Influence of struts on cavity at subsonic speeds: Flow characteristics

2019 ◽  
Vol 233 (14) ◽  
pp. 5369-5379 ◽  
Author(s):  
Junjie Miao ◽  
Yuxin Fan
Keyword(s):  
Exchange Rate ◽  
Residence Time ◽  
Mass Exchange ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Critical Length ◽  
Flame Stabilization ◽  
Combined Cycle ◽  
Structure Parameters ◽  
Closed Cavity

Cavity–strut combined flame holder is a promising choice for turbine-based combined cycle engines with its excellent fuel distribution and flame stabilization. In this paper, the effects of the strut structure parameters on the flow characteristics in the cavity were investigated by using particle image velocimetry and numerical simulation. Experimental and numerical results show that the struts induce complex three-dimensional flow patterns, which have a significant influence on the cavity transverse vortex. The relative position between the cavity and the strut influences the critical length-to-depth ratio of the open cavity reverting to the closed cavity. The mass exchange rate of the cavity decreases with the increase in the space between the cavity and the struts, while it increases with the strut inclination angle increases. The variation law of mean cavity residence time with the structure parameters is exactly opposite to that of the mass exchange rate. Compared with a single cavity, at a high subsonic speed, the cavity–strut combined structure has the advantage of increasing the mass exchange rate and cavity residence time simultaneously.

Influence of strut on cavity at subsonic speeds: Ignition characteristics

2020 ◽  
Vol 234 (8) ◽  
pp. 1369-1379 ◽  
Author(s):  
Junjie Miao ◽  
Yuxin Fan ◽  
Tianchi Liu
Keyword(s):  
Exchange Rate ◽  
Residence Time ◽  
Mass Exchange ◽  
High Speed ◽  
Imaging Techniques ◽  
Structural Parameters ◽  
Ignition Limit ◽  
Flame Stabilization ◽  
Structure Parameters ◽  
Ignition Characteristics

In high-speed airflow, the use of cavity and struts in combination can improve fuel distribution and flame-stabilization, but may weaken the ignition performance. Herein, the lean ignition characteristics of several cavity–strut flame holders in a tandem turbine-based combined cycles combustor are experimentally investigated with the flow fields by using particle image velocimetry and high-speed chemiluminescence imaging techniques. Additionally, the effects of the strut structure parameters on the lean ignition performance in the cavity are studied. Experimental results indicate that changes in structural parameters have the opposite effects on the ignition performance and the flame-propagation performance. Reducing the strut inclination angle has a contrary function with the decrease in the cavity–strut space, which also transforms the flame-stabilizing mechanism between strut-stabilizing and cavity-stabilizing, accompanied by the flame morphology behind strut changes from no-flame to intermittent-flame, and finally continuous-flame. The lean ignition limit changes with the structure parameters, mainly due to the inverse change in the mass exchange rate and cavity residence time. Compared with the single cavity, the proper cavity–strut combined structure has a wider lean ignition limit at high subsonic speeds due to the advantage of simultaneously increasing the mass exchange rate and cavity residence time.

Computational Analysis of a Fixed Bed Thermal Oxidizer for Solid Wastes Disposal

2013 ◽  
Vol 699 ◽  
pp. 326-334
Author(s):  
P.L. Mtui
Keyword(s):  
Solid Waste ◽  
Residence Time ◽  
Gas Flow ◽  
Fixed Bed ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Original Design ◽  
Complete Combustion ◽  
Combustion Of Gases ◽  
Waste Incinerators

Combustion control techniques have become a legal requirement to minimize pollution in municipal solid waste incinerators. Typically, incinerator destruction of pollutants is achieved when 2-second gas residence time at 8500 Celsius and about 6% O2 are guaranteed at exit. Performance of a fixed bed (two-stage) thermal oxidizer for solid waste is analyzed numerically using computational fluid dynamics (CFD) technique. The CFD analysis provides three-dimensional view of thermal and gas flow field inside the thermal oxidizer chamber. Localized zones of temperature and species concentration were analyzed and provided critical information for understanding the thermo-chemical processes taking place during incineration leading into design optimization and the operation strategy of the thermal oxidizer. Based on the CFD results, the original design of the thermal oxidizer was modified to optimize the flow characteristics and the residence time in the secondary chamber thereby achieving complete combustion of gases emanating from the lower chamber, hence less emissions of CO.

