PIV application in advanced low reynolds number facility

Voluminous research exists on the effect of combination of low Reynolds number flow over low aspect ratio flat plate wings for usage in micro-aerial vehicles and UAVs, as they also fly under similar conditions and combination of low aspect ratio and low Reynolds number. It has been well established by many researchers (Torres and Mueller in AIAA 42(5):865–873, 2004; Okamoto and Azuma in AIAA 49(6):1135–1150, 2011; Mizoguchi and Itoh in AIAA 51(7):7–52, 2013; Shields and Mohseni in AIAA 50(1):85–99, 2012; Mizoguchi and Kajikawa in Trans Jpn Soc Aero Sp Sci 59(2):56–63, 2016; Pelletier and Mueller in J Aircr 37(5):825–832, 2000; Liu and Hsiao in J Mech 28(01):77–89, 2012; Taira and Colonius in J Fluid Mech 623:187–207, 2009) that low aspect ratio wings in low Reynolds number flow gives a higher lift coefficient and stall angle is also increased which is quite different from the high aspect ratio wing. Also, it is a well-established fact in the existing literature that linear theories cannot be applied as in case of high aspect ratio wings because of non-linear increase in lift coefficient. The reason for such increase in lift and stall angle has been attributed to wingtip vortices that become prominent in low aspect ratio wings called the vortical lift which keeps on increasing up to a certain high angle of attack till it interacts with the separation bubble. In the past, very limited work has been done to study the vortices and their contribution in enhancement of aerodynamic characteristics. In the present work, flat plate model with corrugations at an aspect ratio (AR) of 1.0 are studied and compared with flat plate wing of AR 1.0; also flow visualization in water tunnel has been carried out at Reynolds number of 102 to ascertain the flow physics involved.

Exploring the benefits of utilizing small modular device for sustainable and flexible shale gas water management

For a number of manmade and natural flyers the aerodynamics of low Reynolds number plays a crucial role. Active study of birds and insects is growing rapidly for development of Micro Air Vehicles (MAVs). MAVs are capable of performing tasks like surveillance, environmental monitoring and threat assessment in hostile environment. When compared to general civilian aircrafts MAVs fly at low Reynolds number regime of 105 or lower. A considerable change of aerodynamic characteristics is seen between aircrafts that operate in low and high Reynolds number regimes. Low Reynolds number flyers are sensitive to wing gust and deformation because of being lightweight and operating at low speeds. The birds have nature’s finest locomotion system when it comes to maneuvering effectively through space. This review paper will assist further studies in the field of low Reynolds number flyers that can be used for future development on MAVs. A holistic review of past two decades of research work and studies done on low Reynolds number flyers has been presented in this paper. The Theoretical, Experimental and Numerical techniques followed by researchers have been highlighted so that the study on biological and manmade flyers can be systematically presented. It was found that researchers preferred Numerical and Experimental techniques while conducting aerodynamic analysis of low Reynolds number flyers. An attempt has been made in this paper to fill the research gap that is there in mimicking the flight of animals and thus developing man-made systems having higher efficiency.

Particle image velocimetry (PIV) and optical flow velocimetry (OFV) are important velocity measurement methods in the field of fluid dynamics. Nevertheless, the conventional cross correlation-based PIV method is beset by diminished resolution, while the OFV method exhibits computational sluggishness and susceptibility to noise. These constraints have somewhat delimited the applicability of PIV and OFV techniques. Recent attempts have introduced deep learning-based methods for analyzing PIV images, offering high-resolution velocity fields with computational efficiency, but their accuracy needs improvement. This study proposes four neural networks based on the well-established FlowNetS. They incorporate two distinct velocity constraints, namely, first-order velocity smoothing regularization and second-order grad (curl)–grad (div) regularization. In the networks, these constraints are used either independently or in combination with optical flow conservation (OFC). The performances of the networks have been assessed on six different flow configurations, and the results show that the network with the second-order regularization markedly outperforms the original network across all flows, demonstrating an enhanced capacity to capture larger-scale vortices. The network with the first-order regularization also exhibits superior performance compared to the original network except in the case of cylinder flow. Unexpectedly, the introduction of the OFC constraints results in a decline in network performance. This anomaly may stem from the network's inherent capability to capture optical flow features, rendering the OFC constraint less effective in providing guidance. In summary, this study underscores the substantial potential of neural networks incorporated with judicious physical constraints in PIV applications, enabling the determination of high-resolution, high-accuracy flow fields.

