Rotating Propeller Blade Research Articles

Identification and Analysis of Micro-Doppler Signature of a Bird Versus Micro-UAV

The groundbreaking advancement of micro unmanned aerial vehicles (micro-UAVs) has been staggering. The diversity of micro-UAV operations is demanding in most sectors. However, the current regulatory framework for the civilian use of these devices is still insufficient. The operation of micro-UAVs may pose risks, including privacy violations and collision hazards. To address these concerns, a radar with advanced processing is needed. This study presents a preliminary design of an S-band continuous wave (CW) radar, which was simulated using MATLAB. The size of the rotating propeller blades of the micro-UAV ranges from 20 to 40 cm in length, while the size of a bird’s flapping wing measures 35 cm in length, comprising 22 cm for the upper arm and 13 cm for the lower arm. The analysis was conducted under hovering conditions, where the target's main body is stationary while its micro-parts move continuously. The Short-Time Fourier Transform (STFT) analysis successfully identified the unique signature of both targets. The results showed that the S-band CW radar design at 5 GHz is effective in extracting the micro-Doppler signature of a bird versus a micro-UAV. The extracted features can be used as additional characteristics for target classification in the future.

Analysis of water gap membrane distillation process with an internal gap circulation propeller

A novel propeller-aided water gap membrane distillation (P-WGMD) system has been investigated through detailed mathematical modeling, and its performance was compared with that of a baseline/conventional WGMD system. The proposed system contains a rotating propeller blade, which improves mass and heat transfer within the gap space. The installed propeller and its modeling within the gap chamber represent the novelty of the present work. The influences of various design variables, including propeller diameter, propeller material, propeller thickness, position of the propeller, and the thickness of the gap on the distillate production and the specific thermal energy consumption (STEC) of the proposed propeller-aided P-WGMD system, are investigated. In addition, the effects of different operating parameters such as feed water temperature, coolant temperature, feed water flowrate, and coolant flowrate on the performance of the baseline WGMD and propeller-aided P-WGMD processes were examined. Results revealed that propeller material and propeller thickness showed marginal effects on the system's performance, especially when the thermal conductivity of the propeller material exceeded 100 W/m K. The propeller position has a strong influence on the system performance, and placing the propeller away from the membrane surface improves the system performance. Larger propeller diameters and higher propeller speeds exhibit better system performance. Propeller speed and propeller diameter are found to be the most dominant design factors affecting the performance of the proposed system. Furthermore, the P-WGMD system exhibits superior performance over the baseline WGMD system under the same operating conditions, where the flux of the P-WGMD system could reach a maximum value of 322 kg/m2h at a feed flowrate of 10 L/min, propeller speed of 1000 rev/min, feed temperature of 70 °C, coolant temperature of 20 °C, and coolant flowrate of 2.5 L/min. The presence of a propeller within the gap chamber reduces the resistance to heat transfer from about 0.002057 m2K/W to 0.0001144 m2K/W, reflecting the enhancement gained in the proposed system. Freshwater costs from the proposed system vary between 8.243 $/m3 and 11.57 $/m3 while those from the baseline system fall between 9.971 $/m3 and 21.11 $/m3.

Turbulent inflow noise produced by a shrouded propeller

A theoretical model is presented for predicting the noise produced by the interaction of turbulence with a shrouded propeller in an axisymmetric mean-flow. For cases where the free-stream velocity is low, the turbulent eddies well upstream of the propeller are significantly elongated as they pass through the induced streamtube contraction. These elongated turbulent eddies interact multiple times with the rotating propeller blades causing partially coherent loading on the blades. The resulting radiated acoustic pressure spectrum contains peaks which occur at harmonics of the blade passing frequency. The theory is developed in the frequency domain and incorporates rapid distortion theory to obtain the distorted turbulent field at the propeller face, accounting for the potential mean-flow effect of the propeller and the shroud. The unsteady loading on the rotating blades is calculated using isolated blade response functions. The noise radiated to the far-field is then evaluated using a tailored Green's function approach which accounts for the scattering effect of the shroud and is solved using a boundary integral approach. Results are presented for shrouded and unshrouded propellers operating in flows with a range of different free-stream velocities. It is shown that as the free-stream velocity increases, the peak in the noise spectrum at the blade passing frequency reduces in level and the ‘haystack’ surrounding this peak widens. Results showing the effect of the shroud on the radiated noise levels at different frequencies and observer locations are also presented.

