Generation of Turbulent Inlet Conditions for Thermal/Velocity Boundary Layer Simulations

2006 ◽  
Author(s):  
Guillermo Araya ◽  
Elaine Bohr ◽  
Kenneth Jansen ◽  
Luciano Castillo ◽  
K Peterson
Keyword(s):  
Boundary Layer ◽  
Thermal Velocity ◽  
Velocity Boundary Layer ◽  
Inlet Conditions

A New Method to Measure Prandtl Number and Thermal Conductivity of Fluids

1957 ◽  
Vol 24 (1) ◽  
pp. 25-28
Author(s):  
E. R. G. Eckert ◽  
T. F. Irvine
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Prandtl Number ◽  
High Velocity ◽  
Atmospheric Pressure ◽  
New Method ◽  
Test Results ◽  
Test Setup ◽  
Velocity Boundary Layer ◽  
Layer Flow

Abstract A new method is described by which the Prandtl number and indirectly the thermal conductivity of fluids can be measured. The method is based on the fact that a well-established, unique relation exists between the Prandtl number and the recovery factor for laminar high-velocity boundary-layer flow. The test setup is described which has been devised for such measurements, and test results are presented for air at atmospheric pressure and temperatures between 60 and 350 F.

Exponentially Decaying Heat Source on MHD Tangent Hyperbolic Two-Phase Flows over a Flat Surface with Convective Conditions

2018 ◽  
Vol 387 ◽  
pp. 286-295 ◽  
Author(s):  
S.U. Mamatha ◽  
Chakravarthula S.K. Raju ◽  
Putta Durga Prasad ◽  
K.A. Ajmath ◽  
Mahesha ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Differential Equations ◽  
Heat Source ◽  
Thermal Boundary Layer ◽  
Energy Transport ◽  
Weissenberg Number ◽  
Dust Particles ◽  
Convective Conditions ◽  
Two Phase ◽  
Velocity Boundary Layer

The present framework addresses Darcy-Forchheimer steady incompressible magneto hydrodynamic hyperbolic tangent fluid with deferment of dust particles over a stretching surface along with exponentially decaying heat source. To control the thermal boundary layer Convective conditions are considered. Appropriate transformations were utilized to convert partial differential equations (PDEs) into nonlinear ordinary differential equations (NODEs). To present numerical approximations Runge-Kutta Fehlberg integration is implemented. Computational results of the flow and energy transport are interpreted for both fluid and dust phase with the support of graph and table illustrations. It is found that non-uniform inertia coefficient of porous medium decreases velocity boundary layer thickness and enhances thermal boundary layer. Improvement in Weissenberg number improves the velocity boundary layer and declines the thermal boundary layer.

Engine Design Strategy for Boundary Layer Ingesting Propulsion Systems With Multiple Non-Symmetric Engine Inlet Conditions

2013 ◽  
Author(s):  
Jonathan C. Gladin ◽  
Brian K. Kestner ◽  
Jeff S. Schutte ◽  
Dimitri N. Mavris
Keyword(s):  
Boundary Layer ◽  
Design Strategy ◽  
Total Power ◽  
Design Strategies ◽  
Fuel Burn ◽  
Practical Strategy ◽  
Engine Design ◽  
Vehicle Aerodynamics ◽  
Inlet Conditions ◽  
The Impact

Boundary layer ingesting inlets for hybrid wing body aircraft have been investigated at some depth in recent years due to the theoretical potential for fuel burn savings. Such savings derive from the ingestion of a portion of the low momentum wake into the propulsor to reenergize the flow, thus yielding total power savings and reducing required block fuel burn. A potential concern for BLI is that traditional concepts such as “thrust” and “drag” become less clearly defined due to the interaction between the vehicle aerodynamics and the propulsive thrust achieved. One such interaction for the HWB concept is the lateral location of the inlet on the upper surface which determines the effective Reynolds number at the point of ingestion. This is an important factor in determining the amount of power savings achieved by the system, since the boundary layer, displacement, and momentum thicknesses are functions of the local chord length and airfoil shape which are all functions of the lateral location of the engine. This poses a design challenge for engine layouts with more than two engines as at least one or more of the total engines will be operating at a different set of changing inlet conditions throughout the flight envelope. As a result, the engine operating point and propulsive performance will be different between outboard and inboard engines at flight conditions with appreciable boundary layer influence including key flight conditions for engine design: takeoff, top of climb, and cruise. The optimal engine design strategy in terms of performance to address this issue is to design separate engines with similar thrust performance. This strategy has significant challenges such as requiring the manufacturing and certification of two different engines for one vehicle. A more practical strategy is to design a single engine that performs adequately at the different inlet conditions but may not achieve the full benefits of BLI. This paper presents a technique for cycle analysis which can account for the disparity between inlet conditions. This technique was used for two principal purposes: first to determine the effect of the inlet disparity on the performance of the system; second, to analyze the various design strategies that might mitigate the impact of this effect. It is shown that a single engine can be sized when considering both inboard and outboard engines simultaneously. Additionally, it is shown that there is a benefit to ingesting larger mass flows in the inboard engine for the case with large disparity between the engine inlets.

