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    CFD Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions
    (Amer Soc Mechanical Engineers, 2015) Dogu, Yahya; Sertçakan, Mustafa C.; Bahar, Ahmet S.; Pişkin, Altuğ; Arıcan, Ercan; Kocagül, Mustafa
    Brush seals require custom design and tailoring due to their behavior driven by flow dynamic, which has many interacting design parameters, as well as their location in challenging regions of turbomachinery. Therefore, brush seal technology has not reached a conventional level across the board standard. However, brush seal geometry generally has a somewhat consistent form. Since this consistent form does exist, knowledge of the leakage performance of brush seals depending on specific geometric dimensions and operating conditions is critical and predictable information in the design phase. However, even though there are common facts for some geometric dimensions available to designers, open literature has inadequate quantified information about the effect of brush seal geometric dimensions on leakage. This paper presents a detailed CFD investigation quantifying the leakage values for some geometric variables of common brush seal forms functioning in some operating conditions. Analyzed parameters are grouped as follows; axial dimensions, radial dimensions and operating conditions. The axial dimensions and their ranges are front plate thickness (z(1)=0.040-0.150in.), distance between front plate and bristle pack (z(2)=0.010-0.050in.), bristle pack thickness (z(3)=0.0200.100in.), and backing plate thickness (z(4)=0.040-0.150in.). The radial dimensions are backing plate fence height (r(1)=0.020-0.100in.), front plate fence height (r(2)=0.060-0.400in.), and bristle free height (r(3)=0.300-0.500in.). The operating conditions are chosen as clearance (r(0)=0.0000.020in.), pressure ratio (R-p=1.5-3.5), and rotor speed (n=0-40krpm). CFD analysis was carried out by employing compressible turbulent flow in 2-D axi-symmetric coordinate system. The bristle pack was treated as a porous medium for which flow resistance coefficients were calibrated by using literature based test data. Selected dimensional and operational parameters for a common brush seal form were investigated, and their effects on leakage performance were quantified. CFD results show that, in terms of leakage, the dominant geometric dimensions were found to be the bristle pack thickness and the backing plate fence height. It is also clear that physical clearance dominates leakage performance, when compared to the effects of other geometric dimensions. The effects of other parameters on brush seal leakage were also analyzed in a comparative manner.
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    Öğe
    CFD Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom Shaped Tooth Wear
    (Amer Soc Mechanical Engineers, 2015) Dogu, Yahya; Sertçakan, Mustafa C.; Bahar, Ahmet S.; Piskin, Altuğ; Arıcan, Ercan; Kocagül, Mustafa
    Conventional labyrinth seal applications in turbomachinery encounter a permanent teeth tip damage and wear during transitional operations. This is the dominant issue that causes unpredictable seal leakage performance degradation. Since the gap between the rotor and the stator changes depending on engine transitional operations, labyrinth teeth located on the rotor/stator wear against the stator/rotor. This wear is observed mostly in the form of the labyrinth teeth becoming a mushroom shape. It is known that as a result of this tooth tip wear, leakage performance permanently decreases, which negatively affects the engine's overall efficiency. However, very limited information about leakage performance degradation caused by mushroom wear is available in open literature. This paper presents a study that numerically quantifies leakage values for various radii of mushroom shaped labyrinth teeth by changing tooth-surface clearance, pressure ratio, number of teeth, and rotor speed. Analyzed parameters and their ranges are mushroom radius (R2=0-0.508mm), clearance (c(r)=0.254-2.032mm), pressure ratio (R-p=1.5-3.5), number of teeth (n(t)=1-12), and rotor speed (n=0-80krpm). CFD analyses were carried out by employing compressible turbulent flow in 2-D axi-symmetrical coordinate system. CFD leakage results were also compared with well-known labyrinth seal semi-empirical correlations. Given a constant clearance, leakage increases with the size of the mushroom radius that forms on the tooth. This behavior is caused by less flow separation and flow disturbance and the vena contracta effect for flow over the smoothly shaped mushroom tooth tip compared to the sharp-edged tooth tip. This leakage increase is higher when the tooth tip wear is considered as an addition to the unworn physical clearance, since the clearance dominates the leakage. The leakage affected by the number of teeth was also quantified with respect to the mushroom radius. The rotational effect was also studied as a secondary parameter.