Effect of transition on the aerodynamic characteristics of a spinning cone

2017 ◽  
Vol 232 (11) ◽  
pp. 2048-2058
Author(s):  
Qiao Zhang ◽  
Xiaosheng Wu ◽  
Jintao Yin ◽  
Ran Yao
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Transition Model ◽  
Magnus Force ◽  
The Right

In order to study the effect of transition on the aerodynamic characteristics of a pointed cone at small angles of attack in supersonic flows, the [Formula: see text] transition model, γ transition model, and a trip wire applied with [Formula: see text] transition model coupled with the Reynolds-averaged Navier–Stokes equations were used to simulate the flow over the spinning cone. The γ transition model, including the effects of crossflow instability, is better than other models in the transition and Magnus force prediction. The numerical calculations are in certain agreement with the experimental data. The results indicate that the positions of the maximum boundary layer thickness remain unchanged using different turbulence models, while the results obtained by the transition model shift towards spin direction, intensifying the difference of the boundary layer thickness between the right and the left side bodies; the contribution of the skin friction on the Magnus force increases due to the shift in the transition position; the contribution of pressure on the Magnus force also changes with the distortion of the boundary layer.

Regimes of two-dimensionality of decaying shallow axisymmetric swirl flows with background rotation

2011 ◽  
Vol 691 ◽  
pp. 214-244 ◽  
Author(s):  
M. Duran-Matute ◽  
L. P. J. Kamp ◽  
R. R. Trieling ◽  
G. J. F. van Heijst
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Parameter Space ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Swirl Flows ◽  
Equivalent Boundary ◽  
Radial Length

AbstractBoth background rotation and small depths are said to enforce the two-dimensionality of flows. In the current paper, we describe a systematic study of the two-dimensionality of a shallow monopolar vortex subjected to background rotation. Using a perturbation analysis of the Navier–Stokes equations for small aspect ratio $\delta = H/ L$ (with $H$ the fluid depth and $L$ a typical radial length scale of the vortex), we found nine different regimes in the parameter space where the flow is governed to lowest order by different sets of equations. From the properties of these sets of equations, it was determined that the flow can be considered as quasi-two-dimensional in only five of the nine regimes. The scaling of the velocity components as given by these sets of equations was compared with results from numerical simulations to find the actual boundaries of the different regimes in the parameter space (${h}_{\mathit{Ek}} , {h}_{\mathit{Re}} $), where ${h}_{\mathit{Ek}} $ is the Ekman boundary layer thickness and ${h}_{\mathit{Re}} $ is the equivalent boundary layer thickness for a monopolar vortex without background rotation. Even though background rotation and small depths do promote the two-dimensionality of flows independently, the combination of these two characteristics does not necessarily have that same effect.

Numerical Integration of the Navier-Stokes Equations for a Disk Rotating in a Housing

1985 ◽  
Vol 40 (8) ◽  
pp. 789-799 ◽  
Author(s):  
A. F. Borghesani
Keyword(s):  
Boundary Layer ◽  
Cylindrical Cavity ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Fluid Motion ◽  
Rotating Disk ◽  
Infinite Medium ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Viscous Torque

The Navier-Stokes equations for the fluid motion induced by a disk rotating inside a cylindrical cavity have been integrated for several values of the boundary layer thickness d. The equivalence of such a device to a rotating disk immersed in an infinite medium has been shown in the limit as d → 0. From that solution and taking into account edge effect corrections an equation for the viscous torque acting on the disk has been derived, which depends only on d. Moreover, these results justify the use of a rotating disk to perform accurate viscosity measurements.

scholarly journals Validation of atmospheric boundary layer turbulence model by on-site measurements

2010 ◽  
Vol 14 (1) ◽  
pp. 199-207 ◽  
Author(s):  
Zarko Stevanovic ◽  
Nikola Mirkov ◽  
Zana Stevanovic ◽  
Andrijana Stojanovic
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Linear Models ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Boundary Layer Turbulence ◽  
Askervein Hill ◽  
Neutral Conditions

Modeling atmosperic boundary layer with standard linear models does not sufficiently reproduce wind conditions in complex terrain, especially on leeward sides of terrain slopes. More complex models, based on Reynolds averaged Navier-Stokes equations and two-equation k-? turbulence models for neutral conditions in atmospheric boundary layer, written in general curvilinear non-orthogonal co-ordinate system, have been evaluated. In order to quantify the differences and level of accuracy of different turbulence models, investigation has been performed using standard k-? model without additional production terms and k-? turbulence models with modified set of model coefficients. The sets of full conservation equations are numerically solved by computational fluid dynamics technique. Numerical calculations of turbulence models are compared to the reference experimental data of Askervein hill measurements.