Двухточечная модель вращающихся лопастей

In this paper, the angular noises of the rotating blades of a radar object are considered. A multipoint geometric model of rotating blades of a single propeller is considered. On its basis, analytical expressions are obtained that make it possible to calculate the angular coordinates of the apparent center of radiation of a propeller with rotating blades. Also, on the basis of a multi-point geometric model, relations were obtained that make it possible to synthesize a two-point geometric model of rotating propeller blades. Theoretical results are confirmed by mathematical mode¬ling for two configurations of a single-rotor small-sized aircraft: with one rotating blade and with two rotating blades.

Theoretical and experimental studies on the hydrodynamic damping of elastic rotating propeller blades

The hydrodynamic damping characteristics of elastic rotating propeller blades are investigated theoretically and experimentally. Firstly, the modal hydrodynamic damping ratio of propeller blade rotating in water is theoretically predicted based on the cantilever plate theory. Then, a series of tests are designed to determine the mechanical, acoustic radiation and hydrodynamic damping of the first-order bending mode of the rotating blade. During the hydrodynamic damping test, the bending vibration of the blade is excited by the rotation-induced turbulence and measured by two strain gauges attached to the blade root. The results show that the theoretical prediction is in good agreement with the experimental results. The hydrodynamic damping increases linearly with the rotational speed of the propeller. Theoretical analysis also shows that the modal hydrodynamic damping ratio of the first-order bending mode is much larger than that of higher-order bending modes. The hydrodynamic damping decays exponentially with the increase of frequency ratio while increases slightly with the increase of propeller advance ratio which represents the ratio of free stream fluid speed to the propeller tip speed.

Investigation of underwater environmental effects in rotating propeller blade tracking laser vibrometric measurement

Analyzing the vibration characteristics of an underwater rotating propeller is crucial for predicting the structural damage of the propeller and preventing the failure of an entire propulsion system. The laser Doppler vibrometer (LDV) measurement technology is a good alternative to conventional contact sensors for the analysis of underwater structures. In this paper, a tracking LDV technique for the vibration measurement of propeller blades that rotate underwater is presented. The underwater vibration measurement of a rotating propeller is affected by the environmental conditions of the water, cavitation, and turbidity. The purpose of this study is to investigate the effects of underwater environmental conditions on the vibration measurement of a rotating propeller with the tracking LDV measurement technique. The vibration response measurements were performed in a water environment, and cavitation bubble and turbidity effects were simulated. To improve the quality of the measurement signal, the PCA-based feature extraction technique was used to remove abnormal signals including noise and irrelevant components and determine the natural frequency of the marine propeller. The final results show that the tracking LDV method with PCA-based feature extraction is suitable for in-situ health monitoring of rotating objects in real underwater environments.

Underwater vibration analysis method for rotating propeller blades using laser Doppler vibrometer

