Opposite Direction Of Rotation Research Articles

Angular momentum properties of a circularly polarized vortex beam in the paraxial optical systems

The angular momentum (AM) properties of circularly polarized vortex beams (CPVBs) in two paraxial optical systems [free space and a gradient-index (GRIN) fiber] are demonstrated. The transverse light intensity, the longitudinal light intensity, the phase of the longitudinal electric field, the kinetic momentum, the total spin AM (SAM), the transverse-type SAM (t-SAM), the longitudinal-type SAM (l-SAM), and the orbital angular momentum (OAM) of CPVBs in the two paraxial optical systems are characterized. Spin-orbit coupling of CPVBs is studied during propagation in free space and in a GRIN fiber. When the OAM and the SAM of a CPVB have the same direction of rotation and when they have opposite directions of rotation, the spin-orbit coupling exhibits different characteristics in free space and in the GRIN fiber.

Superresolution and analysis of three-dimensional velocity fields of underexpanded jets in different screech modes

Time-resolved (TR), three-dimensional (3D) velocity fields of screeching, underexpanded jets are estimated using non-time-resolved particle image velocimetry and simultaneous TR microphone measurements. Specifically, we aim to reconstruct TR 3D velocity fluctuation fields associated with the A2, B, and C modes of a screeching jet using a linear regression model and to analyze screech dynamics of these modes. The linear regression model is constructed on the basis of a linear relationship between the velocity and acoustic fields. Three nozzle pressure ratios (NPRs) of 2.30, 2.97, and 3.40 are employed. The dominant azimuthal modes for three cases are investigated using azimuthal Fourier coefficients of the acoustic data obtained by the azimuthal array of eight microphones placed near the nozzle exit. The dominant azimuthal modes at NPRs of 2.30, 2.97, and 3.40 are m=0, 1, and 1, respectively. The first two proper orthogonal decomposition (POD) modes in these azimuthal modes are dominant at all NPRs and are associated with screech. 3D velocity fluctuation fields associated with screech are reconstructed from these leading POD modes of the acoustic data. The reconstructed 3D velocity fluctuation fields at NPRs of 2.97 and 3.40 exhibit two helical structures with opposite rotation directions. The present results demonstrate that, in the B mode, the flapping structure exhibits random clockwise and counterclockwise rotations over an extended time domain, while maintaining a consistent direction within short time domains. In addition, in the C mode, two helical structures with opposite rotation directions, as well as the flapping structure, are observed. Published by the American Physical Society 2024

Unsteady CFD simulation of a rotor blade under various wind conditions

Wind and gusts can significantly impact the performance of rotors and turbines. The transient behavior of the rotor should be carefully examined to account for these effects. This paper investigates the unsteady aerodynamic characteristics of a rotor blade under different wind conditions, such as direction, speed, and angle. A 3D transient Computational Fluid Dynamics (CFD) simulation using the dynamic mesh technique is performed to analyze the rotor dynamics. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations with the k-ω SST turbulence model are solved. The rotor blade used for this study is the U15XXL Combo KV29 industrial blade, which has not been numerically analyzed before. The results show that wind in the same direction as the rotation reduces the thrust more than lateral or opposite wind. Lateral wind with a speed lower than 5 m/s decreases the blade performance, but higher speeds increase it. Higher lateral wind speeds also cause two peaks in the torque curve, forming a butterfly wing shape in the polar torque plot and multiple extrema in the torque curve with increasing speed. The maximum thrust shifts slightly to the left with increasing lateral wind speed. The lateral angle does not affect the average thrust produced in one blade revolution but only causes a spatial shift. The thrust production decreases as the angle approaches the opposite direction of rotation. The motion amplitude decreases, and the curve becomes smoother as this angle increases. A nearly straight line similar to no side wind is observed at 60 and 90 degrees, which is attributed to the constant effective angle of attack during the rotation cycle.

