Direct Determination of the Onset of Transition to Turbulence in Flow Passages

1991 ◽  
Vol 113 (4) ◽  
pp. 602-607 ◽  
Author(s):  
N. T. Obot ◽  
J. A. Jendrzejczyk ◽  
M. W. Wambsganss
Keyword(s):  
Reynolds Number ◽  
Pressure Fluctuations ◽  
Direct Determination ◽  
Wall Pressure ◽  
Transition To Turbulence ◽  
Pressure Data ◽  
Wall Pressure Fluctuations ◽  
Power Spectral ◽  
Critical Reynolds Numbers

Easily applied methods are proposed, based on tests with air and water, for direct determination of the onset of transition in flow passages using static and dynamic wall pressure data. With increasing Reynolds number from laminar flow, the characteristic feature of transition is the change from steady to oscillating pressure readings. It is established that the power spectral density (psd) representations exhibit a distinctive change in profile at transition. Further, it is shown that the root-mean-square (rms) values of the wall pressure fluctuations rise sharply at transition. The critical Reynolds numbers recorded via the change from steady to unsteady pressure readings are almost the same as those deduced from the psd and rms pressure data or from the familiar friction factor-Reynolds number plots.

Pressure and velocity measurements of an incompressible moderate Reynolds number jet interacting with a tangential flat plate

2015 ◽  
Vol 770 ◽  
pp. 247-272 ◽  
Author(s):  
A. Di Marco ◽  
M. Mancinelli ◽  
R. Camussi
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Scaling Laws ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Theoretical Modelling ◽  
Wall Pressure Fluctuations ◽  
Moderate Reynolds Number ◽  
The Mean ◽  
Pressure And Velocity Measurements

The statistical properties of wall pressure fluctuations generated on a rigid flat plate by a tangential incompressible single stream jet are investigated experimentally. The study is carried out at moderate Reynolds number and for different distances between the nozzle axis and the flat plate. The overall aerodynamic behaviour is described through hot wire anemometer measurements, providing the effect of the plate on the mean and fluctuating velocity. The pressure field acting on the flat plate was measured by cavity-mounted microphones, providing point-wise pressure signals in the stream-wise and span-wise directions. Statistics of the wall pressure fluctuations are determined in terms of time-domain and Fourier-domain quantities and a parametric analysis is conducted in terms of the main geometrical length scales. Possible scaling laws of auto-spectra and coherence functions are presented and implications for theoretical modelling are discussed.

Spectral and Temporal Characteristics of Post-Stenotic Turbulent Wall Pressure Fluctuations

1979 ◽  
Vol 101 (2) ◽  
pp. 89-95 ◽  
Author(s):  
W. H. Pitts ◽  
C. F. Dewey
Keyword(s):  
Steady Flow ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Experimental Uncertainty ◽  
Flow Parameters ◽  
Wall Pressure Fluctuations ◽  
Power Spectral ◽  
Fluctuation Amplitude ◽  
Arterial Constriction ◽  
Turbulent Wall

The power spectral density of turbulent wall pressure fluctuations was measured in a tube downstream of a model arterial constriction. The flow parameters were varied from steady flow to conditions simulating human arterial pulsatile flow. Within the experimental uncertainty (±10 percent in characteristic turbulent frequency, fo, and ±25 percent in absolute rms pressure fluctuation amplitude), turbulent flow at the peak of systole produces wall pressure fluctuations identical to those of a steady flow at the same Reynolds number.

Reynolds-number dependence of wall-pressure fluctuations in a pressure-induced turbulent separation bubble

2017 ◽  
Vol 833 ◽  
pp. 563-598 ◽  
Author(s):  
Hiroyuki Abe
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Large Scale ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Local Maximum ◽  
Wall Pressure ◽  
Mean Flow ◽  
Frequency Spectra ◽  
Wall Pressure Fluctuations

