Open Fan Research Articles

A numerical analysis of isolated propeller noise using a lattice Boltzmann method approach

Current environmental needs to achieve carbon neutral commercial aviation by 2050 require the development of new technologies and aircraft configurations. Among the different technological developments proposed, the use of open fan or Ultra-High Bypass Ratio configurations is of interest due to their higher propulsive efficiency and performance. To support the development of such technologies, accurate and efficient tools early in the design stages are needed to predict aerodynamic performances and noise levels. One such tool is the lattice Boltzmann method, which can perform high-fidelity aeroacoustic simulations of flows around propellers and engines. The lattice Boltzmann approach can be advantageous over other numerical methods due to its easy integration with complex geometries, its low numerical dissipation properties, and its high level of computational efficiency. This paper presents the aerodynamic and aeroacoustic numerical study of an isolated propeller using the commercial lattice Boltzmann solver ProLB. Large Eddy Simulations were carried out using a compressible hybrid thermal version of the solver. An aeroacoustic analysis using a Ffowcs-Williams and Hawkings acoustic analogy for far-field noise was carried out. The objective is to assess the capabilities of the solver to predict acoustic emissions of an isolated propeller towards the future study of an installed case.

Long term monitoring of CO2 levels and ventilation rates in a naturally ventilated residential apartment

Indoor CO2 levels became particularly topical during the recent COVID-19 pandemic. In this study a long-term investigation of indoor CO2 levels in a 1970s built residential apartment in single occupancy is presented. Three NDIR CO2 sensors were used to measure CO2 levels over a one-year period. Mean CO2 levels over this period were 1278 ± 504 ppm, with elevated CO2 levels of greater than 2000 ppm not uncommon. Subsequent investigations used the single zone mass balance model and the decay of CO2 in the absence of occupants to estimate the ventilation rates in various configurations. A mean natural ventilation rate of 0.16 ACH was estimated with all windows closed. Opening fan light windows resulted in a mean ventilation rate of 2.86 ACH whereas opening all windows increased the mean ventilation rate to 19.1 ACH. Evidence was observed of the effect of both wind speed and indoor-outdoor temperature difference on the ventilation rates. It was concluded that with all windows closed the natural infiltration rate was insufficient to maintain optimal indoor air quality even in single occupancy. Opening the fan light windows was sufficient to achieve satisfactory indoor air quality but insufficient for the effective inhibition of airborne disease transmission.

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.

Debris flow susceptibility assessment of Leh Valley, Ladakh, based on concepts of connectivity, propagation and evidence-based probability

The Leh Valley which lies within the Trans Himalayan state of Ladakh, India, is known to be affected almost annually by debris flows ranging from minor to catastrophic scale events. The effect has been getting magnified due to increased urbanization and rapid growth in tourism industry. Though these flows are triggered by intense and abnormal rainfall events the conditioning factor has always been the topography and sediment availability. A lucid acknowledgement of the terrain condition and the degree of vulnerability of such events is required. For this a detail investigation of sediment availability, topographic conditions and their relation with known events becomes crucial. This study utilizes index of connectivity (IC) model to understand the sediment source-sink relationship and farther applied Flow-R model to simulate the probable scenario of events through predefined algorithms. We then use the Weights of evidence (WOE) method to compute the statistical probability of debris flow occurrence. This paper demonstrates the application of these three independent techniques and their implementation in a highly rugged terrain of Ladakh which is a region of frequent debris flows onslaught. The IC and Flow-R models are found to be counter supportive and effective in delineating areas which could be affected by flows that will solely originate in upstream areas where high angle channels directly connected to sediment sources are present. WOE-based model determines the probability of the rare and extensive flows that results from downward integration of other drainage networks in an open fan area.

