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.

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.

Temperature Fluctuations Inside the Infinite Heated Slab Cooled With Turbulent Flow From Both Sides

2013 ◽  
Author(s):  
Iztok Tiselj
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Solid Wall ◽  
Flow Direction ◽  
Temperature Fluctuations ◽  
Thermal Fluctuations ◽  
Temperature Fields ◽  
Slab Thickness ◽  
Computational Domain ◽  
Flux Boundary Condition

Direct Numerical Simulation (DNS) of fully developed velocity and passive scalar temperature fields in two-dimensional turbulent channel flow was coupled with the unsteady conduction in the idealized slab heated with constant volumetric heat source. Similar geometry can be found in some experimental nuclear reactors with fuel in the form of parallel slabs. Beside streamwise and spanwise directions, periodicity of the computational domain was assumed also in the wall-normal direction. Simulations were performed at constant friction Reynolds number 180 and Prandtl number 1, and with various geometrical and material properties of the heated slab. Due to the periodicity, the same Reynolds number and the same flow direction is assumed on both sides of the slab. Results of the simulations predict penetration of the turbulent temperature fluctuations into the solid wall. For thick slab, temperature fluctuations from both sides of the slab do not interfere. As the slab gets thinner, fluctuations from both sides interfere and tend to a finite value as the slab thickness limits toward zero. However, due to the non-coherent turbulent flows on each side of the slab, thermal fluctuations of the zero-thickness slab are actually lower than in the case of the zero-thickness wall heated by the same turbulent flow on one side but cooled by the constant heat flux boundary condition on the other side. Results of the present study can serve as benchmarks for less accurate mathematical models used to predict temperature fluctuations and thermal fatigue in realistic conditions.

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