Axial Positions Research Articles

An accessible technique for molecular weight determination by cryoscopy applicable for coordination compounds

An improved computerized method is proposed for determination of molecular weights by cryoscopy. The use of a precision digital platinum resistance thermometer greatly simplifies the measurement process in comparison with the classic Beckmann apparatus. All component parts of the device are factory-made (interchangeable) details, which are widely used in laboratory practice. A test report is formed with the aid of a computer using Microsoft Excel software. The use of molecular sieves for drying dimethyl sulfoxide (DMSO), as well as experimental procedures specific to organolithium compounds, make it possible to obtain reproducible measurement results for coordination compounds that are prone to oligomerization in solutions. The molecular structure of the bis(acetylacetonato)di(dimethyl sulfoxide)nickel(II) obtained from dimethyl sulfoxide solutions was determined by single crystal X-ray diffraction. P21/c, a = 8.7916(2), b = 12.3061(3), c = 8.7421(2) (Å), β = 99.4460(10)°, Z = 2. The complex [Ni(C5H7O2)2(C2H6OS)2] is mononuclear with a square-bipyramidal environment of the central atom. The coordination polyhedron of the Ni ion is formed by four oxygen atoms of two chelating acetylacetonate anions in the equatorial position and two atoms of dimethyl sulfoxide molecules in axial positions.

How Do Differences in Electronic Structure Affect the Use of Vanadium Intermediates as Mimics in Nonheme Iron Hydroxylases?

We study active-site models of nonheme iron hydroxylases and their vanadium-based mimics using density functional theory to determine if vanadyl is a faithful structural mimic. We identify crucial structural and energetic differences between ferryl and vanadyl isomers owing to the differences in their ground electronic states, i.e., high spin (HS) for Fe and low spin (LS) for V. For the succinate cofactor bound to the ferryl intermediate, we predict facile interconversion between monodentate and bidentate coordination isomers for ferryl species but difficult rearrangement for vanadyl mimics. We study isomerization of the oxo intermediate between axial and equatorial positions and find the ferryl potential energy surface to be characterized by a large barrier of ca. 10 kcal/mol that is completely absent for the vanadyl mimic. This analysis reveals even starker contrasts between Fe and V in hydroxylases than those observed for this metal substitution in nonheme halogenases. Analysis of the relative bond strengths of coordinating carboxylate ligands for Fe and V reveals that all of the ligands show stronger binding to V than Fe owing to the LS ground state of V in contrast to the HS ground state of Fe, highlighting the limitations of vanadyl mimics of native nonheme iron hydroxylases.

Platinum (IV) drugs with cannabidiol inducing mitochondrial dysfunction and synergistically enhancing anti-tumor effects

Chemotherapy resistance is an insurmountable problem in clinical anticancer therapy. Although Oxaliplatin is an effective chemotherapeutic agent for the treatment of colorectal cancer (CRC), it still suffers from serious toxicities as well as drug resistance. In this work, three Oxaliplatin tetravalent platinum prodrugs(O1-O3) and three novel mixed ammine/amine analogs(C1-C3) were constructed, introducing cannabidiol with anti-tumor activity in their axial position. All Pt(IV) prodrugs exhibited potent antitumor effects in a variety of tumor cell lines, especially in HCT-116 cells, where complex O3 showed strong inhibitory effects with the half maximal inhibitory concentrations (IC50) value of 6.02 ± 0.69 μM and about 2.6 times higher than that of Oxaliplatin. Further studies revealed that complex O3 decreased cellular mitochondrial membrane potential in a concentration-dependent manner and enhanced reactive oxygen species (ROS) accumulation by decreasing the expression of catalase, superoxide dismutase 2 (SOD2) and superoxide dismutase 3 (SOD3). Complex O3 induces mitochondrial dysfunction and upregulates the pro-apoptotic protein Noxa, ultimately leading to severe DNA damage. The upregulation of Phosphorylated histone protein H2AX (γ-H2AX) expression is clear evidence. In addition, O3 inhibits the expression of RAD51 protein and prevents DNA damage repair, thus overcoming drug resistance. This strategy of combining bioactive molecules cannabidiol with platinum drugs to improve therapeutic efficacy and overcome drug resistance has been proven to be very effective and deserves further investigation.

