Azimuthal Location Research Articles

Effect of discretization on off-axis listeners in binaural synthesis based on the optimal source distribution

3D sound reproduction based on binaural synthesis over loudspeakers is one of the most important techniques in immersive spatial audio. The system inversion involved in the binaural synthesis gives rise to several problems such as dynamic range loss, distortion of the reproduction transfer function, and a lack of robustness to room reflections. The principle of Optimal Source Distribution was proposed to overcome these problems. This utilizes a pair of conceptual monopole transducers whose azimuthal location varies continuously as a function of frequency. Another potential of the principle is that it can provide listening positions for multiple off-axis listeners, in addition to the on-axis listener whose inverse matrix is given, since the phase interference state is aligned at all frequencies. However, these continuously varying transducers are too conceptual to realize in practice. It is necessary to provide discretized sound sources with appropriate frequency ranges according to the principle. In this paper, the effect of discretization of the principle on off-axis listeners' performance is numerically investigated to reveal how those off-axis sweet spots are formed as the discretization becomes finer. An experiment is also carried out using an actual discretized system and the effect of the head-related transfer functions is considered.

Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi

EX Lupi, a low-mass young stellar object, went into an accretion-driven outburst in 2022 March. The outburst caused a sudden phase change of ∼112° ± 5° in periodically oscillating multiband lightcurves. Our high-resolution spectra obtained with the High Resolution Spectrograph (HRS) on board the Southern African Large Telescope also revealed a consistent phase change in the periodically varying radial velocities (RVs), along with an increase in the RV amplitude of various emission lines. The phase change and increase in RV amplitude morphologically translates to a change in the azimuthal and latitudinal location of the accretion hotspot over the stellar surface, which indicates a reconfiguration of the accretion funnel geometry. Our three-dimensional magnetohydrodynamic simulations reproduce the phase change for EX Lupi. To explain the observations, we explored the possibility of forward shifting of the dipolar accretion funnel as well as the possibility of the emergence of a new accretion funnel. During the outburst, we also found evidence of the hotspot’s morphology extending azimuthally asymmetrically with a leading hot edge and cold tail along the stellar rotation. Further, our high-cadence photometry showed that the accretion flow has clumps. We also detected possible clumpy accretion events in the HRS spectra that showed episodically highly blueshifted wings in the Ca ii IR triplet and Balmer H lines.

Intracycle RPM control for vertical axis wind turbines

AbstractThe wind energy market is currently dominated by horizontal axis wind turbines (HAWTs); however, vertical axis wind turbines (VAWTs) are emerging as a design alternative, especially for deep‐water offshore siting due to their low center of gravity, ease of access to drivetrain components, and overall simplicity. Due to the absence of a pitch mechanism in large‐scale Darrieus VAWTs, stall control has often been used to manage power and loads. Introducing a pitching mechanism in H‐type VAWTs has been studied, but this diminishes the mechanical simplicity advantage, and the use of a pitching mechanism in a large‐scale Darrieus‐type VAWT is not practical. This work examines an innovative, alternative method to control the rotor dynamics of a large‐scale 5 MW VAWT to maximize power while constraining loads without introducing any new or complex mechanical elements. This control strategy is termed intracycle revolution per minute (RPM) control, where the rotational speed of the turbine is allowed to vary in an optimal fashion with the azimuthal location of blades as opposed to typical constant RPM operation. An optimization framework is formulated for an open‐loop optimal control problem and solved to maximize power subject to constraints on aerodynamic design loads. Results are presented to demonstrate the benefits and the performance limits of intracycle RPM control for large‐scale 5 MW Darrieus VAWTs, namely, (1) power production (quantified in terms of AEP) that can be increased subject to baseline load limits and (2) opportunities to significantly increase AEP or decrease loads via intracycle RPM control that are examined for both two‐bladed and three‐bladed VAWTs.

