Skin-friction measurements in a turbulent boundary layer under the influence of free-stream turbulence

Esteban, Luis Blay; Doğan, Eda; Rodríguez-López, Eduardo; Ganapathisubramani, Bharathram

doi:10.1007/s00348-017-2397-8

Cited by 16 publications

(20 citation statements)

References 20 publications

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“…An output of this fitting method is the shear stress velocity, , which is used to calculate skin friction. This procedure of determining skin friction has been recently validated against oil film interferometry in high free stream turbulence by Esteban et al [25]. The uncertainty of skin friction measured directly from the near wall velocity profile was determined to be within ±3.6%.…”

Section: Working Sectionsmentioning

confidence: 95%

The Impact of Combustor Turbulence on Turbine Loss Mechanisms

Folk

Miller

Coull

2020

Journal of Turbomachinery

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A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

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Section: Working Sectionsmentioning

confidence: 95%

The Impact of Combustor Turbulence on Turbine Loss Mechanisms

Folk

Miller

Coull

2020

Journal of Turbomachinery

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“…Single-point hot-wire measurements were performed in Dogan et al [5] allowing very near-wall statistics and the Preston tube method was implemented to obtain the skin-friction values. Oil Film Interferometry was later applied to validate the Preston-tube estimates of skin-friction values [18].…”

Section: Flow Conditions and Boundary Layer Statisticsmentioning

confidence: 99%

Spatial characteristics of a zero-pressure-gradient turbulent boundary layer in the presence of free-stream turbulence

et al. 2019

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Particle image velocimetry (PIV) measurements are performed to examine the structural organisation inside a turbulent boundary layer under the influence of free-stream turbulence (FST). In particular, streamwise-wall-normal plane PIV measurements are presented for two cases at two different turbulent intensity levels (about 12% and 8%). The high-intensity free-stream turbulence is generated using an active grid in a wind tunnel. The statistical information of the flow regarding the wall-normal velocity and Reynolds shear stress are presented. The effect of increasing the turbulence level in the free stream for these flows has been found to have similarities with increasing Reynolds number for high Reynolds number canonical flows. Quadrant analysis is performed to determine the contributions of different Reynolds-stress-producing events. In this regard, the distribution of momentum transport events shows some similarity with channel flows, which can be justified by comparison of similar intermittency characteristics of both flows. In addition, the coherent structures found inside the boundary layer have inclined features that are consistent with the previous studies for canonical flows. The fact that the external disturbance, such as FST in this study, does not alter the organisation of the structures inside the boundary layer supports the growing evidence for a universal structure for wall-bounded flows. * jason.hearst@ntnu.no

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“…where r 0 is the first zero-crossing of the autocorrelation. The boundary layer parameters listed in the table (δ, U τ , κ) were fit using the approach of Rodríguez-López et al (2015) as modified for FST by Esteban et al (2017). Due to the relatively high Re τ of the present experiments and the = 1 mm sensing length of the hot-wire probes, the innerunit length of the probes ranged 18 + 33.…”

Section: Experimental Procedures and Free-stream Characteristicsmentioning

confidence: 99%

Robust features of a turbulent boundary layer subjected to high-intensity free-stream turbulence

2018

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The influence of the large scale organisation of free-stream turbulence on a turbulent boundary layer is investigated experimentally in a wind tunnel through hot-wire measurements. An active grid is used to generate high-intensity free-stream turbulence with turbulence intensities and local turbulent Reynolds numbers in the ranges $7.2\,\%\leqslant u_{\infty }^{\prime }/U_{\infty }\leqslant 13.0\,\%$ and $302\leqslant Re_{\unicode[STIX]{x1D706},\infty }\leqslant 760$, respectively. In particular, several cases are produced with fixed $u_{\infty }^{\prime }/U_{\infty }$ and $Re_{\unicode[STIX]{x1D706},\infty }$, but up to a 65 % change in the free-stream integral scale $L_{u,\infty }/\unicode[STIX]{x1D6FF}$. It is shown that, while qualitatively the spectra at various wall-normal positions in the boundary layer look similar, there are quantifiable differences at the large wavelengths all the way to the wall. Nonetheless, profiles of the longitudinal statistics up to fourth order are well collapsed between cases at the same $u_{\infty }^{\prime }/U_{\infty }$. It is argued that a larger separation of the integral scale would not yield a different result, nor would it be physically realisable. Comparing cases across the wide range of turbulence intensities and free-stream Reynolds numbers tested, it is demonstrated that the near-wall spectral peak is independent of the free-stream turbulence, and seemingly universal. The outer peak was also found to be described by a set of global scaling laws, and hence both the near-wall and outer spectral peaks can be predicted a priori with only knowledge of the free-stream spectrum, the boundary layer thickness ($\unicode[STIX]{x1D6FF}$) and the friction velocity ($U_{\unicode[STIX]{x1D70F}}$). Finally, a conceptual model is suggested that attributes the increase in $U_{\unicode[STIX]{x1D70F}}$ as $u_{\infty }^{\prime }/U_{\infty }$ increases to the build-up of energy at large wavelengths near the wall because that energy cannot be transferred to the universal near-wall spectral peak.

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Skin-friction measurements in a turbulent boundary layer under the influence of free-stream turbulence

Cited by 16 publications

References 20 publications

The Impact of Combustor Turbulence on Turbine Loss Mechanisms

The Impact of Combustor Turbulence on Turbine Loss Mechanisms

Spatial characteristics of a zero-pressure-gradient turbulent boundary layer in the presence of free-stream turbulence

Robust features of a turbulent boundary layer subjected to high-intensity free-stream turbulence

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