Uniform Case Research Articles

Impact of planar shear inflow on wake behind a normal flat plate

This study employs a direct numerical simulation to analyze the effects of planar shear inflow on the flow characteristics around a normal flat plate. The influence of shear is examined by comparing it with a uniform inflow condition. Based on the centerline inflow velocity and plate height, the Reynolds number was taken as 170 and the non-dimensional shear rate as 0.1. Flow visualization shows that the wake from uniform inflow is experiencing a temporal beating phenomenon that switches between coherent and incoherent states, whereas the planar shear drives the flow toward a fully incoherent state. A comparison with the uniform inflow case shows that planar shear induces weaker vortex shedding, a lower drag coefficient, and a corresponding increase in the recirculation length. Furthermore, a phase-time analysis using the Hilbert transform revealed that the vortices are shed in-phase in the uniform inflow case, whereas they are mostly out-of-phase in the planar shear case. Reduction of coherent vortices and enhancement of incoherent fluctuations are evident in the planar shear case, thereby affecting the mean velocity and Reynolds stress symmetry and a modest increase in the magnitude of turbulent components.

Thermal performance enhancement for gas turbine blade trailing edge cooling with topology-optimized printable diamond TPMS lattice

The gas turbine blade trailing edge region is a critical concern in the cooling design due to its narrow characteristics, which limit the implementation of cooling structures. With rapid development in additive manufacturing, many complex cooling techniques have been designed to enhance thermal performance and improve flow uniformity for gas turbine blade trailing edges. This study generates a high thermal performance cooling structure for the trailing edge channel using topology optimization and a Diamond-type triply periodic minimal surface (TPMS) structure. The optimized model is obtained by infilling the Diamond structure in the intermediate densities from the topology optimization, where the objective is to maximize heat transfer under constant input power. The flow path constraints are also included to achieve better uniform flow distribution. The optimized models are compared with the baseline circular pin fin and uniform Diamond network at Reynolds numbers of 10,000 to 30,000. The results show that the uniform Diamond structure provides obviously higher heat transfer than the pin fins by up to 314.3 %. The optimized models obtain lower heat transfer but considerably reduce pressure loss by about twice compared to the uniform Diamond case. Even though the pressure loss of the optimized model is higher than in the pin fins, the thermal performance enhancement is increased by 139.7 %-150.2 %. The fluid flow and heat transfer in the optimized model are distributed more uniformly than in the pin fins. Furthermore, a high-resolution CT scan is employed to assess the manufacturability of the proposed design, printed by laser powder bed fusion at a scale of realistic gas turbine blades. The findings show the feasibility of 3D printing for next-generation gas turbine blades.

An Extended Omega-K Algorithm for Automotive SAR with Curved Path

Automotive millimeter-wave (MMW) synthetic aperture radar (SAR) systems can achieve high-resolution images of detection areas, providing environmental perceptions that facilitate intelligent driving. However, curved path is inevitable in complex urban road environments. Non-uniform spatial sampling, brought about by curved path, leads to cross-coupling and spatial variation deteriorates greatly, significantly impacting the imaging results. To deal with these issues, we developed an Extended Omega-K Algorithm (EOKA) for an automotive SAR with a curved path. First, an equivalent range model was constructed based on the relationship between the range history and Doppler frequency. Then, using azimuth time mapping, the echo data was reconstructed with a form similar to that of a uniform linear case. As a result, an analytical two-dimensional (2D) spectrum was easily derived without using of the method of series reversion (MSR) that could be exploited for EOKA. The results from the parking lot, open road, and obstacle experimental scenes demonstrate the performance and feasibility of an MMW SAR for environmental perception.

Testing the non-commutative charged Schwarzschild black hole surrounded by perfect fluid dark matter for thermodynamical features and weak gravitational lensing

This paper is devoted in studying the thermodynamical properties and weak gravitational lensing in the context of a non-commutative charged Schwarzschild black hole surrounded by perfect fluid dark matter. In this context, we study the geometric mass and thermal temperature to discuss the viability of the charged black hole solution by evaluating the specific heat, the phase transition and stability of the configuration. We also study the energy emission process of the black hole. From the thermodynamical properties, we conclude that our studied black hole solution is thermally stable. Moreover, we discuss gravitational lensing in the weak plasma field by considering uniform as well as non-uniform plasma and evaluate the deflection angle where we observe that the deflection angle in the case of uniform plasma is greater than that in non-uniform plasma. We also have studied the image magnification from the source’s brightness and observed that in uniform plasma case, the source image is more magnified than the non-uniform plasma.

