scholarly journals Multi-resolution, time-resolved PIV measurements of a Decelerating Turbulent Boundary Layer near Separation

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Christian E Willert ◽  
Matteo Novara ◽  
Daniel Schanz ◽  
Reinhard Geisler ◽  
Michael Schroll ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Time Resolved ◽  
Piv Measurements ◽  
Peak Energy ◽  
Resolution Imaging

We report on measurements of the time-evolving velocity profile of a turbulent boundary layer subjected to a strong adverse pressure gradient (APG) at Reynolds numbers up to Reθ ≈ 55 000 with an upstream friction Reynolds number exceeding Reτ ≈ 10 000. Near the point of flow separation high-resolution imaging at high camera frame rates captured the time evolving velocity profile using the so-called “profile-PIV” technique in a nested imaging configuration of two cameras operating at different image magnifications. One camera used an image magnification better than unity to resolve the viscous scales directly at the wall while the remainder of the roughly 200 mm thick boundary layer is simultaneous captured by the second camera. In the APG the variance of the stream-wise velocity exhibits no “inner peak” commonly found in turbulent boundary layers without pressure gradient influence. Spectral analysis further shows that the peak energy within the boundary layer shifts away from the wall toward lower frequencies. The overlap between the simultaneously imaged areas allows to assess and, to first order, correct for the effect of spatial smoothing on statistical quantities, spectra and related quantities. A multi-frame cross-correlation algorithm was used to process the extensive data base. In addition, a newly developed 2D-2C “Shake-The-Box” algorithm (STB) provided highly resolved particle tracking data beyond the reach of conventional PIV processing.

A Superposition Analysis of the Turbulent Boundary Layer in an Adverse Pressure Gradient

1951 ◽  
Vol 18 (1) ◽  
pp. 95-100
Author(s):  
Donald Ross ◽  
J. M. Robertson
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Pressure Recovery ◽  
Stress Coefficient ◽  
Wall Shear

Abstract As an interim solution to the problem of the turbulent boundary layer in an adverse pressure gradient, a super-position method of analysis has been developed. In this method, the velocity profile is considered to be the result of two effects: the wall shear stress and the pressure recovery. These are superimposed, yielding an expression for the velocity profiles which approximate measured distributions. The theory also leads to a more reasonable expression for the wall shear-stress coefficient.

scholarly journals On the generation of the mean velocity profile for turbulent boundary layers with pressure gradient under equilibrium conditions

2012 ◽  
Vol 116 (1180) ◽  
pp. 569-598 ◽  
Author(s):  
A. Rona ◽  
M. Monti ◽  
C. Airiau
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Fluid Dynamic ◽  
Predictive Ability ◽  
Adverse Pressure Gradient ◽  
Computational Domain ◽  
Mean Velocity ◽  
Number Range

AbstractThe generation of a fully turbulent boundary layer profile is investigated using analytical and numerical methods over the Reynolds number range 422 ≤ Reθ≤ 31,000. The numerical method uses a new mixing length blending function. The predictions are validated against reference wind tunnel measurements under zero streamwise pressure gradient. The methods are then tested for low and moderate adverse pressure gradients. Comparison against experiment and DNS data show a good predictive ability under zero pressure gradient and moderate adverse pressure gradient, with both methods providing a complete velocity profile through the viscous sub-layer down to the wall. These methods are useful computational fluid dynamic tools for generating an equilibrium thick turbulent boundary layer at the computational domain inflow.

scholarly journals A universal velocity profile for turbulent wall flows including adverse pressure gradient boundary layers

2021 ◽  
Vol 933 ◽  
Author(s):  
Matthew A. Subrahmanyam ◽  
Brian J. Cantwell ◽  
Juan J. Alonso
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Channel Flow ◽  
Adverse Pressure Gradient ◽  
Turbulent Shear ◽  
Model Parameters ◽  
Mixing Length

A recently developed mixing length model of the turbulent shear stress in pipe flow is used to solve the streamwise momentum equation for fully developed channel flow. The solution for the velocity profile takes the form of an integral that is uniformly valid from the wall to the channel centreline at all Reynolds numbers from zero to infinity. The universal velocity profile accurately approximates channel flow direct numerical simulation (DNS) data taken from several sources. The universal velocity profile also provides a remarkably accurate fit to simulated and experimental flat plate turbulent boundary layer data including zero and adverse pressure gradient data. The mixing length model has five free parameters that are selected through an optimization process to provide an accurate fit to data in the range $R_\tau = 550$ to $R_\tau = 17\,207$ . Because the velocity profile is directly related to the Reynolds shear stress, certain statistical properties of the flow can be studied such as turbulent kinetic energy production. The examples presented here include numerically simulated channel flow data from $R_\tau = 550$ to $R_\tau =8016$ , zero pressure gradient (ZPG) boundary layer simulations from $R_\tau =1343$ to $R_\tau = 2571$ , zero pressure gradient turbulent boundary layer experimental data between $R_\tau = 2109$ and $R_\tau = 17\,207$ , and adverse pressure gradient boundary layer data in the range $R_\tau = 912$ to $R_\tau = 3587$ . An important finding is that the model parameters that characterize the near-wall flow do not depend on the pressure gradient. It is suggested that the new velocity profile provides a useful replacement for the classical wall-wake formulation.

Predicting Turbulent Boundary Layer Wall Pressure Fluctuations in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Frank J. Aldrich
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Fluctuations ◽  
Adverse Pressure Gradient ◽  
Wall Pressure ◽  
Prediction Tool ◽  
Pressure Gradients ◽  
Wall Pressure Fluctuations ◽  
The Difference

A physics-based approach is employed and a new prediction tool is developed to predict the wavevector-frequency spectrum of the turbulent boundary layer wall pressure fluctuations for subsonic airfoils under the influence of adverse pressure gradients. The prediction tool uses an explicit relationship developed by D. M. Chase, which is based on a fit to zero pressure gradient data. The tool takes into account the boundary layer edge velocity distribution and geometry of the airfoil, including the blade chord and thickness. Comparison to experimental adverse pressure gradient data shows a need for an update to the modeling constants of the Chase model. To optimize the correlation between the predicted turbulent boundary layer wall pressure spectrum and the experimental data, an optimization code (iSIGHT) is employed. This optimization module is used to minimize the absolute value of the difference (in dB) between the predicted values and those measured across the analysis frequency range. An optimized set of modeling constants is derived that provides reasonable agreement with the measurements.

Effect of Transverse Curvature on Turbulent-Boundary-Layer Characteristics

1958 ◽  
Vol 2 (04) ◽  
pp. 33-51
Author(s):  
Yun-Sheng Yu
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Boundary Layer Thickness ◽  
Axial Flow ◽  
Shearing Stress ◽  
Transverse Curvature ◽  
Similarity Laws

Tests made on the turbulent boundary layer on a circular cylinder in axial flow at zero pressure gradient are described. From the measurements, similarity laws of the velocity profile are formulated, and various boundary-layer characteristics are evaluated and compared with the flatplate results. It is found that the effect of transverse curvature is to increase the surface shearing stress and to decrease the boundary-layer thickness, and that the latter variation is more pronounced than the former.

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