The Cross-sectional Shape and Height Expansion of Coronal Loops: High-resolution Coronal Imager (Hi-C) Analysis of AR 12712

Abstract Coronal loop observations have existed for many decades yet the precise shape of these fundamental coronal structures is still widely debated since the discovery that they appear to undergo negligible expansion between their footpoints and apex. In this work a selection of eight EUV loops and their 22 sub-element strands are studied from the second successful flight of NASA’s High-resolution Coronal Imager (Hi-C 2.1). Four of the loops correspond to open fan structures with the other four considered to be magnetically closed loops. Width analysis is performed on the loops and their sub-resolution strands using our method of fitting multiple Gaussian profiles to cross-sectional intensity slices. It is found that while the magnetically closed loops and their sub-element strands do not expand along their observable length, open fan structures may expand an additional 150% of their initial width. Following recent work, the Pearson correlation coefficient between peak intensity and loop/strand width are found to be predominantly positively correlated for the loops (≈88%) and their sub-element strands (≈80%). These results align with the hypothesis of Klimchuk & DeForest that loops and—for the first time—their sub-element strands have approximately circular cross-sectional profiles.

Open fan sign: An ultrasound finding suggesting postpartum intrauterine forgotten gauze.

Key Clinical MessageGauze counting is regarded as the most essential way to prevent forgotten gauze inside the body during any surgery. However, incident may still occur due to artificial mistake. An open fan sign on ultrasonography may indicate a gauze left in the intrauterine cavity.

Numerical investigations of ducted fan aerodynamic performance with tip-jet

Tip-jet technology has the potential value for application in vertical take-off and landing or short take-off and landing concept aircraft. The main objective of this work is to present a rapid prototyping method to model the power of the tip-jet during the concept design phase, and to investigate the aerodynamic performance of a ducted fan with tip-jet in hover through numerical experiments. The calculated data of the rapid method was compared to the numerical results, while the comparative analysis of the performances of an open fan, a ducted fan and a ducted fan with tip-jet were carried out. The results indicate that the fan lift of the ducted fan with tip-jet was augmented by the jets which formed the Coanda effect on the suction surface of the blade to increase the circulation of the blade. The figure of merit of the ducted fan with tip-jet was reduced and slightly affected by the nozzle area. The flow field represents the same flow features when the nozzle works in subsonic to supersonic operational conditions.

Numerical Investigations of Fan-in-Wing Aerodynamic Performance with Active Flow Control

Aerodynamic performance of a fan-in-wing configuration in hover is numerically investigated using a high-fidelity three-dimensional unsteady Reynolds-averaged Navier–Stokes flow solver based on unstructured grid technology. Fan-in-wing or ducted fan configurations offer the advantage of hover capability with enhanced thrust comparing to open fans, but they suffer from reduced efficiency and thrust levels at offdesign conditions. In this study, the aerodynamic performance and flowfield of a fan-in-wing configuration in hover are numerically investigated over a range of blade pitch angles at two operating speeds. The maximum thrust, peak efficiency, and stall margin of the system are among the main interests of this investigation. An innovative concept using an active flow control is introduced in this study to enhance the operating efficiency and thrust level of the system by increasing the circulation and duct mass flow rate in the fan-in-wing system. Numerical investigations indicate a 25–55% increase in the maximum system thrust, achieved without suffering the peak efficiency loss, when using the proposed active flow control concept. This potentially provides a viable technology to significantly enhance the aerodynamic performance of lift fan devices such as the ducted fans or fan-in-wing configurations to support the research of vertical takeoff and landing aircraft.

Numerical Simulation & Scene Experiment of Metro Tunnel with Crossover Interval under Fire Conditions

In this study, numerical simulation and scene experiment with metro crossover interval are performed to estimate the effect of ventilation model and the position of the most unfavorable smoke removal on passenger’s life safety under fire conditions. Firstly, based on STESS (Metro Thermal Environment Simulation Software), a network model of smoke removal is established with the crossover interval of metro line 10 (Between Wen De Road Station and Yu Shan Road Station), which discusses the effect on smoke flow and fire spread in different indicators, including fire source position and intensity, the number of platform and interval fan used as dealing with emergency. Secondly, combined with FDS (Fire Dynamics Simulator) technology, a three-dimensional field model of metro station with crossover interval is set up, which contributes to the smoke’s variation of temperature field and velocity field as well as concentration field can be simulated and analyzed under fire conditions. And then the model of fire conditions is measured and verified with crossover interval in scene experiment. On the basis of above all, the study puts forward where each opening fan is positioned and what the number is needed, satisfying the requirements of smoke removal and providing references in metro crossover interval at the same time.