The Evolution of Binaries Embedded Within Common Envelopes

Triple stellar systems allow us to study stellar processes that cannot be attained in binary stars. The evolutionary phases in which the stellar members undergo mass exchanges can alter the hierarchical layout of these systems. Yet, the lack of a self-consistent treatment of common-envelope (CE) in triple-star systems hinders the comprehensive understanding of their long-term fate. This paper examines the conditions predicted around binaries embedded within CEs using local 3D hydrodynamical simulations. We explore varying the initial binary separation, the flow Mach number, and the background stellar density gradients as informed by a wide array of CE conditions, including those invoked to explain the formation of the triple system hosting PSR J0337+1715. We find that the stellar density gradient governs the gaseous drag force, which determines the final configuration of the embedded binary. We observe a comparable net drag force on the center of mass but an overall reduction in the accretion rate of the binary compared to the single-object case. We find that, for most CE conditions, and in contrast to the uniform background density case, the binary orbital separation increases with time, softening the binary and preventing it from subsequently merging. We conclude that binaries spiraling within CEs become more vulnerable to disruption by tidal interactions. This can have profound implications on the final outcomes of triple-star systems.

Spin relaxation in persistent spin textures

Abstract Spin relaxation due to the combined diffuse scattering and spin-orbit coupling (SOC) plays a crucial role for the efficient spin transport, which is a prerequisite for spintronic devices. Here, we investigate the spin relaxation in two-dimensional systems with different types of SOC, with a particular focus on the SOC with persistent spin texture (PSO). Based on the Boltzmann transport theory, we calculate spin diffusion matrices within the framework of Dyakonov-Perel mechanism. In the uniform case, it is found that the in-plane and out-of-plane spin relaxations for all considered SOCs are independent. Interestingly, the in-plane spin relaxation for certain PSOs reveals significant anisotropy characterized by the infinite spin relaxation time for the spin oriented along the direction of spin-orbit field. In the non-uniform case, we show that there always exists the static solution for the PSO with SU(2) symmetry, which corresponds the persistent spin helix in real space. Our work is expected to enrich the fundamental understanding of spin relaxation mechanism and provide new guidelines to design spin-orbitronic devices.

Some More For Samoa: The Case for Citizenship Uniformity

Some More For Samoa: The Case for Citizenship Uniformity

Effect of spatially varying earthquake ground motions on seismic response of a railway viaduct considering multiple site configurations

Currently, it is admitted that extended structures are subjected to spatially varying earthquake ground motions. It has been recognized that the causes of this variability are time delay at each support of the structure, coherency loss effect caused by the propagation of seismic waves and local site effect. The spatial variation of local characteristics of the soil profile defines the site effect, which affects the amplitude and the frequency content of seismic ground motion. The main objective of this work is to provide comparative results and evaluate the variation of the dynamic response of a bridge adopting varying characteristics of soil foundation. Based on the density spectral method, an efficient simulation method of spatially varying earthquake ground motions is developed. The simulation of spatially variable seismic ground motions is performed for different locations on the ground surface with varying site conditions. According to of soil classification described in seismic codes, four different soil configurations were considered for generating sixty-four displacement time series. Several dynamics analyses of a bridge to three cases of spatially variable seismic ground motions, besides the uniform case, are made. The results of this study indicate that depending on soil configurations beneath each support, the seismic response may vary significantly.

Trapezoidal and Simpson’s methods with a random design

Abstract The aim of the present paper is first to propose a state-of-art of this domain. Second, some convergence results are established in the case of the Dirichlet distribution. This distribution has the advantage to include both the uniform case and the deterministic one. In a first part, the Dirichlet distribution is defined and some properties are supplied. In a second part, new results are established in connexion with former theorems.

Development of a Uniform Apheresis Case Report Form forStandardized Collection of Apheresis Data.

