Flow Structure Research Articles

The Evolution of Flow Structures and Coolant Coverage in Double-Row Film Cooling with Upstream Forward Jets and Downstream Backward Jets

The spatiotemporal evolution of the flow structures and coolant coverage of double-row film cooling with upstream forward jets and downstream backward jets, having a significant impact on film-cooling performance, is studied using the simplified thermal lattice Boltzmann method (STLBM). Moreover, the effect of the inclination angle of downstream backward jets is considered. The high-performance simulations of film cooling have been conducted by using our verified in-house solver. Results show that special flow structures, such as a sand dune-shaped protrusion, appear in double-row film cooling with upstream forward jets and downstream backward jets, which is mainly because of the blockage effect resulting from the coolant jet with backward injection. The interaction among structures results in the generation of an anti-counterrotating vortex pair (anti-CVP). The anti-CVP with the downwash motion can result in the attachment of coolant to the bottom wall, which promotes the stability and lateral coverage of coolant film. The momentum and heat transport are strengthened as the backward jet is injected into the boundary layer of the mainstream. Although the downstream evolution of the backward jet is not very smooth, its core attaches closely to the bottom wall due to the downwash motion of anti-CVP. Moreover, there is an obvious backflow zone shown in the trailing edge of the downstream backward jet with a large inclination angle. The obvious backflow makes the coolant attach to the bottom wall well. Therefore, the film cooling effectiveness is improved as the inclination angle of the downstream backward jet varies from αdown=135° to αdown=155°, with a constant blowing ratio of BR=0.5. In addition, the fluctuation of the bottom wall’s temperature is weak due to the stable coverage of the coolant layer under αdown=155°. The film-cooling performance with an inclination angle of αdown=155° is the best among all the cases studied in this work. This work provides essential insights into film cooling with backward coolant injection and contributes to obtaining a complete understanding of film cooling with backward coolant injection.

Influence of thermal intrusion on the Alum Shale from south central Sweden

This study investigates the geochemical and petrological characteristics of solid bitumen in the DBH15/73 core from the Furongian (upper Cambrian) and Miaolingian (middle Cambrian) Alum Shale in Billingen, south central Sweden. At Billingen a > 30 m thick Permian diabase (dolerite sill) intruded approximately 100 m above the Alum Shale that promoting the formation of solid bitumen in the uppermost half of the Alum Shale due to enhanced heat flow. The bitumen has been classified into bituminite/diagenetic solid bitumen (DSB), initial-oil solid bitumen (IOSB), and primary-oil solid bitumen (POSB) based on their genesis, morphology and random solid bitumen reflectance (BRo). The Miaolingian shale, constituting the lower part of the Alum Shale, is immature and contains solely bituminite and DSB, with measured BRo ranging from 0.40% to 0.48%. In contrast, the Furongian shale exhibits enrichment in IOSB and POSB and range from marginally mature to peak oil generation with towards the top of the section. Characteristics of uneven heating is seen in the IOSB (BRo: 0.97–1.08%) including oxidation rims and abnormally high maturity surrounding fractures. The POSB (BRo: 0.63–2.01%) is present not only in the Alum Shale but also in the overlying Ordovician Latorp limestone and the underlying Kakeled Limestone Bed, and shows flow structures which is further evidence for migration. The abundance of POSB and IOSB is determined through maceral point counting, revealing POSB as the dominant bitumen type (1.54–7.13 vol%), while IOSB constitutes the minority (0.05–0.31 vol%) within the Furongian shale. This distribution suggests rapid thermal evolution of organic matter within the oil generation window. Additionally, a reduction in free hydrocarbons (Rock-Eval S1), potential hydrocarbons (Rock-Eval S2), and unexpectedly low Tmax was observed in the Furongian shale. Results indicate that hydrocarbon generation resulting from thermal intrusion contributes to the relatively low S2. Migration of POSB and generated oil to adjacent layers leads to the loss of S1, while the reduced Tmax may be attributed to high uranium content which weakens carbon chain bond energy. These anomalies result in an underestimation when evaluating thermal maturity and kerogen type conversion based on Rock Eval data alone.

