scholarly journals Characteristics of Helium Gas with High Temperature and High Pressure Flowing through a 90-Degree Elbow

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Beibei Feng ◽  
Yanfei Sun ◽  
Xingtuan Yang ◽  
Shengqiang Li ◽  
Jiyuan Tu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Separation Process ◽  
Centrifugal Forces ◽  
Helium Flow ◽  
Primary Loop ◽  
Helium Gas ◽  
Simulation Results

There exists a certain 90° elbow structures in the helium circulation of HTGR-10. In terms of energy-saving and design simplification of reactor’s primary loop, 90° elbow can be used to measure the helium flow and the content of water vapor, both of which are significant in an accident. It is necessary to make an in-depth research of the flow characteristics of helium flowing 90° elbow. Simulation results indicate that fluid’s motion in the elbow is under the control of the centrifugal forces. Static pressure near the extrados is higher than that near the intrados. Boundary layer separation occurs at the latter half intrados of the elbow. The vortex emerges during the separation process and increases the energy dissipation. Velocity in the near-intrados region is higher than that in the near-extrados region, which is opposite to the pressure distribution trend. Under the action of the centrifugal forces, the secondary flow emerges in the latter half of the elbow and complicates the flow field by generating two vortexes which rotate in a different direction.

Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Interturbine Ducts

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Ali Mahallati ◽  
Xue-Feng Zhang ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Static Pressure ◽  
Computational Study ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Height Ratio ◽  
Inlet Swirl

This work, a continuation of a series of investigations on the aerodynamics of aggressive interturbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out by varying duct outlet-to-inlet area ratios (ARs) and mean rise angles while keeping the duct length-to-inlet height ratio, Reynolds number, and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the boundary layer separation and counter-rotating vortices in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing's first bend, whereas the duct AR mainly governed the second bend's static pressure rise. The combination of upstream wake flow and the first bend's adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing's first bend and moved farther upstream. At high ARs, a two-dimensional separation appeared on the casing and resulted in increased loss. Pressure loss penalties increased significantly with increasing duct mean rise angle and AR.

scholarly journals The Generation Mechanism of the Flow-Induced Noise from a Sail Hull on the Scaled Submarine Model

2018 ◽  
Vol 9 (1) ◽  
pp. 106 ◽  
Author(s):  
Yongwei Liu ◽  
Yalin Li ◽  
Dejiang Shang
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Boundary Layer Separation ◽  
Horseshoe Vortex ◽  
Generation Mechanism ◽  
Layer Separation ◽  
Eddy Simulation ◽  
Flow Control Devices ◽  
Flow Induced Noise ◽  
Simulation Results

Flow-induced noise from the sail hull, which is induced by the horseshoe vortex, the boundary layer separation and the tail vortex shedding, is a significant problem for the underwater vehicles, while has not been adequately studied. We have performed simulations and experiments to reveal the noise generation mechanism from these flows using the scaled sail hull with part of a submarine body. The large eddy simulation and the wavenumber–frequency spectrum are adopted for simulations. The frequency ranges from 10 Hz to 2000 Hz. The simulation results show that the flow-induced noise with the frequency less than 500 Hz is mainly generated by the horseshoe vortex; the flow-induced noise because of the tail vortex shedding is mainly within the frequency of shedding vortex, which is 595 Hz in the study; the flow-induced noise caused by the boundary layer separation lies in the whole frequency range. Moreover, we have conducted the experiments in a gravity water tunnel, and the experimental results are in good accordance with the simulation results. The results can lay the foundation for the design of flow control devices to suppress and reduce the flow-induced noise from the sail hull.

Effects of Bulk Flow Pulsations on Phase-Averaged and Time-Averaged Film-Cooled Boundary Layer Flow Structure

2001 ◽  
Vol 123 (3) ◽  
pp. 559-566 ◽  
Author(s):  
I.-S. Jung ◽  
P. M. Ligrani ◽  
J. S. Lee
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Streamwise Velocity ◽  
Phase Shifts ◽  
Bulk Flow ◽  
Pulsation Period ◽  
Pulsation Frequency ◽  
Flow Pulsations

Flow structure in boundary layers film cooled from a single row of round, simple angle holes, and subject to bulk flow pulsations, is investigated, including phase-averaged streamwise velocity variations, and alterations of time-averaged flow structure. The bulk flow pulsations are in the form of sinusoidal variations of velocity and static pressure, and are similar to flow variations produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Injection hole length to diameter ratio is 1.6, time-averaged blowing ratio is 0.50, and bulk flow pulsation frequencies range from 0–32 Hz, which gives modified Strouhal numbers from 0–1.02. Profiles of time-averaged flow characteristics and phase-averaged flow characteristics, measured in the spanwise/normal plane at x/d=5 and z/d=0, show that effects of pulsations are larger as imposed pulsation frequency goes up, with the most significant and dramatic changes at a frequency of 32 Hz. Phase shifts of static pressure (and streamwise velocity) waveforms at different boundary layer locations from the wall are especially important. As imposed pulsation frequency varies, this includes changes to the portion of each pulsation phase when the largest influences of static pressure waveform phase-shifting occur. At a frequency of 32 Hz, these phase shifts result in higher instantaneous injectant trajectories, and relatively higher injectant momentum levels throughout a majority of each pulsation period.

