Direct numerical simulation of leading-edge receptivity to sound

AIAA Journal ◽  
2000 ◽  
Vol 38 ◽  
pp. 1159-1165
Author(s):  
David Fuciarelli ◽  
Helen Reed ◽  
Ian Lyttle
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Leading Edge

Direct Numerical Simulation of Discrete Roughness on a Swept-Wing Leading Edge

AIAA Journal ◽  
2010 ◽  
Vol 48 (11) ◽  
pp. 2660-2673 ◽  
Author(s):  
Donald P. Rizzetta ◽  
Miguel R. Visbal ◽  
Helen L. Reed ◽  
William S. Saric
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Leading Edge ◽  
Swept Wing

Direct numerical simulation of a puff and a slug in transitional cylindrical pipe flow

1999 ◽  
Vol 387 ◽  
pp. 39-60 ◽  
Author(s):  
H. SHAN ◽  
B. MA ◽  
Z. ZHANG ◽  
F. T. M. NIEUWSTADT
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Pipe Flow ◽  
Leading Edge ◽  
Transition Process ◽  
Axial Position ◽  
Trailing Edge ◽  
Mean Velocity ◽  
The Mean

A direct numerical simulation of transitional pipe flow is carried out with the help of a spectral element method and used to investigate the localized regions of ‘turbulent’ flow that are observed in experiments. Two types of such regions can be distinguished: the puff and the slug. The puff, which is generally found at low values of the Reynolds numbers, is simulated for Re = 2200 where the Reynolds number Re is based on the mean velocity UB and pipe diameter D. The slug occurs at a higher Reynolds number and it is simulated for Re = 5000. The computations start with a laminar pipe flow to which is added a prescribed velocity disturbance at a given axial position and for a finite time. The disturbance then evolves further into a puff or slug structure.The simulations confirm the experimentally observed fact that for a puff the velocity near the leading edge changes more gradually than for a slug where an almost discontinuous change is observed. The positions of the leading and trailing edges of the puff and slug are computed from the simulations as a function of time. The propagation velocity of the leading edge is found to be constant and equal to 1.56UB and 1.69UB for the puff and slug, respectively. For the trailing edge the velocity is found to be 0.73UB and 0.52UB, respectively. By rescaling the simulation results obtained at various times to a fixed length, we define an ensemble average. This method is used to compute the average characteristics of the puff and slug such as the spatial distribution of the mean velocity, the turbulent velocity fluctuations and also the wall shear stress. By computing particle trajectories we have investigated the entrainment and detrainment of fluid by a puff and slug. We find that the puff detrains through its trailing edge and entrains through its leading edge. The slug entrains fluid through its leading and through most of its trailing edge. As a consequence the fluid inside the puff is constantly exchanged with fluid outside whereas the fluid inside a slug remains there. These entrainment/detrainment properties which are in agreement with the measurements of Wygnanski & Champagne (1973) imply that the puff has the characteristics of a wave phenomenon while the slug can be characterized more as a material property which travels with the flow.Finally, we have investigated in more detail the velocity field within the puff. In a coordinate system that travels with the mean velocity we find recirculation regions both near the trailing and leading edges which agrees at least qualitatively with experimental data. We also find streamwise vortices, predominantly in the trailing-edge region which have been also observed in experiments and which are believed to play an important role in the dynamics of the transition process.

Direct Numerical Simulation and Large Eddy Simulation of Laminar Separation Bubbles at Moderate Reynolds Numbers

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Francois Cadieux ◽  
Julian A. Domaradzki ◽  
Taraneh Sayadi ◽  
Sanjeeb Bose
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Large Eddy

Flows over airfoils and blades in rotating machinery for unmanned and microaerial vehicles, wind turbines, and propellers consist of different flow regimes. A laminar boundary layer near the leading edge is often followed by a laminar separation bubble with a shear layer on top of it that experiences transition to turbulence. The separated turbulent flow then reattaches and evolves downstream from a nonequilibrium turbulent boundary layer to an equilibrium one. Typical Reynolds-averaged Navier–Stokes (RANS) turbulence modeling methods were shown to be inadequate for such laminar separation bubble flows (Spalart and Strelets, 2000, “Mechanisms of Transition and Heat Transfer in a Separation Bubble,” J. Fluid Mech., 403, pp. 329–349). Direct numerical simulation (DNS) is the most reliable but is also the most computationally expensive alternative. This work assesses the capability of large eddy simulations (LES) to reduce the resolution requirements for such flows. Flow over a flat plate with suitable velocity boundary conditions away from the plate to produce a separation bubble is considered. Benchmark DNS data for this configuration are generated with the resolution of 59 × 106 mesh points; also used is a different DNS database with 15 × 106 points (Spalart and Strelets, 2000, “Mechanisms of Transition and Heat Transfer in a Separation Bubble,” J. Fluid Mech., 403, pp. 329–349). Results confirm that accurate LES are possible using O(1%) of the DNS resolution.