Vibration analysis for rotating propeller blades under water is obviously challenging. This study proposes stationary and tracking laser Doppler vibrometer (LDV) based measurement techniques for vibration analysis of the rotating propeller. The vibration measurement setup consists of an LDV, a DAQ and control system, and the rotating propeller that contains five blades mounted to the shaft through a rotor. To confirm the reliability of the proposed stationary and tacking LDV measurement results, the hammer impact tests are performed using a contact PZT accelerometer to obtain the velocity vibration results in time and frequency domain. These results are compared with LDV measurements for both in air and underwater cases. Both LDV and contact PZT measurements were taken simultaneously. The compared results show that the time-velocity signals and the corresponding frequency components obtained using hammer impact tests are very similar to the proposed LDV based measurement techniques. In addition, a numerical simulation is performed using COMSOL Multiphysics software to obtain natural frequencies of the system in air and underwater cases. These numerical simulation results are compared with bolt impact measurements taken on rotating propeller blade using LDV. Comparison of stationary and tracking LDV measurement results with the numerical analysis for in air and underwater cases showed matching results. From these results, it is concluded that the proposed techniques can be effectively used for underwater vibration measurement of the blades of rotating propeller.

An experimental study on the aerodynamic performance degradation of a UAS propeller model induced by ice accretion process

An experimental study was performed to investigate the effects of ice accretion on the aerodynamic performances and wake characteristics of a propeller model used for Unmanned-Aerial-System (UAS) under different icing conditions (i.e., rime vs. glaze). The experimental study was conducted in the unique Icing Research Tunnel available at Iowa State University (ISU-IRT). In addition to acquiring the important features of ice accretion on the rotating propeller blade using a “phase-locked” imaging technique, the wake characteristics of the rotating UAS propeller under the different icing conditions were also resolved by using the Particle Imaging Velocimetry (PIV) technique along with the time-resolved measurements of aerodynamic forces and power consumption of the UAS propeller model. Both “free-run” and “phase-locked” PIV measurements were performed on the propeller model at the different stages of the icing experiments (i.e., before, during and after the dynamic icing processes) to provide both the instantaneous flow characteristics and the ensemble-averaged flow statistics (e.g., mean velocity, vorticity, and turbulence kinetic energy) in the wake of the rotating propeller model. To the best knowledge of the authors, this is the first work of its kind to provide detailed, temporally-resolved wake flow field measurements of UAS propeller under real icing conditions. It is found that while the rime ice accretion could closely follow the original profiles of the propeller blades, the glaze ice usually forms into very irregular structures that can significantly disturb the wake flow field of the rotating propeller model, generating the much larger and more complex vortices. Such complex large-scale vortices are found to enhance the turbulent mixing in the propeller wake and produce an evident velocity deficit channel around the outer board of the propeller blades, providing direct evidences in elucidating the dramatic decrease in thrust generation and the significant increase in power consumption of the rotating propeller model in icing conditions. The findings derived from this study are believed to be essential and very helpful to elucidate the underlying mechanisms of the aerodynamic performance degradation of ice accreting UAS propellers.

Flow-induced vibration analysis of elastic propellers in a cyclic inflow: An experimental and numerical study

In this paper, the flow-induced vibrations of marine propellers in cyclic inflows are investigated both experimentally and numerically. A Laser-Doppler velocimetry (LDV) system is used to measure the axial flow velocity distributions produced by the seven-cycle wake screen in the water tunnel. A customized underwater slip ring and a single axis accelerometer sealed by silicon sealant are employed to measure the acceleration responses of rotating propeller blade. Numerical simulations of pressure fluctuations on the blades are performed using large eddy simulation (LES), while the forced vibrations of the propeller blades are obtained by a combined finite element and boundary element method. Experimental and numerical results are presented for two model propellers with the same geometries and different flexible properties, which show that the propeller blade vibrates at a frequency which is seven times as large as the axial passing frequency (APF) in the seven-cycle inflow. Moreover, the propeller blades are observed to resonance when the 7 APF excitation frequency is equal to the fundamental frequency of the propellers. The results indicate that both the inflow feature and the modal characteristic of blades contribute to flow-induced vibrations of elastic propellers.

