Measurements of the Turbulent Transport of Heat and Momentum in Convexly Curved Boundary Layers: Effects of Curvature, Recovery and Free-Stream Turbulence

1988 ◽  
Vol 110 (1) ◽  
pp. 80-87 ◽  
Author(s):  
J. Kim ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulent Transport ◽  
Turbulent Prandtl Number ◽  
Hot Wire ◽  
Reynolds Analogy ◽  
Curved Boundary ◽  
Free Stream Turbulence ◽  
Wire Probe

The effects of streamwise convex curvature, recovery, and free-stream turbulence intensity on the turbulent transport of heat and momentum in a mature turbulent boundary layer are investigated. A special three-wire hot-wire probe developed for this purpose is described. Two cases with free-stream turbulence levels of 0.68 and 2.0 percent, taken in the same facility with moderate strength of curvature, δ/R = 0.03, are compared. Profiles of u′v′, t′, u′t′, and v′t′ are dramatically reduced within the curve, with asymptotic profiles being achieved quickly for the low TI case. Recovery occurs rapidly, with the profiles often overshooting flat-wall upstream values. Increased free-stream turbulence has the effect of increasing the profiles throughout the boundary layer on the flat developing wall. Profiles agreeing with the asymptotic profiles of the low TI case are observed by the end of the curve, however, illustrating the dominance of curvature over free-stream turbulence intensity. For the higher TI case, a reversal in the sign of u′v′ in the outer half of the boundary layer is observed, leading to negative values of the turbulent Prandtl number in this region. This indicates a breakdown in Reynolds analogy.

scholarly journals Turbulent Transport Measurements in a Heated Boundary Layer: Combined Effects of Free-Stream Turbulence and Removal of Concave Curvature

1995 ◽  
Author(s):  
Michael D. Kestoras ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulent Transport ◽  
Outer Part ◽  
Test Facility ◽  
Free Stream Turbulence ◽  
Concave Wall ◽  
Prandtl Numbers ◽  
Near Wall

Turbulence measurements for both momentum and heat transport are taken in a boundary layer over a flat, recovery wall downstream of a concave wall (R=0.97m). The boundary layer appears turbulent from the beginning of the concave wall and grows over the test wall with negligible streamwise acceleration. The strength of curvature at the bend exit, δ99.5/R, is 0.04. The free-stream turbulence intensity is ∼8% at the beginning of the curve and is nearly uniform at ∼4.5% throughout the recovery wall. Comparisons are made with data taken in an earlier study, in the same test facility, but with a low free-stream turbulence intensity (−0.6%). Results show that on the recovery wall, elevated free-stream turbulence intensity enhances turbulent transport quantities such as -uv¯ and vt¯ in most of the outer part of the boundary layer, but near-wall values of vt¯ remain unaffected. This is in contrast to near-wall vt¯ values within the curve which decrease when free-stream turbulence is increased. At the bend exit, decreases of -uv¯ and vt¯ due to removal of curvature become more profound when free-stream turbulence intensity is elevated, compared to low-TI behavior. Measurements in the core of the flow indicate that the high levels of cross transport of momentum over the upstream concave wall cease when curvature is removed. Other results show that turbulent Prandtl numbers over the recovery wall are reduced to −0.9 when free-stream turbulence intensity is elevated, consistent with the rise in Stanton numbers over the recovery wall.

scholarly journals Studies on Wake-Disturbed Boundary Layers Under the Influences of Favorable Pressure Gradient and Free-Stream Turbulence: Part II — Effect of Free-Stream Turbulence

1997 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Takashi Kitazawa ◽  
Kazuyuki Koizumi ◽  
Tadashi Tanuma
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Transition Model ◽  
Hot Wire ◽  
Time Resolved ◽  
Free Stream Turbulence ◽  
Wire Probe ◽  
Favorable Pressure Gradient ◽  
Probe Measurements

This paper, as Part II of the study on wake-disturbed boundary layer, is aimed at investigation of the effects of free-stream turbulence on wake-induced transition of the boundary layer under a favorable pressure gradient. Hot-wire probe measurements are also made on the wake-disturbed boundary layer to obtain ensemble-averaged shape factor contours on the distance-time diagrams. These data are then used to examine how the favorable pressure gradient and the free-stream turbulence affects time-resolved behaviors of the boundary layer subjected to periodic wakes. In addition, likewise in Part I, the heat transfer data are compared with the transition model proposed by Funazaki (1996) in order to check the capability of the model under the favorable pressure gradient as well as the free-stream turbulence.