High-flexibility reconstruction of small-scale motions in wall turbulence using a generalized zero-shot learning

This study proposes a novel super-resolution (or SR) framework for generating high-resolution turbulent boundary layer (TBL) flow from low-resolution inputs. The framework combines a super-resolution generative adversarial neural network (SRGAN) with down-sampling modules (DMs), integrating the residual of the continuity equation into the loss function. The DMs selectively filter out components with excessive energy dissipation in low-resolution fields prior to the super-resolution process. The framework iteratively applies the SRGAN and DM procedure to fully capture the energy cascade of multi-scale flow structures, collectively termed the SRGAN-based energy cascade reconstruction framework (EC-SRGAN). Despite being trained solely on turbulent channel flow data (via ‘zero-shot transfer’), EC-SRGAN exhibits remarkable generalization in predicting TBL small-scale velocity fields, accurately reproducing wavenumber spectra compared to direct numerical simulation (DNS) results. Furthermore, a super-resolution core is trained at a specific super-resolution ratio. By leveraging this pretrained super-resolution core, EC-SRGAN efficiently reconstructs TBL fields at multiple super-resolution ratios from various levels of low-resolution inputs, showcasing strong flexibility. By learning turbulent scale invariance, EC-SRGAN demonstrates robustness across different TBL datasets. These results underscore the potential of EC-SRGAN for generating and predicting wall turbulence with high flexibility, offering promising applications in addressing diverse TBL-related challenges.

Two-Field Excitation for Contactless Inductive Flow Tomography.

Contactless inductive flow tomography (CIFT) is a flow measurement technique allowing for visualization of the global flow in electrically conducting fluids. The method is based on the principle of induction by motion: very weak induced magnetic fields arise from the fluid motion under the influence of a primary excitation magnetic field and can be measured precisely outside of the fluid volume. The structure of the causative flow field can be reconstructed from the induced magnetic field values by solving the according linear inverse problem using appropriate regularization methods. The concurrent use of more than one excitation magnetic field is necessary to fully reconstruct three-dimensional liquid metal flows. In our laboratory demonstrator experiment, we impose two excitation magnetic fields perpendicular to each other to a mechanically driven flow of the liquid metal alloy GaInSn. In the first approach, the excitation fields are multiplexed. Here, the temporal resolution of the measurement needs to be kept as high as possible. Consecutive application by multiplexing enables determining the flow structure in the liquid with a temporal resolution down to 3 s with the existing equipment. In another approach, we concurrently apply two sinusoidal excitation fields with different frequencies. The signals are disentangled on the basis of the lock-in principle, enabling a successful reconstruction of the liquid metal flow.

Effect of inlet diameter on the flow structure and performance for aluminum-based water-jet engine

Abstract In this study, the flow field and performance for the aluminum based water ramjet was analyzed through numerical simulation. The time decrease in evaporation heat absorption process expands the range of aluminum/water combustion and increase the specific impulse. If the diameter of atomized water droplets from the primary inlet is large, the evaporation efficiency will be further reduced, which is not conducive to the further propagation of the reaction. However, if the diameter is small, the flow field temperature will be rapidly dropped due to rapid evaporation, and a large range of low-temperature areas will appear in the reaction area of the combustor. The diameter reduction of atomized water droplets from the secondary water inlet is conducive to the diffusion of the reaction area downstream, further and makes the combustion range be expanded. This effect is benefit for increasing the specific impulse and can reduce the temperature near the wall.

Influence of an inclined thick partition on free convection heat transfer performance under surface radiation in a hollow block

In the present work, a computational analysis of the combined energy transfer by free convection, radiation, and heat conduction in 2D hollow block with an inclined partition was carried out. The inclined partition was made of a heat-conducting material and had a finite thickness. The closed space inside the brick was filled with air (Pr = 0.71) and the airflow is laminar. The external surfaces of the vertical borders are considered to be isothermal, and the remaining horizontal surfaces are supposed to be adiabatic. The finite difference technique is employed to work out numerically the differential equations. The in-house computational code was verified in detail using various problems. The major characteristics that determine the considered phenomena are surface emissivity of internal walls, Ra number, and material of solid walls and partition. As a result of the research, the distributions of streamlines and isotherms combined with the average Nusselt numbers were obtained. Depending on the material of the partition, the flow structure in the cavity changes significantly, which reflects the distribution of streamlines, namely, for the materials with low thermal conductivity the convective cell in the upper part of the cavity is elongated, while in the lower part it is shifted to the lower and left borders. The isotherms reflect the more intensive heating in the left part of the area. With an increase in the thermal conductivity coefficient, the streamlines reflecting the nature of the flow are restructured. It was shown that the presence of an inclined partition significantly reduces the intensity of convective heat transfer.