The development of Micro Aerial Vehicles (MAVs) in recent years has been hindered by the lack of an available aerodynamic model which correctly predicts the flight dynamics of the aircraft. This can be attributed to the fundamentally different flow regime experienced by MAVs in which flow phenomena such as tip vortices and the leading edge vortex propagate over a high percentage of the lifting surface. The conventional derivation of the linearized equations of motion does not take these effects into account and, thus, does not provide an accurate method of evaluating vehicle dynamics and control. This investigation demonstrates some of the shortcomings of the traditional method such as the significant deviation between theoretical values for stability derivatives and the actual experimental results; for example, the derivative Cl is examined and shown to vary in both magnitude and sign. Surface tuft visualization is conducted to describe the MAV flow regime using canonical flat plate models. In addition, the necessity for a revised derivation of the equations of motion based on the MAV flow regime is discussed. Finally, a new style of control surface is proposed for MAVs which utilizes the associated flow regime and demonstrates an order of magnitude increase in control authority over conventional ailerons.

A series of experiments have been performed to demonstrate the application of Particle Image Velocimetry (PIV) to turbomachinery flows. The tests were performed at transonic speeds on a fully annular engine size turbine nozzle guide vane. The vane cascade was installed in a short duration Isentropic Light Piston Cascade (ILPC) test facility operating with high inlet turbulence levels. The technique has been shown to map the whole flow field with a resolution of 0.5 mm. The quality of the results obtained are not significantly affected by local turbulence rates. The accuracy of the measurements is put at around 4% of absolute velocity and is limited by the quality of the image on the film plane. The velocities derived from the PIV images have been compared with predictions from a three-dimensional viscous numerical calculation. It is shown that the experimental and predicted results are in good agreement. It is considered that this technique has considerable potential in application to turbomachinery flow field diagnostics.

This study explores the aerodynamic performance of flat-plate wings equipped with dihedral wingtip attachments (winglets) meant for micro aerial vehicle (MAV) applications that operate at low Reynolds number (Re). The investigations are performed for the lift and drag forces on wings with dihedral attachments, for different aspect ratios (ARs) of 1.0 and 1.5, and the results are compared with the base wing (without winglets) and wings with planar wingtip attachments. The experiments have been conducted in a subsonic wind tunnel to measure the aerodynamic forces across a range of angles of attack and Re. The findings reveal that dihedral modifications can enhance the lift characteristics significantly. It is also observed that one of the configurations, for an AR=1.0 wing, consistently exhibits superior lift force values, particularly at lower Re, making it a promising candidate for MAV applications. This particular configuration showed improvements in lift coefficients over a base wing of AR=2.0, with a maximum average improvement of 21% at Re=15×104. Despite the lift improvements, the wings with dihedral attachments experienced higher drag forces for both the ARs, as the extra attachments introduced additional aerodynamic resistance. The Oswald’s efficiency factor (e) analysis showed that while dihedral attachments do not surpass the planar wingtip attachments, they still provide significant improvements over the base wings. The dihedral arrangement for the AR=1.0 wing demonstrated the highest e values, ranging between 0.48 and 0.72, indicating an enhanced aerodynamic efficiency.