scholarly journals Computational Characterization of a Rectangular Vortex Generator on a Flat Plate for Different Vane Heights and Angles

2019 ◽  
Vol 9 (5) ◽  
pp. 995 ◽  
Author(s):  
Iosu Ibarra-Udaeta ◽  
Iñigo Errasti ◽  
Unai Fernandez-Gamiz ◽  
Ekaitz Zulueta ◽  
Javier Sancho
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Local Boundary ◽  
Passive Flow Control ◽  
Vortex Size

Vortex generators (VG) are passive flow control devices used for avoiding or delaying the separation of the boundary layer by bringing momentum from the higher layers of the fluid towards the surface. The Vortex generator usually has the same height as the local boundary layer thickness, and these Vortex generators can produce overload drag in some cases. The aim of the present study was to analyze the characteristics and path of the primary vortex produced by a single rectangular vortex generator on a flat plate for the incident angles of β = 10 ∘ , 15 ∘ , 18 ∘ and 20 ∘ . A parametric study of the induced vortex was performed for six VG heights using Reynolds average Navier–Stokes equations at Reynodls number R e = 27,000 based on the local boundary layer thickness, using computational fluid dynamics techniques with OpenFOAM open-source code. In order to determine the vortex size, the so-called half-life radius was computed and compared with experimental data. The results showed a similar trend for all the studied vortex generator heights and incident angles with small variations for the vertical and the lateral paths. Additionally, 0.4H and 0.6H VG heights at incident angles of β = 18 ∘ and β = 20 ∘ showed the best performance in terms of vortex strength and generation of wall shear stress.

Fluid-Acoustics Interaction in Self-Sustained Oscillations Over a Cavity in a Turbulent Boundary Layer

2008 ◽  
Author(s):  
H. Yokoyama ◽  
C. Kato
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Layer Thickness ◽  
Turbulent Flows ◽  
Acoustic Waves ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Practical Applications ◽  
Sustained Oscillations ◽  
Mach Numbers

Self-sustained oscillations with fluid-acoustics interaction over a cavity can radiate intense tonal sound and fatigue nearby components of industrial products. The prediction and the suppression of these oscillations are very important for many practical applications. However, the fluid-acoustics interaction has not been thoroughly clarified in particular for the oscillations in turbulent flows. We investigate the mechanism of the oscillations over a rectangular cavity with a length-to-depth ratio of 2:1 by directly solving the compressible Navier-Stokes equations. The boundary layer over the cavity is turbulent and the freestream Mach numbers are M = 0.4 and 0.7. The results clarify that the self-sustained oscillations occur in the shear layer of the cavity and the oscillations are reinforced by the streamwise acoustic mode in the cavity for both Mach numbers. The shear layer of the cavity undulates. This undulation causes the deformation of fine vortices in the shear layer and radiates acoustic waves from the downstream edge of the cavity. Also, we clarify by the conditional identification of longitudinal vortices that the acoustic waves cause the undulation of the shear layer and a feedback loop is formed. Moreover, the comparison of the flow field over the cavity with that over a simple backstep shows that the shear layer in the cavity becomes two-dimensional by the acoustic feedback. Finally, we show that the oscillations become weaker particularly at M = 0.4 and the frequencies of the oscillations become lower as the boundary layer thickness at the upstream edge of the cavity increases. Considering this effect of the boundary layer thickness, the peak frequencies predicted by our computations are in good agreement with those measured in a past experiment.

A CFD Evaluation of Multiple RANS Turbulence Models for Prediction of Boundary Layer Flows on a Turbine Vane

2013 ◽  
Author(s):  
Thomas E. Dyson ◽  
David G. Bogard ◽  
Sean D. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Prandtl Number ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Turbulence Models ◽  
Experimental Measurements ◽  
Thermal Boundary Layer Thickness ◽  
Mean Velocity ◽  
High Turbulence

There is a growing trend toward the use of conjugate CFD for use in prediction of turbine cooling performance. While many studies have evaluated the performance of RANS simulations relative to experimental measurements of the momentum boundary layer, no studies have evaluated their performance in prediction of the accompanying thermal boundary layer. This is largely due to the fact that, until recently, no appropriate experimental data existed to validate these models. This study compares several popular RANS models — including the realizable k-ε and k-ω SST models — with a four equation k-ω model (“Transition SST”) and experimental measurements at selected positions on the pressure and suction sides of a model C3X vane. Comparisons were made using mean velocity and temperature in the boundary layer without film cooling under conditions of high and low mainstream turbulence. The best performing model was evaluated using modification of the turbulent Prandtl number to attempt to better match the data for the high turbulence case. Overall, the models did not perform well for the low turbulence case; they greatly over-predicted the thermal boundary layer thickness. For the high turbulence case, their performance was better. The Transition SST model performed the best with an average thermal boundary layer thickness within 15% of the experimentally measured values. Prandtl number variation proved to be an inadequate means of improving the thermal boundary layer predictions.

