scholarly journals Buoyant Jets in Cross-Flows: Review, Developments, and Applications

2021 ◽  
Vol 9 (1) ◽  
pp. 61
Author(s):  
Mostafa Taherian ◽  
Abdolmajid Mohammadian
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Pair ◽  
Design Guidelines ◽  
Future Research ◽  
Marine Biota ◽  
Buoyant Jet ◽  
Buoyant Jets ◽  
Practical Applications ◽  
Accurate Design

Significant environmental effects from the use of marine outfall discharges have led to increased efforts by both regulatory bodies and research groups to minimize the negative impacts of discharges on the receiving water bodies. Understanding the characteristics of discharges under conditions representative of marine environments can enhance the management of discharges and mitigate the adverse impacts to marine biota. Thus, special attention should be given to ambient cross-flow effects on the mixing behaviors of jet discharges. A buoyant jet in cross-flow has different practical applications such as film cooling and dilution, and provide a higher mixing capability in comparison with free jets or discharges into stationary environments. The main reason for this is believed to be the existence of various complicated vortical structures including a counter-rotating vortex pair as the jet expands downstream. Although tremendous research efforts have been devoted to buoyant jets issuing into cross-flows over the past five decades, the mixing process of an effluent at the discharge point is not yet well understood because of the highly complex fluid interactions and dispersion patterns involved. Therefore, there is a need for a deeper understanding of buoyant jets in cross-flows in order to obtain better predictive methods and more accurate design guidelines. The main aims of this study were (i) to establish the background behind the subject of buoyant jets in cross-flows including the flow structures resulting from the interaction of jets and cross-flows and the impacts of current on mixing and transport behavior; (ii) to present a summary of relevant experimental and numerical research efforts; and finally, (iii) to identify and discuss research gaps and future research directions.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2011 ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Large Eddy

Large Eddy Simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported with the jet modeled using a plenum/pipe configuration. This configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

Effects of the Swirl Velocity of a Jet in Crossflow From Fan Assemblies Mounted on Lifting Surfaces

2010 ◽  
Author(s):  
Alexandros Terzis ◽  
Charilaos Kazakos ◽  
Nikolaos Papadopoulos ◽  
Anestis I. Kalfas ◽  
Pavlos K. Zachos ◽  
...  
Keyword(s):  
Flight Control ◽  
Film Cooling ◽  
Thermal Protection ◽  
Turbine Blades ◽  
Cross Flow ◽  
Vortex Pair ◽  
Main Stream ◽  
Injection Hole ◽  
Swirl Velocity ◽  
Wide Range

The penetration of a jet of fluid into a traversal moving stream is a basic configuration of a wide range of engineering applications, such as film cooling and V/STOL aircrafts. This investigation examines experimentally the effect of blowing ratio of fans in cross flow, and numerically, the effect of the swirl velocity of jets in cross flow, downstream of the injection hole. The experimental results indicated an agreement with typically straight jets in cross flow (no vorticity), illustrating that the trace of the jet, remains close to the wall and subsequently enhance cooling at low blowing ratios in the case of turbine blade applications. However, the rotation of the jet results in an imparity between the two parts of the counter rotating vortex pair (CVP), and as a consequence, the injected fluid not only bends in the direction of the main stream but also diverts in the direction of the rotation, in order to conserve its angular momentum. The induction of the swirl velocity on the injected jet destructs one of the two parts of the kidney vortex which entrains fluid from the cross flow to the jet promoting the mixing between the two fluids, while the trace of a swirled jet remains closer to the wall downstream of the injection hole. Finally, the use of contra rotating jet or fan configurations reduces the wall shear stress in a very great extent, leading to better thermal protection of turbine blades, as well as cancels out the yaw torques of each fan separately, resulting in better flight control of typical lift surface.

Cooling performance of vortex generator

2021 ◽  
pp. 095765092199396
Author(s):  
Nirmal Halder ◽  
PK Panigrahi
Keyword(s):  
Reynolds Number ◽  
Numerical Investigation ◽  
Film Cooling ◽  
Density Ratio ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Stream Velocity ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

Present numerical investigation proposes to mitigate the effects of Counter rotating vortex pair (CRVP) by employing a pair of vortex generator. Numerical simulation has been carried out to investigate the effect of placement of vortex generator on the characteristics of film cooling effectiveness. Various configuration has been taken based on vortex generator location at upstream, downstream of circular film cooling hole. Along with these utilizing multiple vortex generator at different downstream location also has been detected. The jet to cross flow blowing ratios ( M =  ρ juj/ ρ cfucf) is maintained at unity while Reynolds number based on free stream velocity and film cooling hole dimension is kept at 17,000. The investigation of suitable turbulence model has been studied. The results are compared with baseline case. The numerical investigation is accomplished implementing FLUENT commercial code adopting the K-omega SST model. Among configuration E and all quantity (Density ratio ( DR), Blowing ratio ( M), Reynolds number (Re) and Turbulence intensity ( TI)) better CRVP distribution is depicted for TI and lowest for configuration E.