Analysis and direct numerical simulation of the flow at a gravity-current head. Part 2. The lobe-and-cleft instability

2000 ◽  
Vol 418 ◽  
pp. 213-229 ◽  
Author(s):  
CARLOS HÄRTEL ◽  
FREDRIK CARLSSON ◽  
MATTIAS THUNBLOM
Keyword(s):  
Numerical Simulation ◽  
Stability Analysis ◽  
Direct Numerical Simulation ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Gravity Current ◽  
Leading Edge ◽  
Two Dimensional ◽  
Amplification Rate ◽  
The Stability

Results are presented from a linear-stability analysis of the flow at the head of two-dimensional gravity-current fronts. The analysis was undertaken in order to clarify the instability mechanism that leads to the formation of the complex lobe-and-cleft pattern which is commonly observed at the leading edge of gravity currents propagating along solid boundaries. The stability analysis concentrates on the foremost part of the front, and is based on direct numerical simulation data of two-dimensional lock-exchange flows which are described in the companion paper, Härtel et al. (2000). High-order compact finite differences are employed to discretize the stability equations which results in an algebraic eigenvalue problem for the amplification rate, that is solved in an iterative fashion. The analysis reveals the existence of a vigorous linear instability that acts in a localized way at the leading edge of the front and originates in an unstable stratification in the flow region between the nose and stagnation point. It is shown that the amplification rate of this instability as well as its spanwise length scale depend strongly on Reynolds number. For validation, three-dimensional direct numerical simulations of the early stages of the frontal instability are performed, and close agreement with the results from the linear-stability analysis is demonstrated.

scholarly journals Statistics of Conditional Fluid Velocity in the Corrugated Flamelets Regime of Turbulent Premixed Combustion: A Direct Numerical Simulation Study

2011 ◽  
Vol 2011 ◽  
pp. 1-13 ◽  
Author(s):  
Nilanjan Chakraborty ◽  
Andrei N. Lipatnikov
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Fluid Velocity ◽  
Turbulent Flame ◽  
Leading Edge ◽  
Lewis Number ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Turbulent Premixed Flame ◽  
Turbulent Premixed

The statistics of mean fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes (RANS) simulations have been studied using a Direct Numerical Simulation database of statistically planar turbulent premixed flame representing the corrugated flamelets regime combustion. Expressions for conditional mean velocity and conditional velocity correlations which are derived based on a presumed bimodal probability density function of reaction progress variable for unity Lewis number flames are assessed in this study with respect to the corresponding quantities extracted from DNS data. In particular, conditional surface averaged velocities(ui)¯Rsand the velocity correlations(uiu)j¯Rsin the unburned reactants are demonstrated to be effectively modelled by the unconditional velocities(ui)¯Rand velocity correlations(uiuj)¯R, respectively, for the major part of turbulent flame brush with the exception of the leading edge. By contrast, conditional surface averaged velocities(ui)¯Psand the velocity correlations(uiu)j¯Psin fully burned products are shown to be markedly different from the unconditional velocities(ui)¯Pand velocity correlations(uiuj)¯P, respectively.

Direct numerical simulation of round turbulent jets in crossflow

2007 ◽  
Vol 574 ◽  
pp. 59-84 ◽  
Author(s):  
SUMAN MUPPIDI ◽  
KRISHNAN MAHESH
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Near Field ◽  
Leading Edge ◽  
Turbulent Jets ◽  
Energy Budgets ◽  
Mean Velocity ◽  
Field Peak ◽  
Jet Velocity

Direct numerical simulation is used to study a round turbulent jet in a laminar crossflow. The ratio of bulk jet velocity to free-stream crossflow velocity is 5.7 and the Reynolds number based on the bulk jet velocity and the jet exit diameter is 5000. The mean velocity and turbulent intensities from the simulations are compared to data from the experiments by Su & Mungal (2004) and good agreement is observed. Additional quantities, not available from experiments, are presented. Turbulent kinetic energy budgets are computed for this flow. Examination of the budgets shows that the near field is far from a state of turbulent equilibrium – especially along the jet edges. Also – in the near field – peak kinetic energy production is observed close to the leading edge, while peak dissipation is observed toward the trailing edge of the jet. The results are used to comment upon the difficulty involved in predicting this flow using RANS computations. There exist regions in this flow where the pressure transport term, neglected by some models and poorly modelled by others, is significant. And past the jet exit, the flow is not close to established canonical flows on which most models appear to be based.

scholarly journals Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and direct numerical simulation

2018 ◽  
Vol 842 ◽  
pp. 495-531 ◽  
Author(s):  
Alexander Wagner ◽  
Erich Schülein ◽  
René Petervari ◽  
Klaus Hannemann ◽  
Syed R. C. Ali ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Acoustic Wave ◽  
Direct Numerical Simulation ◽  
Acoustic Waves ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Wind Tunnels ◽  
Wide Range

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels were conducted by means of a slender wedge probe and direct numerical simulation. The study comprises comparative tunnel noise measurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shock tunnel. Surface pressure fluctuations were measured over a wide range of frequencies and test conditions including harsh test environments not accessible to measurement techniques such as Pitot probes and hot-wire anemometry. A good agreement was found between normalized Pitot pressure fluctuations converted into normalized static pressure fluctuations and the wedge probe readings. Quantitative results of the tunnel noise are provided in frequency ranges relevant for hypersonic boundary-layer transition. Complementary numerical simulations of the leading-edge receptivity to fast and slow acoustic waves were performed for the applied wedge probe at conditions corresponding to the experimental free-stream conditions. The receptivity to fast acoustic waves was found to be characterized by an early amplification of the induced fast mode. For slow acoustic waves an initial decay was found close to the leading edge. At all Mach numbers, and for all considered frequencies, the leading-edge receptivity to fast acoustic waves was found to be higher than the receptivity to slow acoustic waves. Further, the effect of inclination angles of the acoustic wave with respect to the flow direction was investigated. An inclination angle was found to increase the response on the wave-facing surface of the probe and decrease the response on the opposite surface for fast acoustic waves. A frequency-dependent response was found for slow acoustic waves. The combined numerical and experimental approach in the present study confirmed the previous suggestion that the slow acoustic wave is the dominant acoustic mode in noisy hypersonic wind tunnels.

Sign in / Sign up

Export Citation Format

Share Document