A rare case of a scuba diver's death due to propeller injuries of a desalination pump

Water skiing, boat racing, skin and scuba diving, as well as pleasure boat cruising are becoming increasingly popular hobbies. As a result, the incidence of injuries secondary to motor propellers is becoming more frequent. Injuries by propellers, amputation, death by drowning, and bleeding are rare reported events in forensic literature. The most common circumstances surrounding boat-propeller-related injuries are concerned with getting into or out of the boat, personal watercraft use or water skiing, and falling or being thrown from the boat. A case of a scuba diver's death that occurred during an illegal scuba fishing trip around a desalination plant is presented. A complete autopsy and histological study of all organs and surfaces of dismembered cadaveric sections, performed in order to determine the phases of death, are reported. An underwater scene investigation was conducted by an engineering team studying the mouth of the pump and the dynamic characteristic of rotating propeller blades.

Electrocavitation in nanofluidics: unique phenomenon and fundamental platform.

In this paper, we will highlight one phenomenon unique to nanofluidics: electrocavitation. Electrocavitation is defined as cavitation induced by electric fields. Cavitation in general occurs in a liquid when it is subjected to a pressure below its vapor pressure, where the liquid can break apart and form a cavity (bubble). This is frequently seen in macroscale systems, for example, rotating propeller blades on the turbines of ships or water columns in the xylem of trees. Electrocavitation in nanochannels was first reported when researchers applied electric fields within nanochannels containing electrolytes discontinuous in conductivity and found that bubbles formed within the channel. The reasons to highlight electrocavitation to both the lab-on-a-chip community and those interested in the fundamental understanding of cavitation in general are detailed below.

추진기 날개 끝 형상변화에 따른 보오텍스 유동에 대한 수치해석

In order to control the tip vortex cavitation occurring around the tip of a rotating propeller blade, researches on the propeller cavitation and blade tip vortex flows have been increased. In this paper, the propeller tip vortex flow for a blunt and sharp tips was studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. In numerical open water test, torques, thrusts, pressure distributions and vortex flows were compared for various rotating speeds. To consider a hull wake, the nominal wake was specified in inlet boundary condition. Pressure distributions and vortex flows with the hull wake were investigated for various propeller rotating angles. From the results, it was confirmed that the blunt tip propeller delayed the tip vortex flow Ke ywords :P ropeller blade tip(추진기 날개 끝), Tip vortex flow(날개 끝 보오텍스 유동), Computational fluid dynamics(CFD, 전산유체역학)

Complex demodulation of broadband cavitation noise.

Cavitation is a prominent source of ship noise resulting from the collapse of bubbles in the wake of rotating propeller blades. This same rotation also induces an audible rhythm, which is often modeled as a periodiclike modulator multiplying a broadband noise carrier signal. Conventional signal models restrict the modulator term to be non-negative and real-valued, accounting only for long-term energetic fluctuations in the time series data. However, recent empirical observations [Versluis et al., Science, 2000] and explanatory simulations [Ida, Phys. Rev. (2009)] reveal that interactions between multiple bubbles can lead to phase inversions in the form of negative pressure spikes. In this context we propose a more general complex-valued modulator that can account for energetic as well as phase-coherence patterns in the signal model. Through the use of synthetic signals and ship data examples, we will briefly discuss issues of detection and maximum-likelihood estimation related to the new complex signal model. For the purpose of fostering scientific understanding, however, our primary focus will be motivation for and estimation of the significance of possible complex modulation in both modeled and observed cavitation noise. [This research was supported by the Office of Naval Research.]

Evaluation of a Potential Flow Model for Propeller and Wind Turbine Design

A three-dimensional, potential flow based, unsteady panel code was used to model the flow over rotating propeller blades. It is assumed that for best performance, flow separations must be avoided on the rotating blades of propellers and wind turbines. In this case, idealized tools such as the one used here are significantly faster and simpler for calculating the surface pressure distribution and the resulting performance parameters. Similar experimental data on the surface pressures and on common performance parameters are widely available on propellers (and less on wind turbines) and, therefore, the validation was performed on a two-blade NACA propeller. In the first part of this study, computed results were validated and were found to compare favorably with the experimental data for a wide range of performance parameters. In the second part of this study, a rotor optimization is performed using a generic rotor blade shape. For simplicity, a rectangular blade with several taper ratios and linear twist was used. The computed results indicate that even with this simple geometry, a more efficient design (than the baseline) is possible. It is concluded therefore that by using this tool more complex blade shapes and customized airfoil sections can be developed, leading to additional improvements in performance and efficiency.