Assessment of the minimal distance for placing household connections downstream of water distribution cross junctions

Abstract This study investigates the solute (chlorine residual) mixing phenomena downstream of a cross junction, considering its critical role in household connections. Experiments were conducted under turbulent flow conditions in a cross junction with two inlets at 90°, varying flow and chlorine concentration ratios at the inlets, i.e., simulating conditions commonly found in real water distribution systems. Results show that outlet chlorine concentrations primarily depend on the flow ratio at the inlets as well as on the inlet chlorine concentrations. Three-dimensional simulations were conducted to predict chlorine concentrations downstream of the cross junction. To evaluate the degree of downstream mixing, the percent coefficient of variation of tracer concentration (%CV) as a function of the axial position at different chlorine and flow ratios was computed from simulations. It was found that the flow ratio strongly affects it at downstream distances less than 50 pipe diameters, whereas the inlet chlorine concentration ratio has a weak effect. A novel correlation was derived as a function of flow ratio to ascertain the minimal distance for achieving the intended mixing level of %CV = 5 downstream of cross junctions. This correlation holds potential as a criterion for household connection location within water distribution networks for high-quality water delivery.

Spectroscopic properties, crystal structure, Hirshfeld surface analysis and DFT study of a new Cu(II) complex based on quinazolinone O,N,O-donor ligand

A quinazolinone-based Schiff base ligand 3-[(2‑hydroxy-5-methoxybenzylidene)amino]-2-(2‑hydroxy-5-methoxyphenyl)-2,3-dihydroquinazolin-4-one (L1) and its new mononuclear copper(II) complex [Cu(L1)Cl(H2O)] (1) were synthesised and fully characterised by various spectroscopic techniques (NMR, FTIR, UV–Vis) and single-crystal X-ray diffraction study. The aspherical model of the crystal structure of the ligand L1 as well as of the copper(II) complex 1 was refined by the Hirshfeld Atom Refinement method. The crystal structure of the copper(II) complex shows the existence of a substitution disorder at the position of the water molecule, which represents two different complex molecules [Cu(L1)Cl(H2O)] (1a) and [Cu(L1)Cl] (1b) with different coordination polyhedra around the copper atom. The majority of the mononuclear complex [Cu(L1)Cl(H2O)] (1a) in the crystal structure contains a coordinated water molecule, but the minority in the crystal structure contains a mononuclear complex [Cu(L1)Cl] (1b) and a water molecule is outside the coordination sphere around the copper atom. The crystal structure of complex 1 showed a penta-coordinated (1a) or tetra-coordinated (1b) Cu atom in the shape of a tetragonal pyramid (1a) or square planar (1b) formed by a chloride atom in the equatorial plane, and a Schiff base bound as an O,N,O-tridentate ligand, and an additional water molecule in the axial position (only 1a). A detailed analysis of the intermolecular interactions was investigated using three-dimensional 3D Hirshfeld surfaces and their associated two-dimensional 2D fingerprint plots. Hirshfeld surface analysis was performed for both crystal structures. Furthermore, theoretical DFT analysis has been performed in order to interpret the experimental data. In order to obtain high quality DFT data, we present here a new basis set B1MH, which is an extension of the LanL2DZ basis with incorporated polarisation and diffusion functions for heavy atoms (C, N, O, Cl and Cu) and added ECPs for Cl and Cu atoms. The presented B1MH basis set allowed us to obtain better theoretical results than those previously published.

