Jinglei Xu

Fluid–Thermal Interaction Investigation of Spiked Blunt Bodies at Hypersonic Flight Condition

A spiked blunt body flying at hypersonic speed could result in significant thermal interactions between the external flowfield and the internal structure, which have not received enough attention in previous investigations. In the present study, time-dependent, loosely coupled fluid–thermal interaction simulations are conducted on a blunt body equipped with a spike with variable length at a M=5, Re=2×106 flight condition. The results show that, in the range of time considered in the study, a blunt body with a longer spike yields a better dynamic thermal performance, that is, a lower peak temperature on the blunt forebody surface and a slower temperature rise both on the forebody surface and inside the structure can be obtained. In addition, various levels of drag coefficient drop can be observed during the coupling process. A maximum decrease of 5.7% is achieved among the investigated models. The study reveals the necessity of the coupled fluid–thermal analysis to accurately predict the aerothermal enviro...

Design of an Asymmetric Scramjet Nozzle with Circular to Rectangular Shape Transition

A novel method for optimizing the shape of a three-dimensional scramjet nozzle with circular to rectangular shape transition, which aims to improve airframe integration, is presented in this paper. To generate the shape of the nozzle, the streamline tracing technique is used based on an annular optimum thrust nozzle flowfield calculated using the method of characteristics. The research is conducted using both the computational fluid dynamics approach and wind-tunnel experiments. Viscous flowfields are computed under the design conditions using commercial software Fluent in order to access the aerodynamic performance of the nozzle. The obtained computational fluid dynamics results on flow static pressures on the upper and lower walls of the three-dimensional nozzle have been validated against the measurement data. Comparisons of the computational fluid dynamics and wind-tunnel experimental results have been conducted under two specific nozzle pressure ratios; that is, underexpansion condition with nozzle p...

Principal Parameters in Flow Separation Patterns of Over-Expanded Single Expansion RAMP Nozzle

Abstract The paper investigates the loss of performance due to flow separation in an over-expanded single expansion ramp nozzle (SERN) during the startup and shutdown process. Characterization of the performance of SERN in this flight regime is complicated as the high degree of asymmetry in the geometry of SERN results in asymmetric separation patterns. In this investigation, the various separation patterns of SERN have been studied by way of numerical simulations. The characteristics of the over-expanded separation patterns have been detailed, and the effects of the critical parameters, such as the length of the flap, the expansion ramp angle and the Mach number, have been analyzed. The outcome of the simulations indicates that restricted shock separation (RSS) accounts for the largest range of over-expanded pressure ratios. The length of the flap can affect the separation patterns, and RSS on the flap does not occur for a short flap SERN. Moreover, with the ramp angle larger than 27 degrees, RSS on the ramp can be avoided, while an angle smaller than 20 degree can circumvent free shock separation (FSS) as well as RSS on the flap. When the vehicle accelerates from very low speeds, the separation pattern is changed in a complex manner, transitioning from FSS to RSS and then back to FSS.

Experimental and Numerical Investigations of a Bypass Dual Throat Nozzle

The bypass dual throat nozzle (BDTN) is a new kind of fluidic vectoring nozzle. A bypass is set between the upstream convergent section and upstream minimum area based on the conventional dual throat nozzle (DTN). The BDTN shows a minimum or even no penalty on the nozzles thrust performance, while it would be able to produce steady and efficient vectoring deflection similar to the conventional DTN. A BDTN model has been designed and subjected to experimental and computational study. The main results show that: (1) BDTN does not consume any secondary injection from the other part of the engine, while it can produce steady and efficient vectoring deflection. (2) Under the same condition, it can provide the maximum thrust vectoring efficiency of all the known fluidic thrust vectoring concepts reported in the literature. (3) The thrust vector angle is also greater than that of the conventional DTN that has been reported up to now. Especially, under NPR = 10, the thrust vector angle of BDTN can reach 21.3 deg. (4) For a wide NPR range from 2 to 10, the BDTN generates the best thrust vectoring performance under NPR = 4. Above all, the BDTN is well suited to produce vectored thrust for nozzles.

Fluid-Structure Interaction Study of the Splitter Plate in Turbine-Based Combined-Cycle Inlet System

AbstractA splitter plate is a key component of the inlet system in turbine-based combined-cycle engines, which divides the whole captured air flow into different engines, namely turbojet and ramjet...

Dynamic Experimental Investigations of a Bypass Dual Throat Nozzle

The bypass dual throat nozzle (BDTN) does not consume any secondary injection from the other part of the engine, while it can produce steady and efficient vectoring deflection similar to the conventional dual throat nozzle (DTN). A BDTN model has been designed and subjected to dynamic experimental study. The main results show that: (1) The frequency spectrums of the dynamic pressures are different between each thrust vector state. (2) The variation rates of dynamic vector of the new BDTN can reach as high as 50 deg/s, 40 deg/s, and 34 deg/s under nozzle pressure ratio NPR = 3, 5, and 10, separately. (3)The dynamic hysteresis time is less than 1 ms.

Effects of Cavity on the Performance of Dual Throat Nozzle During the Thrust-Vectoring Starting Transient Process

The dual throat nozzle (DTN) technique is capable to achieve higher thrust-vectoring efficiencies than other fluidic techniques, without compromising thrust efficiency significantly during vectoring operation. The excellent performance of the DTN is mainly due to the concaved cavity. In this paper, two DTNs of different scales have been investigated by unsteady numerical simulations to compare the parameter variations and study the effects of cavity during the vector starting process. The results remind us that during the vector starting process, dynamic loads may be generated, which is a potentially challenging problem for the aircraft trim and control.