A New Coding System for the Identification of Left Ventricular Rotation Patterns and Their Relevance to Myocardial Function

Rotational mechanics is a fundamental determinant of left ventricular ejection fraction (LVEF). The coding system currently employed in clinical practice does not distinguish between rotational patterns. We propose an alternative coding system that makes possible to identify the rotational pattern of the LV and relate it to myocardial function. Echocardiographic images were used to generate speckle tracking-derived transmural global longitudinal strain (tGLS) and rotational parameters. The existence of twist (basal and apical rotations in opposite directions) is expressed as a rotational gradient with a positive value that is the sum of the basal and apical rotation angles. Conversely, when there is rigid rotation (basal and apical rotations in the same direction) the resulting gradient is assigned a negative value that is the subtraction between the two rotation angles. The rotational patterns were evaluated in 87 healthy subjects and 248 patients with LV hypertrophy (LVH) and contrasted with their myocardial function. Our approach allowed us to distinguish between the different rotational patterns. Twist pattern was present in healthy controls and 104 patients with LVH and normal myocardial function (tGLS ≥ 17%, both). Among 144 patients with LVH and myocardial dysfunction (tGLS < 17%), twist was detected in 83.3% and rigid rotation in 16.7%. LVEF was < 50% in 34.7%, and all patients with rigid rotation had a LVEF < 50%. The gradient rotational values showed a close relationship with LVEF (r = 0.73; p < 0.001). The proposed coding system allows us to identify the rotational patterns of the LV and to relate their values with LVEF.

Sitting Sideways Causes Different Femoral-Tibial Rotations in Each Knee.

Purpose According to a previous study, asymmetrical kneeling, such as sitting sideways, does not exhibit asymmetrical movements. Rotational analyses of each femur and tibia help explain why rotational knee kinematics while sitting sideways do not exhibit asymmetrical movement. We aimed to assess the rotation of the femur and tibia in normal knees while sitting sideways. Methods Each volunteer sat sideways under fluoroscopy. Two-dimensional and three-dimensional registration techniques were used. After evaluating the femoral rotation angle relative to the tibia at each flexion angle, the femoral and tibial sole rotation angles at each flexion angle were compared between the ipsilateral and contralateral knees. Results While sitting sideways, both knees showed femoral external rotation relative to the tibia with flexion. In the ipsilateral knees, the femurs exhibited an external rotation of 26.3 ± 8.0°, from 110° to 150° of flexion. Conversely, the tibia exhibited an external rotation of 12.2 ± 7.8°, from 110° to 150° of flexion. From 110° to 150° of flexion, femoral external rotation was significantly larger than tibial external rotation. In the contralateral knees, the femurs exhibited an internal rotation of 23.8 ± 6.3°, from 110° to 150° of flexion (110°, p < 0.001; 120°, p < 0.001; 130°, p < 0.001; 140°, p < 0.001; and 150°, p < 0.001). Contrastingly, the tibia exhibited an internal rotation of 30.4 ± 8.8°, from 110° to 150° of flexion, which was significantly larger than femoral internal rotation (110°, p = 0.002; 120°, p < 0.001; 130°, p < 0.001; 140°, p < 0.001; and 150°, p < 0.001). Conclusions Although bilateral knees exhibited femoral external rotation relative to the tibia while sitting sideways, the ipsilateral and contralateral knees showed femoral and tibial sole rotations in opposite directions. In particular, the contralateral knees might show a strained movement because both femurs and tibias exhibited internal rotation with flexion. Patients who have undergone guided-motion total knee arthroplasty (TKA) or medial-pivot TKAs might be advised to avoid sitting sideways.

