scholarly journals Effects of Free-Stream Turbulence on Diffuser Performance

1981 ◽  
Vol 103 (3) ◽  
pp. 385-390 ◽  
Author(s):  
J. A. Hoffmann
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Free Stream ◽  
Flow Direction ◽  
Two Dimensional ◽  
Recovery Coefficient ◽  
Axis Orientation ◽  
Free Stream Turbulence ◽  
Displacement Thickness ◽  
Pressure Recovery Coefficient

An experimental evaluation of the effects of free-stream turbulence on the performance of a subsonic two-dimensional diffuser has been made. Increases of the diffuser’s static pressure recovery coefficient of 11.3 and 23.9 percent at total included divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free-stream scale of turbulence in the flow direction was at least 7.2 times larger than the inlet boundary layer displacement thickness, when the inlet total free-stream turbulence intensity was at least 3.5 percent, and when the axes of upstream rods used to generate turbulence were perpendicular to the flow and parallel to the diverging walls of the diffuser. It is hypothesized that a larger scale of turbulence with the specified eddy axis orientation transmits the free-stream energy to the walls more effectively and, when coupled with large turbulence intensities, are mechanisms which act to decrease the distortion and delay separation within the diffuser.

The Removal of the Boundary Layer of a Supersonic Flow by Means of a Slot

1963 ◽  
Vol 30 (2) ◽  
pp. 275-278
Author(s):  
M. Cloutier
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Static Pressure ◽  
Free Stream ◽  
Subsequent Development ◽  
Displacement Thickness ◽  
Free Stream Mach Number ◽  
Slot Opening ◽  
Flow Through ◽  
Transverse Slot

The influence of slot opening and of suction pressure upon the mass flow through the slot and the subsequent development of the boundary layer has been studied for the case of a single transverse slot opening into a boundary layer with a displacement thickness of 0.168 in. at a free-stream Mach number of 2.92. The results show that as much as 85 percent of the mass flow in the boundary layer between the wall and the position of the slot lip enters the slot, and that this result is independent of the slot reservoir pressure, providing the latter is less than approximately twice the tunnel static pressure.

Development of a Large-Scale Wind Tunnel for the Simulation of Turbomachinery Airfoil Boundary Layers

1981 ◽  
Vol 103 (4) ◽  
pp. 678-687 ◽  
Author(s):  
M. F. Blair ◽  
D. A. Bailey ◽  
R. H. Schlinker
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Wind Tunnel ◽  
Boundary Layers ◽  
Test Section ◽  
Large Scale ◽  
Free Stream ◽  
Two Dimensional ◽  
Transfer Data ◽  
Free Stream Turbulence

The procedures employed for the design of a closed-circuit, boundary layer wind tunnel are described. The tunnel was designed for the generation of large-scale, two-dimensional boundary layers on a heated flat surface with Reynolds numbers, pressure gradients, and free-stream turbulence levels typical of turbomachinery airfoils. The results of a series of detailed tests to evaluate the tunnel performance are also described. Testing was conducted for zero pressure gradient flow with natural boundary layer transition. Heat transfer data and boundary layer profiles are presented for a flow with 0.25 percent free-stream turbulence. The flow in the tunnel test-section was shown to be highly uniform and two-dimensional. Test boundary layer profile and convective heat transfer data were self-consistent and in excellent agreement with classic correlations. Test-section free-stream total pressure, multi-component turbulence intensity, longitudinal integral scale, and spectral distributions are presented for grid-generated turbulence levels ranging from 1 to 7 percent. The test-section free-stream turbulence was shown to be both homogeneous and nearly isotropic. Anticipated applications of the facility include studies of the heat transfer and aerodynamics for conditions typical of those existing on gas turbine airfoils.

The Momentum-Integral Equation for a Boundary Layer With Turbulence or Ordered Unsteadiness in the Free Stream

1975 ◽  
Vol 97 (1) ◽  
pp. 126-129 ◽  
Author(s):  
J. H. Horlock ◽  
R. L. Evans
Keyword(s):  
Boundary Layer ◽  
Integral Equation ◽  
Shear Stress ◽  
Free Stream ◽  
Two Dimensional ◽  
Free Stream Turbulence ◽  
Momentum Integral

The two-dimensional momentum integral equation is derived for the case where free-stream turbulence or ordered unsteadiness exist. It is shown that extra terms may arise, of which one, the shear stress at the edge of the boundary layer, is important.

