scholarly journals Implementation of a Compressor Face Boundary Condition Based on Small Disturbances

2000 ◽  
Vol 123 (2) ◽  
pp. 386-391 ◽  
Author(s):  
John W. Slater ◽  
Gerald C. Paynter
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Acoustic Response ◽  
Acoustic Disturbance ◽  
Disturbance Model ◽  
Stagger Angle ◽  
Large Improvement ◽  
Small Disturbances

A compressor-face boundary condition that models the unsteady interactions of acoustic and convective velocity disturbances with a compressor has been implemented into a three-dimensional computational fluid dynamics code. Locally one-dimensional characteristics along with a small-disturbance model are used to compute the acoustic response as a function of the local stagger angle and the strength and direction of the disturbance. Simulations of the inviscid flow in a straight duct, a duct coupled to a compressor, and a supersonic inlet demonstrate the behavior of the boundary condition in relation to existing boundary conditions. Comparisons with experimental data show a large improvement in accuracy over existing boundary conditions in the ability to predict the reflected disturbance from the interaction of an acoustic disturbance with a compressor.

scholarly journals Implementation of a Compressor Face Boundary Condition Based on Small Disturbances

2000 ◽  
Author(s):  
John W. Slater ◽  
Gerald C. Paynter
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Acoustic Response ◽  
Acoustic Disturbance ◽  
Disturbance Model ◽  
Stagger Angle ◽  
Large Improvement ◽  
Small Disturbances

A compressor-face boundary condition that models the unsteady interactions of acoustic and convective velocity disturbances with a compressor has been implemented into a three-dimensional computational fluid dynamics code. Locally one-dimensional characteristics along with a small-disturbance model are used to compute the acoustic response as a function of the local stagger angle and the strength and direction of the disturbance. Simulations of the inviscid flow in a straight duct, a duct coupled to a compressor, and a supersonic inlet demonstrate the behavior of the boundary condition in relation to existing boundary conditions. Comparisons with experimental data show a large improvement in accuracy over existing boundary conditions in the ability to predict the reflected disturbance from the interaction of an acoustic disturbance with a compressor.

scholarly journals Bootstrapping boundary-localized interactions

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Connor Behan ◽  
Lorenzo Di Pietro ◽  
Edoardo Lauria ◽  
Balt C. van Rees
Keyword(s):  
Boundary Condition ◽  
Scalar Field ◽  
Boundary Conditions ◽  
Parameter Space ◽  
Three Dimensional ◽  
Conformal Boundary ◽  
Dimensional Boundary ◽  
Dirichlet And Neumann Conditions ◽  
Boundary Fields ◽  
Boundary Dynamics

Abstract We study conformal boundary conditions for the theory of a single real scalar to investigate whether the known Dirichlet and Neumann conditions are the only possibilities. For this free bulk theory there are strong restrictions on the possible boundary dynamics. In particular, we find that the bulk-to-boundary operator expansion of the bulk field involves at most a ‘shadow pair’ of boundary fields, irrespective of the conformal boundary condition. We numerically analyze the four-point crossing equations for this shadow pair in the case of a three-dimensional boundary (so a four-dimensional scalar field) and find that large ranges of parameter space are excluded. However a ‘kink’ in the numerical bounds obeys all our consistency checks and might be an indication of a new conformal boundary condition.

Assessment of Various Inviscid-Wall Boundary Conditions: Applications to NACA65 Compressor Blade

2011 ◽  
Author(s):  
Habib Khazaei ◽  
Ali Madadi ◽  
Mohammad Jafar Kermani
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Solid Wall ◽  
Inviscid Flow ◽  
Compressor Blade ◽  
The Body ◽  
Wall Boundary Condition ◽  
Velocity Magnitude ◽  
Wall Boundary ◽  
Wall Boundary Conditions

Boundary condition is one of the major factors to influence the numerical stability and solution accuracy in numerical analysis. One of the most important physical boundary conditions in the flow field analysis is the wall boundary condition imposed on the body surfaces. To solve a three-dimensional compressible Euler equation (with five coupled PDE’s), totally five boundary conditions at the body surfaces should be prescribed. The momentum equation in the direction normal to the inviscid solid wall provides the pressure at the surface of the wall. For the cases with no-heat source or sink, the total temperature at the wall and the incoming flow should remain constant, when the steady condition is prevailed. The no-penetration condition through the solid wall and slip condition provides an equation relating the three velocity components. Assuming identical flow direction at the wall with the adjacent node, the last thing is the velocity magnitude that should be cast in such a way to give accurate, stable and robust solution. In this paper, four different methods for calculation of the wall velocity magnitude are proposed and applied to an identical test case of subsonic and supersonic flows such as: (1) Inviscid flow in a 3D converging-diverging nozzle, (2) Inviscid subsonic flow in a single 90° elbow, (3) Inviscid supersonic flow over a wedge, and (4) Inviscid flow through a compressor blade geometry of NACA 65410. A recently implemented 3D in-house CFD code (based on the flux difference splitting scheme of Roe (1981)) is used to compute compressible flows in generalized coordinates. It is found that the way to specify the additional numerical wall boundary condition strongly affects the overall stability and accuracy of the solution. It is concluded that there is no best boundary condition to cover all of the test cases, but the best wall boundary condition should be introduced very carefully for each type of flow.