Failure investigation of fatigue crack initiation and propagation in compressor blade

Blades are integral components of gas turbines and are subjected to critical conditions, bearing radial forces resulting from rotation. Additionally, they directly interact with high-pressure air. This research investigates the failure of GE-Frame9 compressor blades through experimental analyses. Chemical analysis, metallography, and fractography were performed on the fractured blades. The causes of failure in the first-row blades included rubbing with the casing and bending in the opposite direction of rotor rotation. Furthermore, four rows of compressor blades were extensively damaged, with some breaking at the root area. During the turbine overhaul, a shim plate was placed between the compressor blades' root and disk. Metallography confirmed that placing the shim at the blade-disc connection point resulted in stress concentration at blades root. Fractography of the fractured blade surface indicated signs of fatigue failure, and a correlation was found between the crack initiation site and the impact of the shim plates on the blade root. Fatigue crack initiation occurred due to stress concentration caused by the shim's edge, propagating through the blade root during turbine operation and ultimately leading to complete fracture. These results emphasize the importance of avoiding the placement of shims on inclined surfaces of blade roots and ensuring full contact between the surfaces to prevent stress concentration and subsequent failure.

Lattice boltzmann simulation of power-law fluids flow around a forced-oscillation circular cylinder

Direct numerical simulations of power-law non-Newtonian fluids flow around a circular cylinder are performed by lattice Boltzmann method coupled with immersed moving boundary scheme. Obvious differences in macroscopic hydrodynamics and wake vortex dynamics between shear-thinning and shear-thickening fluids are resolved. Results show that shear-thickening effect increased drag coefficient but decreased lift coefficient, and delayed separation of boundary layer leading to lower vortex shedding frequency. The position with lowest viscosity on surface of cylinder in shear-thinning fluid is closer to leading edge stagnation point than the position in shear-thickening fluid. Wake vortex appears from surface of cylinder in shear-thinning fluid, however appears after some distance away from rear end of cylinder in Newtonian and shear-thickening fluid through dynamic mode decomposition. Vortex shedding modes in shear-thinning and shear-thickening fluids are very different at high oscillation amplitudes and transited from Chaos to 2S mode (two single vortexes with opposite directions but same energy shed) or P + S mode (a pair of vortexes with opposite rotation direction shed on one side of the cylinder and a single vortex shed on the other side) when increasing power-law index.

Research on the influence mechanism of internal flow characteristics on energy conversion in radial energy recovery turbines under multiple conditions

The development of Energy Recovery Turbine (ERT) is of great significance for energy saving and emission reduction. The mutual influence mechanism between the flow characteristics and energy conversion of ERT has not yet been mastered. A radial ERT was selected as the research object and a mathematical model based on entropy generation theory was established to evaluate the energy loss of the ERT. The internal flow characteristics and energy loss mechanism of an ERT were studied. The results show that the entropy generation power of the impeller accounts for 17.4 %. The turbulent entropy generation power of the impeller accounts for 76.5 % of the total entropy generation power. The energy loss at the volute tongue is maximized due to the presence of two attached vortexes with opposite rotation directions. The area with significant energy loss in the impeller gradually shifts from hub and pressure surface to the suction surface as the flow increases. The performance degradation under overload conditions is relatively slow, as the flow impact on the pressure surface has a smaller impact on the blade's ability to perform work. Therefore, the hydraulic design should be carried out after appropriately reducing the rated flow rate when designing a radial turbine.

The aggregation of micro-particles based on hydraulic vortices

The large-scale and nondestructive aggregation of micro-particles in the solvent has a crucial role on cell detection and the preparation of micro-nano drugs. To achieve directional aggregation of micro-particles, a piezoelectric cantilever probe structure can be utilized to generate a vortex region by driving the liquid with low-frequency oscillation. By adjusting the driving voltage and frequency of the piezoelectric oscillator, polystyrene microspheres in the liquid can be effectively aggregated and manipulated. Experimental results using fixed concentration polystyrene solvent demonstrated that micro-particle aggregation occurred within the frequency range of 20–70 Hz and voltage range of 20–80 V. The particles were stably concentrated in front of the probe, with a maximum aggregation area of 0.71 mm2 and a maximum number of aggregated particles reaching 2495, when the driving voltage was 60 V and the driving frequency was 60 Hz. Furthermore, the flow field particle image velocimetry experiment revealed that when four main vortices with opposite rotation directions were present, the micro-particle aggregation exhibited a regular Arc and Witch-shaped pattern. Conversely, in the presence of an indefinite number of large main vortices in the flow field, the micro-particle aggregation displayed an irregular Small symmetry and Large symmetry-shaped pattern. This method of micro-particle aggregation manipulation using hydraulic vortices has the potential to meet the demands of biomedical and fine chemical fields for precise micro-particle manipulation.