Heat transfer enhancement mechanics of different micro-disturbing structures for transcritical hydrocarbon fuel using 3-D secondary flow intensity analysis

Heat transfer enhancement based upon micro-disturbing structures becomes increasingly important for thermal protection of air-breathing propulsion systems. To explore the influence mechanism of different structures on heat transfer in regenerative cooling channels of scramjet engines, flow structures and heat transfer of supercritical-pressure n-Decane in mini-channels with dimple and micro-rib arrays are numerically investigated. Results indicate effective heat transfer enhancement inside the channels depends more on efficient transverse turbulence disturbance rather than longitudinal or perpendicular turbulence disturbance. Severe thermal stratification generates strong shear layers in channels, where transverse secondary flows bring much intenser flow mixing than longitudinal secondary flows, especially in transcritical temperature region where the best heat transfer enhancement is obtained. With same characteristic dimensions, longitudinal micro-disturbing structures like dimples have lower flow resistance, but transverse micro-disturbing structures like micro-ribs achieve stronger heat transfer enhancement. Besides, the performance of micro-ribs is much more sensitive to the dimensional change. Therefore, micro-ribs have larger working excursion for enhancing performance factor than dimples. With optimal structure parameters: hr = e = 0.3 mm, pr = 3 mm, hd = 0.225 mm, dd = 1.5 mm, overall performance factor in micro-ribbed channel is 1.14 times of that in dimpled channel. Those conclusions provide effective support for optimization design for the regenerative cooling structures.

A critical meta-analysis of CO2-water-rock interaction in basalt for CO2 storage: A review based on global and Indian perspective

Global warming and energy security lead to the hunt for alternative energy sources and CO2 emission mitigation technologies like carbon capture and storage (CCS). CCS is a prominent technique and its success depends on the sites of storage and agents influencing the storage efficiency. Geological formations are much safer as compared to oceanic injection for CO2 storage and include formations like sedimentary and igneous formations. Igneous formations like peridotite, komatiites, and basalt have huge potential to store CO2 and take the least time to convert the injected gas into solid carbonates along with the advantage of negligible leakage (as injected gas converts to carbonates through carbon mineralization). Carbon mineralization is a complex process involving the interaction of water–CO2–rock to form solid carbonates. In this review, we have highlighted the carbon mineralization in basalt by discussing the dissolution and precipitation mechanism. The discussion includes the uncertainty in the role of aluminum ions and siderite precipitation during CO2 storage in basalt. The review article also presents the first insight for the qualitative assessment of the CO2 storage potential of Deccan volcanic provinces (DVP) in India concerning the rock composition, injection depth, and type of injection. The mineralogy, and structure of the Basaltic province of DVP support CO2 storage. The principal minerals including calcic plagioclase and pyroxene, support mineral carbonation. Out of the total available area of DVP, 95% consists of tholeiitic basalt, exhibiting a simple flow structure. Additionally, the area is seismically safe for CO2 storage. The challenges and future research gap areas highlighted in this review article include suitable depth for injection, lateral continuity, the role of geothermal gradient, water availability, and public acceptance. Thus, the article provides a critical insights into the exploration and development of CCS technologies in India, emphasizing the importance of the Deccan Volcanic Provinces in achieving net-zero goals.

