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1 – 10 of 59The purpose of this paper is to assess state-of-the-art techniques for quantifying flow distortion in the inlets of turbofan engines, particularly with respect to the prospects…
Abstract
Purpose
The purpose of this paper is to assess state-of-the-art techniques for quantifying flow distortion in the inlets of turbofan engines, particularly with respect to the prospects for future flight applications.
Design/methodology/approach
To adequately characterize the flow fields of complex aircraft inlet distortions, the author has incorporated laser velocimetry techniques, namely, stereoscopic particle image velocimetry (PIV) and Doppler velocimetry based on filtered Rayleigh scattering (FRS), into inlet distortion studies.
Findings
Overall, the results and experience indicate that the pathway for integration of FRS technologies into flight systems is clearer and more robust than that of PIV.
Practical implications
While always a concern, the topic of inlet distortion has grown in importance as contemporary airframe designers seek extremely compact and highly integrated inlets. This research offers a means for gaining new understanding of the in situ aerodynamic phenomena involved with complex inlet distortion.
Originality/value
This paper presents unique applications of turbofan inlet velocimetry methods while providing an original assessment of technological challenges involved with progressing advanced velocimetry techniques for flight measurements.
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Wei Xia, Lingwen Kong, Jiahuan Zhang, Hui Hao, Yiping Wang, Xiaoqi Ni, Ming Wang and Dongmei Guo
The purpose of this study aims to modify a self-mixing laser mouse as an extremely cost-effective displacement sensor to measure the mechanical oscillation of a commercial shaker…
Abstract
Purpose
The purpose of this study aims to modify a self-mixing laser mouse as an extremely cost-effective displacement sensor to measure the mechanical oscillation of a commercial shaker and a nano-positioning stage.
Design/methodology/approach
This kind of laser mouse, mostly consisting of a pair of vertical cavity surface emitting lasers, two photodiodes and an integrated signal processing unit, is capable of directly giving the x-axis and y-axis components of the measured vibrating displacement. Based on the laser self-mixing interference, the velocity of the object is coded into the Doppler frequency shift of the feedback light, which allows accurate determination of the vibration of the object.
Findings
A commercial shaker has been used to provide standard harmonic oscillation to test the displacement sensor. Within a vibrating frequency range of 110 Hz, the experimental results show that the micrometer scale resolution has been achieved at the velocity of up to 2 m/s, which is much improved compared with the image-based optical mouse. Furthermore, the measurements of the two dimensional displacement of a nano-positioning stage are performed as well. The minimum measurable velocity limit for this sensor has been discussed in detail, and the relative measurement error can be greatly reduced by appropriate selection of the modulation frequency of the triangular injection current.
Originality/value
These results demonstrate the feasibility of this device for the industrial vibration sensing applications.
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Bench‐top wind tunnels are used extensively by the US Air Force for calibrating anemometers. As anemometers have improved, the need for reduced uncertainties in the bench‐top wind…
Abstract
Purpose
Bench‐top wind tunnels are used extensively by the US Air Force for calibrating anemometers. As anemometers have improved, the need for reduced uncertainties in the bench‐top wind tunnels was required. A three‐pronged approach was used to reduce low velocity uncertainties by a factor of 2‐3.Design/methodology/approach – The reduction in velocity uncertainties was achieved by upgrading the wind tunnel instrumentation that measured the pressure and differential pressure and by improving the velocity calibration of the bench‐top wind tunnel. A detailed uncertainty analysis was performed to determine how much the instrumentation needed to improve. A laser Doppler velocimetry (LDV) was used to calibrate each wind tunnel at low velocities.Findings – The uncertainty analysis indicated that the main contributors to the velocity uncertainty were the differential pressure and the pressure measurements. These two process instruments were upgraded to reduce their individual uncertainties by a factor of 2. Additionally each bench‐top wind tunnel was calibrated using the LDV with special emphasis on flows from 0.15‐3.0 m/s. In all, nine wind tunnels were calibrated and the upgraded systems exhibited a reduction in uncertainties in the low flow region of a factor of 2‐3.Originality/value – A need to reduce velocity uncertainties in bench‐top wind tunnels was a requirement for the US Air Force calibration program. Upgraded instrumentation and individual calibration with an LDV provided the needed reduction. In the low flow region of 0.15 to 3.0 m/s, uncertainties were reduced by a factor of 2‐3.
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David S. Martínez, Elisa Pescini, Maria Grazia De Giorgi and Antonio Ficarella
Reynolds number in small-size low-pressure turbines (LPT) can drop below 2.5 · 104 at high altitude cruise, which in turn can lead to laminar boundary layer separation on the…
Abstract
Purpose
Reynolds number in small-size low-pressure turbines (LPT) can drop below 2.5 · 104 at high altitude cruise, which in turn can lead to laminar boundary layer separation on the suction surface of the blades. The purpose of this paper is to investigate the potential of an alternate current (AC)-driven Single Dielectric Barrier Discharge Plasma Actuator (AC-SDBDPA) for boundary layer control on the suction side of a LPT blade, operating at a Reynolds number of 2 · 104.