Flow Characteristics around Circular Cylinders with a Normal Slit

2017 ◽  
Vol 379 ◽  
pp. 48-57 ◽  
Author(s):  
Cheng Hsiung Kuo ◽  
Hwa Wei Lin ◽  
Chih Tao Chai ◽  
Fred Cheng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Flow ◽  
Rear Surface ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Phase Lock ◽  
Layer Flow

Alterations of boundary layer separation along the upper-rear surface of a baseline and slit cylinder and the formation of a vortex in the near-wake are investigated by particle image velocimetry (PIV) at Reynolds number 1000. The slit ratio (S/D) is 0.3. The phase-lock flow structures are referred to the time-dependent volume flux at the slit exit and are achieved by the modified phase-averaged technique. The alterations and the evolution of boundary-layer flow along the upper-rear surface are demonstrated by the phase-lock flow structures. It is found that the alternate blowing and suction at the slit exit serves as a perturbation to the boundary layer near the shoulder of the slit cylinder leading to a significant delay of flow separation and the flow reattachment of boundary-layer flow along the upper-rear surface of the cylinder. After perturbation, the vortex street behind a slit cylinder is more organized and stronger than that behind a baseline cylinder at Reynolds number 1000.

Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part B — Scale-Resolving Simulations

2015 ◽  
Author(s):  
Bastian Drechsel ◽  
Christoph Müller ◽  
Florian Herbst ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Numerical Approach ◽  
Pressure Recovery ◽  
Experimental Investigations ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Local Flow ◽  
Coherent Vortices

This paper examines the diffuser flow with consideration to turbine outflow conditions. The setup consists of a low-speed axial diffuser test rig, that represents a 1/10 scaled heavy-duty exhaust diffuser with an annular and a conical diffuser part. In part A of this paper it was shown through experimental investigation that the turbulent kinetic energy as well as the Reynolds shear stresses are the relevant physical parameters that correlate with diffuser pressure recovery. To complement the experimental investigations, unsteady scale-resolving CFD simulations are performed, applying the SST-SAS turbulence model. As a first step, the numerical approach is validated by means of the experimental data with regards to the diffuser’s integral parameters as well as the prediction of local flow characteristics. In a second step, the interaction of coherent vortices generated by the rotor and the diffuser’s boundary layer are analyzed by means of the validated SST-SAS results. These vortices are found to have a major impact on the boundary layer separation in the region immediately downstream of the rotor and at the diffuser inlet.

Numerical Simulation of Boundary Layer Separation Flow for Airfoil in a Wind Turbine

2009 ◽  
Author(s):  
Quan Liao ◽  
Wenzhi Cui ◽  
Longjian Li ◽  
Yihua Zhang
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Turbulent Viscosity ◽  
Boundary Layer Separation ◽  
Aerodynamic Performance ◽  
Separation Flow ◽  
Layer Separation ◽  
Simulation Results

The characteristic of static stall for an airfoil is very important for the design of wind turbine. As long as the detailed information of boundary layer separation flow around an airfoil is obtained, the static stall characteristics could be predicted appropriately. In this paper, both two dimensional (2D) and three dimensional (3D) mathematical models are implemented to simulate fluid flow around a NREL S809 airfoil. The steady state compressible Reynolds-Averaged Navier-Stokes equations are adopted and solved numerically in this paper. Both one-equation and two-equation turbulence models (i.e., Spalart-Allmaras and k-ω Shear Stress Transport models) are adopted, respectively, to solve the turbulent viscosity in this paper. The simulation results show that more detailed vortex structures are obtained by using 3D Spalart-Allmaras turbulence model at high attack angle as compared to the two-equation k-ω SST turbulence model, and the obtained aerodynamic performance of an airfoil with Spalart-Allmaras model agrees well with the available experimental data. Therefore, it seems that the 3D Spalart-Allmaras turbulence model is more capable to demonstrate the 3D characteristics of boundary layer separation flow than the k-ω SST model, and it is more efficient to predict the characteristics of static stall for the airfoil. Meanwhile, the simulation results also reveal that the 3D characteristics of separation flow play a very important role for the aerodynamic performance of airfoil after the static stall, and then the 2D mathematical model is no longer suitable to simulate the boundary layer separation flow around the airfoil.