scholarly journals Application of Time-Shifted Boundary Conditions to a 3D Euler/Navier-Stokes Aeroelastic Code

1998 ◽  
Author(s):  
R. Srivastava ◽  
Milind A. Bakhle ◽  
Theo G. Keith ◽  
G. L. Stefko
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Inviscid Flow ◽  
Computer Time ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Blade Passage ◽  
Unsteady Aerodynamic ◽  
Time Marching ◽  
Phase Angles

In the present work the unsteady aerodynamic characteristics of harmonically oscillating fan blades are investigated by applying a time-shifted boundary condition at the periodic boundaries. The direct-store method is used to implement the time-shifted boundary condition in a time-marching Euler/Navier-Stokes solver. Inviscid flow calculations for a flat plate helical fan, in a single-blade passage domain, are used to verify the analysis. The results obtained show good correlation with other published results as well as with the same solver using multiple blade passages stacked together. Significant savings in computer time is realized, especially for smaller phase angles.

scholarly journals A Simplified Method for 3-D Potential Flow in Turbomachinery Using Vortex Sheet Boundary Conditions

1987 ◽  
Author(s):  
H. Jiang ◽  
R. Cai ◽  
Y. Zhu
Keyword(s):  
Boundary Conditions ◽  
Potential Flow ◽  
Three Dimensional ◽  
Vortex Sheet ◽  
Inviscid Flow ◽  
Three Dimensional Flow ◽  
Blade Row ◽  
Simplified Method ◽  
Outlet Flow ◽  
Two Sides

Within the framework of inviscid flow theory, the character of three-dimensional flow in turbomachinery blade row is discussed. One of the important differences between 3-D and 2-D flow in turbomachinery is the discontinuity of velocity at the two sides of trailing edge and across downstream boundary. The inconsistency of the traditional periodicity conditions for downstream boundary and of the axisymmetric assumption for outlet flow with the three-dimensionality of turbomachinery flow is discussed also. For 3-D potential flow, the vortex sheet boundary conditions (VSBC) for downstream boundary and a fully 3-D condition for outlet flow are presented. A simplified method is developed by implementation of VSBC on a fixed vortex boundary in order to predict the fully 3-D flow in blade passage as well as downstream of blade row. In the present investigation two calculations are carried out. In one calculation the traditional boundary conditions are imposed while in another one the VSBC are used to demonstrate the capability of the newly develped boundary conditions. The agreement between some calculated results and the theoretical analysis is very well.

MEMS-Scale Turbomachinery Based Vacuum Roughing Pump

2013 ◽  
Author(s):  
Anthony J. Gannon ◽  
Garth V. Hobson ◽  
Michael J. Shea ◽  
Christopher S. Clay ◽  
Knox T. Millsaps
Keyword(s):  
Boundary Condition ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Boundary Conditions ◽  
Knudsen Number ◽  
Slip Flow ◽  
Three Dimensional ◽  
Slip Boundary Condition ◽  
Slip Boundary ◽  
Three Dimensional Simulations

This study forms part of a program to develop a micro-electro-mechanical-systems (MEMS) scale turbomachinery based vacuum pump and investigates the roughing portion of such a system. Such a machine would have many radial stages with the exhaust stages operating near atmospheric conditions while the inlet stages operate at near vacuum conditions. In low vacuum such as those to the inlet of a roughing pump the flow can still be treated as a continuum however the no-slip boundary condition is not accurate. The Knudsen number becomes a dominant non-dimensional parameter in these machines due to their small size and low pressures. As the Knudsen number increases slip flow becomes present at the walls. The study begins with a basic overview on implementing the slip wall boundary condition in a commercial code by specifying the wall shear stress based on the mean-free-path of the gas molecules. This is validated against an available micro-Poiseuille classical solution at Knudsen numbers between 0.001–0.1 with reasonable agreement found. The method of specifying the wall-shear stress is then applied to a generic MEMS scale roughing pump stage that consists of two stators and a rotor operating at a nominal absolute pressure of 500 Pa. The zero flow case was simulated in all cases as the pump down time for these machines is small due to the small volume being evacuated. Initial transient two-dimensional simulations are used to evaluate three boundary conditions, classical no-slip, specified-shear and slip-flow. It is found that the stage pressure rise increased as the flow began to slip at the walls. In addition it was found that at lower pressures the pure slip boundary condition resulted in very similar predictions to the specified shear simulations. As the specified-shear simulations are computationally expensive it is reasonable to use slip-flow boundary conditions. This approach was used to perform three-dimensional simulations of the stage. Again the stage pressure increased when slip-flow was present compared with the classical no-slip boundaries. A characteristic of MEMS scale turbomachinery are the large relative tip gaps requiring three-dimensional simulations. A tip gap sensitivity study was performed and it was found that when no-slip boundaries were present the pressure ratio increased significantly with decreasing tip gap. When slip-flow boundaries were present this relationship was far weaker.