Design/methodology/approach
Experimental and numerical analyses were conducted. The experimental approach comprised the actuator testing over a curved plate with a shape designed to reproduce the suction surface of a LPT blade. A closed loop wind tunnel was employed. Sinusoidal voltage excitation was tested. Planar velocity measurements were performed by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). The device electrical power dissipation was also calculated. Computational fluid dynamics (CFD) simulations using OpenFOAM© were conducted, modelling the actuator effect as a body force calculated by the dual potential algebraic model. Unsteady RANS (Reynolds Averaged Navier-Stokes equations), also known as URANS approach, with the k-ε Lam-Bremhorst Low-Reynolds turbulence model was used.
Findings
The AC-SDBDPA operation brought to a reduction of the separation region; in particular, the boundary layer thickness and the negative velocity values decreased substantially. Moreover, the flow angle in both the main flow and in the boundary layer was reduced by the plasma control effect. The actuation brought to a reduction of the 17 per cent in the total pressure loss coefficient. The pressure coefficient and skin friction coefficient distributions indicated that under actuation the reattacnment point was displaced upstream, meaning that the flow separation was effectively controlled by the plasma actuation. Adopting slightly higher actuation parameters could bring to a full reattachment of the flow.
Practical implications
The work underlines the potentialities of an AC-SDBDPA to control separation in LPTs of aeroengines.
Originality/value
The present work sets a methodological framework, in which the validated procedure to obtain the body force model combined with CFD simulations can be used to study a configuration with multiple actuators allocated in array without requiring further experiments.
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Clinton B. Morris, John M. Cormack, Mark F. Hamilton, Michael R. Haberman and Carolyn C. Seepersad
Microstereolithography is capable of producing millimeter-scale polymer parts having micron-scale features. Material properties of the cured polymers can vary depending on build…
Abstract
Purpose
Microstereolithography is capable of producing millimeter-scale polymer parts having micron-scale features. Material properties of the cured polymers can vary depending on build parameters such as exposure. Current techniques for determining the material properties of these polymers are limited to static measurements via micro/nanoindentation, leaving the dynamic response undetermined. The purpose of this paper is to demonstrate a method to measure the dynamic response of additively manufactured parts to infer the dynamic modulus of the material in the ultrasonic range.
Design/methodology/approach
Frequency-dependent material parameters, such as the complex Young’s modulus, have been determined for other relaxing materials by measuring the wave speed and attenuation of an ultrasonic pulse traveling through the materials. This work uses laser Doppler velocimetry to measure propagating ultrasonic waves in a solid cylindrical waveguide produced using microstereolithography to determine the frequency-dependent material parameters of the polymer. Because the ultrasonic wavelength is comparable with the part size, a model that accounts for both geometric and viscoelastic dispersive effects is used to determine the material properties using experimental data.
Findings
The dynamic modulus in the ultrasonic range of 0.4-1.3 MHz was determined for a microstereolithography part. Results were corroborated by using the same experimental method for an acrylic part with known properties and by evaluating the natural frequency and storage modulus of the same microstereolithography part with a shaker table experiment.
Originality/value
The paper demonstrates a method for determining the dynamic modulus of additively manufactured parts, including relatively small parts fabricated with microstereolithography.
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Keywords
V. Giuliani, B. de Witt, M. Salluzzi, R.J. Hugo and P. Gu
Particle velocity is a critical factor that can affect the deposition quality in manufacturing processes involving the use of a laser source and a powder‐particle delivery nozzle…
Abstract
Purpose
Particle velocity is a critical factor that can affect the deposition quality in manufacturing processes involving the use of a laser source and a powder‐particle delivery nozzle. The purpose of this paper is to propose a method to detect the speed and trajectory of particles during a laser deposition process.
Design/methodology/approach
A low‐power laser light sheet technique is used to illuminate particles emerging from a custom designed powder delivery nozzle. Light scattered by the particles is detected by a high‐speed camera. Image processing on the acquired images was performed using both edge detection and Hough transform algorithms.
Findings
The experimental data were analyzed and used to estimate particle velocity, trajectory and the velocity profile at the nozzle exit. The results have demonstrated that the particle trajectory remains linear between the nozzle exit and the deposition plate and that the particle velocity can be considered a constant.
Originality/value
The use of low‐power laser light sheet illumination facilitates the detection of isolated particle streaks even in high‐powder flow rate condition. Identification of particle streaks in three subsequent images ensures that particle velocity vectors are in the plane of illumination, and also offers the potential to evaluate in a single measurement both velocity and particle size based on the observed scattered characteristics. The method provides a useful simple tool to investigate particle dynamics in a rapid prototyping application as well as other research fields involving the use of powder delivery nozzles.
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Mathias Vermeulen, Tom Claessens, Benjamin Van Der Smissen, Cedric S. Van Holsbeke, Jan W. De Backer, Peter Van Ransbeeck and Pascal Verdonck
The purpose of this paper is to use rapid prototyping technology, in this case fused deposition modeling (FDM), to manufacture 2D and 3D particle image velocimetry (PIV…
Abstract
Purpose
The purpose of this paper is to use rapid prototyping technology, in this case fused deposition modeling (FDM), to manufacture 2D and 3D particle image velocimetry (PIV) compatible patient‐specific airway models.