A new approach for fast field calculation in electrostatic electron lens design and optimization

In electron optics, calculation of the electric field plays a major role in all computations and simulations. Accurate field calculation methods such as the finite element method (FEM), boundary element method and finite difference method, have been used for years. However, such methods are computationally very expensive and make the computer simulation challenging or even infeasible when trying to apply automated design of electrostatic lens systems with many free parameters. Hence, for years, electron optics scientists have been searching for a fast and accurate method of field calculation to tackle the aforementioned problem in the design and optimization of electrostatic electron lens systems. This paper presents a novel method for fast electric field calculation in electrostatic electron lens systems with reasonably high accuracy to enable the electron-optical designers to design and optimize an electrostatic lens system with many free parameters in a reasonably short time. The essence of the method is to express the off-axis potential in an axially symmetrical coordinate system in terms of derivatives of the axial potential up to the fourth order, and equate this to the potential of the electrode at that axial position. Doing this for a limited number of axial positions, we get a set of equations that can be solved to obtain the axial potential, necessary for calculating the lens properties. We name this method the fourth-order electrode method because we take the axial derivatives up to the fourth order. To solve the equations, a quintic spline approximation of the axial potential is calculated by solving three sets of linear equations simultaneously. The sets of equations are extracted from the Laplace equation and the fundamental equations that describe a quintic spline. The accuracy and speed of this method is compared with other field calculation methods, such as the FEM and second order electrode method (SOEM). The new field calculation method is implemented in design/optimization of electrostatic lens systems by using a genetic algorithm based optimization program for electrostatic lens systems developed by the authors. The effectiveness of this new field calculation method in optimizing optical parameters of electrostatic lens systems is compared with FEM and SOEM and the results are presented. It should be noted that the formulation is derived for general axis symmetrical electrostatic electron lens systems, however the examples shown in this paper are with cylindrical electrodes due to the simplicity of the implementation in the software.

Effect of Surface Reaction on the Distribution Characteristics of Temperature and OH Radicals in Microchannel Combustion

Microchannel burners suffer from low combustion efficiency and poor stability in applications. In order to explore the effect of wall reaction on methane/air premixed combustion performances in the microchannel, the effects of wall activity, inlet velocity, pressure, and equivalence ratio on the temperature and radical distribution characteristics were studied by CFD computational simulations. It is found that as the reaction pressure increases, there are more free-radical collisions, causing the reaction temperature to rise. The OH radicals participate in the reaction at the active near wall so that the mass fraction of the OH radical on the active wall is lower than that on the inert wall. As the equivalence ratio increases from 0.6 to 1.2, the high-temperature regions increase but the maximum temperature decreases. The mass fraction of OH radical increases with the increase of the equivalence ratio, and the increase of OH radical near the inert wall is larger than that of the active wall. As the flow rate increases, the disturbance increases, and the combustion reaction becomes more intense, resulting in an increase in the temperature and the mass fraction of OH radicals. The mass fraction of H, O, OH, and CH3 radicals in the inert wall was slightly higher than that in the active wall, in which the peak mass fraction of CH3 radical appeared at the axial position closest to the entrance, while the other three radicals reached the peak at about the same axial position. This study provides a reference for combustion stability in microcombustors.

Numerical Investigation of the Interaction of a Circumferential Groove Casing Treatment and Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage

Abstract Eckel et al. (2023, “Numerical Investigation of Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage,” ASME J. Turbomach., 145(4), p. 041003) proposed using a convex-profiled pressure side region close to the tip, known as belly, as an effective method of extending the operating range of low-speed axial compressor rotors. In the literature, circumferential grooves are another well-described technique for improving the stable working range of a compressor rotor. No research has been conducted to date to determine which modification is more effective and how they interact when used together. This paper numerically investigates the influence of circumferential casing grooves and near-tip modifications on the flow field in the tip region of a highly loaded, low-speed axial compressor rotor. The simulated rotor consists of a hybrid blade configuration with a tandem profile in the mid-span region and single blade profiles near the endwalls. The single blade profile close to the tip features three different convex-profiled elements, which differ in their respective thicknesses. The aim of the numerical analysis is to explain the interaction of the secondary flow phenomena when applying the circumferential grooves and the belly geometries. For this purpose, eight different axial positions of the circumferential groove are investigated for each of the three belly configurations. These are arranged in 10% increments from −7% to 63% along the axial rotor tip chord. The potential of the concept is evaluated by a numerical investigation in the 1.5-stage setup with an inlet guide vane and tandem stator. It is shown that a circumferential groove can further increase the operating range for all belly configurations when positioned axially correctly. In this respect, equalization of the near-casing deceleration in the circumferential direction leads to an extension of the stall margin with both modifications. Concentrated regions of low-momentum fluid with a large extent in the radial direction should be avoided consequently. A tip vortex stability factor is introduced to quantitatively evaluate this effect. The operating range can thus already be estimated in a first approximation at the design point. In general, the groove and belly should be positioned where the tip leakage vortex meets the pressure side of the adjacent blade. If the groove is used together with the belly, the leading edge of the former should be situated at the location of maximum thickness of the near-tip modification. The effects of the circumferential groove and the belly are then superimposed. If using only one modification, the belly appears better suited for ensuring an extension of the operating range while maintaining high efficiencies.

Oxaliplatin(IV) Prodrugs Functionalized with Gemcitabine and Capecitabine Induce Blockage of Colorectal Cancer Cell Growth-An Investigation of the Activation Mechanism and Their Nanoformulation.

The use of platinum-based anticancer drugs, such as cisplatin, oxaliplatin, and carboplatin, is a common frontline option in cancer management, but they have debilitating side effects and can lead to drug resistance. Combination therapy with other chemotherapeutic agents, such as capecitabine and gemcitabine, has been explored. One approach to overcome these limitations is the modification of traditional Pt(II) drugs to obtain new molecules with an improved pharmacological profile, such as Pt(IV) prodrugs. The design, synthesis, and characterization of two novel Pt(IV) prodrugs based on oxaliplatin bearing the anticancer drugs gemcitabine or capecitabine in the axial positions have been reported. These complexes were able to dissociate into their constituents to promote cell death and induce apoptosis and cell cycle blockade in a representative colorectal cancer cell model. Specifically, the complex bearing gemcitabine resulted in being the most active on the HCT116 colorectal cancer cell line with an IC50 value of 0.49 ± 0.04. A pilot study on the encapsulation of these complexes in biocompatible PLGA-PEG nanoparticles is also included to confirm the retention of the pharmacological properties and cellular drug uptake, opening up to the possible delivery of the studied complexes through their nanoformulation.

A new paddle wheel type Cu(II) complex with photoluminescence and photocatalytic properties

A paddle wheel-shaped complex formulated [Cu2(piv)4(CH3OH)2]·1.5(CH3OH)·0.5(H2O) (1) has been synthesized by a reaction of Cu(NO3)2·3H2O with pivalic acid. The structure of the complex is characterized by FTIR, elemental analysis and single X-ray crystallography. The crystal structure demonstrates that complex exhibits a paddle wheel type configuration. The asymmetric unit of 1 is composed of a half molecule due to the existence of an inversion center between the two Cu(II) centers. The oxygen atoms of the pivalate serve as bridging ligands, and the two methanol molecules occupy the axial position. Each pivalate ion has syn-, syn- coordination mode and its geometry may be described as square pyramidal. The complex works well as a photocatalyst, breaking down methylene blue (MB) by 78.26% after 120 minutes of 30 W ultraviolet light exposure. The optimized photocatalytic parameters were as follows; catalyst loading = 40 mg, primary concentration of MB = 15 mg/L, temperature = 323K, and pH = 8. The reaction kinetics were best demonstrated by a pseudo-first-order kinetic model followed by a rate constant of 0.00715 min–1. The reuse of the catalyst over five photocatalytic runs suggested its excellent sustainability and recyclability. Hydroxyl radicals and superoxide anions were found to be active participants in the catalytic reaction, as investigated by scavenging studies. These findings contributed to a deeper understanding of the mechanistic aspects of the photocatalytic reaction. Theoretical investigation is well support to experimental work.

