Investigation of the Aerodynamic Characteristics for the Low Aspect Ratio Launch Vehicle with the External Structure

Abstract

The Korea Aerospace Research Institute(KARI) has developed the Test Launch Vehicle(TLV) to confirm the performance of a 75 tonf engine in the Korea Space Launch Vehicle(KSLV)-II. And the TLV flight test was successful on November 28, 2018. In this paper, the solutions using CFD of the problem related to the longitudinal control of the launch vehicle due to the flow around the umbilical plate during the development process of the TLV, which intends to use the second and third stages of the KSLV-II with slight changes in configuration has been summarized. Owing to the influence of the flow around the umbilical plate, the normal force changed with the change in roll angle, and the center of pressure shifted accordingly. The controllability of the Resemblant TLV was verified by obtaining the Control Ratio(CR, the ratio of control torque to aerodynamic torque), which is the control requirement of the launch vehicle. Meanwhile, the height of the umbilical plate is lowered and the aerodynamic characteristics are predicted to confirm that the controllability increases compared to the original umbilical plate. In addition, the section shape of the umbilical plate is changed from one ellipse to two small circles to confirm that the CR increases. Finally, the position of the umbilical plate moves forward to Payload Fairing. There are various possible approaches to increase the CR of the Resemblant TLV, such as increasing the deviation angle of the nozzle and increasing the thrust of the engine. However, the simplest way to improve the controllability by increasing the CR is to reduce the height of the protuberance such as the umbilical plate and minimize the influence of the flow around the protuberance. And the section of this plate is smaller circular shape rather than an elliptical shape to increase the controllability. When developing the low aspect ratio launch vehicle using some stages and parts of the mother launch vehicle for the specific purpose such as the engine performance testing during the development of the mother launch vehicle, careful attention should be paid to the design of the protuberance such as the umbilical plate owing to control problems. This study confirmed that controllability can be a problem when the umbilical plate is mounted in the aft body of the low aspect ratio launch vehicle. It is expected that this paper could be used as a reference material in the design of low aspect ratio launch vehicles by providing an intuitive input for the design of the protuberance and control device of this type of launch vehicle.

한국항공우주연구원에서는 한국형발사체를 개발 중에 있으며, 한국형발사체의 75톤 액체로켓엔진의 성능 시험을 위해 시험발사체를 개발하여 2018년 11월 28일 비행시험을 성공하였다. 본 연구에서는 전산유동해석기법을 적용하여 엄빌리칼 플레이트와 같은 외부 구조물을 장착한 시험발사체 유사 형상에 대해 공력 특성을 예측하고, 돌출물 주변 유동 현상을 분석하여 발사체 종안정성에 미치는 영향을 확인하였다. 외부 구조물 주변 유동 현상은 수직력의 변화를 야기하여 최종적으로 발사체 종안정성에 영향을 미칠 수 있다. 이를 확인하기 위해 돌출물의 높이, 단면 형상 및 장착위치를 변화시켜 가며, 그 영향을 분석하였다. 대형 구조물을 장착한 저 세장비 발사체의 종안정성을 확보하려면, 엔진 추력을 높이거나 엔진 노즐의 회전각을 증가시키는 방법 등이 있지만, 가장 간단한 방법은 구조물의 높이를 최대한 낮추는 것이다. 또한 구조물의 단면 형상은 단일 타원 보다는 복수의 작은 원형으로 구성하는 것이 바람직하다. 한국형발사체 시험발사체와 같이 세장비가 작으며 기존 발사체 설계 자료와 부품 및 발사 설비를 이용하여 단시간에 저비용으로 개발할 경우, 본 연구가 저 세장비 발사체의 종안정성 확보에 도움이 될 것이다. 특히 민간 주도의 새로운 우주 개발 시대에 저 세장비 발사체 설계에 본 연구결과를 활용하면 발사체 설계 과정에서 시행착오를 줄일 수 있을 것이다.