Abstracts - KTH Mechanics

Computations of turbulent boundary layers with
streamwise and spanwise pressure gradients
A. Jammalamadaka a, H. Nagib a and K. Chauhan a
The performance of four popular turbulence models, namely, Spalart-Allmaras, k-,
SST and RSM, is evaluated for prediction of turbulent boundary layers subjected to
streamwise and spanwise pressure gradients. The computations are made at one to
one scale for a recently completed 2-D turbulent boundary layer experiment1,2 and a
previously measured 3-D turbulent boundary layer3. Both experiments were carefully
documented with the aid of independent measurement of skin friction. The 2-D
boundary layer comparisons are made for adverse (APG) and favorable pressure
gradients with Re in the range 10,000 to 50,000. The two-equation models fared
better than the one-equation model when the mean velocity and skin friction
coefficient are compared. Overall, the models fail to replicate the non-universal
behavior of the Kármán coefficient , seen in experiments1, although they exhibit
considerable variation in it, as shown in Fig. 1(a). In the more complicated 3-D flow
through an S-duct, with simultaneously varying streamwise and spanwise pressure
gradients, the computations compare well for pressure gradient and skin-friction
coefficients. However, the computations deviate significantly from the experiments
where strong reversal of spanwise pressure gradient occurs and beyond; e.g., Fig 1(b).
In both of these test cases, the Reynolds stress model suffers from lack of welldefined
boundary conditions for u iu j resulting in poor agreement with experiments.
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a Illinois Institute of Technology, Chicago, USA.
1 Chauhan et al., Proceedings of iTi Conference on Turbulence, Germany, Sept. 2005.
2 Nagib et al., IUTAM Symp., One Hundred Years of Boundary Layer Research, Germany, Aug. 2004.
3 Bruns et al., J. Fluid Mech. 393, 179, (1999).
(a) (b)
Figure 1: (a) Downstream variation of in a 2D TBL (APG at Uref = 40 m/s), and
(b) Skin friction coefficient comparisons for 3D TBL.
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