Apheresis is performed worldwide for an increasing number of indications. The development of common data elements (CDE) for apheresis related areas may facilitate conduct of new research, enhance quality initiatives including benchmarking, and improve patient care. This report describes the systematic development of the Uniform Apheresis Case Report Form (UACRF) as part of the Apheresis in the United States (ApheresUS) program. A consensus panel of 17 diverse experts in apheresis, related specialties, and electronic case report form (eCRF), and database development was assembled. The panel met via online conferencing from November 17, 2020 to December 1, 2021. A draft document was posted online for public comment from October 11, 2021 to November 10, 2021. Feedback was collected using an online survey tool. The consensus panel revised the UACRF. This version was converted to an eCRF with additional changes made to improve usability in this format. The final version of the UACRF was created on August 24, 2023. The UACRF contains 16 modules: procedure and subject eligibility, patient demographics, general procedure information, laboratory parameters, vascular access, common procedure elements, eight procedure specific modules (mononuclear cell collection and seven therapeutic modalities), outcomes, and site information. A total of 137 data elements were created, including 57 with one or more subelements. The UACRF is the first systematic attempt to develop CDE for therapeutic apheresis and white blood cell collections. Further validation of the UACRF is necessary to confirm the tool's ability to collect the relevant data elements and determine the usability of the form.

Performance enhancement of frequency-doubling gyroklystron amplifier by magnetic field tapering

A uniform magnetic field across the device is often used to analyze gyroklystron. In this paper, a tapered magnetic field is applied across the two-cavity 35 GHz frequency-doubling gyroklystron to improve its performance. Device performance is compared between tapered and uniform magnetic field cases using particle-in-cell code “CST.” The result confirms that the tapered magnetic field significantly improves the device performance parameters such as output power, efficiency, gain, and bandwidth compared to uniform magnetic field conditions. With a 1.6-kW driver power, 306 kW RF output power along with 22.8 dB gain is achieved for a tapered magnetic field case, while 227 kW RF output power along with 21.5 dB gain is achieved for a uniform magnetic field case. When the magnetic field is uniform, the efficiency and bandwidth of a gyroklystron are approximately 21.6% and 100 MHz, respectively; however, for the tapered magnetic field, it can rise to 29.1% and 120 MHz, respectively. Device efficiency results suggest that a tapered magnetic field improves energy transfer from the electron beam to the RF field. A parametric study for both magnetic field cases examines the effect of magnetic field strength, beam current, beam voltage, and pitch factor on the device. This detailed research recommends optimizing frequency-doubling gyroklystron performance with tapered magnetic fields.

Similarity of the low-occurrence wind profiles within urban turbulent boundary layers of uniform and non-uniform height block arrays

Within urban boundary layers, the safety of pedestrians is markedly affected by wind speed, particularly in urban areas. The characteristics of turbulence above the canopy layers can lead to unpredictable changes in wind speed at the pedestrian level. Therefore, this study analyzes low-occurrence wind speed phenomena above canopy heights for uniform and nonuniform block configurations using wind tunnel experiments (WTE) to understand the background turbulence characteristics which the wind profile is generated by the boundary layer above the canopy. The urban canopy arrays were reproduced using solid blocks arranged in 30 rows in a streamwise direction with a packing density of 25 % at three different heights. An x-type hot-wire anemometer was used to measure the streamwise and vertical velocity components. The low-occurrence values were classified based on wind speed percentiles of 0.1 %, 1.0 %, 99.0 %, and 99.9 % wind speeds. The results demonstrated that above the canopy, there were minor influences of block height variations on the low occurrence factor. The peak factor demonstrated a comparable value between the uniform and nonuniform cases, regardless of the block arrangement. Statistical models based on the Weibull distribution and Gram–Charlier series demonstrating good agreement with the WTE data in predicting the low occurrence and peak factors. This study found that variations in block height have a minor influence on the low occurrence and peak factors within the turbulent boundary layers, implying that we can separate the effect of background turbulence from the local turbulent generation within the urban canopy layers.

