The effect on aerodynamic drag using a model of a truck has been investigated by controlling the boundary layer separation by the momentum injection method using a rotating cylinder. It involves the use of experiments coupled with computational fluid dynamics (CFD) analysis to validate the theory of momentum injection. Modelling of the truck has been done on the software GAMBIT©. The best suitable turbulence model was selected by comparing the results with the experimental results. The rotational speed and radius of the cylinder are varied to establish the effect of momentum injection on aerodynamic drag. The coefficient of drag reduces by approximately 35 per cent from an initial value of 0.51-0.32 for a cylinder of radius 1 cm with rotational speed of 4000 r/min. Chang [4], Schlichting [5], Rosenhead [6], and others. D05104

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The effect of the turning angle on the¯ow and performance characteristics of long Sshaped circular diffusers (length±inlet diameter ratio, L=D iˆ1 1:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 158/158, 22.58/22.58 and 308/308. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a ®ve-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coef®cients for 158/158, 22.58/22.58 and 308/308 diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coef®cient is 0.72. The low performance is attributed to the generation of secondary¯ows due to geometrical curvature and additional losses as a result of the high surface roughness (*0.5 mm) of the diffusers. The pressure recovery coef®cient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (908/908), i.e. 0.53. The total pressure loss coef®cient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The¯ow distribution is more uniform at the exit for the higher angle of turn diffusers. NOTATIONA i cross-sectional area at the diffuser inlet (m 2 ) AR area ratioˆ…D o =D i † 2 C loss coef®cient of total pressure losŝ …P o i ¡ P oo †=P dyn…in † C p coef®cient of static pressure recoverŷ …P s o ¡ P s i †=P dyn…in † CC concave surface CR curvature ratioˆ2R c =D i CV convex surface dA elemental area to calculate the massaveraged quantities D i diameter of the test diffusers at the inlet (m) D n Dean numberˆR n =CR 1=2 D o diameter of the test diffusers at exit (m) F any¯ow parameter (static pressure, total pressure, velocity, etc.) L centre-line length (m) P dyn…in † dynamic pressure at the inlet 1 2rU 2 ave…in † …N=m 2 † P o i mass-averaged total pressure at the inlet (N/m 2 ) P oo mass-averaged total pressure at the outlet (N/m 2 ) P s i mass-averaged static pressure at the inlet (N/m 2 ) P so mass-averaged static pressure at the outlet (N/m 2 ) P wall wall static pressure (N/m 2 ) R radius of test diffuser (m) R c radius of curvature (m) R i radius at inlet (m) R n Reynolds numberˆrD i U ave…in † =m u 0 mean¯uctuating component of velocity (m/s) U local time-averaged (10 s) total velocity (m/s) U ave…in † mass-averaged velocity at the inlet (m/s) U long velocity in the axial direction (m/s) U sec cross-¯ow velocity (secondary motion) (m/s) x distance along the centre-line of the diffuser from the inlet plane (m)The MS was Downloaded from a pitch angle (deg) b turning angle of the curved diffuser (deg) y yaw angle (angle of rotation of the ®ve-hole probe) (deg) m absolute viscosity (Ns/m 2 ) r¯uid density (kg/m 3 ) f total angular position of the section from the inlet (deg)

An analysis is presented for the stability of a viscoelastic liquid film flowing down an inclined plane with respect to three-dimensional disturbances. It is shown that under certain circumstances, these disturbances are more unstable than the two-dimensional ones, contrary to Squire's theorem.

An analysis is made of the stability of a layer of an elastico-viscous liquid flowing down an inclined plane in the presence of two-dimensional disturbances. The modified Orr-Sommerfeld equation is solved by a regular perturbation technique for disturbances of large wavelengths. It is shown that in the absence of surface tension, the layer is more unstable as compared with that for an ordinary viscous liquid if Q1 > Q2, Q1 and Q2 being stress relaxation and strain retardation parameters respectively.

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This paper discusses the effects of Hall currents on the convective instability of a rotating layer of a conducting fluid in the presence of a vertical magnetic field. It is found that the Hall currents are always destabilizing in the absence of rotation but tend to stabilize the flow as soon as the rotation exceeds certain limits. An analytical condition for nonexistence of overstability is also derived.In a collision dominated plasma (wr << 1, where w is the gyration frequency and z is the time of collision of a charged particle), electrical conductivity becomes isotropic and as such a scalar quantity. However, conductivity becomes anisotropic if the medium is rarefied and/or a strong magnetic field is present. The charged particles are in a way tied to the lines of force and their mobility transverse to the magnetic field is checked to some extent. If an electric field is applied transverse to the magnetic field, the whole current will not flow along the electric field, but a part will flow in a direction perpendicular to the electric and magnetic field. This latter part is known as the Hall current. Flow of Hall currents plays a vital role in problems of MHD power generation and in several astrophysical situations.The problem of thermal instability in a rotating layer of a conducting fluid in the presence of a uniform vertical magnetic field has been discussed exhaustively by Chandrasekhar (1961, chap. V).Recently Gupta (1967) investigated the Hall effects on the thermal instability of a horizontal layer of a conducting fluid in the presence of a uniform vertical magnetic field and found that Hall currents are destabilizing. In this paper we investigate the Hall effects on the thermal instability when the layer is subjected to a uniform rotation and permeated by a strong magnetic field.where J, E, H, V are respectively the current density, the electric field, the magnetic field, and the velocity vector. Further, p is the magnetic permeability and o0 is the electiical conductivity given by e2nr/m,, where e, 11, and n1, are the charge, number density, and mass of an electron.Eliminating the electric field from [ I ] and Maxwell's equations, we obtain the modified magnetic diffusion equation where q = 1/4npoo is the magnetic diffusivity. We choose a Cartesian system of coordinates with origin at the lower surface of the layer and z axis taken in the vertical direction.From the equations of conservation of mass, momentum, and the magnetic diffusion equation [2], we have Consider a horizontal layer of a conducting fluid which is in a state of uniform rotation and is [5] (g -qV2)h3 = H 0 -av3 Ho 853 heated from below. A uniform magnetic field H , az 4nen az ' acts in the vertical direction. The linearized hydromagnetic equations and the usual Maxwell [6] (k -V V~) V ' V , = ga($ + $) equations remain unchanged (cf. Chandrasekhar 1961, chap. V). However, Ohm's law gets modified because of the incorporation of the term am3 PHO a -2Q -+ ---v 2 h 3 , arising out of Hall currents and is as follows: az 4np az