Large-Eddy Simulation of Shaped Hole Film Cooling with the Influence of Cross Flow

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Wang Qingsong ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Large Scale ◽  
High Efficiency ◽  
Cross Flow ◽  
Vortex Pair ◽  
Hairpin Vortices ◽  
Eddy Simulation ◽  
Large Eddy ◽  
End Wall

AbstractIn the highly-loaded turbine blade passage, cross flow is driven by the lateral gradient. It strongly influences the cooling performances in the endwall region. In this research, the effect of cross flow on the shaped film cooling hole is studied by Large Eddy Simulation (LES); modal analysis is conducted with an incremental POD (iPOD) approach, which makes the analysis of the large data sets from LES feasible. It is shown that the symmetry of the counter rotating vortex pair (CRVP) is destroyed. The large-scale vortex induced by end-wall cross flow plays an important role in both shape and convection of hairpin vortices and horseshoe vortices, which influences the coolant distribution. This study suggests that the effects of cross flow should be considered for the design of end-wall film cooling. It also indicates the high efficiency of the iPOD approach, which can be used to analyze large amounts of high-dimensional data.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Turbulent Structures ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Large Eddy

Large eddy simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated. Coherent turbulent structures characteristic of a jet in a cross-flow are analyzed and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported for two film-cooling configurations, where the primary difference is the way the jet inflow boundary conditions are prescribed. In the first configuration, the jet conditions are prescribed using a precursor simulation and in the second the jet is modeled using a plenum/pipe configuration. The latter configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

Noncanonical Short Hole Jets-in-Crossflow for Turbine Film Cooling

2005 ◽  
Vol 73 (3) ◽  
pp. 474-482 ◽  
Author(s):  
Michael W. Plesniak
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Pair ◽  
Structural Features ◽  
Global Features ◽  
Vortical Structures ◽  
Jet In Crossflow ◽  
Jet Trajectory ◽  
Image Velocimetry ◽  
Counter Rotating Vortex Pair

This paper presents a review of research done over the past several years at Purdue on non-canonical jets-in-crossflow. It is a retrospective and an integrative compilation of results previously reported as well as some new ones. The emphasis is on jets emanating from “short” holes, with length-diameter ratios of one or less. A canonical jet-in-crossflow configuration is one in which a fully developed jet issues from a long pipe fed by a large plenum, into a semi-infinite cross flow. The configuration presented here is noncanonical in the sense that jet issues from a short hole and thus the flow is unable to “adjust” to the hole, unlike the case of a long hole in which fully developed pipe flow can be attained. This is motivated by gas turbine film cooling applications. Experimental results acquired with particle image velocimetry will primarily be presented, with some complementary information gained from RANS simulations of the flow. Many different aspects of the problem have been investigated, and in this paper the focus will be on structural features within the hole and in the developing jet and crossflow interaction. A significant result is that the in-hole vortical structures, depending on their sense of rotation, tend to augment or weaken the primary counter-rotating vortex pair. This impacts global features such as jet trajectory and spreading.

scholarly journals The Potential of the Synthetic Strigolactone Analogue GR24 for the Maintenance of Photosynthesis and Yield in Winter Wheat under Drought: Investigations on the Mechanisms of Action and Delivery Modes

Plants ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1223
Author(s):  
Mojde Sedaghat ◽  
Yahya Emam ◽  
Ali Mokhtassi-Bidgoli ◽  
Saeid Hazrati ◽  
Claudio Lovisolo ◽  
...  
Keyword(s):  
Winter Wheat ◽  
Foliar Application ◽  
Mechanisms Of Action ◽  
Bioactive Molecules ◽  
Future Research ◽  
Antioxidant Enzyme Activities ◽  
Synthetic Analog ◽  
Practical Applications ◽  
New Family ◽  
Harsh Environmental Condition

Strigolactones (SLs) have been implicated in many plant biological and physiological processes, including the responses to abiotic stresses such as drought, in concert with other phytohormones. While it is now clear that exogenous SLs may help plants to survive in harsh environmental condition, the best, most effective protocols for treatment have not been defined yet, and the mechanisms of action are far from being fully understood. In the set of experiments reported here, we contrasted two application methods for treatment with a synthetic analog of SL, GR24. A number of morphometric, physiological and biochemical parameters were measured following foliar application of GR24 or application in the residual irrigation water in winter wheat plants under irrigated and drought stress conditions. Depending on the concentration and the method of GR24 application, differentiated photosynthesis and transpiration rate, stomatal conductance, leaf water potential, antioxidant enzyme activities and yield in drought conditions were observed. We present evidence that different methods of GR24 application led to increased photosynthesis and yield under stress by a combination of drought tolerance and escape factors, which should be considered for future research exploring the potential of this new family of bioactive molecules for practical applications.

