Extending the surface force apparatus capabilities by using white light interferometry in reflection

The application of surface force apparatus (SFA) capabilities in measuring interactions between surfaces over nanometer separations was described. The technique is used when both the materials are transparent. It was observed that the poorly reflecting surface produce fringes that have low contrast and low finesse. The results show that the technique is successful when the visibility of the interference fringes is maximized.

Aerodynamic characteristics of a wrap-around fin rocket

Purpose – The purpose of this paper is to investigate the aerodynamics characteristics (especially the side force/moment and rolling characteristics), to analyze the impacts generated by different parameters of wrap-around fins (WAFs) and to find the corresponding mechanism.Design/methodology/approach – The paper has adopted three different types of WAFs for the rocket configurations and the sub-regions dividedtechnology to investigate the lateral and rolling characteristics of WAFs, including the fins with variations in span to chord ratio, thickness,leading-edge sweep, curvature radius, fin numbers, setting angles and rotated angles. Simulations have been performed at Mach numbers from 3 to 4 through an angle-of-attack range of about 0° to 10° and at model rolling angles of 45° to 90°.Findings – The paper shows that the WAF configurations can greatly improve the longitudinal stability and enhance the longitudinal aerodynamic characteristics for the whole rocket. The total drag of the whole rocket is mainly stemmed from the body, while the drag generated by the WAF account for only about 7.42 per cent. The extra side forces and rolling moments are due largely to the unequal pressure distributions on both sides of the fin (windward or leeward). Maintaining a certain negative setting angle (d) can effectively avoid the coning movement and improve the flight stability at high angles of attack. The size of the span and chord are two main factors in controlling the longitudinal characteristics. For the side force/moment and rolling characteristics, different geometric parameters of the WAFs have played different roles.Originality/value – The paper provides the qualitative and quantitative analysis for different WAFs configurations by investigating the curves ofdifferent parameters and contouring of static pressure distributions. Findings can provide some suggestions for the designers for avoiding some significant dynamic problems, such as Magnus instability and roll rate variations during flight.

Numerical investigation of a trapped vortex miniature ramjet combustor

The design of a miniature ramjet combustor using gaseous methane fuel for Mach 2.5 has been conducted. The main challenges stem mainly from the insufficient space for mixing and burning, short residence time, and the flame stabilization. Impossible utilization of relatively large air-blast fuel injectors provides more difficulties for the design. The trapped vortex combustor, as a novel way of flameholding by trapping the pilot flame inside a cavity instead of exposing it to the mainstream, is selected. Three main parts are studied numerically, which include the cold flowfield characteristics, the fuel-injection schemes, and the overall combustion performance. The results show that the drag coefficient can helptodetermine the optimum cavity size for trappingastable vortex. Injecting all the fuel inthe cavity always leads to an overly fuel-rich condition, whereas injecting in front of the cavity with a momentum flux ratio q between 0.61 and 1.0 can successfully achieve stoichiometric mixing in the cavity. However, compared to nonreacting fuel mixing, the combustion performance is found to be more sensitive to the value of q. Among the cases studied, the one with a small q of about 0.61 has more intense pilot flames andshorter main combustor flames. The effectsofangled injection, upstream injection location, and the combustor length based on the found q are also investigated.