Transition to turbulence in the boundary layer over a smooth and rough swept plate exposed to free-stream turbulence

2010 ◽  
Vol 646 ◽  
pp. 297-325 ◽  
Author(s):  
LARS-UVE SCHRADER ◽  
SUBIR AMIN ◽  
LUCA BRANDT
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
External Disturbance ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Correct Prediction ◽  
Spanwise Direction ◽  
Free Stream Turbulence ◽  
Displacement Thickness ◽  
Dimensional Boundary

Receptivity, disturbance growth and transition to turbulence of the three-dimensional boundary layer developing on a swept flat plate are studied by means of numerical simulations. The flow is subject to a favourable pressure gradient and represents a model for swept-wing flow downstream of the leading edge and upstream of the pressure minimum of the wing. The boundary layer is perturbed by free-stream turbulence and localized surface roughness with random distribution in the spanwise direction. The intensity of the turbulent free-stream fluctuations ranges from conditions typical for free flight to higher levels usually encountered in turbo-machinery applications. The free-stream turbulence initially excites non-modal streak-like disturbances as in two-dimensional boundary layers, soon evolving into modal instabilities in the form of unsteady crossflow modes. The crossflow modes grow faster than the streaks and dominate the downstream disturbance environment in the layer. The results show that the receptivity mechanism is linear for the disturbance amplitudes under consideration, while the subsequent growth of the primary disturbances rapidly becomes affected by nonlinear saturation in particular for free-stream fluctuations with high intensity. Transition to turbulence occurs in the form of localized turbulent spots randomly appearing in the flow. The main features of the breakdown are presented for the case of travelling crossflow vortices induced by free-stream turbulence. The flow is also receptive to localized roughness strips, exciting stationary crossflow modes. The mode with most efficient receptivity dominates the downstream disturbance environment. When both free-stream fluctuations and wall roughness act on the boundary layer at the same time, transition is dominated by steady crossflow waves unless the incoming turbulence intensity is larger than about 0.5% for roughness amplitudes of about one tenth of the boundary-layer displacement thickness. The results show that a correct prediction of the disturbance behaviour can be obtained considering the receptivity and evolution of individual modes. In addition, we provide an estimate for the amplitudes of the external disturbance sources above which a fully nonlinear receptivity analysis is necessary.

The Effect of a Turbulent Wake on the Stagnation Point: Part II—Heat Transfer Results

1994 ◽  
Vol 116 (1) ◽  
pp. 46-56 ◽  
Author(s):  
A. J. Hanford ◽  
D. E. Wilson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Stagnation Point ◽  
Free Stream ◽  
Turbulent Wake ◽  
Energy Spectra ◽  
Incoming Flow ◽  
Two Dimensional ◽  
Free Stream Turbulence ◽  
Energy Equations

A phenomenological model is proposed that relates the effect of free-stream turbulence to the increase in stagnation point heat transfer. The model requires both turbulence intensity and energy spectra as inputs to the unsteady velocity at the edge of the boundary layer. The form of the edge velocity contains both a pulsation of the incoming flow and an oscillation of the streamlines. The incompressible unsteady and time-averaged boundary layer response is determined by solving the momentum and energy equations. The model allows for arbitrary two-dimensional geometry; however, results are given only for a circular cylinder. The time-averaged Nusselt number is determined theoretically and compared to existing experimental data.

Performance of a Diffuser with Fully-Developed Pipe Flow at Entry

1963 ◽  
Vol 67 (635) ◽  
pp. 733-733 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Pipe Flow ◽  
Boundary Layer Thickness ◽  
Static Pressure ◽  
Pressure Coefficient ◽  
Mean Velocity ◽  
Recovery Coefficient ◽  
Conical Diffuser ◽  
Definition Of ◽  
Pressure Recovery Coefficient

Cockrell and Markland have found that the static-pressure recovery coefficient of a conical diffuser, which is well known to decrease as the (turbulent) boundary layer thickness at entry increases, actually rises again when the inlet boundary layer is so thick as to approximate to fully-developed pipe flow. It may be noted that this is not a consequence of the definition of the pressure coefficient because, for typical pipe flow velocity profiles, the pressure coefficient based on mean velocity, , is very nearly the same as that based on momentum flux .

Outlet Surface Area Influence in Spiral Casing Design on Centrifugal Fan Performance

2020 ◽  
Vol 5 (1) ◽  
pp. 37-41
Author(s):  
Ardit Gjeta ◽  
Lorenc Malka
Keyword(s):  
Surface Area ◽  
Static Pressure ◽  
Total Efficiency ◽  
Centrifugal Fan ◽  
Recovery Coefficient ◽  
Fan Performance ◽  
Parameter Variations ◽  
Set Up ◽  
Spiral Casing ◽  
Pressure Recovery Coefficient

In this paper, the effect of the outlet surface area of the spiral casing on the performance of a centrifugal fan was investigated using open source CFD software OpenFOAM [1]. An automized loop with RANS and data post-processing is set up using Matlab, for allowing a large number of parameter variations. The effect was analyzed as a function of total pressure loss and static pressure recovery coefficient and on total efficiency as well.

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