Performance of lamella clarifiers for juice and syrup clarification

2017 ◽  
pp. 144-150
Author(s):  
Peter W. Rein ◽  
M. Getaz ◽  
A. Raghunandan ◽  
N. du Pleissis ◽  
H. Saleh ◽  
...  
Keyword(s):  
Residence Time ◽  
Flow Characteristics ◽  
Preliminary Test ◽  
Practical Experience ◽  
Operating Costs ◽  
Capital Costs ◽  
Computational Fluid Dynamics Cfd ◽  
Improved Performance ◽  
Work Done ◽  
Good Flow

A new design for syrup and juice clarifiers is presented. The design takes advantage of the considerably improved performance of clarifiers incorporating lamella plates, and the reasons for the improvement are outlined. Computational fluid dynamics (CFD) work done to simulate the performance is summarised. This design enables the residence time to be dramatically reduced and the simplified design leads to cheaper and better clarifiers. Practical experience with factory scale units is described, confirming the good flow characteristics. The results of preliminary test work on a factory syrup clarifier are presented, which is also shown to operate efficiently as a phosphatation clarifier. In addition the performance of a full-scale juice clarifier has been evaluated and compared with the performance of a Rapidorr clarifier. This work confirms the considerable advantages which this type of design provides, in realising substantial reductions in residence time, capital costs and operating costs.

scholarly journals Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1718
Author(s):  
Hasan Zobeyer ◽  
Abul B. M. Baki ◽  
Saika Nowshin Nowrin
Keyword(s):  
Turbulent Flow ◽  
Open Channel ◽  
Recirculation Zone ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Recirculation ◽  
Tandem Cylinders ◽  
Flow Development ◽  
The Mean ◽  
Recirculation Length

The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.

Design and optimization of bump (compression surface) for diverterless supersonic inlet

2021 ◽  
pp. 095441002110029
Author(s):  
Irsalan Arif ◽  
Hassan Iftikhar ◽  
Ali Javed
Keyword(s):  
Fitness Function ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Least Square ◽  
Pressure Recovery ◽  
Design Parameters ◽  
Inlet System ◽  
Design And Optimization ◽  
Supersonic Inlet

In this article design and optimization scheme of a three-dimensional bump surface for a supersonic aircraft is presented. A baseline bump and inlet duct with forward cowl lip is initially modeled in accordance with an existing bump configuration on a supersonic jet aircraft. Various design parameters for bump surface of diverterless supersonic inlet systems are identified, and design space is established using sensitivity analysis to identify the uncertainty associated with each design parameter by the one-factor-at-a-time approach. Subsequently, the designed configurations are selected by performing a three-level design of experiments using the Box–Behnken method and the numerical simulations. Surrogate modeling is carried out by the least square regression method to identify the fitness function, and optimization is performed using genetic algorithm based on pressure recovery as the objective function. The resultant optimized bump configuration demonstrates significant improvement in pressure recovery and flow characteristics as compared to baseline configuration at both supersonic and subsonic flow conditions and at design and off-design conditions. The proposed design and optimization methodology can be applied for optimizing the bump surface design of any diverterless supersonic inlet system for maximizing the intake performance.

scholarly journals Numerical and experimental study on turbulence statistics in a large fan-stirred combustion vessel