Direct numerical simulations are used to examine the behaviour of wall-pressure fluctuations $p_{w}$ in a flat-plate turbulent boundary layer with large adverse and favourable pressure gradients, involving separation and reattachment. The Reynolds number $Re_{\unicode[STIX]{x1D703}}$ based on momentum thickness is equal to 300, 600 and 900. Particular attention is given to effects of Reynolds number on root-mean-square (r.m.s.) values, frequency/power spectra and instantaneous fields. The possible scaling laws are also examined as compared with the existing direct numerical simulation and experimental data. The r.m.s. value of $p_{w}$ normalized by the local maximum Reynolds shear stress $-\unicode[STIX]{x1D70C}\overline{uv}_{max}$ (Simpson et al. J. Fluid Mech. vol. 177, 1987, pp. 167–186; Na & Moin J. Fluid Mech. vol. 377, 1998b, pp. 347–373) leads to near plateau (i.e. $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{uv}_{max}=2.5\sim 3$) in the adverse pressure gradient and separated regions in which the frequency spectra exhibit good collapse at low frequencies. The magnitude of $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{uv}_{max}$ is however reduced down to 1.8 near reattachment where good collapse is also obtained with normalization by the local maximum wall-normal Reynolds stress $\unicode[STIX]{x1D70C}\overline{vv}_{max}$. Near reattachment, $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{vv}_{max}=1.2$ is attained unambiguously independently of the Reynolds number and pressure gradient. The present magnitude (1.2) is smaller than (1.35) obtained for step-induced separation by Ji & Wang (J. Fluid Mech. vol. 712, 2012, pp. 471–504). The reason for this difference is intrinsically associated with convective nature of a pressure-induced separation bubble near reattachment where the magnitude of $p_{w\,rms}$ depends essentially on the favourable pressure gradient. The resulting mean flow acceleration leads to delay of the r.m.s. peak after reattachment. Attention is also given to structures of $p_{w}$. It is shown that large-scale spanwise rollers of low pressure fluctuations are formed above the bubble, whilst changing to large-scale streamwise elongated structures after reattachment. These large-scale structures become more prominent with increasing $Re_{\unicode[STIX]{x1D703}}$ and affect $p_{w}$ significantly.

scholarly journals Numerical investigation of wall pressure fluctuations downstream of concentric and eccentric blunt stenosis models

2019 ◽  
Vol 234 (1) ◽  
pp. 48-60
Author(s):  
Kamil Ozden ◽  
Cuneyt Sert ◽  
Yigit Yazicioglu
Keyword(s):  
Reynolds Number ◽  
Root Mean Square ◽  
Acoustic Radiation ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Mean Square ◽  
Spectrum Level ◽  
Wall Pressure Fluctuations ◽  
Maximum Root ◽  
Calculated Amplitude

Pressure fluctuations that cause acoustic radiation from vessel models with concentric and eccentric blunt stenoses are investigated. Large eddy simulations of non-pulsatile flow condition are performed using OpenFOAM. Calculated amplitude and spatial-spectral distribution of acoustic pressures at the post-stenotic region are compared with previous experimental and theoretical results. It is found that increasing the Reynolds number does not change the location of the maximum root mean square wall pressure, but causes a general increase in the spectrum level, although the change in the shape of the spectrum is not significant. On the contrary, compared to the concentric model at the same Reynolds number, eccentricity leads to an increase both at the distance of the location of the maximum root mean square wall pressure from the stenosis exit and the spectrum level. This effect becomes more distinct when radial eccentricity of the stenosis increases. Both the flow rate and the eccentricity of the stenosis shape are evaluated to be clinically important parameters in diagnosing stenosis.

LES Prediction of Wall-Pressure Fluctuations and Noise of a Low-Speed Airfoil

2009 ◽  
Vol 8 (3) ◽  
pp. 177-197 ◽  
Author(s):  
Meng Wang ◽  
Stephane Moreau ◽  
Gianluca Iaccarino ◽  
Michel Roger
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Transition To Turbulence ◽  
Trailing Edge ◽  
Frequency Spectra ◽  
Potential Core ◽  
Low Speed ◽  
Wall Pressure Fluctuations

This paper discusses the prediction of wall-pressure fluctuations and noise of a low-speed flow past a thin cambered airfoil using large-eddy simulation (LES). The results are compared with experimental measurements made in an open-jet anechoic wind-tunnel at Ecole Centrale de Lyon. To account for the effect of the jet on airfoil loading, a Reynolds-averaged Navier-Stokes calculation is first conducted in the full wind-tunnel configuration, and the mean velocities from this calculation are used to define the boundary conditions for the LES in a smaller domain within the potential core of the jet. The LES flow field is characterized by an attached laminar boundary layer on the pressure side of the airfoil and a transitional and turbulent boundary layer on the suction side, in agreement with experimental observations. An analysis of the unsteady surface pressure field shows reasonable agreement with the experiment in terms of frequency spectra and spanwise coherence in the trailing-edge region. In the nose region, characterized by unsteady separation and transition to turbulence, the wall-pressure fluctuations are highly sensitive to small perturbations and thus diffcult to predict or measure with certainty. The LES, in combination with the Ffowcs Williams and Hall solution to the Lighthill equation, also predicts well the radiated trailing-edge noise. A finite-chord correction is derived and applied to the noise prediction, which is shown to improve the overall agreement with the experimental sound spectrum.

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