scholarly journals A Survey on Deep Learning Based Methods and Datasets for Monocular 3D Object Detection

Electronics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 517
Author(s):  
Seong-heum Kim ◽  
Youngbae Hwang
Keyword(s):  
Deep Learning ◽  
Object Detection ◽  
Low Cost ◽  
Detection Methods ◽  
Future Research ◽  
3D Object ◽  
Practical Applications ◽  
Depth Sensors ◽  
Significant Research ◽  
3D Object Detection

Owing to recent advancements in deep learning methods and relevant databases, it is becoming increasingly easier to recognize 3D objects using only RGB images from single viewpoints. This study investigates the major breakthroughs and current progress in deep learning-based monocular 3D object detection. For relatively low-cost data acquisition systems without depth sensors or cameras at multiple viewpoints, we first consider existing databases with 2D RGB photos and their relevant attributes. Based on this simple sensor modality for practical applications, deep learning-based monocular 3D object detection methods that overcome significant research challenges are categorized and summarized. We present the key concepts and detailed descriptions of representative single-stage and multiple-stage detection solutions. In addition, we discuss the effectiveness of the detection models on their baseline benchmarks. Finally, we explore several directions for future research on monocular 3D object detection.

scholarly journals Distributed Ledger Technology Applications in Food Supply Chains: A Review of Challenges and Future Research Directions

2021 ◽  
Vol 13 (8) ◽  
pp. 4206
Author(s):  
Jamilya Nurgazina ◽  
Udsanee Pakdeetrakulwong ◽  
Thomas Moser ◽  
Gerald Reiner
Keyword(s):  
Supply Chains ◽  
Food Supply ◽  
Information Exchange ◽  
Security And Privacy ◽  
Future Research ◽  
Research Directions ◽  
Practical Applications ◽  
Food Supply Chains ◽  
Distributed Ledger ◽  
Future Research Directions

The lack of transparency and traceability in food supply chains (FSCs) is raising concerns among consumers and stakeholders about food information credibility, food quality, and safety. Insufficient records, a lack of digitalization and standardization of processes, and information exchange are some of the most critical challenges, which can be tackled with disruptive technologies, such as the Internet of Things (IoT), blockchain, and distributed ledger technologies (DLTs). Studies provide evidence that novel technological and sustainable practices in FSCs are necessary. This paper aims to describe current practical applications of DLTs and IoT in FSCs, investigating the challenges of implementation, and potentials for future research directions, thus contributing to achievement of the United Nations’ Sustainable Development Goals (SDGs). Within a systematic literature review, the content of 69 academic publications was analyzed, describing aspects of implementation and measures to address the challenges of scalability, security, and privacy of DLT, and IoT solutions. The challenges of high costs, standardization, regulation, interoperability, and energy consumption of DLT solutions were also classified as highly relevant, but were not widely addressed in literature. The application of DLTs in FSCs can potentially contribute to 6 strategic SDGs, providing synergies and possibilities for more sustainable, traceable, and transparent FSCs.

Hierarchical Reinforcement Learning

2021 ◽  
Vol 54 (5) ◽  
pp. 1-35
Author(s):  
Shubham Pateria ◽  
Budhitama Subagdja ◽  
Ah-hwee Tan ◽  
Chai Quek
Keyword(s):  
Reinforcement Learning ◽  
Future Research ◽  
Comprehensive Overview ◽  
Open Problems ◽  
Practical Applications ◽  
Hierarchical Reinforcement Learning ◽  
The Past ◽  
Agent Learning ◽  
Multi Agent ◽  
Supplementary Material

Hierarchical Reinforcement Learning (HRL) enables autonomous decomposition of challenging long-horizon decision-making tasks into simpler subtasks. During the past years, the landscape of HRL research has grown profoundly, resulting in copious approaches. A comprehensive overview of this vast landscape is necessary to study HRL in an organized manner. We provide a survey of the diverse HRL approaches concerning the challenges of learning hierarchical policies, subtask discovery, transfer learning, and multi-agent learning using HRL. The survey is presented according to a novel taxonomy of the approaches. Based on the survey, a set of important open problems is proposed to motivate the future research in HRL. Furthermore, we outline a few suitable task domains for evaluating the HRL approaches and a few interesting examples of the practical applications of HRL in the Supplementary Material.

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