Sub boundary-layer vortex generators for the control of shock induced separation

2006 ◽  
Vol 110 (1106) ◽  
pp. 215-226 ◽  
Author(s):  
G. S. Cohen ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Pressure Recovery ◽  
Flow Visualisation ◽  
Pressure Distributions ◽  
Pressure Profiles

Abstract The results of an investigation into the effects that sub-boundary layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation are presented. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Total pressure profiles, static pressure distributions, surface total pressure distributions, oil flow visualisation and Schlieren photographs were used in the results analysis. The effects of SBVG height, lateral spacing and location upstream of the shock were investigated. A novel curved shape SBVG was also evaluated and comparisons against the conventional flat vane type were made. The results show that in all but two cases, separation was completely eliminated. As expected, the largest SBVGs with height, h = 55%δ, provided the greatest pressure recovery and maximum mixing. However, the shock pressure rise was highest for this case. The experiments showed that the mid height SBVG array with the largest spacing provided similar results to the SBVG array with the largest height. Reducing the distance to shock to 10δ upstream also showed some improvement over the SBVG position of 18δ upstream. It was suggested that total elimination of the separated region may not be required to achieve a balance of improved static pressure recovery whilst minimising the pressure rise through the shock. The effect of curving the SBVGs provided an improved near wall mixing with an improved static and surface total pressure recovery downstream of the separation line. The optimum SBVG for the current flow conditions was found to be the curved vanes of h = 40%δ, with the largest spacing, located at 18δ upstream of the shock. Overall, it was apparent from the results that in comparison to larger vortex generators with a height comparable to δ, for SBVGs the parameters involved become more important in order to obtain the highest degree of mixing from a given SBVG configuration.

Numerical Simulation of the Supersonic Inlet Flow Field

2010 ◽  
Vol 29-32 ◽  
pp. 2119-2123
Author(s):  
Da Min Cao ◽  
Hong Yang Lv ◽  
Xing Yuan Zhang ◽  
Sheng Bin Hu
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Static Pressure ◽  
Pressure Rise ◽  
Back Pressure ◽  
Supersonic Inlet ◽  
Simulation Results ◽  
Cfd Method

The 2-D internal steady flow of the scramjet inlet-isolator was numerically simulated by the CFD method. The static pressure contours of the scramjet inlet-isolator under different boundary thickness and different back pressure were given. The numerical simulation results of two kinds of reasons which make the inlet un-start are obtained. One is the boundary layer thickness and another is the high back pressure at the exit of the isolator. When the boundary layer thickness increased, air can not smoothly flow into the inlet isolator and caused inlet un-start. Sameness along with the back pressure rise, have the phenomenon of inlet un-start, too. But the reason of un-start is disaffiliate. In the text analyzed the reasons of un-start phenomenon which from two different perspectives on the problem.

Influence of the height of the vortex generators in the control of shock-induced separation of the boundary layers

2008 ◽  
Vol 112 (1133) ◽  
pp. 415-420
Author(s):  
G. S. Cohen ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Flow Visualisation ◽  
Near Surface ◽  
Pressure Distributions

Abstract Experiments have been conducted to assess the effects that sub-boundary-layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Detailed measurements of a fully developed, flat plate turbulent boundary layer were used in order to assess the performance of ten different SBVG configurations. The SBVG performance was assessed by comparing total pressure profiles measured upstream of separation and downstream of reattachment. Static pressure distributions, near surface total pressure distributions, oil flow visualisation and Schlieren photographs were also used. The effect of SBVG height was investigated. The results show the largest SBVGs with height, h = 55%δ, provided the greatest static pressure recovery and maximum mixing. However, the shock pressure rise (wave drag) was highest for this case.

scholarly journals Effects of shaft inclination angle on the capacity of smoke exhaust under tunnel fire

2017 ◽  
Vol 28 (1) ◽  
pp. 77-87 ◽  
Author(s):  
Yongzheng Yao ◽  
Shaogang Zhang ◽  
Long Shi ◽  
Xudong Cheng
Keyword(s):  
Boundary Layer ◽  
Inclination Angle ◽  
Influence Factor ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Road Tunnel ◽  
Smoke Control ◽  
Layer Separation ◽  
Tunnel Fires ◽  
Tunnel Fire

Vertical shaft is one of the most important approaches for smoke control under tunnel fires. However, the boundary layer separation is a common phenomenon of hampering the smoke exhaust for vertical shafts. A tilted shaft has been proposed to solve problems and improve the capacity of smoke exhaust. In this study, the effect of shaft inclination angle (θ decreases from 90° to 14°) and shaft height on the capacity of smoke exhaust was addressed numerically. A series of scenarios were simulated in a full-scale road tunnel. Numerical results showed that the tilted shaft could eliminate the boundary layer separation. However, small shaft inclination angle could lead to a relatively higher resistance to the smoke and a smaller cross-section area of shaft, which could have an adverse effect on the capacity. Under these two factors, an optimal inclination angle exists in the shaft of around 76° in this study. Based on the smoke flow characteristics and exhaust effect, the inclination angle was roughly divided into three regions. The main influence factor of the inclination angle on the mass flow rate of smoke in each region was examined. For a comprehensive consideration, the low and slightly tilted shaft was applied to tunnel fires, which can improve the capacity of smoke exhaust obviously.

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