An Experimental Study of Skewed Turbulent Boundary Layers in Low Speed Flows

1967 ◽  
Vol 89 (3) ◽  
pp. 597-607 ◽  
Author(s):  
G. P. Francis ◽  
F. J. Pierce
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Three Dimensional ◽  
Turbulent Boundary Layers ◽  
Free Stream Turbulence ◽  
Wire Probe ◽  
Curved Channels ◽  
Flow Directions

A detailed experimental investigation is described for the flow of air in skewed turbulent boundary layers on the floor of various curved channels. Measurements of time average velocities, flow directions, turbulence intensities, and growth are made for both the development and decay of the skewed boundary layer. All measurements were made with a unique hot wire probe arrangement. Tests were run with a free stream Reynolds number of approximately one million per ft and a free stream turbulence intensity of approximately 0.0016. The boundary layer was of the order of one inch in thickness. Both the turbulence intensity and velocity profiles indicate that the inner and outer regions, characteristic of two-dimensional profiles, are not necessarily appropriate to skewed three-dimensional flows.

Free-Stream Turbulence From a Circular Wall Jet on a Flat Plate Heat Transfer and Boundary Layer Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 78-86 ◽  
Author(s):  
R. MacMullin ◽  
W. Elrod ◽  
R. Rivir
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Flow Characteristics ◽  
Surface Profile ◽  
Constant Heat Flux ◽  
Length Scale ◽  
Wall Jet ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

The effects of the longitudinal turbulence intensity parameter of free-stream turbulence (FST) on heat transfer were studied using the aggressive flow characteristics of a circular tangential wall jet over a constant heat flux surface. Profile measurements of velocity, temperature, integral length scale, and spectra were obtained at downstream locations (2 to 20 x/D) and turbulence intensities (7 to 18 percent). The results indicated that the Stanton number (St) and friction factor (Cf) increased with increasing turbulence intensity. The Reynolds analogy factor (2St/Cf) increased up to turbulence intensities of 12 percent, then became constant, and decreased after 15 percent. This factor was also found to be dependent on the Reynolds number (Rex) and plate configuration. The influence of length scale, as found by previous researchers, was inconclusive at the conditions tested.

Effects of Concave Curvature on Boundary Layer Transition Under High Free-Stream Turbulence Conditions

2001 ◽  
Author(s):  
Michael P. Schultz ◽  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Turbulent Transport ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Turbulent Shear ◽  
Radius Of Curvature ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbulent Shear Stress

An experimental investigation has been carried out on a transitional boundary layer subject to high (initially 9%) free-stream turbulence, strong acceleration K=ν/Uw2dUw/dxas high as9×10-6, and strong concave curvature (boundary layer thickness between 2% and 5% of the wall radius of curvature). Mean and fluctuating velocity as well as turbulent shear stress are documented and compared to results from equivalent cases on a flat wall and a wall with milder concave curvature. The data show that curvature does have a significant effect, moving the transition location upstream, increasing turbulent transport, and causing skin friction to rise by as much as 40%. Conditional sampling results are presented which show that the curvature effect is present in both the turbulent and non-turbulent zones of the transitional flow.

scholarly journals Effects of Free-Stream Turbulence Intensity on a Boundary Layer Recovering From Concave Curvature Effects

1993 ◽  
Author(s):  
Michael D. Kestoras ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Outer Region ◽  
Free Stream Turbulence ◽  
Flat Wall ◽  
Curvature Effects ◽  
Turbulent Eddies ◽  
Concave Wall