Future changes in the vertical structure of severe convective storm environments over the U.S. central Great Plains

Abstract The effect of warming on severe convective storm potential is commonly explained in terms of changes in vertically-integrated (“bulk”) environmental parameters, such as CAPE and 0–6-km shear. However, such events are known to depend on details of the vertical structure of the thermodynamic and kinematic environment that can change independently of these bulk parameters. This work examines how warming may affect the complete vertical structure of these environments for fixed ranges of values of high CAPE and bulk shear, using data over the central Great Plains from two high-performing climate models (CNRM and MPI). To first order, projected changes in the vertical sounding structure is consistent between the two models: the environment warms approximately uniformly with height at constant relative humidity and the shear profile remains relatively constant. The boundary layer becomes slightly drier (−2–6% relative humidity) while the free troposphere becomes slightly moister (+1–3%), with a slight increase in moist static energy deficit aloft with stronger magnitude in CNRM. CNRM indicates enhanced low-level shear and storm-relative helicity associated with stronger hodograph curvature in the lowest 2 km, whereas MPI shows near zero change. Both models strongly underestimate shear below 1 km compared to ERA5, indicating large uncertainty in projecting subtle changes in the low-level flow structure in climate models. Evaluation of the net effect of these modest thermodynamic and kinematic changes on severe convective storm outcomes cannot be ascertained here but could be explored in simulation experiments.

Effect of Jet-to-Target Spacing on Flow and Heat Transfer Characteristics for Swirling Impinging Micro-Slot Jets

The influence of jet-to-target spacing on flow and heat transfer behaviors for swirling impinging micro-slot jets has been extensively studied. In this study, two complete revolutions of the generated helix under the slot nozzle thickness of 1.0 mm constrained the total spiraling length to 290 mm. The range of jet-to-target spacing varied from 1 to 6. The turbulent kinetic energy-epsilon model was employed to make predictions at Reynolds numbers from 5000 to 20000. The results showed that the heat transfer enhancement on the target wall depended on the pacing between the jet and the target. This is the jet flow structure exhibited a notable intensity of high-velocity vortices at the low jet-to-target spacing, whereas the jet flow impingement was abruptly reduced at the high jet-to-target spacing. The heat transfer rate also tended to increase as the Reynolds number increased. In addition, when the jet-to-target spacing was at 1, the average heat transfer value was between 32.9% and 54.2% higher than in other conditions due to high fluid acceleration.

Effects of Crosswinds on the Aerothermal Behaviour of a Double-Skin Façade

Abstract In double-skin facades, airflow is mainly induced by buoyancy forces due to temperature gradients and air compressibility. In practice, this passive system is also affected by ambient crosswind. The present work is focused on the analysis of the aerothermal behavior of an asymmetrically heated channel interacting with a transverse airflow. To achieve this, we utilized the computational fluid dynamics (CFD) technique based on the finite volume method to predict the system’s performance. After validating the adopted numerical model, we examined the flow structure for different channel widths, and we determined the corresponding ventilation flow rates. We integrated the effect of wind with the thermosiphon effect. The thermo-aerodynamic performance of the facade was presented as a function of wind velocities, which significantly influence the airflow through the cavity and its openings.

Towards Sustainable Energy Development: Integrating Traditional and Renewable Energy in Azerbaijan’s Energy Policy

The article examines the formation of Azerbaijan's energy policy and the multivector development of its fuel and energy complex. In the context of global transformations and changes in energy flow structures, the author emphasizes the balanced development of both hydrocarbon and carbon-free segments of energy. The proposed concept of sustainable energy development envisages the harmonious coexistence of traditional and renewable energy, enhancing Azerbaijan's economic stability and geopolitical influence. The significant role of the oil and gas sector, demonstrated by successful projects and substantial foreign investments, is reinforced by the active development of renewable energy sources. Azerbaijan implements large-scale projects in wind and solar energy, as well as initiatives for the production of «green» hydrogen, which contributes not only to the reduction of emissions but also to the expansion of the country's export potential. The article highlights the importance of balanced FEC development, focusing on emission minimization through the application of carbon capture and utilization (CCUS) technologies, as well as the need for infrastructure modernization to improve energy efficiency. Azerbaijan demonstrates a unique case where traditional and renewable energy do not compete but complement each other, strengthening its positions in international cooperation and within the framework of the Greater Eurasian Partnership.

