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.

Unsteady Simulations of a Counter-Rotating Aspirated Compressor

2013 ◽  
Author(s):  
Robert D. Knapke ◽  
Mark G. Turner
Keyword(s):  
Boundary Condition ◽  
Flow Field ◽  
Boundary Conditions ◽  
Mass Flow ◽  
Solid Wall ◽  
Flow Path ◽  
Computational Domain ◽  
Wall Boundary ◽  
Wall Boundary Conditions ◽  
Adiabatic Boundary Condition

An unsteady analysis of the MIT counter-rotating aspirated compressor (CRAC) has been conducted using the Numeca FINE™/Turbo 3D viscous turbulent solver with the Non-Linear Harmonic (NLH) method. All three blade rows plus the aspiration slot and plenum were included in the computational domain. Both adiabatic and isothermal solid wall boundary conditions were applied and simulations with and without aspiration were completed. Comparison of the aspirated case with data is good. When compared to the adiabatic boundary condition, the isothermal boundary condition solutions showed improvements in predicting stage performance, most notably at the endwalls. The aspiration has a significant impact on the flow field and provides a 4.2% increase in efficiency over the non-aspirated case. Although the slot and plenum had been designed to aspirate 1% of the inlet mass flow, the experiment and simulations show that it chokes at about 0.5%. Details of the aspiration flow path choking mechanism, which was previously not well understood, are presented.

Implicit particle wall boundary condition in molecular dynamics

2008 ◽  
Vol 222 (5) ◽  
pp. 855-864 ◽  
Author(s):  
P Spijker ◽  
H M M ten Eikelder ◽  
A J Markvoort ◽  
S V Nedea ◽  
P A J Hilbers
Keyword(s):  
Molecular Dynamics ◽  
Boundary Condition ◽  
Boundary Conditions ◽  
Solid Wall ◽  
Computational Cost ◽  
Md Simulations ◽  
Parallel Plates ◽  
Wall Boundary Condition ◽  
Wall Boundary ◽  
Different Temperatures

Thin film and nano-tube manufacturing, micro-channel cooling, and many other similar interesting techniques demand the prediction of heat transfer characteristics at the nanometre scale. In this respect, the transport properties at gas—solid and liquid—solid interfaces are very important. The processes at these interfaces can be studied in detail with molecular dynamics (MD) simulations. However, the computational cost involved in simulating the solid wall currently restrains the size of channels, which can be simulated. Therefore, the solid wall is sometimes replaced by boundary conditions, which often compromise on macroscopic quantities, such as density, temperature, pressure, and heat flux. In the current paper, a new particle wall boundary condition is presented, which is in good agreement with existing boundary conditions, but allows for the pressure calculation. This new boundary condition is based on averaging the contributions of an explicit solid wall and is derived using knowledge on common practices in MD algorithms, such as truncation and shifting. Moreover, it allows for different crystal lattices to be included in the new potential. The applicability of the new method is demonstrated by MD simulations of a gas between two parallel plates at different temperatures and densities. Furthermore, these simulations are compared with explicit wall simulations and existing boundary conditions.

Effect of Constant Heat Flux Boundary Condition on Wall Temperature Fluctuations

2000 ◽  
Vol 123 (2) ◽  
pp. 213-218 ◽  
Author(s):  
A. Mosyak ◽  
E. Pogrebnyak ◽  
G. Hetsroni
Keyword(s):  
Boundary Conditions ◽  
Wall Temperature ◽  
Solid Wall ◽  
Rectangular Channel ◽  
Temperature Fluctuations ◽  
Temperature Fields ◽  
Flux Boundary Condition ◽  
Wall Boundary ◽  
Wall Boundary Conditions ◽  
Thermal Entrance

An experimental study of the wall temperature fluctuations under different thermal-wall boundary conditions was carried out. Statistics obtained from the experiments are compared with existing experimental and numerical data. The wall temperature fields are also examined in terms of the coherent thermal structures. In addition the effect of the thermal entrance region on the wall temperature distribution is also studied. For water flow in a flume and in a rectangular channel, the mean spacing of the thermal streaks does not depend on the thermal entrance length and on the type of thermal-wall boundary conditions. The wall temperature fluctuations depend strongly on the type of wall thermal boundary conditions. Overall, the picture that emerges from this investigation confirms the hypothesis that moderate-Prandtl-number heat transfer at a solid wall is governed by the large-scale coherent flow structures.

