundant design research is carried out, including 1 set of 9-hole algorithm and 3 sets of redundant algorithms. Among them, the 9-hole algorithm has a higher accuracy, with the solution error of the angle of attack within 0.07∘, the solution error of the sideslip angle within 0.3∘, the solution error of the Mach number within 0.0012, and the relative error of the solution of the incoming flow pressure and static pressure within 1.5%. In addition, a system solution process with a certain fault tolerance was established, which can continue to maintain the effective output of the incoming flow parameters in the event of failure of any single pressure measuring hole.