Blunt body

Vortex-Shedding Flowmeters These flowmeters take advantage of vortex shedding, which occurs when a fluid flows past a non-streamlined objec t (a Blunt body). The flow cannot follow the shape of the object and separates from it, forming turbulent vortices or eddies at the object s side surfaces. As the vortices move downstream, they grow in size and are eventually shed or detached from the objec t. 

Comparison of drag for a blunt body and a streamlined body. 

Interestingly, the shape of the wake is similar to that developed behind a hypersonic blunt body where the flow converges to form a narrow recompression neck region several body diameters downstream of the rear stagnation point due to strong lateral pressure gradients. The liquid material, that is continuously stripped off from the droplet surface, is accelerated almost instantaneously to the particle velocity behind the wave front and follows the streamline pattern of the wake, suggesting that the droplet is reduced to a fine micromist. 

The formation of a shock wave is dependent on the objects that affect the flow field. The conservation of mass, momentum, and energy must be satisfied at any location. This is manifested in the formation of a shock wave at a certain location in the flow field to meet the conservahon equations. In the case of a blunt body in a supersonic flow, the pressure increases in front of the body. The increased pressure generates a detached shock wave to satisfy the conservation equations in the flow field to match the conserved properties between the inflow and outflow in front of the body. The velocity then becomes a subsonic flow behind the detached shock wave. However, the shock wave distant from the blunt body is less affected and the detached shock wave becomes an oblique shock wave. Thus, the shock wave appears to be curved in shape, and is termed a bow shock wave, as illustrated in Fig. C-1. 

Figure C-1. A bow shock wave formed in front of a blunt body.

Chang, S. S.-H. (1975). Nonequilibrium Phenomena in Dusty Supersonic Flow Past Blunt Bodies of Revolution. Phys. Fluids, 18,446. 

The wave field produced in the steady, two-dimensional flow of a reacting gas past a wavy wall has been treated in [63] and [64]. Lick [65] has obtained solutions to the nonlinear, steady, two-dimensional conservation equations governing the flow of a reacting gas mixture about a blunt body. Reviews of these and other studies may be found in [1], [2], and [66]-[71]. 

W. Lick, 7. Fluid Mech. 7, 128 (1960) Inviscid Flow Around a Blunt Body of a Reacting Mixture of Gases, Part A, General Analysis Part B, Numerical Solutions, AFOSR Tech. Note No. 58-522 R.P.I. Tech. Rept. No. AE5810) and AFOSR Tech. Note No. 58-1124 R.P.I. Tech. Rept. No. AE 5814), Rensselaer Polytechnic Institute, Troy (1958). 

P. A. Libby, Laminar Hypersonic Heat Transfer on a Blunt Body According to the Integral Method, 1958 Heat Transfer and Fluid Mechanics Institute, Stanford Stanford University Press, 1958, 216-230. 

The pressure drag is proportional to the frontal area and to the differ ence between the pressures acting on the front and back of the Linmersed body. Therefore, the pressure drag is usually dominant for blunt bodies, negligible for streamlined bodies such as airfoils, and zero for thin flat plates parallel to the flow. 

In the moderate range of 10 < Re < 1 O . Ihe drag coefficient remains relatively constant. This behavior is characteristic of blunt bodies. Tlie flow in the boundary layer is laminar in this range, but the flow in the separated region past the cylinder or sphere is highly turbulent with a wide turbulent wake. 

C What is the difference between sireamlined and blunt bodies Is a tennis ball a streamlined or blunt body ... 

C In flow over blunt bodies such as a cylinder, how does the pressure drag differ from the friction drag ... 

The Chilton-Colburn analogy has been obserx ed to hold quite well in laminar or turbulent flow over plane surfaces. But this is not always the case for internal flow and flow over irregular geometries, and in such cases specific relations developed should be used. When dealing with flow over blunt bodies, it is important to note that/in these relations is the skin friction coefficient, not the total drag coefficient, which also includes tlie pressure drag. 

A particularly interesting phenomenon connected with transition in the boundary layer occurs with blunt bodies, e.g., spheres or circular cylinders. In the region of adverse pressure gradient (i.e., dP/dx > 0 in Fig. 1.9) the boundary layer separates from the surface. At this location the shear stress goes to zero, and beyond this point there is a reversal of flow in the vicinity of the wall, as shown in Fig. 1.9. In this... 

G. M. Harpole and I. Catton, Laminar Natural Convection About Downward Facing Heated Blunt Bodies to Liquid Metals, J. Heat Transfer (98) 208-212,1976. 

Hence, the ordinate in Fig. 6.22 can also be used in conjunction with Eq. 6.107 or 6.109 to calculate the cross flow skin friction coefficient for cases of very small yaw angles (ts =1). Note that Iaw is equal to unity because the solution of Eq. 6.102 with Pr = 1 and an insulated surface is / = 1. Although the trends exhibited in Figs. 6.21 and 6.22 are generally similar, it must be cautioned that such large variations in the Reynolds analogy factor occur that the latter is no longer a useful concept. The heat transfer parameter for a cooled surface shows a rather small variation with Pp for Pp > Vi, a fact first utilized in Ref. 44 to obtain relatively simple expressions for the local heat flux to blunt bodies in hypersonic flow. 

The material presented earlier was confined to steady-state flows over simply shaped bodies such as flat plates, with and without pressure gradients in the streamwise direction, or stagnation regions on blunt bodies. The simplicity of these flow configurations allows reduction of the problems to the solution of steady-state ordinary differential equations. The evaluation of convective heat transfer to more complex three-dimensional configurations, characteristic of real aerodynamic vehicles, involves the solution of partial differential equations. Even when the latter are confined to steady-state problems, they require extensive use of computers in the solution of finite difference or finite element formulations Nonsteady flows further complicate the problems by introducing another dimension, namely, time. 

Natural convection to blunt bodies such as cylinders (2-dimensional) and spheres (3-dimensional) has been studied by Acrivos (9) and from his analysis one can show that these configurations are characterized by constant boundary-layer thicknesses. For 2-dimensional bodies,... 

Kemp, N.H., Rose, P.H., Detra, R.W. (1959). Laminar heat transfer around blunt bodies in dissociated air. Journal of the Aerospace Sciences 26(7) 421-430. 

Bronin, S.Ya., Zheleznyak, M.B., Mnatsakanyan, A.Kh., and Pervukhin, S.B., Nonstationary Flow Near the Critical Current Line When a Blunt Body is Flown by a Variable Density Gas, IVTAN preprint, Moscow, 1985, No. 1-164, pp. 20. 

Lang, T, G. and H. V. L. Patrick, Drag of blunt bodies in polymer solutions. Winter Annual Meeting of ASME, 1966, paper 66 WA/FE33. 

Vol. 38 S J. Dunnett, D B. Ingham The Mathematics of Blunt Body Sampling VIII, 213 pages 1988... 

Count vortices shed by blunt body in flow stream... 

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