Free-Stream Turbulence Effects on Convex-Curved Turbulent Boundary Layers

1989 ◽  
Vol 111 (1) ◽  
pp. 66-72 ◽  
Author(s):  
S. M. You ◽  
T. W. Simon ◽  
J. Kim
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Radius Of Curvature ◽  
Free Stream Turbulence ◽  
Curvature Effects ◽  
Asymptotic Shape ◽  
Turbulence Effects

Free-stream turbulence intensity effects on a convex-curved turbulent boundary layer are investigated. An attached fully turbulent boundary layer is grown on a flat plate and is then introduced to a downstream section where the test wall is convexly curved, having a constant radius of curvature. Two cases, with free-stream turbulence intensities of 1.85 and 0.65 percent, are discussed. They were taken in the same facility and with the same strength of curvature, δ/R = 0.03−0.045. The two cases have similar flow conditions upon entry to the curve, thus separating the free-stream turbulence effects under study from other effects. The higher turbulence case displayed stronger curvature effects on the skin friction coefficient Cf, and on streamwise-normal and shear stress profiles, than observed in the lower turbulence case. Observations of this are: (1) As expected, the higher turbulence case has a higher Cf value ( ∼ 5 percent) upstream of the curve than does the lower turbulence case, but this difference diminishes by the end of the curve. (2) Streamwise turbulence intensity profiles, differing upstream of the curve for the two cases, are found to be similar near the end of the curve, thus indicating that the effect of curvature is dominating over the effect of free-stream turbulence intensity. Many effects of curvature observed in the lower turbulence intensity case, and reported previously, e.g., a dramatic response to the introduction of curvature and the rapid assumption of an asymptotic shape within the curve, are also seen in the higher turbulence case.

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.

scholarly journals Comparison of k-ε Models in Predicting Heat Transfer and Skin Friction Under High Free Stream Turbulence

1996 ◽  
Author(s):  
Ganesh R. Iyer ◽  
Savash Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Empirical Correlations ◽  
Free Stream Turbulence ◽  
Boundary Layer Equations

Calculations of the effects of high free stream turbulence (FST) on heat transfer and skin friction in a flat plate turbulent boundary layer using different k-ε models (Launder-Sharma, K-Y Chien, Lam-Bremhorsi and Jones-Launder) are presented. This study was carried out in order to investigate the prediction capabilities of these models under high FST conditions. In doing so, TEXSTAN, a partial differential equation solver which is based on the ideas of Patankar and Spalding and solves steady-flow boundary layer equations, was used. Firstly, these models were compared as to how they predicted very low FST (≤ 1% turbulence intensity) cases. These baseline cases were tested by comparing predictions with both experimental data and empirical correlations. Then, these models were used in order to determine the effect of high FST (>5% turbulence intensity) on heat transfer and skin friction and compared with experimental data. Predictions for heat transfer and skin friction coefficient for all the turbulence intensities tested by all the models agreed well (within 1–8%) with experimental data. However, all these models predicted poorly the dissipation of turbulent kinetic energy (TKE) in the free stream and TKE profiles. Physical reasoning as to why the aforementioned models differ in their predictions and the probable cause of poor prediction of free-stream TKE and TKE profiles are given.

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

1995 ◽  
Vol 117 (2) ◽  
pp. 240-247 ◽  
Author(s):  
M. D. Kestoras ◽  
T. 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 been little 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 percent, 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.

Hydrodynamic and Thermal Measurements in a Turbulent Boundary Layer Recovering From Concave Curvature

1992 ◽  
Vol 114 (4) ◽  
pp. 891-898 ◽  
Author(s):  
M. D. Kestoras ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Free Stream Turbulence ◽  
Flat Wall ◽  
Concave Wall ◽  
Thermal Measurements ◽  
Streamwise Pressure Gradient ◽  
Curved Section

The behavior of a boundary layer on a flat wall downstream of sustained concave curvature is documented. Experiments are conducted with negligible streamwise pressure gradient and a low free-stream turbulence intensity (0.6 percent). The turbulent boundary layer has a moderate strength of curvature (δ/R = 0.024) at the entry to the recovery section. Results show that the skin friction coefficient, which increases over the concave wall, decreases rapidly at first over the recovery wall, then slowly approaches flat-wall values. Stanton number values decrease rapidly, undershooting expected flat-wall values. A discussion of this behavior, supported by profile measurements, is given. Effects include destabilization in the concave-curved flow and rapid streamline readjustment (acceleration) at the end of the curved section. Goertler vortices established on the curved wall persist onto the recovery wall; however, their effects weaken.

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