Reverse Thrust Aerodynamics of Variable Pitch Fans with Inlet Distortion

Abstract Variable pitch fans can improve the operability of low pressure ratio fan systems by re-pitching the rotor blades. If a variable pitch fan can generate sufficient reverse thrust on landing it also eliminates the need for heavy, cascade-type thrust reversers. However, any reverse thrust generation is impacted by high levels of inlet distortion generated as air is drawn into the exhaust nozzle. This paper uses RANS computations and low-speed rig experiments to explore how a representative inlet distortion from the engine installation affects the aerodynamics and performance of a variable pitch fan operating in reverse thrust mode. The simulations and the experiments show that the distortion from the engine installation leads to a highly three-dimensional flow field with a large recirculation region within the bypass duct. The distortion substantially redistributes the mass flow, thrust and power in the engine. Streamline tracking combined with a power balance analysis reveals highly radial flow within the fan rotor, with almost all the fan power used to drive the recirculating flow in the bypass duct, generating high loss and high total temperature. The recirculation reduces the net mass flow through the engine to around 5% of a uniform inflow case and greatly reduces the effective reverse thrust. With uniform inflow, the net reverse thrust was found to be 35% of the nominal takeoff thrust. With inlet distortion, this was reduced to 20%. This demonstrates the importance of designing and operating variable pitch fan systems to minimise reverse thrust inlet distortion.

Effects of aspect ratio on flow characteristics on free surface-mounted rectangular cylinders

Turbulent flow characteristics around free surface-mounted rectangular cylinders of different streamwise aspect ratios (AR=1, 2, 2.5, 3, 4, 5, and 8 denoted as AR1, AR2, AR2.5, AR3, AR4, AR5, and AR8, respectively) at a Reynolds number based on the freestream velocity and cylinder height, Reh = 11100, were investigated experimentally using a time-resolved particle image velocimetry system. The results reveal distinct flow behaviors for different aspect ratios. The separated shear layer is shed directly into the wake for AR1, while AR2 and AR2.5 exhibits intermittent reattachment on the cylinder and direct shedding into the wake. However, for AR≥3 cylinders, the separated shear layer reattaches onto the cylinder and is later shed into the wake after subsequent separation from the trailing edge of the cylinder. Comparative analysis with previous studies on rectangular cylinders in uniform flow and wall-mounted conditions demonstrates similarities in reattachment behavior on the cylinder to uniform flow cases and wake reattachment mechanism akin to wall-mounted cylinders subjected to a thin turbulent boundary layer. The Reynolds stresses, turbulence production, and vortex shedding patterns examined with frequency spectra and proper orthogonal decomposition of velocity fluctuations exhibit significant dependence on streamwise aspect ratio.

Shadow and gravitational weak lensing for quantum improved charged black hole in plasma* *Supported partly by Grants F-FA-2021-432, F-FA-2021-510, and MRB-2021-527 of the Ministry of Higher Education, Science and Innovations of the Republic of Uzbekistan

We investigated the shadow and weak gravitational lensing for the quantum-improved charged black hole (BH). First, the photon motion and BH shadow were studied in a plasma medium. It can be seen from our analysis that the radius of the photon sphere of the quantum-improved charged BH and size of the BH shadow decrease under the influence of the plasma parameter . Furthermore, the gravitational weak lensing is considered for the quantum-improved charged BH, and we have obtained the deflection angle of light rays around a compact object for uniform and non-uniform plasma cases. It is shown that the value of the deflection angle for uniform plasma increases with increasing plasma parameter, and vice versa for non-uniform plasma. It has been also indicated that under the influence of the plasma parameter and BH charge , the values of the deflection angles for the two cases decrease. Finally, we investigated the magnification of image brightness using the deflection angle of the light rays around the quantum-improved charged BH.

Flow characteristics and thermal fields in fan-coupled jet impingement

Numerical methods are used to analyze the flow properties and thermal fields of a fan-coupled jet impingement. The shear stress transport(SST) k−ω model has been utilized in the numerical simulation conducted in ANSYS CFX. Initially, the study focuses on flow structures that are driven by pressure gradients. Due to the presence of the pressure gradient, there is a tip leakage vortex moving through the tip gap. In the vicinity of the hub, the boundary layer rolls up to form a passage vortex close to the blade. The presence of these secondary flow structures affects the features of the cooling flow provided by the axial fan. Velocity deficit and high turbulence exist in the regions as a result of the secondary flow structures. Furthermore, to demonstrate how the 3D structures affect the performance of the jet impingement, two comparison cases, named LF-Q and LF-curve, are introduced with uniform incoming flow. In the comparison cases, the axial fan is abstracted as a solid body with pressure rise and flow rate. Compared to the counterparts with uniform incoming flow, the fan-coupled jet shows a greater re-circulation and a narrower main jet as a result of the velocity deficit exiting near the hub. In terms of thermal performance, the fan-coupled jet outperforms a uniform impinging jet with the same flow rate by 1.18 times in total heat transfer. The velocity deficit and larger re-circulation have reduced the heat transport in the central target, while the mainstream with high velocity and strong turbulence has enhanced the heat transfer in the outer region. The fan-coupled jet impingement with high velocity in the narrower jet also shows improved local heat transfer, with a peak Nusselt number (Nu) approximately 1.37 times larger than that of the uniform case with the same flow rate.