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
M. E. Morsy ◽  
J. Yang
Keyword(s):  
Isotropic Turbulence ◽  
Burning Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Initial Pressure ◽  
Dynamics Modeling ◽  
Turbulence Statistics ◽  
Experimental Conditions ◽  
Measured Velocity

Abstract Particle image velocimetry (PIV) has become a popular non-intrusive tool for measuring various types of flows. However, when measuring three-dimensional flows with two-dimensional (2D) PIV, there are some uncertainties in the measured velocity field due to out-of-plane motion, which might alter turbulence statistics and distort the overall flow characteristics. In the present study, three different turbulence models are employed and compared. Mean and fluctuating fields obtained by three-dimensional computational fluid dynamics modeling are compared to experimental data. Turbulence statistics such as integral length scale, Taylor microscale, Kolmogorov scale, turbulence kinetic energy, dissipation rate, and velocity correlations are calculated at different experimental conditions (i.e., pressure, temperature, fan speed, etc.). A reasonably isotropic and homogeneous turbulence with large turbulence intensities is achieved in the central region extending to almost 45 mm radius. This radius decreases with increasing the initial pressure. The influence of the third dimension velocity component on the measured characteristics is negligible. This is a result of the axisymmetric features of the flow pattern in the current vessel. The results prove that the present vessel can be conveniently adopted for several turbulent combustion studies including mainly the determination of turbulent burning velocity for gaseous premixed flames in nearly homogeneous isotropic turbulence. Graphic abstract

Tip Leakage Flow Characteristics Downstream of an Axial Flow Fan

1996 ◽  
Author(s):  
P. Puddu
Keyword(s):  
Vortex Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Tip Leakage Flow ◽  
Single Wire ◽  
Vortex System ◽  
Tip Leakage ◽  
Stress Components ◽  
Computer Controlled

The three-dimensional viscous flow characteristics and the complex vortex system downstream of the rotor of an industrial exial fan have been determined by an experimental investigation using hot-wire anemometer. Single-wire slanted and straight type probes have been rotated about the probe axis using a computer controlled stepper motor. Measurements have been taken at four planes behind the blade trailing edge. The results show the characteristics of the relative flow as velocity components, secondary flow and kinetic energy defect. Turbulence intensity and Reynolds stress components in the leakage vortex area are also presented. The evolution of the leakage vortex flow during the decay process has also been evaluated in terms of dimension, position and intensity.

Circulation control in magnetohydrodynamic rotating flows

2017 ◽  
Vol 829 ◽  
pp. 328-344 ◽  
Author(s):  
V. D. Borisevich ◽  
E. P. Potanin ◽  
J. Whichello
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Exact Analytical Solution ◽  
External Rotation ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Rotating Cylinder ◽  
Rotating Disc ◽  
Angular Velocities ◽  
Energy Equations

A model of a laminar viscous conducting flow, near a dielectric disc in a uniform magnetic field and in the presence of external rotation, is considered, where there is a uniform suction and an axial temperature gradient between the flow and the disc’s surface. It is assumed that the parameters of the suction or the magnetohydrodynamic (MHD) interaction are such that the nonlinear inertial terms, related to the circulation flow, are negligible in the differential equations of the MHD boundary layer on a rotating disc. Analysis of the motion and energy equations, taking the dependence of density on temperature into account, is carried out using the Dorodnitsyn transformation. The exact analytical solution for the boundary layer and heat transfer equations is obtained and analysed, neglecting the viscous and Joule dissipation. The dependence of the flow characteristics in the boundary layer on the rate of suction and the magnetic field induction is studied. It is shown that the direction of the radial flow in the boundary layer on a disc can be changed, not only by variation of the ratio between the angular velocities in the external flow and the boundary layer, but also by changing the ratio of the temperatures in these two flows, as well as by varying the hydrodynamic Prandtl number. The approximate calculation of a three-dimensional flow in a rotating cylinder with a braking disc (or lid) is carried out, demonstrating that a magnetic field slows the circulation velocity in a rotating cylinder.

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