Centrifugal instabilities in an experimental open cavity flow

2016 ◽  
Vol 788 ◽  
pp. 670-694 ◽  
Author(s):  
C. L. Douay ◽  
L. R. Pastur ◽  
F. Lusseyran
Keyword(s):  
Aspect Ratio ◽  
Parametric Study ◽  
Travelling Waves ◽  
Cavity Flow ◽  
Secondary Flows ◽  
Open Cavity ◽  
Large Aspect Ratio ◽  
Small Aspect Ratio ◽  
The Family ◽  
Steady Mode

We present an experimental parametric study of spanwise centrifugal instabilities in an open cavity flow. We show that the mode selected at threshold depends on the cavity streamwise aspect ratio. For small aspect ratio, a steady mode is enhanced, while travelling waves are observed for large aspect ratio. The bifurcation is found to be supercritical for all configurations. Sidewall effects are shown to generate secondary flows that carry the vortical patterns. Spanwise confinement enhances the family of steady modes relative to the family of oscillatory modes. These results are discussed with respect to predictions from linear stability analyses and other flows developing centrifugal instabilities.

Cavitating Flow Past a Large Aspect-Ratio Hydrofoil

1961 ◽  
Vol 5 (01) ◽  
pp. 1-8
Author(s):  
E. Cumberbatch
Keyword(s):  
Aspect Ratio ◽  
Cavity Flow ◽  
Horseshoe Vortex ◽  
Cavitating Flow ◽  
Large Aspect Ratio ◽  
Central Section ◽  
Tip Vortices ◽  
Vortex Model ◽  
Flow Past ◽  
Good Comparison

Tip effects on the cavitating flow past a large aspect-ratio lifting hydrofoil are considered. The tip vortices arising from the flow leakage around the tip from the lower to the upper side of the hydrofoil are assumed to cavitate. The flow over the central section of the hydrofoil is taken as two-dimensional cavity flow and hence there is a wide planar cavity there. The separate cavity regions are taken not to coalesce. The flow is represented by a simple horseshoe-vortex model and descriptions of the flow over the central section, near the tip and well downstream, are derived and appropriately matched. The lift on the hydrofoil is then calculated, taking the downwash into account. The lift is seen to be reduced by the tip effects, and shows good comparison with experimental results.

Modification of MnS inclusion by tellurium in 38MnVS6 micro-alloyed steel

2020 ◽  
Vol 117 (6) ◽  
pp. 615
Author(s):  
Ping Shen ◽  
Lei Zhou ◽  
Qiankun Yang ◽  
Zhiqi Zeng ◽  
Kenan Ai ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Aspect Ratio ◽  
Strong Influence ◽  
Experimental Results ◽  
Alloyed Steel ◽  
Equivalent Diameter ◽  
Small Aspect Ratio ◽  
Steel Quality ◽  
Eds Analysis ◽  
Micro Alloyed Steel

In 38MnVS6 steel, the morphology of sulfide inclusion has a strong influence on the fatigue life and machinability of the steel. In most cases, the MnS inclusions show strip morphology after rolling, which significantly affects the steel quality. Usually, the MnS inclusion with a spherical morphology is the best morphology for the steel quality. In the present work, tellurium was applied to 38MnVS6 micro-alloyed steel to control the MnS inclusion. Trace tellurium was added into 38MnVS6 steel and the effect of Te on the morphology, composition, size and distribution of MnS inclusions were investigated. Experimental results show that with the increase of Te content, the equivalent diameter and the aspect ratio of inclusion decrease strikingly, and the number of inclusions with small aspect ratio increases. The inclusions are dissociated and spherized. The SEM-EDS analysis indicates that the trace Te mainly dissolves in MnS inclusion. Once the MnS is saturated with Te, MnTe starts to generate and wraps MnS. The critical Te/S value for the formation of MnTe in the 38MnV6 steel is determined to be approximately 0.075. With the increase of Te/S ratio, the aspect ratio of MnS inclusion decreases and gradually reaches a constant level. The Te/S value in the 38MnVS6 steel corresponding to the change of aspect ratio from decreasing to constant ranges from 0.096 to 0.255. This is most likely to be caused by the saturation of Te in the MnS inclusion. After adding Te in the steel, rod-like MnS inclusion is modified to small inclusion and the smaller the MnS inclusion, the lower the aspect ratio.

Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratio

2012 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Large Aspect Ratio ◽  
Flow Method ◽  
Dynamic Coefficients ◽  
Aspect Ratios

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with large aspect ratio are calculated by means of a three dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor. For comparison, the dynamic coefficients were also calculated using two other codes: one developed on the bulk flow method and one based on finite difference method. These two sets of dynamic coefficients were compared with those obtained from CFD. Results show a reasonable correlation for the direct stiffness estimates, with largest value predicted by CFD. In terms of cross-coupled stiffness, which is known to be directly related to cross-coupled forces that contribute to rotor instability, the CFD predicts also the highest value; however a much larger discrepancy can be observed for this term (73% higher than value predicted by finite difference method and 79% higher than bulk flow code prediction). Similar large differences in predictions one can see in the estimates for damping and direct mass coefficients, where highest values are predicted by the bulk flow method. These large variations in damping and mass coefficients, and most importantly the large difference in the cross-coupled stiffness predictions, may be attributed to the large difference in seal geometry (i.e. the large aspect ratio AR>1.0 of this seal model vs. the short seal configuration the bulk flow code is usually calibrated for, using an empirical friction factor).

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