Interaction mechanism between cloud cavitation and micro vortex flows

Micro vortex generators (micro-VGs) could affect cavitation, but the control mechanism is not yet fully understood. Simulating and analyzing the effect of micro vortex generators (micro-VGs) on cloud cavitation is crucial as it can help in suppressing the collapse of cavitation clouds, which is beneficial for marine machinery. In this work, micro-VGs were installed parallel to the initiation of the attached cavity on a NACA0015 hydrofoil. A compressible simulation method was used to obtain the cavitating flows around both the smooth hydrofoil and the one with micro-VGs. Subsequently, the generation of micro vortex flows and the effect of micro-VGs on transient evolution of cloud cavitation were analyzed. The results indicate that the installation of triangular micro vortex generators alters the flow vectors around them, inducing micro vortex flows with opposite rotational directions behind adjacent vortex generators. These vortex generators potentially affect cavitation on the hydrofoil by modifying pressure distribution, vortex structures, and turbulent kinetic energy. Under the specified cloud cavitation operating condition, the shedding and collapse of clouds on the smooth hydrofoil are replaced by the partial separation and collapse of sheet cavitation on the hydrofoil with micro-VGs. Despite a minor loss in time-averaged lift, the lift-to-drag ratio is improved, and the stability of the flow field is enhanced. After installing micro-VGs, the pressure fluctuation is primarily caused by the partial collapse and separation of sheet cavitation. Installing micro VGs at the hydrofoil's leading edge suppresses pressure pulsation.

Magnetic field properties inside the jet of Mrk 421

Aims. We aim to probe the magnetic field geometry and particle acceleration mechanism in the relativistic jets of supermassive black holes. Methods. We conducted a polarimetry campaign from radio to X-ray wavelengths of the high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry Explorer (IXPE) measurements from 2022 December 6–8. During the IXPE observation, we also monitored Mrk 421 using Swift-XRT and obtained a single observation with XMM-Newton to improve the X-ray spectral analysis. The time-averaged X-ray polarization was determined consistently using the event-by-event Stokes parameter analysis, spectropolarimetric fit, and maximum likelihood methods. We examined the polarization variability over both time and energy, the former via analysis of IXPE data obtained over a time span of 7 months. Results. We detected X-ray polarization of Mrk 421 with a degree of ΠX = 14 ± 1% and an electric-vector position angle ψX = 107 ± 3° in the 2–8 keV band. From the time variability analysis, we find a significant episodic variation in ψX. During the 7 months from the first IXPE pointing of Mrk 421 in 2022 May, ψX varied in the range 0° to 180°, while ΠX remained relatively constant within ∼10–15%. Furthermore, a swing in ψX in 2022 June was accompanied by simultaneous spectral variations. The results of the multiwavelength polarimetry show that ΠX was generally ∼2–3 times greater than Π at longer wavelengths, while ψ fluctuated. Additionally, based on radio, infrared, and optical polarimetry, we find that the rotation of ψ occurred in the opposite direction with respect to the rotation of ψX and over longer timescales at similar epochs. Conclusions. The polarization behavior observed across multiple wavelengths is consistent with previous IXPE findings for HSP blazars. This result favors the energy-stratified shock model developed to explain variable emission in relativistic jets. We considered two versions of the model, one with linear and the other with radial stratification geometry, to explain the rotation of ψX. The accompanying spectral variation during the ψX rotation can be explained by a fluctuation in the physical conditions, for example in the energy distribution of relativistic electrons. The opposite rotation direction of ψ between the X-ray and longer wavelength polarization accentuates the conclusion that the X-ray emitting region is spatially separated from that at longer wavelengths. Moreover, we identify a highly polarized knot of radio emission moving down the parsec-scale jet during the episode of ψX rotation, although it is unclear whether there is any connection between the two events.