Integrated Single Camera µPTV And Florescence Imaging For Cell Tracking And Flow Investigation In Centrifugal Microfluidic Devices

A micro-hydrocyclone is investigated as a high throughput particle/cell sorting microfluidic device. A complex flow structure has been reported by limited numerical works that increases the importance of undertaking a comprehensive experimental investigation. In addition to the flow, utilizing damageable bio cells in a micro-hydrocyclone, requires a deep understanding of the interaction between the cells entering the device, the flow structure and its instabilities forming in different operational phases. In such cases the implementation of multiple measurement techniques can be challenging due to the small scale of devices, here < 5 mm diameter. Therefore, for this complex flow an experimental approach is introduced to capture the flow structure and the motion of cells. In this method, tracer particles and fluorescent stained cells are captured simultaneous by a single camera in the same flow field. A custom image processing scheme is used for partitioning cells and particles from the raw data. To determine velocity vectors, µPTV is employed on the segmented data sets to study the effect of flow on trajectory and velocity of each individual cell in the system. By a combined investigation in a vast range of Reynolds number (50<Re<800) the dynamics of cells are investigated in response to different flow structures and flow regimes.

Scanning Lagrangian Particle Tracking To Measure 3D Large Scale Aerodynamics Of Quadcopter Flight

We present large-scale time-resolved and volumetric measurements of the flow surrounding a quadcopter drone. Cases with hovering flight, forward flight - with and without ground-effect - as well as lift-off scenarios have been realized. Five high-speed cameras were used to capture images of hundreds of thousands heliumfilled soap bubbles being illuminated by pulsed LED arrays. The arrays were operated in a dual-scanning mode, where the front and the back part of the volume are illuminated intermittently, each with a frequency of 3 kHz. The cameras were recording at 6 kHz, thereby capturing both sub-time-series in a single measurement run. Compared to a full illumination of the volume, we can either reduce the number of particles imaged on the cameras given a fixed tracer concentration - facilitating the reconstruction - or operate at a higher tracer concentration while keeping the number of imaged particles fixed. The dual time-series were evaluated by Lagrangian Particle Tracking, using the Shake-The-Box method, yielding dense fields of particle tracks. For the current results, the time series for both sub-volumes were evaluated independently. For the final contribution, an integrated evaluation scheme, alternatingly operating on both time-series is foreseen. After the tracking step, flow structures were identified using the data assimilation method FlowFit. The temporally and spatially highly resolved results document the strong interaction of the wakes induced by several rotors, as well as the interaction of wing tip vortices stemming from a single rotor. Brown-out effects are documented in forward flight. Averaged results of hovering flight enable an evaluation of the azimuthal distribution of the downwash- and outwash-velocities resulting from the geometric layout of the four rotors. By having highly resolved data encompassing the whole flight vehicle, the forces conveyed by the drone to the liquid can be determined via surface- or volume-integration.

Evaluating High-Frequency Fluctuations And Its Effect On Hemodynamics At Varying Heart Rates In Intracranial Aneurysms Via 4D PTV

Hemodynamics have been shown to affect the growth and rupture of intracranial aneurysms (IA). Studies have increasingly reported the presence of high frequency velocity fluctuations in aneurysms. However, it remains undetermined how transient physiological factors like heart rate and inflow blood waveform amplitude affect the hemodynamic parameters and high frequency fluctuations in and around an IA, as well as the risk of IA progression. In this work, we address this question using a volumetric particle tracking velocimetry (PTV) study where a patient-specific right middle cerebral artery (R MCA) aneurysm model was subjected to two heart rate conditions (60 bpm and 137 bpm). The input waveform amplitude for the 137 bpm case was increased by a factor of 1.6 to be physiologically consistent. Captured PTV images were processed using the Shake-the-Box (STB) workflow. Flow parameters including velocity, vorticity, and turbulent kinetic energy (TKE) were evaluated. To evaluate the presence of high frequency fluctuations, a direct numerical simulation (DNS) using the R MCA geometry and same two heart rate cases was conducted and a method for use with STB particle tracks was proposed. As compared to the 60 bpm case, the 137 bpm case had a more concentrated inflow jet that extended further into the aneurysmal sac and a stronger and larger vortical flow structure in the aneurysmal sac. The 60 bpm case maintained a region of slightly elevated TKE at the main junction point where the aneurysmal sac and all vessels merge. In the 137 bpm case, TKE in this region was dramatically higher. Using probe points, the DNS data revealed high frequency velocity fluctuations in an outflow vessel during the deceleration phase of the cycle. Notably, these fluctuations were only observed for the 137 bpm case. For both the DNS and STB data, high frequency components were more prevalent and stronger outside of the aneurysmal sac as opposed to inside the aneurysmal sac. Overall, these results suggest that changes in heart rate induce changes to the flow structure and can induce significant increases in TKE and high frequency fluctuations. Based on our findings, a higher heart rate would be expected to yield a flow field more akin to IA progression. The specific correlation between the high frequency components computed using our proposed STB-based method and the high frequency fluctuations in the flow field could not be well understood. Thus, additional analysis and development of this method is needed.

