Introduction and objectives
The great majority of the published work on the strati ed ow around circular topography for the non-
linear regime (Nh0 =U0 > 1) neglects the in uence of the obstacle width, NLh=U0 . N is the Brunt-V ais al a
frequency, U0 is the uniform upstream velocity, and h0 and Lh are the maximum height and width of
the circular topography whose shape is given by h(x; y) = h0 =f[1 +(x=Lh)2+ (y=Lh)2]3 = 2g.
The linear theory [3] enables us a crude estimation on the behaviour of ows over topography with variable ratio
between the transversal and longitudinal characteristic lengths (r = ay=ax). Ref. [3] also shows that for
topography with r < 1 , the most visible feature is the occurrence of ow splitting, which is replaced by
wave breaking for r > 1. If r = 1, [3] indicates that the two phenomena (wave breaking and ow splitting)
occur almost simultaneously, although the theory [3] could not be used to predict the ow characteristics
when the width of a circular topography is changed, within the hydrostatic regime.
Previouly published work (e.g.: [4], [1], [2]) indicates that if Nh0 =U0 =1.5 there is a high pressure drag,
whereas accordingly with [4], [1], [2] and [5], for Nh0 =U0 =4.5 the mountain drag is much reduced and
regions of separated ow arise both upstream and downstream of the topography.
The main objectives of our work is studying the in uence of the obstacle width, the parameter NLh=U0 .
Two typical regimes based on the Nh0 =U0 (1.5 and 4.5) were studied, i.e. while Nh0 =U0 was kept
constant, NLh=U0 was changed between 5 and 60, uncovering di erent ow regimes and characteristics.
Results and conclusions
Our results led to the conclusion that apart from Nh0 =U0 , NLh=U0 is a parameter also relevant and
may a ect the ow regime. For instance, when Nh0 =U0 =1.5 and NLh=U0 changes from 10 to 20, the
nondimensional drag along the ow direction (Dx=Dlin) is reduced; that is related with a reduction of
amplitude of the gravity waves and the occurrence of a well de ned region of separated ow downstream
of the topography