Genetic determinism and hemispheric influence in hair whorl formation

BackgroundThe mechanisms determining the laterality and the rotation direction of hair whorls are unknown. Here we report observations on twins investigating the genetic bases of whorl pattern formation. Knowing that vortex phenomena may depend on geographic effects, we also provide comparative data on whorls from children born in the Northern hemisphere (France) versus children born in the Southern hemisphere (Chile). Material and methodsWe retrospectively included children from three populations: (1) Northern hemisphere general population, (2) Southern hemisphere general population, and (3) same-sex Northern hemisphere twins. We recorded whorl rotation direction (clockwise, counterclockwise), whorl position (left, right, central) and twinning type. Univariate logistic models were used to screen for associations between rotation direction and whorl position. For twins, the variable of interest was binary, i.e. same rotation direction (reference class) or opposite directions for each twin pair. For controls, all single combinations were included as virtual twins, and compared to real twins. Odds ratios (OR) were compared for both hemispheres, for real twins and virtual (control) twins. ResultsSeventy-four (37 pairs) twins and 50 children from the general population of each hemisphere were included. The OR for opposite rotation directions between two twins was ≠1 (p = 0.017), meaning that whorls rotated preferentially in the same direction in twins. ORs were <1 for Northern and Southern hemispheres, meaning that whorls rotated preferentially in the same direction in simulated twins. OR for the Northern hemisphere (0.04 [0.03; 0.05]) was less than the OR for the Southern hemisphere (0.28 [0.24; 0.32]) with no confidence interval superimposition, indicating than counterclockwise whorls were more frequent in the Southern hemisphere (p < 0.001). ConclusionsWe suggest that hair whorl formation is a genetically determined developmental process that can be influenced by extrinsic environmental factors. Our results furthermore underline the general importance of studies focused on limit phenomena that can provide insights on general developmental mechanisms. We plead for large-scale epidemiological assessments of hair whorls in several Northern and Southern hemisphere populations to confirm these surprising findings suggesting significant modulations of craniofacial development by geographic effects.

Super-resolution of time-resolved three-dimensional density fields of the B mode in an underexpanded screeching jet

The estimation of time-resolved three-dimensional (3D) density fields of an underexpanded jet at the nozzle pressure ratio of 2.42, a so-called “spatiotemporal super-resolution” was conducted using non-time-resolved three-dimensional background-oriented schlieren (3D-BOS) and time-resolved microphone measurements. This approach aims to reconstruct three-dimensional density fields associated with the intermittent and switching behavior of the B mode of a screeching jet from the microphone data by constructing a linear regression model. An azimuthal Fourier decomposition is applied to the 3D-BOS and microphone data, and the proper orthogonal decomposition (POD) is performed for each of their azimuthal Fourier modes. The m=1 azimuthal Fourier mode is dominant in both cases, and the leading two POD modes in the m=1 azimuthal mode of the microphone data are associated with the B mode. The linear regression model is constructed from the POD modes of the m=1 azimuthal 3D-BOS data and the first two microphone POD modes of the m=1 azimuthal mode of the microphone data. The three-dimensional density fields reconstructed from each POD mode of the m=1 azimuthal mode of the microphone data have helical structures with opposite rotation directions. The amplitudes of those POD modes change with time, and the azimuthal structure associated with the B mode is determined depending on those amplitudes. The present result showed that intermittency in the flapping to helical structures and their strength can be interpreted by the temporal changes in the strengths of two rotating helical structures with opposite rotation directions.

Swirling flow analysis of Eyring–Powell fluid between coaxial disks with variable property

Abstract The main objective of this study is to examine an unsteady swirling flow of a non-Newtonian Eyring–Powell fluid between two coaxial disks. The lower and upper disks are considered to rotate with different angular velocities. The three-dimensional axisymmetric flow phenomenon and heat transfer mechanism are observed with the consequences of the magnetic field and variable thermal conductivity of the fluid. The variable thermal conductivity is taken to be dependent on the fluid temperature. The implementation of the Von Karman similarity transformations on the constituting equations of the flow phenomenon yields the dimensionless system of the non-linear equations. An optimal homotopy analysis technique is adopted to obtain analytical solutions for highly non-linear equations. In view of the same and opposite directions of disks rotation, the various aspects of the flow system corresponding to the pertinent parameters are discussed with physical significance. The obtained results indicate that both radial and axial fields are the escalating functions of the Eyring–Powell fluid parameter. Moreover, the heat transfer rate enhances with the improving variable thermal conductivity parameter.