An Experimental Investigation On The Effect Of Laser Energy Deposition In An Over-Expanded Jet

The shock train structure of a supersonic over-expanded jet is the product of the interaction between the jet flow at the nozzle exit and the ambient environment. Although the effect of flow disturbances on the performance of the supersonic inlets has been studied in detail, a limited understanding of the shock train dynamics subject to flow disturbances is available for over-expanded jets. This experimental investigation focuses on understanding the influence of perturbations due to short-duration energy deposition on the shock train structure and its dynamics in an axisymmetric over-expanded Mach 2.52 jet. The flow is perturbed by laser-induced breakdown, creating a shock wave and a high-temperature plasma zone in the shock train. A high-speed self-aligning focusing schlieren system is used to visualize the flow structure variations by measuring the shock angles and Mach disk height and width to characterize the shock train dynamics and the flow structure recovery process. The response of jet flow to the perturbation at the nozzle exit and the pre-reflection point is found to be similar, however, the response of the supersonic jet to the post-reflection energy deposition is significantly different. The damping ratio for the pre-reflection point and nozzle exit cases found are nearly constant for all scenarios whereas it is linearly dependent on the jet chamber pressure for the post-reflection cases. The frequency of the oscillations is found to be the same for all cases and irrespective of the chamber pressure, laser energy, and deposition location, approximately 10 kHz. The transition from Mach to regular reflection and vice versa are observed at a chamber pressure of Pc = 689 kPa. Any perturbation to the shock structure of a supersonic over-expanding jet at close to the steady-state bifurcation condition between Mach and regular reflection will exhibit Mach-to-regular transition or vice versa.

Event Based Cameras: A Comparative Study For Fluid Event Detection

A feasibility study using an event-based camera for the detection of plane-wise motion of a 2D array of bio-inspired sensing pillars to detect generated flow events. EBCs show potential for future applications where PIV may have been classically used. They have the benefit of only generating data when an event happens and with comparatively cheaper setups, they hold great potential for flow monitoring. EBCs collect pixel x and y locations, as well as pixel contrast change data at each time there is an event and can be trained on regions of interest. Comparative experiments were carried out in the labs at City, University of London, to investigate the feasibility of using EBCs for the detection of generated large flow structures in both air and water. The disturbances were produced by a gust generator, an upstream cylinder and an air gun for a variety of controlled situations, such as disturbances caused by gusts, crossflows and wake downstream oscillations. Some results were also compared to known PIV results from our lab to see how EBCs can detect a known flow structure over the sensing pillars. The results presented demonstrate the capability of the pillars and EBC to detect large flow structures. These initial results show promise for future applications of flow monitoring, such as real-time flow monitoring via a machine learning algorithm that is trained to detect certain flow patterns over the sensing pillars. This would be an intermediate step into a fully automated flow control loop.

Flow Measurements Above A DBD Plasma Actuator Array By Means Of Defocusing PTV

Lagrangian defocusing particle tracking velocimetry (DPTV) measurements are conducted in a thin, wall-parallel volume above a plasma actuator array that is applied to mimic the effect of wall oscillations by inducing alternating, wall-parallel forcing in opposite directions into the air above the actuator surface. The aim of the experiments is to capture the plasma-induced flow structures in otherwise quiescent air in order to increase the understanding of different actuation parameters. For this purpose, high-speed particle image velocimetry equipment with one camera is used in a DPTV setup, where the out-of-plane particle coordinate is obtained through the diameter of a defocused particle image. On this basis, an approach for continuous particle tracking in several consecutive frames is presented, allowing to derive three component, three dimensional velocity and acceleration data. Light reflections that occur on the adjacent actuator surface give raise to particular challenges concerning the measurement uncertainty estimation as well as the calibration procedure for the evaluation of the wall-normal coordinate of tracer particles. To overcome the latter, a calibration approach is presented for which solid particles are applied to the actuator surface and their particle image diameter is captured at different camera positions in a separate measurement. The estimation of in-plane and out-of-plane displacement measurement uncertainties is conducted following a newly-developed procedure where the deviation of particle displacements from a straight track is evaluated for measurements in quasi-quiescent air. The obtained results show the suitability of DPTV measurement technique for the practical application of the characterization of flow structures above a plasma actuator array. The measurement accuracy is found to be limited due to the available illumination, which depends on the used components. The measured flow fields together with optical and electrical measurement data allow for a further analysis of the present forcing strategy. Particularly, by recording phase-resolved, three-dimensional flow velocity and acceleration fields in the vicinity of the wall, the spatio-temporal occurrence and homogeneity of the near-wall forcing effects can be analyzed in future investigations.

