scholarly journals A CFD-based procedure for airspace integration of small unmanned aircraft within congested areas

2017 ◽  
Vol 9 (4) ◽  
pp. 235-252 ◽  
Author(s):  
Craig WA Murray ◽  
David Anderson
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Characteristics ◽  
Unmanned Aircraft ◽  
Prevailing Wind ◽  
A Posteriori ◽  
Vehicle Performance ◽  
Inlet Velocity ◽  
Congested Area ◽  
The City

Future integration of small unmanned aircraft within an urban airspace requires an a posteriori understanding of the building-induced aerodynamics which could negatively impact on vehicle performance. Moving away from generalised building formations, we model the centre of the city of Glasgow using Star-CCM+, a commercial CFD package. After establishing a critical turbulent kinetic energy for our vehicle, we analyse the CFD results to determine how best to operate a small unmanned aircraft within this environment. As discovered in a previous study, the spatial distribution of turbulence increases with altitude. It was recommended then that UAVs operate at the minimal allowable altitude within a congested area. As the flow characteristics in an environment are similar, regardless of inlet velocity, we can determine areas within a city which will have consistently low or high values of turbulent kinetic energy. As the distribution of turbulence is dependent on prevailing wind directions, some directions are more favourable than others, even if the wind speed is unchanging. Moving forward we should aim to gather more information about integrated aircraft and how they respond to turbulence in a congested area.

scholarly journals Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1481
Author(s):  
Xinrui Li ◽  
Zhenggui Li ◽  
Baoshan Zhu ◽  
Weijun Wang
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Instability ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

Study on Turbulent Kinetic Energy in Closed Photobioreactor

2013 ◽  
Vol 448-453 ◽  
pp. 1675-1678
Author(s):  
Lin Li ◽  
Jun Ying Zhu ◽  
Jun Feng Rong ◽  
Wei Liu ◽  
Cheng Gang Bai
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Cross Section ◽  
Slope Angle ◽  
Control Variable ◽  
Structure Parameters ◽  
Inlet Velocity ◽  
Operation Conditions ◽  
Interval Distance ◽  
Computational Fluid Dynamics Cfd

Microalgae are an important source for biodiesel, one kind of renewable energy. The turbulence of the algal fluid can be intensified through optimizing the structure parameters of the disturbing devices and the operation conditions in photobioreactor, thereby the algae production increased. Turbulent kinetic energy is the measurement of turbulence intensity. Through control variable method, turbulent kinetic energy is simulated by means of Computational Fluid Dynamics (CFD). Based on the simulation, the slope angle and interval distance of two neighboring disturbing devices whose cross section is a right triangle, the ratio of disturbing device height to the fluid-depth, and the inlet velocity are all optimized, which is effectively enhance the turbulence.

scholarly journals Experimental determination of tunnel ventilation axial ducted fan performance

2016 ◽  
Vol 20 (1) ◽  
pp. 209-221 ◽  
Author(s):  
Milan Sekularac
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Ventilation System ◽  
Flow Characteristics ◽  
Pollutant Removal ◽  
Reynolds Stresses ◽  
Scaled Model ◽  
Tunnel Ventilation ◽  
Longitudinal Ventilation ◽  
Traffic Tunnel

To investigate traffic tunnel ventilation flows, a scaled model of a traffic tunnel with longitudinal ventilation system based on ducted fans is used. Flows in tunnels are influenced by tunnel geometry, fan characteristics, ventilation operation scenario, vehicle traffic, atmospheric factors, etc. To analyze flow fields of tunnels in detail, knowledge of tunnel jet-fan properties and turbulent flow characteristics at the fan exit are required, and can be used as input data for CFD boundary conditions of tunnel flow computation. For this purpose experimental measurements were done using the hot wire anemometry technique. The obtained results, trough ensemble-averaged and time averaged profiles of all velocity components, turbulence intensity, turbulent kinetic energy, integral flow length scales, available Reynolds stresses, Turbulent kinetic energy production rates and the fan thrust performance, are presented. These data allow us to analyze in more detail the influence of fan flow on energy and pollutant removal efficiencies of the tunnel ventilation and to evaluate accuracy of CFD studies on fan improvements.

