Optimum Nose Shape Research Articles

Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

Investigation and comparison of performance of some air gun projectiles with nose shape modifications

Shooting accuracy of air gun projectiles is very important in sport tournaments and has always been questioned by enthusiasts. For this purpose, the performance of four samples of air gun projectiles (pellets) with various shapes and calibers of 4.5, 5.5 and 6.35 mm was studied in this article. The projectiles were four basic shapes: flat nose, sharp nose, round nose and spherical. After these projectiles were modeled geometrically, the three-dimensional compressible turbulent Navier–Stokes equations and dynamic equations of the projectiles’ motion were solved in a coupled form and in a moving computational grid. The computed results describe the trajectory, velocity variations and the altitude loss of the projectiles with time and location. Comparisons indicate that the round nose projectile had the best performance at long distances compared to the other samples. The flat nose projectile exhibited great performance at short distances, but behaved weakly at long distances. In addition, the effect of nose shape on the performance of the sharp and round nose projectiles was studied and the optimum nose shapes were identified.

Optimum nose shape of a front-rear symmetric train for the reduction of the total aerodynamic drag

For a high-speed train, the same power car is used as the first car and as the last car in a reverse direction simultaneously. Therefore, the previously optimized nose shape, considering only the first car position, is not well adopted in the last car position of a front-rear symmetric train in view of the aerodynamic drag. The three-dimensional nose shape optimization of a front-rear symmetric train is conducted to minimize the total aerodynamic drag of the entire train using CFD. The 3-D nose model is constructed by the vehicle modeling function with the optimized area distribution to minimize the micro-pressure wave. It is revealed that the total aerodynamic drag of the optimum shape for the entire train is reduced by 23.0% when compared to that of the conventionally optimized shape only for the first car of the symmetric train.

High-Energy Atmospheric Reentry Test Aerothermodynamic Analysis

The aerothermodynamic environment around an 8.3 m High-Energy Atmospheric Reentry Test vehicle is assessed. Twelve nose-shape configurations are generated, and their responses at the peak heating trajectory point are compared against the baseline nose shape. The possibility of a two-piece thermal protection system design at the nose is also considered, as are the surface catalytic affects of the aeroheating environment of such a configuration. Based on these analyses, an optimum nose shape is proposed to minimize the surface heating. The heat flux sensitivity of the optimum geometry to the angle of attack variations are also studied. A recommendation is also made for a two-piece thermal protection system design, for which the surface catalytic uncertainty associated with the jump in heating at the nose-inflatable aerodynamic decelerator juncture is reduced by a minimum of 93%. In this paper, the aeroshell is assumed to be rigid, and the inflatable fluid interaction effect is left for future investigations.

The construction of a nose shape of minimum drag for specified external dimensions and volume using Euler equations

The problem of constructing the axisymmetric nose shape which gives minimum wave drag for a specified volume and external dimensions is solved by a direct method using Euler equations. As in the Newton's formula approximation, the optimum contours together with the front faces – a segment of the boundary extremum along the longitudinal coordinate and the gently sloping segment of the bilateral extremum – may contain a cylindrical end part with a horizontal segment of the boundary extremum with respect to the maximum admissible radial coordinate. In the direct method, the required parameters (“controls”), which define the shape of the optimum contour, are the radii corresponding to the points of the segment of a bilateral extremum, including the radius of the face for fixed abscissas. For each aspect ratio (the ratio of the length to the radius of the base), when a certain value of the volume coefficient (the ratio of the volume to the volume of a cylinder of maximum external dimensions) is exceeded, the optimum nose shape is completed by a rear cylindrical part. The optimum nose shape, which begins from a certain initial contour, that satisfies the limitations of the problem, is constructed after a finite number of cycles. In each cycle, all the controls are corrected, and together with the directions of the change, their increments are found, while the information necessary for this for any number of controls is obtained after three direct calculations. One other advantage of the method is the rapid, close to quadratic, convergence. The nose shapes constructed are compared with the nose shapes that are optimum in the Newton's formula approximation.

The axisymmetric nose shape of minimum wave drag for given size and volume

Within the limits of Newton's formula, a solution of the problem of designing axisymmetric nose shapes that minimize wave drag for given volume and maximum admissible size is presented. The solution is obtained both in the slender-body approximation and in the complete formulation (without assuming a small angle between the axis of the body and the tangent to its contour). In both formulations, the optimum contours, besides a two-sided extremum segment, may contain a cylindrical generator — a boundary extremum segment with respect to the maximum admissible radial coordinate. In addition, in the complete formulation the optimum contours may include a leading or trailing flat end — a boundary extremum segment in the sense of both the longitudinal coordinate and the limit of applicability of Newton's formula. Determination of the drag coefficient of the nose shapes designed using numerical integration of the equations of the axisymmetric flow of an ideal gas confirmed the advantages of convex configurations. In the same approximation, the drag of optimum nose shapes (within the limits of Newton's formula) with concave segments may exceed the drag of equivalent cones. The formulation of the variational problem modified for such cases (in particular, with the fixed specification of the volume replaced by a lower bound) yields Newton's solution with a free volume.

1642 トンネル微気圧波を低減する列車先頭部形状について

The principle of alleviation of "micro-pressure wave" is to decrease the pressure gradient of the compression wave generated by a train entering a tunnel. "Optimum nose shape" minimizes the pressure gradient under the given conditions of train cross-sectional area and nose length. After reviewing the results of numerical optimization of the nose using CFD, we performed aeroacoustic analysis. As a result, the characteristics of the optimum area distribution and the influence of the offset of the train axis was clarified.

On Optimum Nose Shapes for Missiles in the Superaerodynamic Region

On Optimum Nose Shapes for Missiles in the Superaerodynamic Region

Optimum Nose Shapes for Missiles in the Superaerodynamic Region

SUMMARY The mechanics of the kinetic theory of gases is employed to describe the drag force on the nose of a missile moving in the superaerodynamic region of the atmosphere. Three separate cases are considered—ideal specular reflection, specular-type reflection from a slightly rough surface, and surface absorption followed by random emission of the striking molecules. The calculus of varia­ tions is employed to obtain the differential equation of the nose shape which minimizes the drag force for each of the three cases. The resulting differential equations are then solved by a numerical procedure. The drag coefficients for the optimum nose shapes are likewise determined and these are compared with the drag co­ efficients given by other nose shapes. It is further shown that the drag coefficients arising when specular-t3^pe reflections occur are significantly dependent on the nose shape. When surface absorption followed by random emission occurs, the drag co­ efficient is not strongly dependent on either the missile nose shape or the fineness ratio of the nose.