Influence of traffic force on pollutant dispersion of CO, NO and particle matter (PM2.5) measured in an urban tunnel in Changsha, China

Environmental safety issues and ventilation problems caused by the construction of urban tunnel have increasingly been attracting people’s attention. Previous studies in China have mainly focused on vehicle emissions and ventilation control technologies in road tunnels, resulting in a research gap on urban tunnel ventilation engineering design. Therefore, a detailed monitoring investigation was conducted from May 22 to June 2, 2013 in Changsha Yingpan Road Tunnel, China. The study aim was to measure the traffic characteristics, air velocity and the carbon monoxide (CO), nitrogen oxides (NOx) and fine particulate matter (PM2.5) concentrations in this tunnel, which has two lanes per bore and multiple ramps. Measurement results show that during the workday morning peak, the maximum traffic flow was 1560 passenger-car-unit/h per lane with vehicle speed around 33.6km/h in the eastbound tunnel, the average air velocity was 3.07m/s, and the proportion of the light-duty vehicles (LDV) was 97.3%. Under the traffic force (not open fan), the CO and NO average concentrations at the main tunnel outlet were 20.3ppm and 1.65ppm, respectively. The gas pollutant concentrations are effectively controlled within the multiple-ramps tunnel and the design air volume flow is noticeably reduced. The traffic air flow was found to provide 32.5% of the required air volume to dilute NOx in blocked traffic condition (vehicle speed of 10km/h). In addition, the PM2.5 concentration is mainly affected by the value of background outside the tunnel. The result can provide a quantitative assessment method to support pollutant concentration control and contribution of requested air volume by traffic flow in urban complex structure tunnel.

Adaptive noise cancellation system for low frequency transmission of sound in open fan aircraft

This paper describes the use of a structural/acoustic model of a section of a large aircraft to help define the sensor/actuator architecture that was used in a hardware demonstration of adaptive noise cancellation. Disturbances considered were representative of propeller-induced disturbances from an open fan aircraft. Controller on and controller off results from a hardware demonstration on a portion of a large aircraft are also included. The use of the model has facilitated the development of a new testing technique, closely related to modal testing, that can be used to find good structural actuator locations for adaptive noise cancellation.

Adaptive Noise Cancellation System for Low Frequency Transmission of Sound in Open Fan Aircraft

This paper describes the use of a structural/acoustic model of a section of a large aircraft to help define the sensor/actuator architecture that was used in a hardware demonstration of adaptive noise cancellation. Disturbances considered were representative of propeller-induced disturbances from an open fan aircraft. Controller on and controller off results from a hardware demonstration on a portion of a large aircraft are also included. The use of the model has facilitated the development of a new testing technique, closely related to modal testing, that can be used to find good structural actuator locations for adaptive noise cancellation.

Dark-field hyperlens exploiting a planar fan of tips

Metallo-dielectric superlenses transfer subwavelength-scale information without magnification. The so-called hyperlenses additionally magnify, transferring images into traditional far-field optics. We target hyperlenses based on the “canalization” phenomenon in an array of wires, modified to form an open fan, also called “endoscope.” We use an integrated optics design with silicon wires, fed for instance by grating couplers, accessing gold wire fans. This alleviates the need to care for wire length. We explore a regime where we do not only image a near-field source, but where we image illuminated nano-objects, as done in microscopy, light being fed by a second fan before the object plane. In order to counter the low contrast from illuminated nano-objects, we propose here a dark-field hyperlens concept: We show that the illumination fan can be fed so as to get a dark output for a “void” object field, as occurs in the eponym microscopy method. We obtain, at a wavelength as large as 1200 nm, a well-resolved imaging capability for a scene of two 30 nm silicon particles.