scholarly journals Local turbulent kinetic energy modelling based on Lagrangian stochastic approach in CFD and application to wind energy

2021 ◽  
Author(s):  
Kerlyns Martínez ◽  
Mireille Bossy ◽  
Jean-François Jabir
Keyword(s):  
Kinetic Energy ◽  
Wind Energy ◽  
Stochastic Model ◽  
Turbulent Kinetic Energy ◽  
Flow Characteristics ◽  
Direct Methods ◽  
Physical Parameters ◽  
Uncertainty Distribution ◽  
Deterministic Modelling ◽  
Wind Measurements

<p>In order to better integrate the underlying meteorological processes with the developing technologies within wind energy industry, acquiring relevant statistical information of air motion at a local place, and quantifying the subsequent uncertainty of involved parameters in the models, are fundamental tasks. Special emphasis should be made on the growing interest in energy production forecasting and modelling for wind energy developments that rises the issue of accounting for the uncertain nature of the local forecast. Taking this into consideration, we present the construction of an original stochastic model for the instantaneous turbulent kinetic energy at a given point of a flow, and we validate estimator methods on this model with observational data examples from annual historic of a 10 Hz anemometer wind measurements. <br>More precisely, starting from the viewpoint of Lagrangian modelling of the wind in the boundary layer, we establish a mathematical link between 3D+time computational fluid dynamics (CDF) models for turbulent near-wall flows and stochastic time series models by deriving a family of mean-field dynamics featuring the square norm of the turbulent velocity. Then, by approximating at equilibrium the characteristic nonlinear terms of the dynamics, we recover the so called Cox-Ingersoll-Ross stochastic model, which was previously suggested in the literature for modelling wind speed. Remarkably, our stochastic model for the instantaneous turbulent kinetic energy is parametrised by physical constants in CFD, which provides a more direct link between the stochastic nature of the underlying processes and the classical physics behind these phenomena. Nevertheless, these physical parameters may vary with the flow characteristics and situations, so we consider it relevant to adjust their values while constructing the forecasts. Such tuning of the physical parameters was previously proposed in the literature from a deterministic modelling context with RANS equations. We then propose a two-step procedure for the calibration of the parameters: a training stage where we construct a priori distribution for the parameter vector using direct methods and wind measurements, and a stage of refinement of the uncertainty distribution using Bayesian inference combined with Markov Chain Monte Carlo sample techniques. In particular, we show the accuracy of the calibration method and the performance of the calibrated model in predicting the wind distribution through the quantification of uncertainty.</p>

scholarly journals Aerodynamic Studies on Non-Premixed Oxy-Methane Flames and Separated Oxy-Methane Cold Jets

Processes ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 429 ◽  
Author(s):  
Tamal Jana ◽  
Mrinal Kaushik ◽  
Dipankar Deb ◽  
Vlad Mureşan ◽  
Mihaela Ungureşan
Keyword(s):  
Kinetic Energy ◽  
Radial Velocity ◽  
Turbulent Kinetic Energy ◽  
Large Scale ◽  
Inlet Temperature ◽  
Centerline Velocity ◽  
Inlet Velocity ◽  
Jet Mixing ◽  
Mixing Characteristics ◽  
Jet Velocity