Design/methodology/approach
This research has been performed through a case study where patient‐specific airway geometry was used to manufacture a PIV compatible model. The sacrificial kernel of the airways was printed in waterworks™ which is a support material used by Stratasys Maxum FDM devices. Transparent silicone with known refractive index was vacuum casted around the kernel and after curing out, the kernel was removed by washing out in sodium hydroxide.
Findings
The resulting PIV model was tested in an experimental PIV setup to check the PIV compatibility. The results showed that the model performs quite well when the refractive index (RI) of the silicone and the fluid are matched.
Research limitations/implications
Drawbacks such as the surface roughness, due to the size of the printing layers, and the yellowing of the silicone, due to the wash out of the kernel, need to be overcome.
Originality/value
The paper presents the manufacturing process for making complex thick walled patient‐specific PIV models starting from a strong workable sacrificial kernel. This removable kernel is obtained by switching the building and the support materials of the FDM machine. In this way, the kernel was printed in support material while the building material was used to support the kernel during printing. The model was tested in a PIV setup and the results show that the airway model is suitable for performing particle image velocimetry.
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Keywords
Konghua Yang, Chunbao Liu, Jing Li and Jiawei Xiong
The flow phenomenon of particle image velocimetry has revealed the transition process of the complex multi-scale vortex between the boundary layer and mainstream region…
Abstract
Purpose
The flow phenomenon of particle image velocimetry has revealed the transition process of the complex multi-scale vortex between the boundary layer and mainstream region. Nonetheless, present computational fluid dynamics methods inadequately distinguish the discernable flows in detail. A multi-physical field coupling model, which was applied in rotor-stator fluid machinery (Umavathi, 2015; Syawitri et al., 2020), was put forward to ensure the identification of multi-scale vortexes and the improvement of performance prediction in torque converter.
Design/methodology/approach
A newly-developed multi-physical field simulation framework that coupled the scale-resolving simulation method with a dynamic modified viscosity coefficient was proposed to comparatively investigate the influence of energy exchange on thermal and flow characteristics and the description of the flow field in detail.
Findings
Regardless of whether quantitative or qualitative, its description ability on turbulence statistics, pressure-streamline, vortex structure and eddy viscosity ratio were visually experimentally and numerically analyzed. The results revealed that the modification of transmission medium viscous can identify flows more exactly between the viscous sublayer and outer boundary layer. Compared with RANS and large eddy simulation, a stress-blended eddy simulation model with a dynamic modified viscosity coefficient, which was further used to achieve blending on the stress level, can effectively solve the calculating problem of the transition region between the near-wall boundary layer and mainstream region.
Research limitations/implications
This indeed provides an excellent description of the transient flow field and vortex structure in different physical flow states. Furthermore, the experimental data has proven that the maximum error of the external performance prediction was less than 4%.
Originality/value
An improved model was applied to simulate and analyze the flow mechanism through the evolution of vortex structures in a working chamber, to deepen the designer with a fundamental understanding on how to reduce flow losses and flow non-uniformity in manufacturing.
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Ling Zhou, Ling Bai, Wei Li, Weidong Shi and Chuan Wang
The purpose of this study is to validate the different turbulence models using in the numerical simulation of centrifugal pump diffuser. Computational fluid dynamics (CFD) has…
Abstract
Purpose
The purpose of this study is to validate the different turbulence models using in the numerical simulation of centrifugal pump diffuser. Computational fluid dynamics (CFD) has become the main method to study the pump inner flow patterns. It is important to understand the differences and features of the different turbulence models used in turbomachinery.
Design/methodology/approach
The velocity flow fields in a compact return diffuser under different flow conditions are studied and compared between CFD and particle image velocimetry (PIV) measurements. Three turbulence models are used to solve the steady flow field using high-quality fine structured grids, including shear stress transport (SST) k-w model, detached-eddy simulation (DES) model and SST k-w model with low-Re corrections.
Findings
SST k-w model with low-Re correction gives better results compared to DES and SST k-w model, and gives a good predication about the vortex core position under strong part-loading conditions.
Originality/value
A special test rig is designed to carry out the 2D PIV measurements under high rotating speed of 2850 r/min, and the PIV results are used to validate the CFD results.
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Keywords
– Review of the advancements in non-contact laser sensors for much more accurate real time speed as well as length measurements. The paper aims to discuss these issues.
Abstract
Purpose
Review of the advancements in non-contact laser sensors for much more accurate real time speed as well as length measurements. The paper aims to discuss these issues.
Design/methodology/approach
In-depth review of a number of applications of laser sensors.
Findings
A wide range of manufacturers in the converting industries have solved measurement problems and realized major improvements in product quality, cost of production and productivity by applying laser measurement as well as reduction in scrap.
Practical implications
Others with the need to make very accurate measurements of speed and length in real time may find that laser sensors may provide the answer.
Originality/value
An expert insight into how to solve real time speed and length measurement problems.
Details