ON THE FREE RESPONSE OF PROPELLER BLADES

The free vibration of a rotating ship propeller blade is studied using an iterative scheme based on Galerkin's method. The blade is idealized as a cantilever beam with variable cross section of airfoil shape. The effects of pitch angle, shear deflection, rotary inertia and speed of rotation are studied. Agreement with results available in the literature and with results obtained using a finite element method is excellent. It is important to have sufficiently accurate estimates for the natural frequencies and mode shapes for the bending vibration of a propeller blade early in the design stage. These estimates are required, not only to avoid dangerous operating speeds but also to calculate the dynamic bending stresses at the root of the blade. A suffi­ ciently accurate assessment of the dynamic stresses at the root of the blade is essen­ tial for the determination of the strength requirement in view of the recent propel­ ler blade fatigue failure incidents. The natural frequency of the propeller blade can also be used to obtain an estimate for the tail shape propeller assembly. This can prove useful in engine speed and reduction ratio selection. Several investigators used the finite element method for the dynamic analysis of propeller blades, see [1]. In the early design stages a more expedient method is pre­ ferred. Such a method should require neither an extensive amount of input data nor a large amount of computer time. In this respect, the modelling of the propeller blade as a symmetric cantilever with a variable section area can be considered. Shear deflection and rotary inertia effects should be taken into account. The literature on free vibration analysis of rotating cantilever beams is abun­ dant, see for example [2]. In [2] Subrahmamyam et al. used the Reissner and the potential energy method for the analysis of lateral vibrations of a uniform rotating blade taking shear deflection and rotary inertia into account. More recently, the bending vibration of a class of variable cross-section rotating beams has been dealt

Holographic vibration study of a rotating propeller blade

Holographic interferometry has often been used to determine the natural frequencies and the associated mode patterns of vibrating objects with rigidly fixed or stationary boundaries. This paper describes a new pulse-laser holographic technique whereby the vibration-mode patterns of a rotating propeller blade were determined. This technique consists of rotating the holographic plate on the same axis as the rotating object and using spherically symmetric wavefronts for object and reference beams.

Centrifugal loads on propeller blades

The prediction of loads experienced by a rotating propeller blade is of great importance in propeller design, especially in view of the recent increase in failures of propeller blades and pitch control mechanisms. In this paper, analytical expressions are derived for the forces and moments induced on a propeller blade due to uniform shaft rotation. Methods are then outlined for the numerical evaluation of these expressions using digital computers. An approximate formula is also derived for the centrifugal spindle torque on a controllable-pitch propeller blade, displaying explicitly the influence of independent variations in skew and rake. A discussion is finally given of the implications of these results in blade design.

A Tabular Method of Propeller Blade Stress Analysis

A tabular, trial-and-error method of evaluating the steadybending stresses in a rotating propeller blade is developed and examples of its application are given. The bending moment at a shank section of the blade is estimated and, by tabular integration, the corresponding radial bending moment distribution is calculated. Additional trials with appropriately revised shank section bending moment estimates are made until the correct distribution is found, having the physically required moment value of zero a t the blade tip. Tilted blades and blades whose section centers of gravity do not in general fall on the blade axis are shown to be readily analyzed. Because the final analysis can be quickly checked on a calculating machine and because the method is easily learned, versatile, and fast, its general adoption by the propeller industry is advocated.

Calculation of stresses and natural frequencies for a rotating propeller blade vibrating flexurally

Calculation of stresses and natural frequencies for a rotating propeller blade vibrating flexurally