Investigation of the Flow Fields of Coaxial Co-Rotating and Counter-Rotating Rotors in Hover Using Measurements and Simulations

The flow fields of a 2-m diameter two-bladed single rotor, a 2× 2-bladed coaxial corotating (stacked) rotor, and a 2× 2-bladed coaxial counterrotating (CCR) rotor in hover were measured using particle image velocimetry and computed using a finitevolume unsteady Reynolds-averaged Navier–Stokes (URANS) CFD model. Phase-resolved measurements were performed on the stacked rotor at nine azimuthal locations, and time-resolved measurements were performed on the CCR rotor at 64/rev with at least 500 flow realizations per azimuth for each operating condition. The goal of this study was to compare the flow features of these rotor configurations and explore the interactions between the rotors. Overall, there was good correlation between the measurements and simulations. In particular, the effect of index angle on the upper and lower rotor thrust sharing for the stacked rotor was predicted well by the simulation. The slipstream boundary for the stacked rotor was found to vary with the index angle. The slipstream boundary and vortex trajectories for the CCR rotor were found to vary with azimuthal location, indicating the effect of blade passage on the wake geometry. Simulations indicated a stronger dependence of the tip vortex trajectory on the index angle and thrust for the stacked rotor compared to the CCR rotor. The radial thrust distribution along the upper blades was found to depend on the index angle for the stacked rotor and showed small variation due to blade passage for the CCR rotor. A larger azimuthal dependence was seen for the radial thrust distribution on the lower rotor blades, primarily due to the proximity of the upper rotor tip vortices. The lower rotor radial thrust distribution was biased towards the blade tip, outside the upper rotor slipstream.

Quantifying the influence of bars on action-based dynamical modelling of disc galaxies

ABSTRACT Action-based dynamical modelling, using stars as dynamical tracers, is an excellent diagnostic to estimate the underlying axisymmetric matter distribution of the Milky Way. However, the Milky Way’s bar causes non-axisymmetric resonance features in the stellar disc. Using RoadMapping (an action-based dynamical modelling framework to estimate the gravitational potential and the stellar distribution function), we systematically quantify the robustness of action-based modelling in the presence of a bar. We construct a set of test-particle simulations of barred galaxies (with varying bar properties), and apply RoadMapping to different survey volumes (with varying azimuthal position, size) drawn from these barred models. For realistic bar parameters, the global potential parameters are still recovered to within ∼1–17 per cent. However, with increasing bar strength, the best-fitting values of the parameters progressively deviate from their true values. This happens due to a combination of radial heating, radial migration, and resonance overlap phenomena in our bar models. Furthermore, the azimuthal location and the size of the survey volumes play important roles in the successful recovery of the parameters. Survey volumes along the bar major axis produce larger (relative) errors in the best-fitting parameter values. In addition, the potential parameters are better recovered for survey volumes with larger spatial coverage. As the Sun is located just ∼28°–33° behind the bar’s major axis, an estimate for the bar-induced systematic bias – as provided by this study – is therefore crucial for future modelling attempts of the Milky Way.

Numerical Investigation of Asymmetric Mach 2.5 Turbulent Shock Wave Boundary Layer Interaction

Supersonic shock wave boundary layer interactions are common to inlet flows of supersonic and hypersonic vehicles. This paper reports on wall-resolved implicit large-eddy simulations of a canonical Mach 2.5 turbulent shock wave boundary layer interaction experiment at the NASA Glenn Research Center. The boundary layer upstream of the interaction was nominally axisymmetric and two-dimensional. A conical centerbody with a 16 deg half-angle and a maximum radius of 0.147D of the test section diameter was employed to generate a conical shock wave, where D is the test section diameter. Asymmetric (swept) interactions were obtained by displacing the shock generator away from the test section centerline. The present simulation is for a shock generator displacement of D/6. Results from the asymmetric simulation are compared with results from an earlier simulation of a corresponding axisymmetric interaction. The experimental Reynolds number based on test section diameter was ReD=4×106. For the simulations, the Reynolds number was lowered to ReD=4×105 to keep the computational expense of the simulations within limits. Compared to the axisymmetric interaction, the streamwise extent of the separation varies considerably in the azimuthal direction for the asymmetric interaction. The separation is strongest at the azimuthal location that is closest to the shock generator. The streamwise extent of the separated flow regions is noticeably reduced and substantial crossflow is observed between the locations that are closest and farthest from the shock generator. A Fourier analysis of the unsteady flow data indicates low-frequency content for the separated region that is closest to the shock generator. Away from this region, with increasing sweep angle and cross-flow, the low-frequency content is diminished. A proper orthogonal decomposition captures spanwise coherent structures for the more two-dimensional parts of the interaction.