Rayleigh number scaling in numerical convection

1996 ◽  
Vol 310 ◽  
pp. 139-179 ◽  
Author(s):  
Robert M. Kerr
Keyword(s):  
Boundary Layer ◽  
Rayleigh Number ◽  
Large Scale ◽  
Stokes Equations ◽  
Good Evidence ◽  
Navier Stokes ◽  
Fixed Temperature ◽  
Navier Stokes Equations ◽  
Local Boundary ◽  
Velocity Boundary Layer

Using direct simulations of the incompressible Navier-Stokes equations with rigid upper and lower boundaries at fixed temperature and periodic sidewalls, scaling with respect to Rayleigh number is determined. At large aspect ratio (6:6:1) on meshes up to 288 × 288 × 96, a single scaling regime consistent with the properties of ‘hard’ convective turbulence is found for Pr = 0.7 between Ra = 5 × 104 and Ra = 2 × 107. The properties of this regime include Nu ∼ RaβT with βT = 0.28 ≈ 2/7, exponential temperature distributions in the centre of the cell, and velocity and temperature scales consistent with experimental measurements. Two velocity boundary-layer thicknesses are identified, one outside the thermal boundary layer that scales as Ra−1/7 and the other within it that scales as Ra−3/7. Large-scale shears are not observed; instead, strong local boundary-layer shears are observed in regions between incoming plumes and an outgoing network of buoyant sheets. At the highest Rayleigh number, there is a decade where the energy spectra are close to k−5/3 and temperature variance spectra are noticeably less steep. It is argued that taken together this is good evidence for ‘hard’ turbulence, even if individually each of these properties might have alternative explanations.

scholarly journals Experimental Study of a Boundary Layer on a Heated Flat Plate

2019 ◽  
Vol 213 ◽  
pp. 02002
Author(s):  
Pavel Antoš ◽  
Sergei Kuznetsov
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Heat Flux ◽  
Flat Plate ◽  
Hot Wire ◽  
Velocity Boundary Layer ◽  
Temperature Boundary Layer ◽  
Temperature Boundary ◽  
Measurement Experiment ◽  
Set Up

Boundary layer on a uniformly heated flat plate was studied experimentally. Both, the velocity boundary layer and the temperature boundary layer, was investigated by means of hot-wire anemometry. A probe with parallel wires was used for velocity-temperature measurement. Experiment was performed in the closed-circuit wind tunnel with several levels of heat flux at the wall. The wall temperature was set up in the interval from 20 ºC to 200 ºC.

scholarly journals Fractional Boundary Layer Flow and Heat Transfer Over a Stretching Sheet With Variable Thickness

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Lin Liu ◽  
Liancun Zheng ◽  
Yanping Chen ◽  
Fawang Liu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Stretching Sheet ◽  
Magnetic Parameter ◽  
Governing Equations ◽  
Velocity Boundary Layer ◽  
Flow And Heat Transfer ◽  
Temperature Boundary ◽  
Layer Flow ◽  
Fractional Parameter

The paper gives a comprehensive study on the space fractional boundary layer flow and heat transfer over a stretching sheet with variable thickness, and the variable magnetic field is applied. Novel governing equations with left and right Riemann–Liouville fractional derivatives subject to irregular region are formulated. By introducing new variables, the boundary conditions change as the traditional ones. Solutions of the governing equations are obtained numerically where the shifted Grünwald formulae are applied. Good agreement is obtained between the numerical solutions and exact solutions which are constructed by introducing new source items. Dynamic characteristics with the effects of involved parameters on the velocity and temperature distributions are shown and discussed by graphical illustrations. Results show that the velocity boundary layer is thicker for a larger fractional parameter or a smaller magnetic parameter, while the temperature boundary layer is thicker for a larger fractional parameter, a smaller exponent parameter, or a larger magnetic parameter. Moreover, it is thicker at a smaller y and thinner at a larger y for the velocity boundary layer with a larger exponent parameter while for the velocity and temperature boundary layers with a smaller weight coefficient.