Fan noise visualization and noise source identification by using nearfield acoustical holography.

A nearfield acoustical holography (NAH) method combined with a non-stationary source compensation procedure is applied to identify the noise sources of two open fans. The measured noise data of a low-speed, small fan indicate the highest peak levels at the blade passing frequencies (BPFs) of 102 and 204 Hz. It is observed that there is no noise component induced by vortex shedding at the blade tips, or leading or trailing edges of the small fan. It is also observed that the structural resonance frequencies of the small fan blades are not coincident with the BPFs: thus, the structural vibration responses of the blades contribute insignificantly to the fan noise. The NAH results of the small fan show acoustic pressure fluctuations on the blade surfaces at the BPFs. The measured noise data of a high-speed, large fan show the frequency components associated with BPFs as well as vortices shed at blade edges. Similar to the small fan case, the resonance frequencies of the fan blades cannot be observed in the measured acoustic data. The NAH results of the high-speed, large fan successfully exhibit acoustic pressure fluctuations at BPFs as well as noise patterns radiated from the vortex shedding.

Preliminary evidences of circadian fan activity rhythm in <i>Sabella spallanzanii</i> (Gmelin, 1791) (Polychaeta: Sabellidae)

The fan activity rhythm of Sabella spallanzanii (Gmelin, 1791) and its entrainment capability to light were studied. Animals were tested under constant darkness (DD) followed by two consecutive 24 h light-darkness regimes: a first 11 h light period (LD) and a second 9 h light period, with its phase inverted (DL). An infrared analogical video-camera took shots each 30 s. A number of pictures with open fan were counted every 15 min. In DD a weak free-running periodicity in the circadian range was found, thus reinforcing the matching of the 24 h period under study in both photoperiod regimes. A nocturnal activity was characterised with a consistent anticipation to lightOFF (i.e. entrainment). Moreover, this phase of entrainment differed between DL and LD. The presence of endogenous activity rhythm with a variable phase angle of entrainment is a distinctive feature of circadian pacemakers.

Po-Thur Eve General-33: Feasibility of a Multileaf Collimator and Method for Multi-slice Tomotherapy

Purpose: Current methods for delivery of serial or helical tomotherapy are based on a collimator design which can, at most, irradiate two slices simultaneously as the source rotates around the patient. We investigate the feasibility of a novel multileaf collimator design and method for multi‐slice tomotherapy. Method and Materials: The MLC incorporates a compact pivoting leaf design. Intensity modulation is achieved through binary actuation of adjacent leaves. Multiple leaf banks are employed for multi‐slice tomotherapy delivery. Each fan beam will have a different divergence in the axial direction. Two multi‐slice delivery methods are evaluated where (a) pitch is determined by a given collimated slice which does not irradiate beyond the adjacent slice (regular pitch) or (b) pitch is determined by different collimated slices irradiating the same region in the patient (multi‐slice pitch). Junctioning effects were studied for a cylindrical phantom irradiated with open (unmodulated) fan beams. Results: A prototype MLC leaf has been tested which can switch between open and closed positions in a few tens of milliseconds. Regular pitch delivery produced the greatest inhomogeneity between regions irradiated by different collimated slices. The proposed multi‐slice pitch delivery method avoids regular pitch junctioning effects by irradiating all areas with all collimated slices. Conclusions: These results indicate that multi‐slice tomotherapy is feasible with the benefits of shorter treatment times and it may allow for the use of Co‐60 as a tomotherapy radiation source. Conflict of Interest: Research was supported in part through a licensing agreement with TomoTherapy Inc.