Experiments are conducted on a flat recovery wall downstream of sustained concave curvature in the presence of high free-stream turbulence (TI∼8%). This flow simulates some of the features of the flow on the latter parts of the pressure surface of a gas turbine airfoil. The combined effects of concave curvature and TI, both present in the flow over a turbine airfoil, have so far little been studied. Computation of such flows with standard turbulence closure models has not been particularly successful. This experiment attempts to characterize the turbulence characteristics of this flow. In the present study, a turbulent boundary layer grows from the leading edge of a concave wall then passes onto a downstream flat wall. Results show that turbulence intensities increase profoundly in the outer region of the boundary layer over the recovery wall. Near-wall turbulent eddies appear to lift off the recovery wall and a “stabilized” region forms near the wall. In contrast to a low-free-stream turbulence intensity flow, turbulent eddies penetrate the outer parts of the “stabilized” region where sharp velocity and temperature gradients exist. These eddies can more readily transfer momentum and heat. As a result, skin friction coefficients and Stanton numbers on the recovery wall are 20% and 10%, respectively, above their values in the low-free-stream turbulence intensity case. Stanton numbers do not undershoot flat-wall expectations at the same ReΔ2 values as seen in the low-TI case. Remarkably, the velocity distribution in the core of the flow over the recovery wall exhibits a negative gradient normal to the wall under high free-stream turbulence intensity conditions. This velocity distribution appears to be the result of two effects: 1) cross transport of kinetic energy by boundary work in the upstream curved flow and 2) readjustment of static pressure profiles in response to the removal of concave curvature.

scholarly journals Effect of turbulence on the wake of a wall-mounted cube

2016 ◽  
Vol 804 ◽  
pp. 513-530 ◽  
Author(s):  
R. Jason Hearst ◽  
Guillaume Gomit ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reattachment Length ◽  
Free Stream Turbulence ◽  
Boundary Layer Development ◽  
Image Velocimetry ◽  
Shedding Frequency ◽  
Layer Development

The influence of turbulence on the flow around a wall-mounted cube immersed in a turbulent boundary layer is investigated experimentally with particle image velocimetry and hot-wire anemometry. Free-stream turbulence is used to generate turbulent boundary layer profiles where the normalised shear at the cube height is fixed, but the turbulence intensity at the cube height is adjustable. The free-stream turbulence is generated with an active grid and the turbulent boundary layer is formed on an artificial floor in a wind tunnel. The boundary layer development Reynolds number ($Re_{x}$) and the ratio of the cube height ($h$) to the boundary layer thickness ($\unicode[STIX]{x1D6FF}$) are held constant at $Re_{x}=1.8\times 10^{6}$ and $h/\unicode[STIX]{x1D6FF}=0.47$. It is demonstrated that the stagnation point on the upstream side of the cube and the reattachment length in the wake of the cube are independent of the incoming profile for the conditions investigated here. In contrast, the wake length monotonically decreases for increasing turbulence intensity but fixed normalised shear – both quantities measured at the cube height. The wake shortening is a result of heightened turbulence levels promoting wake recovery from high local velocities and the reduction in strength of a dominant shedding frequency.

The reduction and elimination of a closed separation region by free-stream turbulence

2001 ◽  
Vol 446 ◽  
pp. 271-308 ◽  
Author(s):  
M. KALTER ◽  
H. H. FERNHOLZ
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Reverse Flow ◽  
Flow Region ◽  
Adverse Pressure Gradient ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Free Stream Turbulence ◽  
The Mean

This paper is an extension of an experimental investigation by Alving & Fernholz (1996). In the present experiments the effects of free-stream turbulence were investigated on a boundary layer with an adverse pressure gradient and a closed reverse-flow region. By adding free-stream turbulence the mean reverse-flow region was shortened or completely eliminated and this was used to control the size of the separation bubble. The turbulence intensity was varied between 0.2% and 6% using upstream grids while the turbulence length scale was on the order of the boundary layer thickness. Mean and fluctuating velocities as well as spectra were measured by means of hot-wire and laser-Doppler anemometry and wall shear stress by wall pulsed-wire and wall hot-wire probes.Free-stream turbulence had a small effect on the boundary layer in the mild adverse-pressure-gradient region but in the vicinity of separation and along the reverse-flow region mean velocity profiles, skin friction and turbulence structure were strongly affected. Downstream of the mean or instantaneous reverse-flow regions highly disturbed boundary layers developed in a nominally zero pressure gradient and converged to a similar turbulence structure in all three cases at the end of the test section. This state was, however, still very different from that in a canonical boundary layer.

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