3D Lagrangian Particle Tracking In A Model Of The Human Airways

The three-dimensional flow field in the trachea of a physiologically correct model of the human respiratory tract from the nasal/oral cavities up to the 6th bronchi generation is investigated. The investigations comprise steady inflow conditions, i.e., steady inhalation and oscillatory flow combining inspiration and expiration to simulate calm breathing. A realistic breathing pattern is approximated by a sinusoidal waveform for two Womersley numbers of 3 and 4.5 and two Reynolds numbers of 400 and 1200. Due to the inherent three-dimensional and asymmetric nature of the flow field, 3D particle-tracking velocimetry (3D-PTV) measurements are performed using the Shake-The-Box (StB) algorithm to determine the influence of oral and nasal inhalation and exhalation on the flow field in the lower human airways. By using a refractive-index matched fluid consisting of water and glycerin, the complex flow structures inside the trachea are fully resolved. During oscillatory inhalation/exhalation, an integration window size of 6/40 pi was chosen as it can be considered short enough to assume a steady state. The PTV measurements confirm that the nasal and/or oral cavity must be taken into account when analyzing the flow field in the lower respiratory tract. Characteristic sets of velocity profiles in the sagittal and coronal plane of the trachea as well as contour plots evidence nearly identical flow structures for both oral and nasal inhalation, but also reveal that the presence of both cavities possesses a huge impact on the flow field compared to ideal, i.e., fully developed inflow conditions

On The Determination Of Conditional Statistics Along Gradient Trajectories At The Turbulent/Non-Turbulent Interface Of Jet Flows.

Conditional sampling and averaging are valuable techniques for discerning and quantifying notable regions within turbulent flows. These methods have been particularly prevalent in experimental and numerical investigations of turbulent shear flows. Conditional statistics effectively analyze the dynamics and characteristics of turbulent flows, offering insights into transitional behaviors and distinct features within these regimes. This approach is instrumental in studying turbulent shear flows, such as jets or mixing layers, where a well-defined zone separates the turbulent core from the non-turbulent surrounding fluid. This zone, known as the Turbulent/Non-Turbulent Interface (TNTI), plays a crucial role in various phenomenological changes, including the transfer of mass, momentum, and scalar fluxes. While statistics in jet flows are often reported along the radial direction for a given downstream position, this method can obscure the underlying physical processes. Scalar dissipation rate, transport, or turbulent kinetic energy involve velocity or concentration gradients at the flow interface. To date, the impact of sampling direction on conditional statistics within jet flows has not yet been thoroughly discussed. This study focuses on determining gradient trajectories at the interface of turbulent flows. Gradient trajectories have been used to explore structures in turbulent flows, proving effective in analyzing homogeneous shear turbulence. This study introduces a methodology for sampling conditional data by computing gradient trajectories intersecting the TNTI. The primary objective is to verify whether sampling statistics along the gradient of scalar concentration provide a more detailed understanding of the processes occurring near the TNTI. The methodology involves computing a field of gradient trajectories from concentration fields obtained through Planar Laser-Induced Fluorescence (PLIF) in a N2/N2 jet with Re = 2900. Conditional statistics at the TNTI of a jet flow along the gradient trajectory for a given downstream position are calculated and reported. The paper aims to compare conditional statistics along gradient trajectories with those obtained along radial and normal directions at the TNTI. It is expected that gradient trajectory statistics align more closely with normal direction statistics near the interface and diverge as it gets into the jet or coflow fluid.