Turbulent Energy Budget in a Tip Leakage Flow: A Comparison Between RANS and LES

2017 ◽  
Author(s):  
Jean-François Monier ◽  
Jérôme Boudet ◽  
Joëlle Caro ◽  
Liang Shao
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Constitutive Relation ◽  
Energy Budget ◽  
Reynolds Stresses ◽  
Turbulent Kinetic Energy Budget ◽  
Potential Core ◽  
Kinetic Energy Budget ◽  
The Mean ◽  
Rans Simulations

An academic configuration of a single airfoil and a flat casing with clearance, put in the potential core of a jet at Rec = 9.3 × 105, is studied in order to analyse the turbulence modelling. A zonal large-eddy simulation (ZLES), validated against experimental results, is considered as a reference to evaluate two steady Reynolds-averaged Navier-Stokes (RANS) simulations. Both RANS simulations use the original Wilcox k-ω model. They differ on the constitutive relation: one uses the classical Boussinesq constitutive relation, while the other relies on the quadratic constitutive relation (QCR). The analysis focuses on the mean velocities, the Reynolds stresses and a term-to-term decomposition of the turbulent kinetic energy budget on a plane through the clearance. RANS represents quite well the mean velocities, but under-estimates the Reynolds stresses, thus under-estimates every turbulent kinetic energy budget term. The QCR has little effect on the flow and the turbulent quantities. The method allowed a fine analysis of the physics of the turbulence.

The influence of shear-dependent rheology on turbulent pipe flow

2017 ◽  
Vol 822 ◽  
pp. 848-879 ◽  
Author(s):  
J. Singh ◽  
M. Rudman ◽  
H. M. Blackburn
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Budget ◽  
Shear Thinning ◽  
Turbulent Pipe Flow ◽  
Turbulent Kinetic Energy Budget ◽  
Mean Velocity ◽  
Kinetic Energy Budget ◽  
Power Law Fluids ◽  
The Mean

Direct numerical simulations of turbulent pipe flow of power-law fluids at $Re_{\unicode[STIX]{x1D70F}}=323$ are analysed in order to understand the way in which shear thinning or thickening affects first- and second-order flow statistics including turbulent kinetic energy production, transport and dissipation in such flows. The results show that with shear thinning, near-wall streaks become weaker and the axial and azimuthal correlation lengths of axial velocity fluctuations increase. Viscosity fluctuations give rise to an additional shear stress term in the mean momentum equation which is negative for shear-thinning fluids and which increases in magnitude as the fluid becomes more shear thinning: for an equal mean wall shear stress, this term increases the mean velocity gradient in shear-thinning fluids when compared to a Newtonian fluid. Consequently, the mean velocity profile in power-law fluids deviates from the law of the wall $U_{z}^{+}=y^{+}$ in the viscous sublayer when traditional near-wall scaling is used. Consideration is briefly given to an alternative scaling that allows the law of wall to be recovered but which results in loss of a common mean stress profile. With shear thinning, the mean viscosity increases slightly at the wall and its profile appears to be approximately logarithmic in the velocity log layer. Through analysis of the turbulent kinetic energy budget, undertaken here for the first time for generalised Newtonian fluids, it is shown that shear thinning decreases the overall turbulent kinetic energy production but widens the wall-normal region where it is generated. Additional dissipation terms in the mean flow and turbulent kinetic energy budget equations arise from viscosity fluctuations; with shear thinning, these result in a net decrease in the total viscous dissipation. The overall effect of shear thinning on the turbulent kinetic energy budget is found to be largely confined to the inner layers, $y^{+}\lesssim 60$.

Turbulence Structure of the Hurricane Boundary Layer between the Outer Rainbands

2009 ◽  
Vol 66 (8) ◽  
pp. 2455-2467 ◽  
Author(s):  
Jun A. Zhang ◽  
William M. Drennan ◽  
Peter G. Black ◽  
Jeffrey R. French
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Budget ◽  
Specific Humidity ◽  
Turbulent Kinetic Energy Budget ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Kinetic Energy Budget ◽  
Hurricane Boundary Layer

Abstract As part of the Coupled Boundary Layers Air–Sea Transfer (CBLAST)-Hurricane program, flights were conducted to directly measure turbulent fluxes and turbulence properties in the high-wind boundary layer of hurricanes between the outer rainbands. For the first time, vertical profiles of normalized momentum fluxes, sensible heat and humidity fluxes, and variances of three-dimensional wind velocities and specific humidity are presented for the hurricane boundary layer with surface wind speeds ranging from 20 to 30 m s−1. The turbulent kinetic energy budget is estimated, indicating that the shear production and dissipation are the major source and sink terms, respectively. The imbalance in the turbulent kinetic energy budget indicates that the unmeasured terms, such as horizontal advection, may be important in hurricane boundary layer structure and dynamics. Finally, the thermodynamic boundary layer height, estimated based on the virtual potential temperature profiles, is roughly half of the boundary layer height estimated from the momentum flux profiles. The latter height where momentum and humidity fluxes tend to vanish is close to that of the inflow layer and also of the maximum in the tangential velocity profiles.

Sign in / Sign up

Export Citation Format

Share Document