Both cold and flame jets find numerous applications in different fields, ranging from domestic applications to aerospace and space technology. Indeed, the applications of isothermal and non-isothermal jets in the flame heating industry fascinated the researchers to gain an in-depth understanding. Nevertheless, these benefits are not standalone, rather, they are associated with major disadvantages such as improper jet mixing and flame instabilities that require careful remedies. In the present investigation, three-inline jets, having methane jet at the center and two oxygen jets at the periphery, are studied computationally in a three-dimensional domain, with and without considering the effects of combustion. To study the mixing characteristics of cold jets, the radial velocity distributions at different streamwise locations have been analyzed at the jet inlet velocity of 27 m/s. However, for oxygen and methane flame jets, inlet velocities are varied as 27 m/s and 54 m/s. Moreover, to investigate the effects of temperature variation on mixing characteristics at a particular jet velocity, the inlet temperatures of reactants are varied as 300 K, 500 K, and 700 K, at the jet inlet velocity of 27 m/s. Combustion is found to have a profound impact on the mixing characteristics. At the inlet temperature of 300 K, a higher centerline velocity decay is observed for non-reactive jets as compared to reactive flame jets. Moreover, the turbulent kinetic energy distribution is relatively higher in the case of non-reactive jets, which is the direct evidence of an augmented mixing. As is obvious, the turbulent kinetic energy at the jet shear layer is maximum due to the formation of large-scale coherent eddies. The decay in centerline velocity is found to be increasing with an increase of inlet temperature. Additionally, with an increase of jet velocity, the radial velocity profiles become more asymmetrical, consequently yielding an unstable flame.

scholarly journals Sensitivity analysis of nuclear main pump annular casing tongue blend

2017 ◽  
Vol 9 (7) ◽  
pp. 168781401770659 ◽  
Author(s):  
Xiaorui Cheng ◽  
Wenrui Bao ◽  
Li Fu ◽  
Xiaoting Ye
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Turbulent Kinetic Energy ◽  
Stokes Equations ◽  
Flow Instability ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Simple Algorithm ◽  
Operating Conditions ◽  
Navier Stokes

Based on the Reynolds-averaged Navier–Stokes equations of relative coordinates and the RNG k-ε turbulence model, using our SIMPLE algorithm, we performed numerical simulations for an AP1000 nuclear main pump model with water as the medium. By changing the size of the tongue blend in the annular casing, seven different schemes were designed. Three-dimensional numerical simulations were conducted for the flow within the pump under various settings, and the flow characteristics of the annular casing using different tongue blends were obtained. The results show that for different operating conditions, there is a specific tongue blend that optimizes pump performance. Based on the calculation results, a larger tongue blend leads to a larger flow rate. Off-design conditions caused flow instability, which in turn caused the tongue blend to have a certain impact on the performance of the impeller. However, the performance of the pump was not primarily affected by changes in the impeller performance, but was instead affected by the performance of the annular casing, which was itself affected by tongue blend. When changing the tongue blend, the change in static pressure and total pressure of the annular casing was larger under the condition of 0.6 Qd and was smaller under the conditions of 1.0 Qd and 1.4 Qd. The turbulent kinetic energy in the annular casing changed mainly in the tongue impact zone and outlet diffuser under the condition of 1.0 Qd; furthermore, the turbulent kinetic energy in the whole of the annular casing demonstrated significant changes under the conditions of 0.6 Qd and 1.4 Qd.

Comparative analysis of transient valve-induced flow characteristics between opening and closing processes

2021 ◽  
pp. 095440892110630
Author(s):  
Qi Liu ◽  
Shuai Tian ◽  
Yong-xiang Wang ◽  
Zhe Lin ◽  
Zu-chao Zhu
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Flow Stability ◽  
Adjustment Process ◽  
Unstable Flow ◽  
Valve Opening ◽  
Induced Flow ◽  
Opening And Closing