Eustatic and tectonic control on Late Quaternary alluvial fans along the Tyrrhenian Sea coast of Calabria (South Italy)

The Late Quaternary evolution of the western Coastal Range (northern Calabria) has been reconstructed by means of a multidisciplinary approach. We have focused on the role of allocyclic mechanisms, tectonics and base-level change considered as factors influencing alluvial fan development. In particular we identify no clear evidence for a major influence of climate. Age constraints were provided by a tephra layer and a paleosol, coupled with geomorphological correlations. Middle Pleistocene perched terraces and fan relicts hanging above fault scarps, indicate that tectonics caused switches in fan dynamics between aggradational and erosional phases. As tectonic activity declined during late Middle Pleistocene, eustatically driven changes in base-level, possibly plus low rates of tectonic subsidence, represent the main factor which controlled Late Pleistocene fan development. The two major fan aggradation phases occurred during periods of climate amelioration prior to highstands, whereas high sea levels (OIS 5 and 1) promoted channel incision into the fan surfaces; this continued during periods of climate deterioration with a seaward progradation of alluvial deposition. Sea-level rise is seen as creating accommodation space, producing very open fans, locally within mountain embayments. The fans are characterised by a mushroom shape in plan-view and by a retrograde stacking pattern of alluvial fan facies.

Visualization and experiment of tip vortex phenomenon in cooling fan using digital particle image velocimetry

The Digital Particle Image Velocimetry (DPIV) is an efficient method for measuring the internal flow field of a low-speed cooling fan. This paper studied the velocity field by means of PIV technology for a leading edge swept axial-flow fan without casing, and the tip vortex phenomenon was observed. Time-averaged velocity measurements were taken near the pressure surface, the suction surface and the tip of blade, etc. Moreover, the flow characteristics were visualized using numerical techniques. Experimental results showed that this tip vortex existed at the leading edge of the blade. The generating, developing and dissipating evolvement process of the tip vortex from the blade leading edge to downstream were discussed in detail. In addition, by comparing DPIV results and numerical results, a good agreement between them indicated a possibility to predict flow field using CFD tools. The experimental data provided in this paper are reliable for improving the aerodynamic characteristics of the open axial fan.

Giambattista Tiepolo's Young Lady in a Tricorn Hat.

Giambattista Tiepolo's Young Lady in a Tricorn Hat.

Differential features of alluvial fans controlled by tectonic or eustatic accommodation space. Examples from the Betic Cordillera, Spain

The creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area (along basin–margin faults) or to a rise in base level. Depending (amongst others) on the relative importance of these two factors, the margins of terrestrial sedimentary basins (where alluvial fans develop) produce aggradational, progradational or retrogradational stratigraphic architecture. We studied a total of 43 Quaternary alluvial fans in the Granada and Bajo Segura basins (Betic Cordillera, Spain). The analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns, which is the result of differences in eustasy and tectonics. The qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related, in each case, to the main mechanism operative in the creation of accommodation space. These patterns are described as follows. (1) Alluvial aggradation is the main result of high tectonic subsidence with the development of quite open, but small fans with a constant steep slope lacking incised channels and headward-eroding gullies. (2) In contrast, when the principal mechanism in creating accommodation space is low tectonic subsidence, progradation occurs and the fans are narrower and larger. Moreover, the slopes of such fans are less steep in relation to the drainage area than in the above case, being constant or even concave in longitudinal profile. They also have short, deep incised channels, culminating downfan in a depositional lobe. In inactive zones, long, deep headward-eroding gullies develop. (3) Areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin, although with a pronounced mountain embayment, which gives them a characteristic “mushroom” shape in plan view. In the latter case, retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas, usually showing a segmented longitudinal profile with a low gradient. The feeder channels do not surpass stream order 3, and various extremely long and shallow incised channels can appear. (4) Contrary to the case of fans developing under a regime of subsidence, when the accommodation is due to base level rise, the fan slopes bear no relation to the extent of the catchment basins. In such a case, the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet-flows over the alluvial surface.