scholarly journals Numerical Simulation of the Motion of a Large Scale Unmanned Surface Vessel in High Sea State Waves

2021 ◽  
Vol 9 (9) ◽  
pp. 982
Author(s):  
Shuo Huang ◽  
Weiqi Liu ◽  
Wanzhen Luo ◽  
Kai Wang
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Navier Stokes ◽  
Material Strength ◽  
Stable Range ◽  
Sea State ◽  
Unmanned Surface Vessel ◽  
Surface Vessel

The motion stability of the Unmanned Surface Vessel (USV) is threatened by the action of waves under a rough sea state. In the present paper, the motion of a large-scale USV is numerically simulated under high sea state of level 5 and 7. The overset grid method and Reynolds Averaged Navier–Stokes (RANS) approach are employed to solve Navier–Stokes (N-S) equations. For the case of wave incident angle 0° and 30°, the heave, pitch and roll motion response of a large scale USV are investigated by using the six Degrees of Freedom (6-DOF) numerical model. The effects of different sea states, as well as different wave directions, on the motion of USV are compared. The comparative results indicate that the response of this USV in waves is the periodic free-motion according to the corresponding amplitude, which does not exceed the stable range, and there are no overturning and other situations that may affect the safety, in the case of level 5 and 7 sea states. The corresponding pressure at the bottom of this USV meets the range of material strength, and no structural damage or injury to the hull occurs, although the pressure varies at different wave periods. For the case of different wave directions, the analysis of the boundary layer thickness shows that the wave direction is of great importance to the boundary layer thickness distribution, both in the level 5 and level 7 sea states.

scholarly journals Numerical investigations of flow around subsea covers at high Reynolds numbers

2021 ◽  
Vol 1201 (1) ◽  
pp. 012013
Author(s):  
G Yin ◽  
Y Zhang ◽  
M C Ong
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Numerical Simulations ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Layer Flow ◽  
High Reynolds

Abstract Two-dimensional (2D) numerical simulations of flow over wall-mounted rectangular and trapezoidal ribs subjected to a turbulent boundary layer flow with the normalized boundary layer thickness of δ/D = 0.73,1.96,2.52 (D is the height of the ribs) have been carried out by using the Reynolds-averaged Navier-Stokes (RANS) equations combined with the k – ω SST (Shear Stress Transport) turbulence model. The angles of the two side slopes of trapezoidal rib varies from 0° to 60°. The Reynolds number based on the free-stream velocity U ∞ and D are 1 × 106 and 2 × 106. The results obtained from the present numerical simulations are in good agreement with the published experimental data. Furthermore, the effects of the angle of the two side slopes of the trapezoidal ribs, the Reynolds number and the boundary layer thickness on the hydrodynamic quantities are discussed.

k ‐ ϵ Model for the Atmospheric Boundary Layer Under Various Thermal Stratifications

2005 ◽  
Vol 127 (4) ◽  
pp. 438-443 ◽  
Author(s):  
Cédric Alinot ◽  
Christian Masson
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Similarity Theory ◽  
Turbulence Models ◽  
Boussinesq Approximation ◽  
Momentum Equation ◽  
Navier Stokes ◽  
Production Term

This paper presents a numerical method for predicting the atmospheric boundary layer under stable, neutral, or unstable thermal stratifications. The flow field is described by the Reynolds’ averaged Navier-Stokes equations complemented by the k‐ϵ turbulence model. Density variations are introduced into the momentum equation using the Boussinesq approximation, and appropriate buoyancy terms are included in the k and ϵ equations. An original expression for the closure coefficient related to the buoyancy production term is proposed in order to improve the accuracy of the simulations. The resulting mathematical model has been implemented in FLUENT. The results presented in this paper include comparisons with respect to the Monin-Obukhov similarity theory, measurements, and earlier numerical solutions based on k‐ϵ turbulence models available in the literature. It is shown that the proposed version of the k‐ϵ model significantly improves the accuracy of the simulations for the stable atmospheric boundary layer. In neutral and unstable thermal stratifications, it is shown that the version of the k‐ϵ models available in the literature also produce accurate simulations.

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