Detection of river flow slow-down through sensing system and quasi-real time imaging

Flow slow-down in rivers and artificial canals is a basic aspect to be monitored and kept strictly under control. Flow slow-downs can become a major concern in the event of extreme phenomena. The paper illustrates an advanced image processing method that uses particle tracking velocimetry in conjunction with a monadic approach to better characterize water flow in the presence of waste or debris that block normal water flow within a river. An high-speed camera installed beneath a bridge takes periodic images of the water flow. The measured water level and the images taken by the camera are sent to a central system in real-time. Results demonstrate the capability of the proposed method to accurately detect the presence of debris from the measured water flow

High-resolution microscale velocity field measurement using light field particle image-tracking velocimetry

Light field microparticle image velocimetry (LF-μPIV) can realize the three-dimensional (3D) microscale velocity field measurement, but the spatial resolution of the velocity field is low. Therefore, this study proposes a high-resolution LF particle image-tracking velocimetry (PIV–PTV) in combination with a cross-validation matching (CVM) algorithm. The proposed method performs motion compensation for the distribution of particle center position based on the low-resolution velocity field achieved by PIV and then conducts the CVM on tracer particles with the nearest neighbor method. The motion compensation reduces the particle displacement during the matching, while the CVM reduces the impact of missing particles on the matching accuracy. Thus, the proposed method enables precise tracking of individual particles at higher particle concentrations and improves the spatial resolution of the velocity field. Numerical simulations were conducted on the 3D displacement field reconstruction. The influence of interrogation window size, particle diameter, and concentration was analyzed. Experiments were conducted on the microscale 3D velocity field within the microchannel with right-angle bends. Results indicate that the proposed method provides the high-resolution measurement of the microscale 3D velocity field and improves the precision of the velocity field compared to the PTV at higher particle concentrations. It demonstrates that the proposed method outperforms PIV by 26% in resolution and PTV by 76% in precision at a higher particle concentration of 1.5 particles per microlens

DEVELOPMENT OF A LAGRANGIAN-LAGRANGIAN METHODOLOGY TO PREDICT BROWNOUT DUST CLOUDS

A Lagrangian-Lagrangian dust cloud simulation methodology has been developed to help better understand the complicated two-phase nature of the rotorcraft brownout problem. Brownout conditions occur when rotorcraft land or take off from ground surfaces covered with loose sediment such as sand and dust, which decreases the pilot's visibility of the ground and poses a serious safety of flight risk. The present work involved the development of a comprehensive, computationally efficient three-dimensional sediment tracking method for dilute, low Reynolds number Stokes-type flows. The flow field generated by a helicopter rotor in ground effect operations over a mobile sediment bed was modeled by using an inviscid, incompressible, Lagrangian free-vortex method, coupled to a viscous semi-empirical approximation for the boundary layer flow near the ground. A new threshold model for the onset of sediment mobility was developed by including the effects of unsteady pressure forces that are induced in vortically dominated rotor flows, which can significantly alter the threshold conditions for particle motion. Other important aspects of particle mobility and uplift in such vortically driven dust flows were also modeled, including bombardment effects when previously suspended particles impact the bed and eject new particles. Bombardment effects were shown to be a particularly significant contributor to the mobilization and eventual suspension of large quantities of smaller-sized dust particles, which tend to remain suspended. A numerically efficient Lagrangian particle tracking methodology was developed where individual particle or clusters of particles were tracked in the flow. To this end, a multi-step, second-order accurate time-marching scheme was developed to solve the numerically stiff equations that govern the dynamics of particle motion. The stability and accuracy of this scheme was examined and matched to the characteristics of free-vortex method. One-way coupling of the flow and the particle motion was assumed. Particle collisions were not considered. To help reduce numerical costs, the methodology was implemented on graphic processing units, which gave over an order of magnitude reduction in simulation time without any loss in accuracy. Validation of the methodology was performed against available measurements, including flow field measurements that have been made with laboratory-scale and full-scale rotors in ground effect operations. The predicted dust clouds were also compared against measurements of developing dust clouds produced by a helicopter during taxi-pass and approach-to-touchdown flight maneuvers. The results showed that the problem of brownout is mostly driven by the local action of the rotor wake vortices and the grouping or bundling of vortex filaments near the sediment bed. The possibilities of mitigating the intensity of brownout conditions by diffusing the blade tip vortices was also explored. While other means of brownout mitigation may be possible, enhancing the diffusion of the tip vortices was shown to drastically reduce the quantity of mobilized particles and the overall severity of the brownout dust cloud

Bibliography of Lewis Research Center Technical Publications announced in 1991

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific engineering work performed and managed by the Lewis Research Center in 1991. All the publications were announced in the 1991 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Flow-3D CFD model of bifurcated open channel flow: setup and validation

Bifurcation is a morphological feature present in most of fluvial systems; where a river splits into two channels, each bearing a portion of the flow and sediments. Extensive theoretical studies of river bifurcations were performed to understand the nature of flow patterns at such diversions. Nevertheless, the complexity of the flow structure in the bifurcated channel has resulted in various constraints on physical experimentation, so computational modelling is required to investigate the phenomenon. The advantages of computational modelling compared with experimental research (e.g. simple variable control, reduced cost, optimize design condition etc.) are widely known. The great advancement of computer technologies and the exponential increase in power, memory storage and affordability of high-speed machines in the early 20th century led to evolution and wide application of numerical fluid flow simulations, generally referred to as Computational Fluid Dynamics {CFD). In this study, the open-channel flume with a lateral channel established by Momplot et al (2017) is modelled in Flow-3D. The original investigation on divided flow of equal widths as simulated in ANSYS Fluent and validated with velocity measurements

A gravel-sand bifurcation:a simple model and the stability of the equilibrium states

A river bifurcation, can be found in, for instance, a river delta, in braided or anabranching reaches, and in manmade side channels in restored river reaches. Depending on the partitioning of water and sediment over the bifurcating branches, the bifurcation develops toward (a) a stable state with two downstream branches or (b) a state in which the water discharge in one of the branches continues to increase at the expense of the other branch (Wang et al., 1995). This may lead to excessive deposition in the latter branch that eventually silts up. For navigation, flood safety, and river restoration purposes, it is important to assess and develop tools to predict such long-term behavior of the bifurcation. A first and highly schematized one-dimensional model describing (the development towards) the equilibrium states of two bifurcating branches was developed by Wang et al (1995). The use of a one-dimensional model implies the need for a nodal point relation that describes the partitioning of sediment over the bifurcating branches. Wang et al (1995) introduce a nodal point relation as a function of the partitioning of the water discharge. They simplify their nodal point relation to the following form: s*=q*k , where s* denotes the ratio of the sediment discharges per unit width in the bifurcating branches, q* denotes the ratio of the water discharges per unit width in the bifurcating branches, and k is a constant. The Wang et al. (1995) model is limited to conditions with unisize sediment and application of the Engelund & Hansen (1967) sediment transport relation. They assume the same constant base level for the two bifurcating branches, and constant water and sediment discharges in the upstream channel. A mathematical stability analysis is conducted to predict the stability of the equilibrium states. Depending on the exponent k they find a stable equilibrium state with two downstream branches or a stable state with one branch only (i.e. the other branch has silted up). Here we extend the Wang et al. (1995) model to conditions with gravel and sand and study the stability of the equilibrium states