Improved Beam Steering Method Using OAM Waves

Orbital Angular Momentum (OAM) is an intrinsic feature of electromagnetic waves which has recently found many applications in several areas in radio and optics. In this paper, we use OAM wave characteristics to present a simple method for beam steering over both elevation and azimuth planes. The design overcomes some limitations of traditional steering methods, such as limited dynamic range of steering, the design complexity, bulky size of the steering structure, the limited bandwidth of operation, and low gain. Based on OAM wave characteristics, the proposed steering method avoids design complexities by adopting a simple method for generating the OAM-carrying waves. The waves are generated by an array of Planar Circular Dipole (PCD) elements. These elements are designed to cover a wide bandwidth range between 3 and 30 GHz. The transmitting array shows an enhanced gain value from 8.5 dBi to almost 11.5 dBi at the broadside angle. Besides the enhanced PCD-based OAM generation, the novelty of the design lies in a new method of beam steering. Beam steering is then performed by controlling the electrical feeding of the PCD elements; the beam azimuthal location is managed by turning off some of the PCD elements, while the elevation is determined by changing the gradient phase of excitation for the turned-on PCD elements. Detailed analysis of the steering method is carried out by finding the mathematical model of the system and the generated waves. The performance has been verified through numerical simulators.

Power yield improvement of wind turbine and fatigue load mitigation using predictive-based Active flow controller

The wind turbine construction aging caused by fatigue components of a wind field over a long period affects the physical structure. Flow controlling methodologies are used to alleviate turbine assembly stress. The flow regulation approach controller is critical in the fatigue load minimization procedure. This paper offers a Predictive controller for Independent pitch control (IPC)-based flow management. Because of the azimuthal position of the blade, the flow dynamics of the blades are vulnerable to cyclic fluctuations. This paper considers the azimuthal angle blade dynamics since there is a significant variation in movements between the bottom and top blades. The suggested controller (which takes into account the wind turbine’s Azimuthal angle characteristics) outperforms the existing controllers in terms of its capacity to forecast the blade’s reaction as it approaches the azimuthal location. The complete replication was effectively done.

Boiling Heat Transfer on Cylindrical Surface: An Experimental Study

In this paper, pool boiling heat transfer data from experiments are presented to investigate bubble formation patterns and film growth on a large sized cylinder dipped in a pool. A wide range of heat flux has been applied over the cylinder to observe different regimes in boiling heat transfer. Nucleation, bubble merging during the transition, and sliding are captured through careful experimental efforts. Bubble sliding on the cylinder after inclining it with respect to horizontal has also been captured during the experiment which prompts the formation of large-sized bubbles on the surface. It has been established that the heat transfer coefficient varies nearly 2 times based on the azimuthal location of a large cylinder, bottom location of the cylinder showing the highest. Studies from inclined cylinder showed azimuthally bottom-most point of higher end has faster bubble release and highest heat transfer coefficient (∼2 times higher than top-most point of lower end). Spiral-like bubble motion has been noticed after detachment from nucleation sites over the inclined surface. Effect of cylinder surface inclination on boiling pattern has been also presented along with observations of bubble formation.

Optimization of the flow distribution in a gyrotron cavity using evolutionary CFD simulations driven by a genetic algorithm

The steadily increasing performance requested to gyrotrons, to comply with their function of heating and current drive in fusion reactors, put a progressively increasing burden on the heat removal from the interaction cavity, where the heat flux can easily reach 20 MW/m2 on its inner surface. The cavity is actively cooled by subcooled water in forced flow in an annular region, and the water flow typically enters and exits through a single inlet and outlet. The high-speed flow entering from the inlet potentially drives an inhomogeneous flow azimuthally in the cavity region, but helps in locally bursting the heat removal due to the impinging effect of the cold-water flow. Here a new design of the water inlet in the cavity region is performed through a simplified genetic algorithm, in such a way that the flow homogeneity in the gyrotron cavity is maximized, without reducing the beneficial cooling due to the impact of the water jet on the cavity wall. The presence of multiple holes feeding the cavity, with their azimuthal location driven by the genetic algorithm, is analyzed through Computational Fluid Dynamics (CFD) simulations. Once the multi-inlet location is optimized, the dimension of the inlet holes is tuned to burst the heat transfer effect, reaching a high level of temperature and flow homogeneity in the cavity.

Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine

This study focuses on wind tunnel testing of a 3-bladed H-rotor vertical axis wind turbine (VAWT) under various conditions. Different performance metrics such as power coefficient (CP ), thrust load coefficient (CX ), and lateral load coefficient (CY ) are presented at four wind speeds. Parked loads, which are key parameters in designing VAWTs, are reported for the baseline case. Apart from presenting the benchmark results for the baseline model, the impact of two control strategies to boost the energy production of the VAWT are investigated. First, the effect of installing the plasma actuators on all blades is tested at four plasma input voltages. The results indicate that plasma actuators are an efficient approach to enhance the aerodynamic efficiency of VAWTs through modification of drag and lift loads acting on the blades. The second control strategy evaluated is intracycle RPM control. In this control method, the rotational speed of the turbine is varied with the azimuthal location of blades at each cycle so that the power production is increased. The results observed for this control strategy encourage further research development to expand the limited knowledge on its application for VAWTs.

Statistical Analysis of Convective Updrafts in Tropical Cyclone Rainbands Observed by Airborne Doppler Radar

AbstractTen years of airborne Doppler radar observations are used to study convective updrafts' kinematic and reflectivity structures in tropical cyclone (TC) rainbands. An automated algorithm is developed to identify the strongest rainband updrafts across 12 hurricane‐strength TCs. The selected updrafts are then collectively analyzed by their frequency, radius, azimuthal location (relative to the 200–850 hPa environmental wind shear), structural characteristics, and secondary circulation (radial/vertical) flow pattern. Rainband updrafts become deeper and stronger with increasing radius. A wavenumber‐1 asymmetry arises, showing that in the downshear (upshear) quadrants of the TC, updrafts are more (less) frequent and deeper (shallower). In the downshear quadrants, updrafts primarily have in‐up‐out or in‐up‐in secondary circulation patterns. The in‐up‐out circulation is the most frequent pattern and has the deepest updraft and reflectivity tower. Upshear, the updrafts generally have out‐up‐in or in‐up‐in patterns. The radial flow of the updraft circulations largely follows the vortex‐scale radial flow shear‐induced asymmetry, being increased low‐level inflow (outflow) and midlevel outflow (inflow) in the downshear (upshear) quadrants. It is hypothesized that the convective‐scale circulations are significantly influenced by the vortex‐scale radial flow at the updraft base and top altitudes. Other processes of the convective life cycle, such as bottom‐up decay of aging convective updrafts due to increased low‐level downdrafts, can influence the base altitude and, thus, the base radial flow of the updraft circulation. The findings presented in this study support previous literature regarding convective‐scale patterns of organized rainband convection in a mature, sheared TC.

The effect of inertia and vertical confinement on the flow past a circular cylinder in a Hele-Shaw configuration

The Poiseuille flow (centreline velocity $U_c$ ) of a fluid (kinematic viscosity $\nu$ ) past a circular cylinder (radius $R$ ) in a Hele-Shaw cell (height $2h$ ) is traditionally characterised by a Stokes flow ( $\varLambda =(U_cR/\nu )(h/R)^2 \ll 1$ ) through a thin gap ( $\epsilon =h/R \ll 1$ ). In this work we use asymptotic methods and direct numerical simulations to explore the parameter space $\varLambda$ – $\epsilon$ when these conditions are not met. Starting with the Navier–Stokes equations and increasing $\varLambda$ (which corresponds to increasing inertial effects), four successive regimes are identified, namely the linear regime, nonlinear regimes I and II in the boundary layer (the ‘ inner’ region) and a nonlinear regime III in both the inner and outer region. Flow phenomena are studied with extensive comparisons made between reduced calculations, direct numerical simulations and previous analytical work. For $\epsilon =0.01$ , the limiting condition for a steady flow as $\varLambda$ is increased is the instability of the Poiseuille flow. However, for larger $\epsilon$ , this limit is at a much higher $\varLambda$ , resulting in a laminar separation bubble, of size ${O}(h)$ , forming for a certain range of $\epsilon$ at the back of the cylinder, where the azimuthal location was dependent on $\epsilon$ . As $\epsilon$ is increased to approximately 0.5, the secondary flow becomes increasingly confined adjacent to the sidewalls. The results of the analysis and numerical simulations are summarised in a plot of the parameter space $\varLambda$ – $\epsilon$ .