Unveiling geometric and electronic structures of NbSi4−/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation

AbstractThis article presents computational insights into the geometric and electronic structures of NbSi4−/0 clusters using density functional theory and the CASSCF/CASPT2 method. The anionic and neutral ground states are identified as the 1A′ and 2A′ states, respectively, within a trigonal bipyramidal isomer where the Nb atom occupies the equatorial position. The adiabatic detachment energy for the transition from the anionic ground state 1A′ to the neutral ground state 2A′ is estimated to be 2.30 eV. Additionally, an evaluation of the vertical detachment energies for transitions to the neutral states 12A′, 12A″, 22A′, 22A″, 32A′, 32A″, and 42A′ yields respective values of 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, and 4.28 eV. These computed electron detachment energies successfully account for all five bands observed in the photoelectron spectrum of the anionic cluster. Furthermore, the Franck–Condon factor simulations reveal extensive vibrational progressions associated with the transition to the neutral ground state 12A′, manifesting as an unresolved broad band at 2.41 eV in the spectrum.

Platinum(IV) Prodrugs Incorporating an Indole-Based Derivative, 5-Benzyloxyindole-3-Acetic Acid in the Axial Position Exhibit Prominent Anticancer Activity.

Kinetically inert platinum(IV) complexes are a chemical strategy to overcome the impediments of standard platinum(II) antineoplastic drugs like cisplatin, oxaliplatin and carboplatin. In this study, we reported the syntheses and structural characterisation of three platinum(IV) complexes that incorporate 5-benzyloxyindole-3-acetic acid, a bioactive ligand that integrates an indole pharmacophore. The purity and chemical structures of the resultant complexes, P-5B3A, 5-5B3A and 56-5B3A were confirmed via spectroscopic means. The complexes were evaluated for anticancer activity against multiple human cell lines. All complexes proved to be considerably more active than cisplatin, oxaliplatin and carboplatin in most cell lines tested. Remarkably, 56-5B3A demonstrated the greatest anticancer activity, displaying GI50 values between 1.2 and 150 nM. Enhanced production of reactive oxygen species paired with the decline in mitochondrial activity as well as inhibition of histone deacetylase were also demonstrated by the complexes in HT29 colon cells.

Reconstruction and prediction of the rotor wake flow field in hovering state

A clear understanding of the flow structure and evolution of the rotor wake flow field is one of the key problems to be solved in the development of rotor aerodynamics. The tip vortices are the primary structure of the rotor wake flow field. A theoretical model of the vortex ring was established to verify the feasibility of flow field reconstruction. Particle image velocimetry (PIV) is used to measure the two-dimensional velocity field in the rotor wake. Because of the wandering motion of tip vortices, a new conditional average algorithm is proposed to deal with the flow field. On this basis, it is proposed that the plane interval of the rotor wake flow field reconstructed by interpolation should be less than 20 deg. The vortex core radius is obtained by the analysis method based on the circulation. A Back Propagation (BP) neural network was established to predict the axial and radial positions of the tip vortices and the radius of the vortex core. The inputs are the vortex ages measured by the experiment, and the outputs are the position and radius of the vortex core under any vortex ages. The predicted values were in good agreement with the experimental results. The study provides further analytical methods and new insights for the characteristics and evolution of tip vortices.

The isotopic composition of the new enriched silicon crystal Si28-31Pr11: maintaining the realization and dissemination of the mole and the kilogram via the XRCD method

