Phase-lag Method Research Articles

Noise Prediction of an Open Fan Using Acoustic Analogy Approaches

The purpose of this study is to evaluate numerical aero-acoustic methods for the noise prediction of an open fan, which is expected to reduce CO2 emissions for the next generation of aircraft engines. The far-field noise is computed using a CFD/CAA approach. The unsteady Reynolds Averaged Navier-Stokes (uRANS) and the Ffowcs Williams-Hawkings (FWH) analogy using solid and permeable surfaces are applied. The phase-lag method (single-blade passage) is used for the purpose of calculation for aerodynamic flow and noise sources with ONERA elsA finite volume solver. The sensitivities to the numerical CFD setup as well as the position and formulation of FWH permeable surface for noise computation are discussed in this paper. The present noise prediction strategy is evaluated for approach and take-off operating conditions. In particular, several spatial discretization schemes and FWH surface locations are tested and compared to evaluate their influence on the noise levels and directivity.

Effect of Phyisco-chemical Parameters on the Thermal Diffusivity and Soil Heat Flux over Ayadi, Ondo State, Nigeria

This study assesses the effect of some soil physical properties on the thermal diffusivity and soil heat flux over Ayadi in Ondo State, Nigeria. Physical properties of the soil at different depths were determined using laboratory techniques. In-situ measurement of air temperature and surface soil temperature were carried out. The phase lag method was used to determine the thermal diffusivity of the soil, while the subsoil heat flux was determined from values obtained for the thermal diffusivity. The result showed that the subsoil heat flux values during the dry season ranged between 0.58 and 52.84 W/m2, while that of the wet season ranged between -0.77 and 98.50 W/m2. The average thermal diffusivity values at the different depths had values between 0.74 × 10-7 and 238.7 × 10-7 m2/s for the dry season, while the wet season had a range of 1.97 × 10-7 to 238.7 × 10-7 m2/s.
 Keywords: soil moisture content, air temperature, soil temperature, soil heat flux, thermal diffusivity.

Comparison of dynamic models based on backbone curve for rotary magneto-rheological damper

To realize the accurate control of magneto-rheological system, the nonlinear dynamic model as the joint of damper and control strategy is worthy of being investigated. In this study, the modeling methods based on the backbone curve are proposed to portray the dynamic characteristics of magneto-rheological damper. The modeling methods contain the phase lag method and the hysteresis division method. Six novel algebraic models are deduced from the two methods and compared systematically. The parameters identification of models is conducted by the nonlinear least square method. The nonlinear least square optimization problem is solved by the Levenberg–Marquardt algorithm. The evaluation indexes including the root-mean-square error, mean deviation and computation time are calculated to evaluate the accuracy and feasibility of the novel models. Results show that the modeling methods and their models can describe the nonlinear hysteretic characteristics with feasibility and accuracy.

Distances of Stars by mean of the Phase-lag Method

AbstractVariable OH/IR stars are Asymptotic Giant Branch (AGB) stars with an optically thick circumstellar envelope that emit strong OH 1612 MHz emission. They are commonly observed throughout the Galaxy but also in the LMC and SMC. Hence, the precise inference of the distances of these stars will ultimately result in better constraints on their mass range in different metallicity environments. Through a multi-year long-term monitoring program at the Nancay Radio telescope (NRT) and a complementary high-sensitivity mapping campaign at the eMERLIN and JVLA to measure precisely the angular diameter of the envelopes, we have been re-exploring distance determination through the phase-lag method for a sample of stars, in order to refine the poorly-constrained distances of some and infer the currently unknown distances of others. We present here an update of this project.

Simultaneous determination of the thermal diffusivity and a drum factor for CdBeMnTe crystals with the photoacoustic method

The paper presents results of photoacoustic studies of the thermal diffusivity of CdTe and Cd1−x−yBexMnyTe crystals. The drum effect strongly influences the photoacoustic characteristics that have been measured. The values of the thermal diffusivity of the crystals have been extracted from the amplitude and phase frequency characteristics measured in reflection and transmission configurations in the Sf/Sr and Phase-Lag method. This paper presents that it is possible to extract simultaneously the thermal diffusivity and a drum factor B from photoacoustic frequency measurements.