Rough Wall Boundary Condition Derivation for Particle Continuum Equations: Validation From LES/DPS of Gas-Solid Turbulent Channel Flow

2006 ◽  
Author(s):  
N. A. Konan ◽  
O. Simonin ◽  
K. D. Squires
Keyword(s):  
Boundary Condition ◽  
Carrier Phase ◽  
Turbulent Channel Flow ◽  
Rough Wall ◽  
Wall Roughness ◽  
Continuum Approach ◽  
Two Phase ◽  
Wall Boundary Condition ◽  
Wall Boundary ◽  
Wall Boundary Conditions

This paper presents a theoretical approach leading to the establishment of practical rough wall boundary conditions within the framework of continuum approach for the dispersed phase simulation in two-phase flows. The study is based on a similar statistical description of the rebounds on the wall adopted by Sakiz et al. [1] and take into account “the shadow effect” as proposed by Sommerfeld et al [2]. The validity of these eulerian rough wall boundary condition formulations is checked by carrying out LES of carrier phase flow in channel and coupled with DPS, with a given wall roughness standard deviation.

A Unified Wall-Boundary Condition for the Lattice Boltzmann Method and its Application to Force Evaluation

2014 ◽  
Vol 31 (1) ◽  
pp. 55-68 ◽  
Author(s):  
S.-Y. Lin ◽  
Y.-H. Chin ◽  
F.-L. Yang ◽  
J.-F. Lin ◽  
J.-J. Hu ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Solid Wall ◽  
Immersed Boundary ◽  
Equilibrium Pressure ◽  
Good Convergence ◽  
Wall Boundary Condition ◽  
Wall Boundary ◽  
Boltzmann Method

AbstractA unified wall-boundary condition for the pressure-based lattice Boltzmann method (LBM) is proposed. The present approach is developed from the direct-forcing technique in the immersed boundary method and is derived from the equilibrium pressure distribution function. The proposed method can handle many kinds of wall boundaries, such as fixed wall and moving wall boundaries, in the same way. It is found that the new method has the following advantages: (1) simple in concept and easy to implement, (2) higher-order accuracy, (3) mass conservation, and (4) a stable and good convergence rate. Based on this wall-boundary condition, if a solid wall is immersed in a fluid, then by applying Gauss's theorem, the formulas for computing the force and torque acting on the solid wall from fluid flow are derived from the volume integrals over the solid volume instead of from the surface integrals over the solid surface. Based on the pressure-based LBM, inlet and outlet boundary conditions are also proposed. The order of accuracy of the proposed boundary condition is demonstrated with the errors of the velocity field, wall stress, and gradients of velocity and pressure. The steady flow past a circular cylinder is simulated to demonstrate the efficiency and capabilities of the proposed unified method.

scholarly journals Effect of Wall Boundary Conditions on a Wall-Modeled Large-Eddy Simulation in a Finite-Difference Framework

Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 112
Author(s):  
H. Jane Bae ◽  
Adrián Lozano-Durán
Keyword(s):  
Boundary Condition ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Eddy Viscosity ◽  
Grid Point ◽  
Eddy Simulation ◽  
Wall Boundary ◽  
Wall Boundary Conditions ◽  
Wide Range ◽  
Large Eddy

We studied the effect of wall boundary conditions on the statistics in a wall-modeled large-eddy simulation (WMLES) of turbulent channel flows. Three different forms of the boundary condition based on the mean stress-balance equations were used to supply the correct mean wall shear stress for a wide range of Reynolds numbers and grid resolutions applicable to WMLES. In addition to the widely used Neumann boundary condition at the wall, we considered a case with a no-slip condition at the wall in which the wall stress was imposed by adjusting the value of the eddy viscosity at the wall. The results showed that the type of boundary condition utilized had an impact on the statistics (e.g., mean velocity profile and turbulence intensities) in the vicinity of the wall, especially at the first off-wall grid point. Augmenting the eddy viscosity at the wall resulted in improved predictions of statistics in the near-wall region, which should allow the use of information from the first off-wall grid point for wall models without additional spatial or temporal filtering. This boundary condition is easy to implement and provides a simple solution to the well-known log-layer mismatch in WMLES.

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