The molar mass and isotopic composition of a new silicon single crystal material (Si28-31Pr11) highly enriched in 28Si has been determined in the context of the x-ray crystal density method used for the realization and dissemination of the SI base units‒the mole and the kilogram. Isotope ratio measurements have been performed using a high-resolution multicollector-inductively coupled plasma mass spectrometer (MC-ICP-MS) with improved technical performance. By applying the Virtual-Element Isotope Dilution Mass Spectrometry method, different crystal areas enclosing the locations of two silicon spheres have been investigated with respect to the magnitude of tentative variations in the molar mass and isotopic composition of the respective samples as a function of their original location in the crystal ingot. In total, 18 subsamples from four different axial and several related radial positions have been characterized. An average molar mass M(Si28-31Pr11) = 27.976 941 464(41) g mol−1 corresponding to a relative combined uncertainty u c,rel(M(Si28-31Pr11)) = 1.4 × 10−9 was yielded. The average enrichment in 28Si of the crystal is expressed by the mean amount-of-substance fraction x(28Si) = 0.999 985 350(37). Two spheres were cut from the crystal ingot. The average molar masses of the spheres Si28kg_03_a and Si28kg_03_b are: M(Si28kg_03_a) = 27.976 941 467(43) g mol−1 and M(Si28kg_03_b) = 27.976 941 461(44) g mol−1, respectively. The results are discussed using uncertainty budgets according to the Guide to the expression of uncertainty in measurement. A homogeneous distribution of the molar mass throughout the crystal is suggested, qualifying it as a material for a primary standard–a silicon sphere–for the realization and dissemination of the mole and the kilogram. A comparison with enriched silicon crystals that are already available is given.

Tuning Fluorescence and Singlet Oxygen Quantum Yields of Subporphyrazines by Axial Functionalization.

The axial functionalization of Subporphyrazines (SubPzs) with unreported alkoxy groups, carboxy and carboperoxy rests, as well as sulfanyl, aryl and amino groups, forming B-O, B-S, B-C, and B-N bonds, respectively, has been investigated. The studied oxygen nucleophiles include aromatic and sterically demanding aliphatic alcohols, along with carboxylic acids and peracids. In general, direct substitution of the chloro-SubPz by oxygen nucleophiles of diverse nature proceeds smoothly, with yields of the isolated alkoxy and carboxy-substituted SubPzs ranging from 49 to 100 %. Conversely, direct substitution with sulphur, carbon and nitrogen nucleophiles do not afford the corresponding substituted SubPzs. In these cases, a stepwise procedure involving an axial triflate-SubPz intermediate was employed, affording only the phenyl-SubPz in 8 % yield. The major compound under these conditions was the unreported SubPz μ-oxo dimer, presumably arising from substitution of the triflate-SubPz by the in situ generated hydroxy-SubPz. This result indicates a quite low reactivity of the TfO-SubPz intermediate with carbon, sulphur and nitrogen nucleophiles. All SubPzs prepared in this work exhibited fluorescence at 510-515 nm with quantum yields ranging from 0.1 to 0.24. Additionally, all SubPzs generated singlet oxygen, with ΦΔ values ranging from 0.15 to 0.57, which show no apparent correlation with the axial substituents.

Non-uniform flow characteristics and rotating instability of a transonic high-pressure compressor rotor with cavity bleed

The presence of bleed in an aero engine’s compressor can significantly impact its flow characteristics and contribute to rotating instability. This study focuses on the impact of a typical cavity bleed structure on the internal flow characteristics of a compressor, specifically its circumferential non-uniformity and aerodynamic stability. A numerical simulation involving multiple flow passages was conducted on the transonic high-pressure rotor of the E3 compressor, considering its typical bleed structure. The study delves deep into the non-uniform flow characteristics and the mechanisms behind their generation in the compressor flow field. Furthermore, the influence of bleed on the rotating instability of the compressor is explored by comparing changes in compressor instability and adiabatic efficiency under uniform and non-uniform flow field conditions. The findings indicate that the axial position of the cavity bleed structure plays a crucial role in influencing key parameters such as rotor stall margin, peak efficiency, and total pressure ratio under near-stall conditions. The circumferential non-uniformity, resulting from the presence of the cavity bleed, intensifies with higher bleed air flow rates. For the upstream bleed configuration applied to the rotor, with a total bleed rate of 5%, the maximum variation in absolute flow angle at the inlet of different rotor channels can reach up to 1°. Additionally, the maximum difference in inlet flow coefficient can reach 0.0392. These findings demonstrate that the non-uniformity caused by the typical bleed structure leads to a loss in stall margin for the rotor when compared to a uniform flow field scheme.

