In this study, a new centrifugal instability mode, which dominates within the boundary-layer flow over a slender rotating cone in still fluid, is used for the first time to model the problem within an enforced oncoming axial flow. The resulting problem necessitates an updated similarity solution to represent the basic flow more accurately than previous studies in the literature. The new mean flow field is subsequently perturbed leading to disturbance equations that are solved via numerical and short-wavelength asymptotic approaches, importantly yielding favourable comparison with existing experiments. Essentially, the boundary-layer flow undergoes competition between the streamwise flow component, due to the oncoming flow, and the rotational flow component, due to effect of the spinning cone surface, which can be described mathematically in terms of a control parameter, namely the ratio of streamwise to axial flow. For a slender cone rotating in sufficiently strong axial flow rates, the instability mode breaks down to Görtler-type counter-rotating spiral vortices, governed by an underlying centrifugal mechanism, which is consistent with experimental and theoretical studies for a slender rotating cone in otherwise-still fluid.

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et al.. Phase transitions and hygroscopic growth of aerosol particles containing humic acid and mixtures of humic acid and ammonium sulphate. Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Print VersionInteractive Discussion EGU Atmos. Chem. Phys. Discuss., 5, 9581-9620, 2005 www.atmos-chem-phys.org/acpd/5/9581/ SRef-ID: 1680-7375/acpd/2005-5-9581 European Geosciences Union Atmospheric Chemistry and Physics Discussions AbstractThe phase transitions and hygroscopic growth of two humic acid aerosols (Aldrich sodium salt and Leonardite Standard (IHSS)) and their mixtures with ammonium sulphate have been investigated using a combination of two techniques, Fourier transform infra-red (FTIR) spectroscopy and tandem differential mobility analysis (TDMA). A 5 growth factor of 1.16 at 85% relative humdity (RH) was found for the Aldrich humic acid which can be regarded as an upper limit for growth factors of humic-like substances (HULIS) found in atmospheric aerosol and is significantly smaller than that of typical atmospheric inorganics. We find that the humic acid aerosols exhibit water uptake over all relative humidites with no apparent phase changes, suggesting that these aerosols 10 readily form supersaturated droplets. In the mixed particles, the humic acid component decreases the deliquescence relative humidity (DRH) and increases the efflorescence relative humidity (ERH) of the ammonium sulphate component, and there is some degree of water uptake prior to ammonium sulphate deliquescence. In addition, at low RH, the FTIR spectra show that the ammonium is present in a different chemical envi-15 ronment in the mixed aerosols than in crystalline ammonium sulphate, perhaps existing as a complex with the humic materials. The growth factors of the mixed aerosols are intermediate between those of the single component aerosols and can be predicted assuming that the inorganic and organic fractions take up water independently. 25 character: i) neutral compounds; ii) mono/di carboxylic acids; iii) polycarboxylic acids, 9582 ACPD 5, 9581-9620, 2005 Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Print Version Interactive DiscussionEGU allowing ∼90% of the organic matter to be classified. The polycarboxylic fraction can account for between 20 and 50% of WSOC (McFiggans et al., 2005) and consists of molecules that have similar molecular weights and functional groups to naturally occurring humic or fulvic acids, hence they are often referred to as humic-like substances (HULIS) in the literature. Humic and fulvic acids are a heterogeneous mixture of chem-5 icals containing mainly carboxylic, hydroxyl and carbonyl functional groups. They are a major component of soils, formed through the decomposition of plant and animal materials. Limbeck et al. (2003) have shown that primary sources, e.g. biomass burning and dust from wind erosion, alone cannot account for the observed levels of HULIS in ambient aerosol. Possible secondary sources include the hete...

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This paper is concerned with the convective instabilities associated with the boundary-layer flow due to a rotating disk. Shear-thinning fluids that adhere to the power-law relationship are considered. The neutral curves are computed using a sixth-order system of linear stability equations which include the effects of streamline curvature, Coriolis force and the non-Newtonian viscosity model. Akin to previous Newtonian studies it is found that the neutral curves have two critical values, these are associated with the type I upper-branch (cross-flow) and type II lower-branch (streamline curvature) modes. Our results indicate that an increase in shear-thinning has a stabilising effect on both the type I and II modes, in terms of the critical Reynolds number and growth rate. Favourable agreement is obtained between existing asymptotic predictions and the numerical results presented here.