Experimental studies of the viscous boundary layer properties in turbulent Rayleigh–Bénard convection

2008 ◽  
Vol 605 ◽  
pp. 79-113 ◽  
Author(s):  
CHAO SUN ◽  
YIN-HAR CHEUNG ◽  
KE-QING XIA
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Rayleigh Number ◽  
Power Law ◽  
Thermal Boundary Layer ◽  
Viscous Sublayer ◽  
Viscous Boundary Layer ◽  
Velocity Boundary Layer ◽  
Viscous Boundary

We report high-resolution measurements of the properties of the velocity boundary layer in turbulent thermal convection using the particle image velocimetry (PIV) technique and measurements of the temperature profiles and the thermal boundary layer. Both velocity and temperature measurements were made near the lower conducting plate of a rectangular convection cell using water as the convecting fluid, with the Rayleigh number Ra varying from 109 to 1010 and the Prandtl number Pr fixed at 4.3. From the measured profiles of the horizontal velocity we obtain the viscous boundary layer thickness δυ. It is found that δυ follows the classical Blasius-like laminar boundary layer in the present range of Ra, and it scales with the Reynolds number Re as δυ/H = 0.64Re−0.50±0.03 (where H is the cell height). While the measured viscous shear stress and Reynolds shear stress show that the boundary layer is laminar for Ra < 2.0 × 1010, two independent extrapolations, one based on velocity measurements and the other on velocity and temperature measurements, both indicate that the boundary layer will become turbulent at Ra ~ 1013. Just above the thermal boundary layer but within the mixing zone, the measured temperature r.m.s. profiles σT(z) are found to follow either a power law or a logarithmic behaviour. The power-law fitting may be slightly favoured and its exponent is found to depend on Ra and varies from −0.6 to −0.77, which is much larger than the classical value of −1/3. In the same region, the measured profiles of the r.m.s. vertical velocity σw(z) exhibit a much smaller scaling range and are also consistent with either a power-law or a logarithmic behaviour. The Reynolds number dependence of several wall quantities is also measured directly. These are the wall shear stress τw ~ Re1.55, the viscous sublayer δw ~ Re−0.91, the friction velocity uτ ~ Re0.80, and the skin-friction coefficient cf ~ Re−0.34. All of these scaling properties are very close to those predicted for a classical Blasius-type laminar boundary layer, except that of cf. Similar to classical shear flows, a viscous sublayer is also found to exist in the present system despite the presence of a nested thermal boundary layer. However, velocity profiles normalized by wall units exhibit no obvious logarithmic region, which is likely to be a result of the very limited distance between the edge of the viscous sublayer and the position of the maximum velocity. Compared to traditional shear flows, the peak position of the wall-unit-normalized r.m.s. profiles is found to be closer to the plate (at z+ = z/δw ≃ 5). Our overall conclusion is that a Blasius-type laminar boundary condition is a good approximation for the velocity boundary layer in turbulent thermal convection for the present range of Rayleigh number and Prandtl number.

Effects of Inlet Conditions on the Flow in a Fishtail Curved Diffuser With Strong Curvature

1996 ◽  
Vol 118 (4) ◽  
pp. 772-778 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Large Scale ◽  
Static Pressure ◽  
Pressure Recovery ◽  
Centrifugal Impeller ◽  
Flow Development ◽  
Diffuser Flow ◽  
Inlet Conditions ◽  
Strong Curvature

The paper presents detailed measurements of the incompressible flow at the exit of a large-scale 90-degree curved diffuser with strong curvature and significant stream-wise variation in the cross-section aspect ratio. The diffuser flow path approximates the so-called fish-tail diffuser utilized on small gas turbine engines for the transition between the centrifugal impeller and the combustion chamber. Five variations of the inlet boundary layer are considered. The results provide insight into several aspects of the diffuser flow including: the effect of flow turning on diffusion performance; the dominant structures influencing the flow development in the diffuser; and the effect of the inlet boundary layer integral parameters on the diffusion performance and the exit velocity field. The three-dimensional velocity distribution at the diffuser exit is found to be sensitive to circumferentially uniform alterations to the inlet boundary layer. In contrast, circumferential variations in the inlet boundary layer are observed to have only secondary effects on the velocity field at the diffuser exit. The static pressure recovery is observed to be comparable to the published performance of conical diffusers with equivalent included angle and area ratios. Furthermore, both the static pressure recovery and the total pressure losses are observed to be relatively insensitive to variations in the inlet boundary layer. The physical mechanisms dominating the flow development in the diffuser are discussed in light of these observations.

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