Vibration analysis of a double-row planetary gear set considering the sun gear axial position.

Double-row planetary gear set (PGS) is a common form of the PGS, which is relatively more complex than the regular PGSs. It consists of one sun gear, several long planets, several short planets, two ring gears, and one carrier. Due to the significantly wider tooth width of the long planet compared to the sun gear, the axial meshing position between the sun gear and the long planet can be adjusted. The vibrations of PGS should vary with different axial meshing positions. If the axial position of the sun gear is optimized, the vibrations of PGS can be reduced. This work establishes a dynamic model of a double-row PGS. The dynamic model considers the mesh forces of the gear pairs and the supporting forces of the bearing. The effect of the sun gear axial position on the sun gear and ring gear #2 vibrations are investigated. Finally, the recommended axial position for the sun gear is provided.

An in-depth examination of flow structures organization downstream of a delta-winglet pair vortex generator under laminar, transitional, and turbulent flow regimes

In the present study, we experimentally investigate the time-averaged and time-evolving flow structures generated downstream of a delta-winglet pair vortex generator in an airflow channel. The Stereoscopic Particle Image Velocimetry technique is used to measure the velocity fields in the cross-sectional planes at various axial positions along the channel. The analysis of time-averaged flow topology shows that the flow is predominantly composed of two main counter-rotating longitudinal vortices under laminar, transitional, and turbulent regimes. While the time-averaged flow behavior might appear simple, the real-time organization of the instantaneous flow structures presents more complex features. The study of the flow's temporal evolution indicates that the transition from laminar to turbulent regime is controlled by a meandering mechanism referred to the motion of the main vortex centers around their axis and the emergence of secondary structures that evolve periodically over time.

Active control of thermoacoustic oscillation based on the x-nlms algorithm

Thermoacoustic oscillations, caused by the coupling of unsteady heat release and pressure fluctuation, can result in severe damage to the combustion chamber of gas turbines. This paper presents a novel approach to active control of thermoacoustic oscillations, which is based on a Filtered-X normalized least mean square algorithm (X-NLMS). The controller employs the pressure magnitude at a predetermined axial position preceding the flame as the control variable, which is acquired through microphones installed around the combustor periphery. Control is accomplished by modifying the output frequency and phase of a loudspeaker. The performance of the control system is evaluated through simulations on a Rijke tube, with the classical PID method used as a comparison. The experimental results showcase the efficacy of the X-NLMS algorithm in actively controlling thermoacoustic oscillations. By adaptively estimating and attenuating pressure fluctuations, the algorithm effectively suppresses the undesired acoustic disturbances associated with thermoacoustic instabilities. Comparative analysis reveals that the X-NLMS algorithm outperforms PID control in terms of oscillation suppression and system stability. Its ability to adapt to time-varying dynamics and its low computational complexity make it a promising candidate for real-time thermoacoustic control applications.

Numerical investigation of axial force of a centrifugal pump in the reverse mode

This paper numerically investigates the hydraulic performance and axial force of a low specific speed centrifugal pump in the turbine mode using the k - ω SST model. Numerical results are validated against the experimental data in the literature and a good agreement is observed. Results show that the rotation factor increases by flowrate, since the head, which is directly proportional to the transferred circumferential momentum, increases by the flowrate in the turbine mode. Moreover, values of rotation factors on both sides varies in radial direction due to geometrical parameters and, they reduce where larger axial gaps are present. Additionally, the pressure distributions on the hub and shroud sides are correlated with rotation factors on these areas. Interestingly, the axial position of the impeller plays an important role in the axial force of the PAT. By applying impeller movement of 5 mm from its original position, the point of zero axial force has shifted to higher flowrates and the maximum axial force is reduced 50%. Finally, with 10 mm movement of the impeller, the axial force exhibits distinct behavior so that its direction is preserved and, the returned magnitude is almost constant in the working range by 60% decrease in the maximum axial force.