Non-Hermitian coupling of orbital angular momentum modes in optical waveguides

We investigate the optical coupling of orbital angular momentum (OAM) modes in a multimode waveguide assisted by a lossy single-mode waveguide. By utilizing coupled mode theory, we show that the coupling coefficients between two OAM modes with opposite rotation directions become imaginary-valued in cylinder waveguides, which further gives rise to polarization-locked wave dynamics. Any injections with different polarizations finally evolve into linear polarization (LP) modes, as the output modes are synthetized by antisymmetric supermodes of two OAM modes. In addition, non-Hermitian asymmetric couplings are induced in elliptical waveguides, which stem from the interaction between synthetical gauge fields and dissipation. By increasing the ellipticity of waveguides, the degree of asymmetric coupling increases, and the system experiences a phase transition, which can be reflected from propagation characteristics of OAM modes. The study provides a promising approach for controlling modal coupling of OAM modes and may find potential applications in OAM generation and polarization conversion.

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

RANS simulations are performed for flow past rectangular cylinders with different elongation ratios (L/D= 1, 2, 4, 6, 8, 10, 12, 14 and 16) at Re= 22 000 using the k-ω SST turbulence model. As L/D increases from 1 to 6, stepwise increase of Strouhal number (St) exists, whereas an almost linear variation of St with respect to L/D can be found (St= 0.1618*L/D) at L/D⩾ 8. In the flow, two small secondary vortices beneath the shear layers are identified and the trailing-edge secondary vortex presents opposite rotational direction comparing with the leading-edge main vortex. Analysis of the shear layer and vortex characteristics is carried out to correlate with the wall normal stress and shear stress on the rectangular cylinder surfaces. Further, four coupling modes between leading-edge vortex (L-vortex) and trailing-edge vortex (T-vortex) among cylinders with different L/D are observed, named L-Vortex Mode (i.e. L/D= 1–2), L-T-Vortex Mode (i.e. L/D= 4–8), T-L-Vortex Mode (i.e. L/D= 10–14), and T-Vortex Mode (i.e. L/D ⩾ 16). When L/D > 4, the convective velocity of the L- and T-vortex is not sensitive to the L/D.

Numerical and Experimental Study on Flame Dynamics of the Premixed Methane-Air Mixture at Different Ignition Positions in a Two-Side 45° Branch Tube.

The combustion characteristics of premixed methane-air flames in a half-open tube with a two-sided 45° branch structure at different ignition positions were investigated by experiments and large eddy simulations. The numerical results were compared with the experimental results to verify the correctness of the model. The results show that the simulation results are highly consistent with the experiment. This study provides a basic understanding of the effects of the branch tube structure and the ignition position on flame dynamics. When the flame propagates to the branch interface, it forms a symmetrical vortex structure at the branch tube with the opposite rotation direction. When the ignition position is at IP0 and IP900, the maximum overpressures obtained in the experiment are 10.1 and 10.7 kPa, respectively, and 9.2 and 10.4 kPa in the simulation, respectively. At IP0, the Karlovitz number indicating the interaction intensity between the flame surface and the turbulence during flame propagation is a maximum of 9.2 and a minimum of 0.04. The premixed flame has a folded small flame, a corrugated small flame, and a thin reaction zone.