Influence of Periodic Unsteady Effects on Flow and Performance Prediction on an Axial High Pressure Compressor

A numerical assessment of unsteadiness and information losses due to boundary conditions, especially the rotor-stator interface treatment in an axial high pressure compressor (HPC) is proposed. Steady and unsteady computations are performed on a three-stage axial HPC with a 3D Navier-Stokes code. The steady simulation is based upon periodic boundary condition for azimuthal frontiers and the mixing plane approach which averages circumferentially the information coming from the adjacent blade row. The unsteady one uses the phase-lag method for both azimuthal frontiers and rotor-stator interface. The unsteady simulation highlights the wake effects in the stator passage due to the wakes released by the rotor and the potential effects on the wall pressure of the rotor blades due to the stator blades. The comparison between the steady and the time-averaged unsteady simulations shows a good agreement in the information transfer at the rotor-stator interface. The main discrepancy appears in the static pressure field on the rotor side of the interface, due to the inability of the steady computation to capture the potential effects. The radial profiles and the performances obtained with these two simulations are very similar. Thus a steady computation results in flow field and performance predictions with a sufficient accuracy. This comparison confirms the validity of using the mixing plane approach for HPC design.

Comparison of Harmonic and Time Marching Unsteady Computational Fluid Dynamics Solutions With Measurements for a Single-Stage High-Pressure Turbine

The unsteady aerodynamics of a single-stage high-pressure turbine has been the subject of a study involving detailed measurements and computations. Data and predictions for this experiment have been presented previously, but the current study compares predictions obtained using the nonlinear harmonic simulation method to results obtained using a time-marching simulation with phase-lag boundary conditions. The experimental configuration consisted of a single-stage high-pressure turbine (HPT) and the adjacent, downstream, low-pressure turbine nozzle row (LPV) with an aerodynamic design that is typical to that of a commercial high-pressure ratio HPT and LPV. The flow path geometry was equivalent to engine hardware and operated at the proper design-corrected conditions to match cruise conditions. The high-pressure vane and blade were uncooled for these comparisons. All three blade rows are instrumented with flush-mounted, high-frequency response pressure transducers on the airfoil surfaces and the inner and outer flow path surfaces, which include the rotating blade platform and the stationary shroud above the rotating blade. Predictions of the time-dependent flow field for the turbine flow path were obtained using a three-dimensional, Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) code. Using a two blade row computational model of the turbine flow path, the unsteady surface pressure for the high-pressure vane and rotor was calculated using both unsteady methods. The two sets of predictions are then compared to the measurements looking at both time-averaged and time-accurate results, which show good correlation between the two methods and the measurements. This paper concentrates on the similarities and differences between the two unsteady methods, and how the predictions compare with the measurements since the faster harmonic solution could allow turbomachinery designers to incorporate unsteady calculations in the design process without sacrificing accuracy when compared to the phase-lag method.

Soil thermal diffusivity estimated from data of soil temperature and single soil component properties

Under field conditions, thermal diffusivity can be estimated from soil temperature data but also from the properties of soil components together with their spatial organization. We aimed to determine soil thermal diffusivity from half-hourly temperature measurements in a Rhodic Kanhapludalf, using three calculation procedures (the amplitude ratio, phase lag and Seemann procedures), as well as from soil component properties, for a comparison of procedures and methods. To determine thermal conductivity for short wave periods (one day), the phase lag method was more reliable than the amplitude ratio or the Seemann method, especially in deeper layers, where temperature variations are small. The phase lag method resulted in coherent values of thermal diffusivity. The method using properties of single soil components with the values of thermal conductivity for sandstone and kaolinite resulted in thermal diffusivity values of the same order. In the observed water content range (0.26-0.34 m³ m-3), the average thermal diffusivity was 0.034 m² d-1 in the top layer (0.05-0.15 m) and 0.027 m² d-1 in the subsurface layer (0.15-0.30 m).

A non-destructive method for determination of thermal conductivity of YSZ coatings deposited on Si substrates

Thermal diffusivity (α) of YSZ coatings was determined by the phase lag method of the photo-acoustic signal for rear and frontal illuminations using a two-beam photo-acoustic cell. XRD results show the presence of a tetragonal phase with (101) and (112) orientations, and FTIR spectra exhibit the 2Eu and F1u modes as two broad bands in the frequency at 453 cm−1, 468 cm−1, corresponding to the tetragonal phase of ZrO2. Thermal diffusivity was measured in the Si/YSZ system and also on the Si (100) substrate from which a simple two-layer system model. Via specific heat measurements at constant pressure (Cp) using the (DSC) technique, and mass density (ρ) calculations using Archimedes and Aleksandrov's methods for both in-bulk and film YSZ samples, thermal conductivity (κ) was obtained. The results were: α = (0.0021 ± 0.0002) and (0.0023 ± 0.0002) cm2 s−1, ρ = (4.7725 ± 0.005) × 103 and (5.883 ± 0.005) × 103 kg m−3, Cp = (427 ± 14) J kg−1 K−1, and κ = (0.43 ± 0.06) and (0.57 ± 0.06) W m−1 K−1 for in-bulk and film YSZ samples, respectively.