Active control assessments towards optimizing the performance of a cycloidal rotor at hover

The present study demonstrates an improved performance of cycloidal rotors by actively controlling the pitching oscillations and rotational speeds. The computational fluid dynamics (CFD) coupled with artificial neural network (ANN) were the methodologies used in the optimization analysis for the hover-state operation rather than the take-off mode under ground effects [1]. The former is carried out to obtain numerical predictions at various operating conditions for an UAV-scale cyclorotor. The oscillating-rotating blades and the corresponding flowfield is computed unsteadily along the complete circular trace for performance considerations. From CFD simulations, the optimum operational state is predicted for a 30∘ and 500 (rpm) pitch angle and rotating speed, respectively. On a second step, by training the ANN with the CFD database at various operating conditions and parameters, the ANN was then capable of analyzing the optimum states for operating at different conditions. The pitching oscillation schedule is then optimized for each rotational speed by using ANN and for each azimuthal location over the traversing trace. This will imply to perform on-board control in active mode for the blades, rather than assigning constant pitching oscillations for all operating states. This active control concept showed to be a potential approach to enhance the cyclorotor efficiency by 12 percent in average.

STDP and the distribution of preferred phases in the whisker system.

Rats and mice use their whiskers to probe the environment. By rhythmically swiping their whiskers back and forth they can detect the existence of an object, locate it, and identify its texture. Localization can be accomplished by inferring the whisker's position. Rhythmic neurons that track the phase of the whisking cycle encode information about the azimuthal location of the whisker. These neurons are characterized by preferred phases of firing that are narrowly distributed. Consequently, pooling the rhythmic signal from several upstream neurons is expected to result in a much narrower distribution of preferred phases in the downstream population, which however has not been observed empirically. Here, we show how spike timing dependent plasticity (STDP) can provide a solution to this conundrum. We investigated the effect of STDP on the utility of a neural population to transmit rhythmic information downstream using the framework of a modeling study. We found that under a wide range of parameters, STDP facilitated the transfer of rhythmic information despite the fact that all the synaptic weights remained dynamic. As a result, the preferred phase of the downstream neuron was not fixed, but rather drifted in time at a drift velocity that depended on the preferred phase, thus inducing a distribution of preferred phases. We further analyzed how the STDP rule governs the distribution of preferred phases in the downstream population. This link between the STDP rule and the distribution of preferred phases constitutes a natural test for our theory.

Breaking the symmetry to structure light.

We show that by breaking the symmetry of a beam subjected to tight focusing, namely by obscuring half of it or, equivalently, shifting the beam away from the lens axis, it is possible to obtain novel light properties in the focal spot which, to the best of our knowledge, have not been observed before. For example, a linearly polarized beam half-obstructed or shifted from the axis generates longitudinal and transverse electrical field components, both of which peak on-axis. The ratio of the intensities of these two components can be tuned by changing the shift distance, the size, and the azimuthal location of the displaced incoming beam. Moreover, such symmetry breaking of a linearly polarized beam acts as a catalyst for producing distributions of circular polarization/longitudinal spin angular momentum, as well as orbital angular momentum, in the focal plane. The simple method for generating co-incident longitudinal and transverse components with a controllable ratio may find applications in laser machining, particle manipulation, etc.

Anisotropic neutron response of trans-stilbene and impact on a handheld dual particle imager