Simulation of Outgoing Waves at the Boundaries of a Three Dimensional Fully Nonlinear Numerical Wave Tank

2003 ◽  
Author(s):  
Alaa M. Mansour ◽  
A. Neil Williams
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Nonlinear Wave ◽  
Three Dimensional ◽  
Damping Factor ◽  
Numerical Wave Tank ◽  
Frequency Range ◽  
Wave Tank ◽  
Numerical Wave ◽  
Numerical Beach

This paper presents an efficient boundary condition to simulate outgoing waves at the boundaries of the truncated domain in a three-dimensional numerical wave tank. The present study is based on coupling of two prescribed boundary conditions, namely, numerical beach and Orlanski boundary conditions. The use of a numerical beach is known to be efficient in the high frequency range, however, Orlanski boundary condition has been successfully applied in the low frequency range. The proposed study is based on coupling of these two prescribed boundary conditions to make use of their complementary bandwidths. The model has been calibrated to determine the optimal length and the most efficient damping factor within the numerical beach region. The semi-infinite tank has then been used to simulate nonlinear wave propagation in shallow water. The results of this simulation have been verified through a comparison with previous published experimental measurements. The model is then further applied to simulate the nonlinear wave diffraction by and the associated hydrodynamic forces on a bottom mounted surface piercing circular uniform cylinder. Further investigation of the efficiency of the coupled boundary condition when using a spatially-varying damping factor in the presence of scattered wave field is presented.

scholarly journals Effect of Periphery Fixity on Ballistic Limit of Thin Aluminum Plate Subjected to Blunt and Ogival Projectile Impact

2014 ◽  
Vol 19 (2) ◽  
pp. 379-395
Author(s):  
G. Tiwari ◽  
M.A. Iqbal ◽  
P.K. Gupta
Keyword(s):  
Boundary Condition ◽  
Finite Element ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Ballistic Limit ◽  
Element Analysis ◽  
Explicit Finite Element ◽  
Projectile Impact ◽  
Thin Aluminum ◽  
The Finite Element Analysis

Abstract Three-dimensional numerical simulations were carried out with the ABAQUS/explicit finite element code to study the influence of target boundary conditions on its ballistic limit. 1mm thick 1100-H12 aluminum target of 255 mm span diameter was hit by 19 mm diameter and 50.8 mm length blunt nosed projectile. The mass of the projectile was kept as 52.5 gm. The boundary condition effects on the ballistic limit were investigated by varying the target periphery boundary condition as fully clamped and partially clamped target (75%, 50% and 25%) subjected to projectile impact. The energy absorption and ballistic limit of the target was found to be significantly affected by the boundary conditions. Some of the finite element analysis results were compared with experimental and numerical results reported in international literature and a good agreement between the two was found.

Effects of Downstream Stator Pressure Field on Upstream Rotor Performance

1996 ◽  
Author(s):  
Martin B. Graf ◽  
Om P. Sharma
Keyword(s):  
Boundary Condition ◽  
Static Pressure ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Radial Pressure ◽  
Pressure Profile ◽  
Inviscid Flow ◽  
Tip Clearance ◽  
Radial Profiles ◽  
Rotor Loss

Results of numerical simulations conducted for a high pressure compressor rotor with two different levels of tip clearance are presented. A three-dimensional, steady, Reynolds-Averaged Navier-Stokes code was utilized to perform the computations. The simulations were executed over a range of flow coefficients by specifying different axisymmetric radial profiles in static pressure downstream of the rotor. In this manner, the effect of the downstream stator row was approximated using a simple, circumferentially averaged, radial pressure profile as the boundary condition behind the rotor. The back pressure profiles utilized were those deduced from inviscid flow computations for two different stator designs: (1) a conventional radial stator, and (2) a three-dimensional “bowed” stator. Results of the rotor simulations with nominal tip clearance show that the boundary condition induced by the bowed stator causes a 2% decrease in rotor pressure rise capability, and a 9% increase in rotor loss as compared with the conventional stator. In addition, as the tip clearance is increased to twice the nominal value, the rotor loss grows at a rate 25% higher for the rotor subjected to the bowed stator pressure profile. Accompanying this is a dramatic reduction in rotor speedline slope and pressure rise capability. Analysis of the simulations shows these effects to be linked to the response of the rotor tip clearance vortex to the exit pressure profile set by the downstream stator. These results indicate the need to accurately model the effects of the radial variation in static pressure imposed by the downstream airfoil rows.

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