Cepheid investigations using the Kepler space telescope

We report results of initial work done on selected candidate Cepheids to be observed with the Kepler space telescope. Prior to the launch 40 candidates were selected from previous surveys and databases. The analysis of the first 322 days of Kepler photometry, and recent ground-based follow-up multicolour photometry and spectroscopy allowed us to confirm that one of these stars, V1154 Cyg (KIC 7548061), is indeed a 4.9-d Cepheid. Using the phase lag method we show that this star pulsates in the fundamental mode. New radial velocity data are consistent with previous measurements, suggesting that a long-period binary component is unlikely. No evidence is seen in the ultra-precise, nearly uninterrupted Kepler photometry for nonradial or stochastically excited modes at the micromagnitude level. The other candidates are not Cepheids but an interesting mix of possible spotted stars, eclipsing systems and flare stars.

Numerical solution of the two-dimensional time independent Schr�dinger equation with Numerov-type methods

The solution of the two-dimensional time-independent Schrodinger equation is considered by partial discretization. The discretized problem is treated as an ordinary differential equation problem and Numerov type methods are used to solve it. Specifically the classical Numerov method, the exponentially and trigonometrically fitting modified Numerov methods of Vanden Berghe et al. [Int. J. Comp. Math 32 (1990) 233–242], and the minimum phase-lag method of Rao et al. [Int. J. Comp. Math 37 (1990) 63–77] are applied to this problem. All methods are applied for the computation of the eigenvalues of the two-dimensional harmonic oscillator and the two-dimensional Henon–Heils potential. The results are compared with the results produced by full discterization.

Resonant photoacoustic cell for low temperature measurements

This paper describes a resonant photoacoustic cell for low temperature measurements. It has the shape of the Helmholtz resonator, with the microphone separated from the sample by a resonant tube. In this way the microphone is kept at room temperature while the sample temperature is lowered. When the sample is placed in a liquid nitrogen tank it is possible to change its temperature from 77 K to 300 K, with the aid of a furnace, which surrounds the sample holder. Two optical fibres lead the laser light to both sides of the sample, making possible the determination of the thermal diffusivity in all temperature intervals, by using the photoacoustic phase-lag method.

Low temperature thermal diffusivity of LiKSO4 obtained using the photoacoustic phase lag method

This paper describes the determination of the thermal diffusivity of LiKSO4 crystals using the photoacoustic phase lag method, in the 77 K to 300 K temperature interval. This method is quite simple and fast and when it is coupled to a specially designed apparatus, that includes a resonant photoacoustic cell, allows for the determination of the thermal diffusivity at low temperatures. The thermal diffusivity is an important parameter that depends on the temperature, and no values of this parameter for LiKSO4, at low temperature, have yet been reported. The LiKSO4 is a crystal with many phase transitions which can be detected via the anomalies in the variation of the thermal diffusivity as a function of the temperature.

Thermal diffusivity of BaLiF 3 crystals

BaLiF 3 crystals doped with transition metal ions are potential new laser active media. Thermal diffusivity of a pure BaLiF 3 crystal was determined at room temperature using the photoacoustic two-beam phase lag method, which consists in measuring the relative phase-lag for the photoacoustic signal between rear and front surface illumination at a single modulation frequency.

Theory of narrow-angle x-ray scattering and its measurement by the M ssbauer effect

It is shown how the Mossbauer effect may be used to measure the total scattered energy, on an absolute basis, for single scattering by an inhomogeneous medium, and to measure the angular distribution for the case of multiple scattering. The method, which involves moving the scatterer transversely to the gamma-ray beam with speeds of the order of 10-103 cm sec-1, is interpreted in terms of the Doppler effect and also in terms of the time modulation of photon wave trains. Expressions relating the total scattered intensity in single scattering to the structure of the medium are derived which allow for interference and particle size distributions by using the Born approximation and also by using the phase-lag approach. Multiple scattering is treated by the phase-lag method, and it is shown that the distinction between diffractive and refractive scattering is unimportant in certain cases. It is shown that the angular distribution in the case of multiple scattering is related simply to the autocorrelation function of the refractive index gradient within the material.

An ultrasonic phase lag method for measuring the thickness of rubber

An ultrasonic phase lag method for measuring the thickness of rubber when only one surface is available is described. This method, working at 50 kc/s frequency, was chosen because at this frequency ultrasonic absorption losses in rubber are low. The method was developed to measure thickness of rubber in the range 5-20 mm with an accuracy of ±1 mm.