Arctic curves of the T-system with slanted initial data

We study the T-system of type A∞ , also known as the octahedron recurrence/equation, viewed as a 2+1 -dimensional discrete evolution equation. Generalizing earlier work on arctic curves for the Aztec Diamond obtained from solutions of the octahedron recurrence with ‘flat’ initial data, we consider initial data along parallel ‘slanted’ planes perpendicular to an arbitrary admissible direction (r,s,t)∈Z+3 . The corresponding solutions of the T-system are interpreted as partition functions of dimer models on some suitable ‘pinecone’ graphs introduced by Bousquet–Mélou, Propp, and West in 2009. The T-system formulation and some exact solutions in uniform or periodic cases allow us to explore the thermodynamic limit of the corresponding dimer models and to derive exact arctic curves separating the various phases of the system. This direct approach bypasses the standard general theory of dimers using the Kasteleyn matrix approach and uses instead the theory of Analytic Combinatorics in Several Variables, by focusing on a linear system obeyed by the dimer density generating function.

Novel Spectrometer Designs for Laser-Driven Ion Acceleration

We propose novel spectrometer designs that aim to enhance the measured spectral range of ions on a finite-sized detector. In contrast to the traditional devices that use a uniform magnetic field, in which the deflection of particles increases inversely proportional to their momentum, in a gradient magnetic field, the deflection of particles will decrease due to the reduction of the magnetic field along their propagation. In this way, low-energy ions can reach the detector because they are deflected less, compared to the uniform field case. By utilizing a gradient magnetic field, the non-linear dispersion of ions in a homogeneous magnetic field approaches nearly linear dispersion behavior. Nonetheless, the dispersion of low-energy ions, using a dipole field, remains unnecessarily high. In this article, we discuss the employed methodology and present simulation results of the spectrometer with an extended ion spectral range, focusing on the minimum detectable energy (energy dynamic range) and energy resolution.

A multi-domain model for microcirculation in optic nerve: Blood flow and oxygen transport

Microcirculation of blood and transport of oxygen play important roles in the biological function of the optic nerve and its diseases. This work develops a multi-domain model for the optic nerve, that includes important biological structures and various physical mechanisms in blood flow and oxygen delivery. The two vascular networks are treated as five domains in the same geometric region, with various exchanges among them (such as Darcy’s law for fluid flow) and with the tissue domain (such as water leak, diffusion). The numerical results of the coupled model for a uniform case of vasculature distribution show mechanisms and scales consistent with literature and intuition. The effects of various important model parameters (relevant to pathological conditions) are investigated to provide insights into the possible implications. The vasculature distribution (resting volume fractions here) has significant impacts on the blood circulation and could lead to insufficient blood supply in certain local regions and thereby affect the delivery of oxygen. The water leak across the capillary wall will have nontrivial effects after the leak coefficients pass a threshold. The pulsatile arterial pressure leads to expected pulsatile patterns and stable spatial profiles, and the uniform case is almost the averaged version of pulsatile case. The effects of viscosity, the stiffness of blood vessel wall, oxygen demand, etc. have also been analyzed. The framework can be extended to include ionic transport or to study the retina when more biological structural information is available.

Hybrid simulation of shock interaction with highly nonuniform plasmas

The impact of capsule imperfections is one of the challenges in achieving reproducible, high-gain ignition of inertial confinement fusion (ICF). The nonuniformities of capsule imperfections, which create instability seeds during the shock propagation, may cause significant performance degradation. A systematic study of the propagation of collisional shock wave in highly nonuniform plasmas is carried out using a hybrid fluid-PIC code, which enables the analysis of electromagnetic fields, ion mixing, and plasma viscosity self-consistently. During shock propagation, it interacts with multiple bubbles and significant material mixing in the nonuniform plasmas are observed. Consequently, the average viscosity of the post-shock plasma in the nonuniform case increases to 1∼2 times that of the uniform case. These results provide a better understanding of the possible influence of capsule imperfections in ICF implosions.