Simulation of streamwise vortices at the flaps of re-entry vehicles

The present study investigates separated flows in the flap region of the X-38 re-entry demonstrator with respect to the heat loads downstream reattachment induced by streamwise vortices. In a first step generic numerical flow simulations of turbulent ramp configurations with artificially induced vortex disturbances are compared with wind tunnel data of the Ludwieg tube facility in Göttingen (RWG). The results allow insight into the perturbed flow field, the associated flow topology and the influence of different flow parameters that affect the perturbations. For numerical resolution of streamwise vortices in the boundary layer of re-entry vehicles local grids are generated around the flaps of the X-38 vehicle. Extensive studies of arranging and refining the local grids demonstrate good grid convergence. For laminar cases and cases with fixed transition vortex effects on the heat transfer are observed with and without artificial vortex excitation.

Zusammenfassung

Ziel der vorgelegten Studie ist die Untersuchung abgelöster Strömungen im Klappenbereich des X-38 Wiedereintrittsdemonstrators hinsichtlich der durch Längswirbel entstehenden thermischen Belastungen stromab der Anlegelinie. Im ersten Schritt werden turbulente generische Rampenkonfiguratiorien mit künstlich induzierten Wirbelstörungen mit Windkanaldaten des Ludwierohrkanals in Göttingen (RWG) verglichen. Die Ergebnisse erlauben einen Einblick in die Störströmung, der zugehörige Strömungstopologie und der Einflüsse verschiedener Parametervariationen auf die Störströmung. Zur numerischen Auflösung der Längswirbel in der Grenzschicht von Wiedereintrittsvehikeln wurden lokale Netze um die X-38 Klappen generiert. Ausführliche numerische Studien nach Umordnung und Verfeinerung der lokalen Netze zeigen eine gute Netzkonvergenz der Ergebnisse. In laminaren Fällen und solchen mit fester Transition wurden Wirbeleinflüsse auf den Wärmestrom mit und ohne künstliche Wirbelanregung beobachtet.     

Experimental investigations on hull-fin interferences of the LOTTE airship

In the present paper experimental aerodynamic investigations on an airship configuration at angle of attack with special emphasis on the hull-fin region are reported. In particular, visualizations of flow phenomena on both hull and fins are studied. Quantitative measurements of the integral force and moment characteristics as well as local pressure coefficients serve to establish a data pool for code validation.     

Flap contour optimization for highly integrated SERN nozzles

The performance of a Single Expansion Ramp Nozzle (SERN) for hypersonic cruise vehicles is examined with focus on the flow at the nozzle flap and the corresponding separation of the boundary layer. Two wind tunnel models are used to analyze the interaction of the free stream and the nozzle flow and the flow at the flap in detail. A finite element flow code is employed to support the design of the flap model and the analysis of the flow.Comparative contour studies show that the size and the location of the separation at the flap cowl and therefore the aerodynamic quality can be influenced by optimizing the flap cowl contour. The position of the separation is measured for different contours and varying Reynolds numbers at laminar, transitional and turbulent flow conditions. Numerical studies of a nozzle/afterbody configuration suggest an improvement of up to 3.5% in axial thrust for optimized flap contours in the examined Mach range between 1.64 and 6. At the same time the rotation of the thrust vector is reduced by up to 5° at lower Mach numbers.