Advances in unmanned aerial vehicles (UAV) and especially micro aerial vehicle (MAV) technology together with increasing quality and decreasing price of imaging devices have resulted in growing use of MAVs in photogrammetry. The practicality of MAV mapping is seriously enhanced with the ability to determine parameters of exterior orientation (EO) with sufficient accuracy, in both absolute and relative senses (change of attitude between successive images). While differential carrier phase GNSS satisfies cm-level positioning accuracy, precise attitude determination is essential for both direct sensor orientation (DiSO) and integrated sensor orientation (ISO) in corridor mapping or in block configuration imaging over surfaces with low texture. Limited cost, size, and weight of MAVs represent limitations on quality of onboard navigation sensors and puts emphasis on exploiting full capacity of available resources. Typically short flying times (10-30 minutes) also limit the possibility of estimating and/or correcting factors such as sensor misalignment and poor attitude initialization of inertial navigation system (INS). This research aims at increasing the accuracy of attitude determination in both absolute and relative senses with no extra sensors onboard. In comparison to classical INS/GNSS setup, novel approach is presented here to integrated state estimation, in which vehicle dynamic model (VDM) is used as the main process model. Such system benefits from available information from autopilot and physical properties of the platform in enhancing performance of determination of trajectory and parameters of exterior orientation consequently. The navigation system employs a differential carrier phase GNSS receiver and a micro electro-mechanical system (MEMS) grade inertial measurement unit (IMU), together with MAV control input from autopilot. Monte-Carlo simulation has been performed on trajectories for typical corridor mapping and block imaging. Results reveal considerable reduction in attitude errors with respect to conventional INS/GNSS system, in both absolute and relative senses. This eventually translates into higher redundancy and accuracy for photogrammetry applications.

Essential for achieving fully autonomous igh t and good igh t performances of Mini and Micro Aerial Vehicles (MAV) is a reliable determination of position, velocity and attitude of the aircraft. In the institute its current MAV navigation concept, an IMU providing acceleration and angular rate measurements at 100 Hz is used for this purpose among other systems. An important task of the IMU is the supply of angular velocities so that a high-frequency attitude solution can be computed. A high attitude update frequency is necessary because of the high rotational dynamics of MAVs which can be less than 0.1 s. Due to the small size and weight of a MAV only miniaturized sensors are applicable. Unfortunately, such small and usually silicon-based inertial sensors (micro-electromechanical systems, MEMS) have signican t and strong temperature correlated deterministic errors. To overcome the temperature inuence, temperature was taken into account during sensor calibration. After calibration of the sensor pack a test igh t with the university’s research aircraft, a Dornier Do 128-6, was carried out. The aircraft was equipped with a high-precision INS Honeywell Lasernav and a Novatel OEM3 GPS receiver as reference sensors. The postprocessing of the measurement data shows that the calibration results can be conrmed by the reference sensors. First and second order approximations for the calibration tables turned out to provide equivalent navigation accuracy compared to the original calibration tables while saving computational power. Satellite and inertial navigation data were integrated within a tightly-coupled Kalman Filter. In order to improve the navigation performance especially during loss of GPS the attitude information derived from on-board camera images is used to aid the lter. The results presented are based on real igh t measurement data for the MEMS-based sensors and on simulated GPS measurements.

An experimental study on flapping wing flexibility in hovering flight has been conducted to investigate the wing flexibility for insect-inspired flapping Micro Aerial Vehicles (MAVs). Hawkmoth-like wing models, constructed from Plexiglas® (3 mm thick) and pristine Polycarbonate (PC) sheet (1, 0.5, and 0.2 mm thick) with a spanwise length of 200 mm and an aspect ratio of 6.18, were selected for preliminary experiment. The wing models were constrained to a simple harmonic flapping motion with sweeping and rotating amplitudes of 120° and 90° for hovering in water tank with size of 3.5 m×1.0 m×1.1 m. A six-axis force/torque sensor and a high speed camera with a Diode-Pumped Solid-State (DPSS) laser using Digital Particle Image Velocimetry (DPIV) were utilized to measure the aerodynamic forces and obtain flow visualization. Based on the experimental results, the aerodynamic forces diminish as the wing becomes flexible except for the wing with thickness of 1 mm. Consequently, this finding will instrumental in identifying the range of wing flexibilities that improve the aerodynamic efficiency for the development of insect-inspired flapping MAVs.

