Forebody Wake Research Articles

Effects of Forebody on Supersonic Parachute Aerodynamic Performance

As a typical aerodynamic deceleration device, supersonic parachute is widely used in aerospace return and recovery. The influence of the precursor on the aerodynamic performance of parachute is very important due to operating conditions under the wake of the precursor.In order to study the effects of supersonic forebody wake on parachute performance, numerical simulation of supersonic parachute is carried out, and the calculation results are in good agreement with the results of the wind tunnel test. The flow characteristics and flow field distribution of supersonic parachutes under free flow are analyzed. On this basis, the flow field characteristics and distribution laws of forebody and parachutes under different inflow Mach numbers and the aerodynamic characteristics of parachutes are studied. The results show that the compression wave and expansion wave generated by the forebody are reflected through the wall, and the reflected wave alternately appears in the downstream flow field. Affected by the forebody wake and reflected waves, the inflow velocity of the parachute has been asymmetrically distributed, and the velocity in the upper area has been seriously attenuated.

Computational and Experimental Study for Reducing Forebody Wake Effect by Proper Designing of a Slit cut Square Parachute used for Sonobuoy Drop

This paper discusses the design of a square parachute based on classical approach, computational analysis and experimentation. This parachute will be used to drop directional sonobuoy on the sea to locate and classify the submarines. Design improvements are brought out by providing slits into a solid square canopy of parachute to bring in more stability and minimum drift during descend. Specifically, the effect of upstream sonobuoy, RANS model, suspension line length, canopy size and slit size in flow structure were considered. The predicted drag coefficients obtained from CFD for square canopy with slit-cuts compared with the results of wind tunnel experiment and found that the increase in the suspension-line length and/or of the surface area of the parachute canopy helps in better stability and results in the minimum drag loss.

Numerical study of forebody wake effect on axisymmetric parachute opening shock and drag reduction

ABSTRACTParachute–forebody distance is a parameter which is amongst the most critical factors to be considered in forebody wake effect. In this study, a new axisymmetric parachute–forebody coupling model is developed. Axisymmetric wrinkling membrane element is built to assess the dynamic response of the parachute canopy membrane under fluid pressure. Besides, fluid model and its further implementation on the fluid structure analysis are discussed. With the proposed method, the wake effect on both the opening shock during inflation state and the drag reduction during steady state can be obtained efficiently. Finally, numerical model is validated with published experimental result and further employed to investigate the influence of distance parameters on fluid–parachute coupling behaviour. On the basis of numerical results, failure distance during the inflation process and critical forebody–parachute distance are determined. The results show that forebody–parachute distance has a strong influence on flow behaviour around the parachute in both inflation state and steady descent state.

Surface Wave Contours Associated with the Forebody Wake of Stepped Planing Hulls

Results of an extensive series of model tests that define the longitudinal surface wake profiles aft of prismatic hulls having deadrise angles of 10º, 20º and 30º are presented. Empirical equations are developed that quantitatively define these profiles and are in a form that can be easily applied by designers of stepped planing hulls. These equations are applicable for an expected range of variations in trim angle, speed coefficient, and loading coefficient typical for these hulls. A brief introduction to the concept and to the hydrodynamic advantages of stepped planing hulls is presented to orient the reader as to the importance of wake data in their design. Examples are presented that illustrate the application of these wake data for stepped planing hulls with wetted forebody chine to achieve maximum hydrodynamic lift/drag ratios. Finally experimental results are presented that illustrate the potential resistance penalty associated with the operation of chines dry forebodies where the stagnation line crosses the step.

낙하산 캐노피 전개특성에 관한 실험적 연구

낙하산 축소모형으로부터 캐노피의 전개시간과 최대 전개력을 측정하기 위하여 낙하산 캐노피의 전개특성에 관한 실험연구를 수행하였다. 시험에는 낙하산 모형을 풍동 유동장 내부로 사출하고 모형에 작용하는 항력을 측정하도록 하기 위한 장치가 사용되었다. 시간에 따른 전개력 변화특성과 최대 전개력이 획득되었으며, 전방체로 인한 후류효과를 비롯한 이들 공력특성에 대한 비교평가를 실시하였다. 링슬롯형 낙하산의 경우 기존의 시험자료들에 비해 약 10~40% 가량 빠른 전개특성을 보였으며, reefing 형상의 리본형은 기존의 결과들과 잘 일치하였다. Inflating characteristics of the parachute canopies have been experimentally investigated with the objective of measuring the parachute opening parameters such as canopy filling time and the peak opening force using scaled parachute models. A device has been made and tested to eject a model parachute into a wind tunnel flow and to measure the drag force acting on it. The force-time histories and the peak opening force are obtained, and these comparative aerodynamic characteristics were analyzed and discussed, including the effect of forebody wake. The opening of the ringslot parachute model appeared to be faster than that of the available similar data by about 10~40%, and fair to good agreement was obtained for the reefed ribbon parachute.

Proportional Control of Asymmetric Forebody Vortices

The ability of the unsteady bleed technique to control the asymmetry of the steady tip vortices separating from a forebody model is demonstrated. Mean velocity profiles measured behind the forebody model at α = 45 deg and Re = 6.3 x 10 3 clearly show the exponential spatial growth of the disturbance in the wake. This exponential growth is consistent with a spatial type of flow instability. The type of spatial instability governing the flow determines the behavior of the vortex system. The continuous variation of vortex position with control input found at α = 45 deg is consistent with a convective type of instability and allows proportional control of the forebody vortices with very low forcing amplitudes and input power levels. The forebody wake shows characteristics similar to a global type of instability for the bistable behavior found at α=55 deg. For the global type of flow instability, the vortex system is locked into one of two stable configurations, and proportional control does not seem feasible under these conditions

Forebody Influence on Rotating Parachute Aerodynamic Properties

For certain requirements of trajectory e ight conditions, some parachute ‐ payload systems are mechanically closely coupled systems and have a small diameter ratio of the canopy to the payload. The effect of decreasing diameter ratio on the aerodynamic performance of the system has been experimentally investigated on cross-type rotating parachutes. The results show a signie cant decrease in the drag coefe cient with decreasing diameter ratios, as the forebody wake interferes with the e ow around the parachute. Similarly, with an increase of the forebody’ s diameter, a decrease in the spin was observed. The diameter ratio also affects the static stability. This effect varies between improved stability for short cord cone gurations, commonly used for submunitions, to a reduction in stability when the cords are longer. The investigation also included the effects of the canopy aspect ratio, different support systems, and the attachment diameter of the cords to the payload.

Reductions in parachute drag due to forebody wake effects

An experiment was conducted to evaluate approximate analytical methods for predicting the reduction in parachute drag due to forebody wake effects. The drag of a 20/sup 0/ conical ribbon parachute was measured at several axial stations behind an ogive-cylinder forebody with and without fins. The same parachute was tested in undisturbed flow (where wake effects were negligible) so that the effects of suspension line length on parachute drag could be separated from the drag losses caused by the turbulent wake. Total head pressure surveys were made across the forebody wake and integrated across the canopy skirt area to determine the effective dynamic pressure acting on the parachute. Experimental results confirmed the validity of the underlying physical model of the parachute/wake interaction: the ratio of parachute drag behind a forebody divided by wake-free parachute drag is equal to the ratio of effective dynamic pressure acting on the parachute divided by freestream dynamic pressure.