Transient control of process valves, including opening and closing processes, is consistently encountered in many fluid transportation and control industries. During opening and closing processes, valve-induced transient flow presents different unstable flow characteristics. This transient valve-induced unstable flow that develops along the pipeline can cause violent pressure and velocity fluctuations that considerably influence accurate flow measurement downstream. In this paper, gate valve-induced flow characteristics during opening and closing processes were comparatively studied. An experimental system was developed to monitor the downstream pressure along the pipeline, and corresponding transient numerical simulations were performed on opening and closing processes using a user-defined function and dynamic grid technology. The pressure distributions along the pipeline's downstream area during valve opening and closing processes were investigated to verify the accuracy of the numerical simulation. The mechanism of transient flow difference under the same valve opening during opening and closing processes was determined to be a hysteresis effect. The jet flow intensity under a small valve opening in the opening process was greater than that in the closing process, and the difference in flow field under the 50% valve opening was the largest. Moreover, the velocity and turbulent kinetic energy distributions in different downstream cross-sections during valve opening and closing processes were comparatively analyzed. The change rate of the maximum turbulent kinetic energy was introduced to further analyze the different effects of opening and closing processes on the transient flow stability downstream of the valve. Results showed that the flow stability between 40% and 50% valve opening was the worst irrespective of the adjustment process, that is, a large pipeline distance was required to stabilize this transient flow. This study helps in understanding transient valve-induced flow characteristics in fluid transportation pipelines and provides guidance for accurate flow metering industrial applications.

scholarly journals Numerical investigation of mixture generation due to different inlet and outlet positions

2019 ◽  
Vol 15 (2) ◽  
pp. 308-317
Author(s):  
Hussain Saad Abd ◽  
Abdulmunem R Abdulmunem ◽  
Mohammed Hassan Jabal
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dead Zone ◽  
Sudden Change ◽  
Flow Characteristics ◽  
Reynolds Stress Model ◽  
Accurate Solution ◽  
Flow Properties ◽  
Navier Stokes Equation ◽  
Rate Of Dissipation

Abstract A numerical simulation is a method carried out to study the flow characteristics of compressible fluid through different channels. Two approaches using air as a working substance were used to study the flow characteristics. In the first approach, two inlets and one outlet horizontally in the x direction was depended on to generate different flow characteristics; the flow properties were calculated along the diagonal line inside the channel. In the second approach, one inlet and outlet horizontally with sudden change in the area of the channel was employed. In this research, the flow properties were calculated along the center line inside the channel and the flow fields have been investigated. A non-linear k-Є model is employed to solve the flow characteristics by using the finite difference method with a curvilinear coordinate system near the dead zone and the k-Є and Reynolds stress model area semi-empirical model based on modeling of the equations of transport that contain the dissipation rate (ε) as well as turbulent kinetic energy (k). The derivation of turbulent kinetic energy and its rate of dissipation derived from the Navier–Stokes equation. In this work, the simulation outcomes of the proposed k-ε turbulence model indicated a good compatibility with published correlations. In order to get an accurate solution, the value of 10–8 for the maximal normalized equation residual was considered to be the convergence between computation and steady solution. The model applied for flow velocity 30 m/s and the obtained results presented as curves, surface and contours for velocities turbulent kinetic energy, rate of dissipation of turbulent kinetic energy and vortices. The builder model can be utilized for academic purposes since it is widely used for many physical and engineering applications.

scholarly journals Study of a Rock-Ramp Fish Pass with Staggered Emergent Square Obstacles

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1175
Author(s):  
Flavia Cavalcanti Miranda ◽  
Ludovic Cassan ◽  
Pascale Laurens ◽  
Tien Dung Tran
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Design Process ◽  
Water Depth ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Fish Passage ◽  
Lower Velocity ◽  
Water Depths

A rock-ramp fish passage with square obstacles was experimentally and numerically studied in this work with the objective of investigating in detail the hydraulic behind such fishways and to evaluate the importance of the shape of the obstacles. The LES and VOF methods were used for the simulations, and for the measurements, shadowgraphy and ADV were applied. Two different validations were successfully performed. In the first one, the experimental and numerical results of a chosen case were compared in detail. In the second validation, the focus was given to the stage-discharge. Following the validation, a numerical study was carried out to point out the differences in the flow characteristics from a configuration with square and circular obstacles. The discharge was nearly the same for both configurations, which implies different water depths. The results showed a lower velocity field, lower turbulent kinetic energy, and lower lateral fluctuations for the configuration with square blocks, which indicated a better passability for this geometry. However, it also presented a higher water depth, which led to a less attractive discharge. The differences in the flow generated in the two configurations indicated that the shape is an important modifiable parameter to be considered in the design process.

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