This manuscript details measurements of the anisotropic light-output response of trans-stilbene, henceforth referred to as stilbene, along the three primary crystal planes and analyzes how this anisotropic response impacts neutron image reconstruction in a handheld dual particle imager (H2DPI). A prototype H2DPI composed of stilbene pillars (6×6×50 mm3) coupled to silicon photomultipliers was built and is capable of imaging both fast neutrons and gamma rays from kilogram quantities of special nuclear material. Stilbene was chosen as the scintillating medium for the imager because of its pulse shape discrimination capability, time resolution and relatively high light output. A drawback to using stilbene, however, is the anisotropic response. A recoiling proton from a neutron elastic-scattering event in stilbene will yield different amounts of scintillation light depending on the direction of the recoiling proton with respect to the crystal lattice. This manuscript analyzes how this anisotropic response impacts neutron image reconstruction in 4π. The light output in the three primary crystal planes of stilbene were independently measured 6–7 times for proton recoil energies ranging from 0.5–5.0 MeV using a quasi-monoenergetic time-of-flight neutron source. The measured light-output data in the three crystal planes were fit with a semi-empirical function based on Birks’ formula. These fits were used to reconstruct the location of a 252Cf source in front of the imager (0°, −0.8°), to the left of the imager (−90°, −0.8°) and directly above the imager (0°, 90°) to determine if it is necessary to apply the directionally-dependent response of stilbene to accurately reconstruct source locations. A bootstrapping technique was applied to the measured data sets to produce 1000 images composed of 2000 cone projections for each source location and each measured light-output curve. List-mode maximum likelihood expectation maximization was applied to each image; the highest pixel location and the full width at half maximum (FWHM) were then recorded. The average and standard deviations of these parameters were taken for each set of images. The maximum difference in the average azimuthal pixel location when varying between the appropriate and incorrect light-output curves for the source locations at (0°, −0.8°) and (−90°, −0.8°) were respectively found to be 1.85±1.39° and 2.03±1.78°. All other pixel locations and FWHMs were within a single standard deviation of uncertainty. Taken together, the anisotropic response of stilbene has negligible impact on the neutron image reconstruction capability of the H2DPI.

Protection and Identification of Thermoacoustic Azimuthal Modes

Abstract This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular, the amplitude, orientation, and nature of the acoustic field of azimuthal order n are characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient α and for the turbulent combustion noise, modeled by means of the background noise coefficient σ. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with α and σ, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier component affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a nonhomogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain β and a nonlinear saturation constant κ. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters {α,β,κ,σ} is then carried out on engine time-series data. The optimal four parameters {α,σ,β,κ} are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.

Experimental determination and analysis of the transverse pressure difference in a wire-wrapped rod bundle

Wire-wrapped rod bundles are widely used in different applications for their enhanced heat transfer capability. The complex behavior of the flow in these rod bundles is strongly affected by the geometrical parameters, and flow regime. Experimental measurements of the transverse pressure difference (between adjacent faces) of a replica of a 61-rod wire-wrapped hexagonal bundle have been conducted under a wide range of Reynolds number (3,000–18,000), to study the effects of the wire azimuthal position for transition and turbulent flow regimes. As a result of the higher horizontal velocity, the transverse pressure difference was found to increase with the bundle Reynolds number. At higher Reynolds number, the maximum (positive) transverse pressure difference between two adjacent faces occurred when the wire is directed at the corner between these faces (θ=0∘), with the minimum (negative) occurring at a wire azimuthal location of θ=120∘. Pressure at adjacent walls equalizes at an angle 60∘<θ<120∘, and near θ=−90∘. For the lower Reynolds numbers investigated, a positive minimum pressure difference was observed at θ=0∘. The experimental results improved the understanding of the flow behavior in wire-wrapped bundles, and provided a unique set of data that can be used for validation of high-fidelity computational fluid dynamics codes.

Wave identification in upward annular flow - a focus on ripple characterization

The interfacial structure of annular flow in upward inclined pipes is examined experimentally by a non-intrusive multilayer conductance liquid film sensor (LFS). In horizontal and inclined pipes, cross-sectional distribution of gas and liquid phases is asymmetric even on average. Thus, the ratio between the characteristic film thickness and the mean dominant wave parameters may vary significantly as a function of the azimuthal and inclination angles. Interface structure in upward annular flow is characterized by two kinds of waves, ripples and disturbance waves. An interface dominated by consecutive large amplitude disturbance waves may also contain numerous ripples. To differentiate between ripples and disturbance waves, a criterion based on statistical wave properties is required. Identification of individual waves is carried out using a zero-crossing procedure with a new reference value. This approach allows to identify both small and large amplitude waves at the interface, calculating the wave heights based on their individual crest and trough. The wave height probability density function (pdf) for a wave system consisting of ripples and disturbance waves is bimodal, with the first peak representing ripples and the second disturbance waves. The local minima between the two peaks in the pdf defines the boundary between ripples and disturbance waves for each flow condition and azimuthal angle. The clear differentiation of the two kinds of waves allows to focus on detailed description of the statistical properties of ripples that are presented as a function of the pipe inclinations angles (ranging from near horizontal to vertical) and for all azimuthal location across the pipe circumference.