Application of particle image velocimetry for measuring He II thermal counterflow jets

Fluid flow distribution among parallel channels usually plays an important role on the global performance improvement of tubular process equipment, but remains difficult to be properly measured by experimental methods. This paper presents a systematic study on the measurement of flow distribution in a multi‐channel fluidic network using Particle Image Velocimetry (PIV) technique. For the precise measurement of flow‐rate in each individual channel, standard 2 dimensions, 2 components PIV technique is used to obtain velocity vectors on multiple sampling planes parallel to the flow direction, so as to reconstruct accurate velocity profiles on the cross‐sectional surface. Such procedure is repeated for every micro‐ (mini‐) channel to obtain the actual flow distribution properties in the fluidic network.Pre‐test results on a double‐channel device indicate that the maximum possible deviation of PIV measurements is 13.1% with respect to those of a flange flowmeter, implying that the PIV technique is relatively accurate and reliable. PIV results on the flow distribution in a 15‐channel fluidic network are then compared with Computational Fluid Dynamics simulation results under the same working conditions. A quite good agreement could be observed. Moreover, the locations and sizes of vortices in the distributor have a significant influence on the flow distribution. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

In this research, the flow physics and aerodynamic performance of dragonfly cross sections, used in Micro Aerial Vehicles (MAVs), in low Reynolds are investigated. The main objective of the research is to study the performance of dragonfly wing cross-sections flapping motion in Reynolds 5000 and 10,000. Pitching motion is one of the most important mechanisms in force lifting generation, and the effects of Reynolds number and mean angle of attack on aerodynamic coefficients have been extensively investigated for the pitching motion. In the present study, the geometry of two cross sections of dragonfly was extracted. Incompressible, two-dimensional and unsteady Navier–Stokes equations have been used to simulate the flow. k − ɛ RNG model was used for turbulence modeling. To simulate the wing pitching motion, the dynamic mesh method was used. The results showed that in flapping motion, pitching-up rotation has caused a rapid increase in lift coefficient. Furthermore, it was found that the absence of stall does not increase the lift and drag coefficients, while formation of new strong vorticity layers have caused an increase in lift coefficient. On the other hand, corrugations on the cross sections of the dragonfly in the pitching motion cause the delay of separation and increasing the lift coefficient. In flapping motion and the pitching motion, the lift coefficients of three cross sections were increased due to stronger vorticity layers by reducing the Reynolds number. Due to the existence of corrugations, the first and the second cross sections have good aerodynamic performance, compared to the flat plate. The comparison carried out in the current research showed that the second cross section is a proper replacement for the flat plate in MAVs.

Low Reynolds number refers to a specific range of values of the dimensionless parameter known as the Reynolds number (Re) in fluid dynamics. The Reynolds number is a critical factor used to characterize and predict fluid flow behaviour around objects or within fluid systems. Low Reynolds numbers (typically Re < 2000), laminar flow prevails, where fluid particles move in smooth, orderly layers with minimal mixing or turbulence. Low Reynolds number aerodynamics is a focal point of interest, especially for micro air vehicles (MAVs), drones, and small-scale aircraft. Understanding the nuanced aerodynamic performance of aerofoils and wings in this regime is pivotal for designing efficient and controllable flight systems, ushe ring in innovations in the field of aviation. The unique characteristics of low Reynolds number flow to advance technology, science, and our understanding of fluid dynamics.

Throughout their useful life structures demand monitoring to verify their conditions of use. Thus, the need arises to seek methodologies capable to evaluate displacements and deformations in structural components of buildings. The objective of this research was to evaluate the use of the particle image velocimetry (PIV) technique to analyze test specimen behavior during a static bending test, additionally a displacement map is presented. The PIV technique measures variations of position of a region in an object from consecutive images from a loading session. The tests were performed on wood of Pinus oocarpa and Eucalyptus grandis, plywood panels, laminated veneer lumber (LVL) and oriented strand board (OSB). The results obtained by the PIV technique were compared to values obtained from dial indicators. It was verified that in all the materials tested, the PIV technique presented results similar to those found in the dial indicators. By means of the Student t test, with a significance level of 1%, some regions of analysis the values found by the PIV technique and the dial indicators were statistically similar. For the analyzed regions that did not achieve statistical equality, a correction equation was calculated (R² higher than 0.99). It was concluded that the PIV technique, with properly adjusted setup, presented results similar to those obtained in the conventional tests, proving its accuracy and reliability in displacement measurements, with the advantage of being a non-destructive and contactless structure monitoring technique.