Conical Afterbody Research Articles

Drag Reduction by Controlled Base Flow Separation.

THEproblem of wake .ow at high speeds and the drag associated with it are a signi.cant source of observation in the design of missiles, projectiles, and other typical high-speed vehicles. A large wake at the base of a vehicle would cause an increase in the overall drag due to the reduced base pressure. The wake studies of highspeed bodies also gain importance due to the severe aerodynamic heating problem and a high rise in the temperature of the base .ow. Many methods were devised to reduce the base drag of such highspeed bodies. These included boat tailing, base bleed, base combustion, locked vortex afterbodies, ventilated cavities, etc. Among these methods, the boat-tailed or conical afterbody concept was very popular and was found very effective in reducing base drag. But to achieve this drag reduction, the length of the conical/boattailed afterbody has to be suf.ciently large, terminating in a sharp trailing end. A short, conical/boat-tailed afterbody does not offer a suf.cient pressure recovery on its surface and, moreover, incurs considerable skin friction drag. On the other hand, using a short multistep afterbody that utilizes the concept of controlled .ow separation at the base of the vehicle can work out to be a better method of reducing base drag, provided a careful optimization of the con.guration geometry is carried out; thereby, permitting the use of shorter, lighter, and hence possibly lower cost afterbodies [1].

Three-dimensional vortical flow past bodies of revolution with conical afterbodies

Three-dimensional separated flows past bodies of revolution with conical afterbodies are studied both experimentally and numerically. The sudden increase in drag force due to the small increase in the semi-apex angle of the conical afterbody which is related to the critical geometry is revealed by force measurement and flow visualization. The details of the associated physical phenomenon, i. e. 3D separation and vortex shedding is elucidated by numerical simulations based on the finite-volume solution method for the Navier-Stokes equation in the curvilinear, boundary-fitted grid system. It is shown by the computer graphic drawings that the large-scale structure of separated vortices is composed of ring vortices and longitudinal vortices originating from the center of the ring vortices.

Shock standoff from blunt cones in high-enthalpy nonequilibrium nitrogen flow

Measurements of standoff distance from blunted cones of various bluntness raio in high-enthalpy nonequilibrium nitrogen flow have been made. The results show that the nondimensional shock detachment distance is a function both of bluntness ratio and the relaxation distance. The results show that shock detachment is more influenced by flow nonequilibrium in the shock layer than the conical afterbody.

Supersonic Axisymmetric Flow over Boattails Containing a Centered Propulsive Jet

The influence of underexpanded jets on a supersonic afterbody flowfield is investigated using computational techniques. The thin-shear-layer formulation of the compressible, Reynolds-averaged, Navier-Stokes equations is solved using a time-dependent, implicit numerical algorithm. Solutions are obtained for supersonic flow over an axisymmetric conical afterbody containing a centered propulsive jet where the freestream Mach number is 2.0 and the jet exit Mach number is 2.5. Exhaust-jet static pressures are considered in the range of 2 to 9 times the freestream static pressure and with nozzle-exit half-angles from 15 to 43 deg. Comparisons are made with experimental results for base pressure, separation distance, afterbody pressure distribution, and flowfield structure. Although good quantitative agreement with experimental separation distance and base pressure level is not observed, the parametric trends induced by exhaust-jet pressure level and nozzle-exit angle are well predicted, as well as the flowfield details in the vicinity of the afterbody and in the exhaust plume.

Afterbody Pressure Correlations for Vehicles with Ablated Nose Shapes

ACORRELATION method is presented for determining the afterbody pressure distributions over the conical afterbodies of slender re-entry vehicles at small angles of attack that have been severely ablated or eroded in the nosetip region. The technique utilizes flowfield solutions for the pressure distributions over symmetrical sphere-cone re-entry vehicles at zero angle of attack. The method is shown to reduce the afterbody pressure data obtained using seven distinctly different nosetip configurations to a single correlation curve. Contents A comprehensive wind tunnel test program to obtain pressure distribution data was conducted at M^ = 8 in tunnel B at the Arnold Engineering Test Center, Arnold Air Force Station, Tenn. The baseline sphere-cone model which was tested was a 6.7-deg half-angle conical afterbody with a bluntness ratio (RN/RB) of 0.227. The seven nose configurations shown in Fig. 1 were tested and the nose attachment plane was located at body station X/L = 0.173. The pressure data from the present experiments were correlated using the axial distance parameter (CPc /^Tc~A N . XS/DN) suggested by Mirels and Thornton1 and a pressure parameter, CP/CP where CP is the sharp cone pressure, DN is the diameter of the nose, CAN is the nose axial force coefficient referenced to the nose base area, and Xs is the axial distance from the nosetip sonic point. The experimental pressure data for each of the ablated nosetips is correlated against the spherical nosetip data in Fig. 2, using the modified distance parameter. The pressure parameter was not utilized in this exercise since experimental data were available for only one cone angle. It can be seen from the plot that the axial distance correlation parameter has quite effectively collapsed the afterbody pressure data that were obtained with rather diverse nose shapes to the correlation curve obtained for the spherical nose. The pressures in the region less than one nose diameter from the nosetip are not well correlated. The experimental results previously presented clearly indicate that reasonable afterbody pressure distributions for vehicles with severely ablated nosetips can be obtained from sphere-cone pressure distributions. The a = 0 pressure distribution along the length of a spherecone re-entry vehicle with a cone half-angle of 6.7 deg was calculated for M00=8, using the Rakich2 method of characteristics solution, out to a distance of 160 nose radii

Influence of initial flow direction on the turbulent base pressure in supersonic axisymmetric flow

Turbulent base pressure on conical afterbodies in supersonic axisymmetric flow, including initial direction effect

Characteristics of Separation at Conical Afterbodies

The mean-flow and turbulence characteristics of motion following separation from a conical afterbody were investigated for various combinations of initial boundary-layer thickness and angle of convergence of the boundary. For a given boundary geometry, the rate of turbulence production increases with decrease in the value of the boundary-layer thickness, and the increasing importance of the inertial effects of turbulence causes similarity profiles to be achieved earlier. For a given boundary-layer thickness, the flow characteristics remain almost unchanged for cone angles greater than 60○. When the cone angle is progressively reduced to 50○, the rate of turbulence production increases and the size of the eddy pocket decreases. On reattachment of the separation profile to the boundary of the tailpiece, any further reduction in the cone angle causes the cumulative turbulence production to decrease continuously.

A Correlation of Nose-Bluntness-Induced Pressures on Cylindrical and Conical Afterbodies at Hypersonic Speeds

A Correlation of Nose-Bluntness-Induced Pressures on Cylindrical and Conical Afterbodies at Hypersonic Speeds