Dynamic analysis of a translating five-bar linkage mechanism

In this paper, the dynamic analysis of a translating five-bar linkage mechanism is presented. The dynamic model of the mechanism is developed with the applied force to the crank arm resolved into the two principal planes, that is, x- and y- directions and the resulting reaction forces and moments at the pin joints determined at various translating acceleration of 0, 10, 20, 30 and 40 m/s2 in the direction as well as in the opposite direction of the crank rotation. It was observed that the horizontal reaction forces at the pin joints were decreasing as the translating acceleration increases in the direction of crank rotation while it increases when the acceleration increases in the opposite direction to the crank rotation. It was also observed that the pin joint moments at point A decreases as the translation velocities increases in the crank arm rotation direction while it increases as the acceleration increases in the opposite direction. The converse is the case for pin joint B, while there were no significant differences for pin joint moments at pin joints C and D in all the considered acceleration in both directions. Also, the vertical reaction forces at the pin joints did not change in magnitude as the magnitude and directions of the acceleration were altered. The analysis brings to the fore the importance of the consideration of translating acceleration in the design, development and utilization of five – bar linkage to avoid failure at any of the joints.

An investigation on 3-hydroxybenzaldehyde for exploring terahertz low-frequency vibration modes with quasi-harmonic approximation method

3-Hydroxybenzaldehyde (3-HBA) was investigated in the range of 0.6–2.8 THz by terahertz time-domain spectroscopy (THz-TDS) and solid-state density functional theory (ss-DFT) with first-principles calculation. Four distinct peaks were found respectively, and among them, the intensity disparity between experiment and simulation spectra at 2.04 THz was recognized as the biggest inconsistency. Considering thermal behavior can be responsible for this, quasi-harmonic approximation (QHA) method was introduced to mimic the unit cell volume expansion. According to vibrational modes analysis, it was ascertained that the biggest vibrational modes discrepancy was also located at 2.04 THz. Molecules in 0% and 4% unit cell expansion exhibit an opposite rotational direction in a-b plane compared with 2% unit cell expansion. Noncovalent intermolecular interactions were investigated with independent gradient model (IGM), and the result indicates that hydrogen bonding is the dominating noncovalent interaction of 3-HBA. While calculating systematic potential energy to the displaced bonds stretching involving hydrogen atoms, it was found the anomalous potential energy variation to the bond stretching provides a possible explanation for the rotation direction divergence, that is, the rotation direction divergence can be related to some hydrogen atoms seeking lower overall potential energy around their equilibrium positions during bond stretching in response to the variational intermolecular van der Waals force. This research combined THz-TDS with the quasi-harmonic approximation method, elucidating the principle of vibrational characteristics in different volumes, which is beneficial to the investigation of the terahertz low-frequency vibration to thermal behavior as a reference in biochemistry and other fields.

An LBM-Based Investigation on the Mixing Mechanism of Double Rows Film Cooling with the Combination of Forward and Backward Jets

Film cooling has been widely applied to the highly efficient thermal protection of gas turbines. By using the simplified thermal lattice Boltzmann method (STLBM), a series of large-scale simulations of film cooling are performed to dig up the mixing mechanism of double rows film cooling with the combination of forward and backward jets at the first attempt. The combination of an upstream row with forward jet and a downstream row with backward jet is considered. The Reynolds number is 4000. The blowing ratio of the upstream coolant jet is fixed as BR1=0.5. For the downstream coolant jet (BR2), five values ranging from 0.2–0.8 are considered. The inclination angles of forward jet and backward jet are 35° and 145°, respectively. The numerical results reveal that the performance of film cooling is greatly improved by backward downstream jet due to the suppression of counterrotating vortex pair (CVP). Moreover, the flow structure is changed with the blowing ratio of backward jet. An anti-CVP having the opposite rotational direction to CVP appears as the blowing ratio of backward jet is large. The special flow structure weakens the adverse effect of CVP and transports much coolant jet to the cooled wall. Correspondingly, the time-averaged film cooling effectiveness is increased and the fluctuation of film cooling effectiveness is decreased. All of these indicate that a backward downstream jet with a large blowing ratio improves film cooling performance. The results obtained in this work help to the optimization of film cooling scheme, which also benefit the promotion and application of STLBM in gas turbine engineering.