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In order to increase the survivability of the fighter aircraft, the serpentine nozzle has been applied in series of stealth bombers and unmanned aerial vehicles due to its excellent potentiality of evidently suppressing the infrared radiation signatures and radar cross section emitted by engine exhausts. Among the geometric parameters of the serpentine nozzle, the aspect ratio (AR) at the nozzle exit is one of the most critical parameters for the nozzle design as the infrared suppression effect could be greatly enhanced with the increment of AR by strengthening the mixing between the exhaust plume and atmosphere; the aim of this paper is to study the influence of the AR on the flow characteristics of the double serpentine nozzle. The flow features of six double serpentine convergent nozzles, i.e. AR = 3, 5, 7, 9, 11, 15 respectively, were numerically simulated with the shear stress transport κ–ω turbulent model adopted, which had been validated by the experimental data. The characteristics of internal flow and external jet, and the aerodynamic performances of these six nozzles were compared. Results show that the Ma contours at the symmetric plane are different due to the distinct flow accelerations caused by the change of the curvature and the duct height for diverse AR, and the surface pressure and the shock wave features are different correspondingly. The lateral divergence and the lateral convergence characteristics of the nozzle configuration lead to opposite lateral flow under diverse AR, and the change of lateral width induced different lateral pressure gradient, then lead to various lateral vortex distributions. The length of potential core is the contribution of the comprehensive effects of geometry parameters, and it is decreased with the increase of AR due to the dominated effect of the increased mixing area; however, the declining rate is slowed down. The AR of 5 should be chosen for the best aerodynamic performance of the double serpentine nozzle under the qualifications to completely shield the high-temperature turbine.

Shock vector control (SVC) based on transverse jet injection is one of the fluidic thrust vectoring (FTV) technologies, and is considered as a promising candidate for the future exhaust system working at high nozzle pressure ratio (NPR). However, the low vector efficiency (η) of the SVC nozzle remains an important problem. In the paper, a new method, named as the improved SVC, was proposed to improve the vector efficiency (η) of a SVC nozzle, which enhances the vector control of primary supersonic flow by adopting a bypass injection. It needs less secondary flow from high pressure component of an aero-engine and has smaller influence on the working character of an aero-engine. The flow mechanism of the improved SVC nozzle was investigated by solving three-dimensional Reynolds-averaged Navier--Stokes with shear stress transport (SST) κ–ω turbulence model. The shock waves, jets-primary flow interactions, flow separation, and vector performance were analyzed. The influences of aerodynamic and geometric parameters, namely, NPR, secondary pressure ratio (SPR), and bypass injection position (Xj.ad.) on flow characteristics and vector performance were investigated. Based on the design of experiment (DOE), the response surface methodology (RSM) and the simulation model of an aero-engine, a method to estimate the coupling performance of the improved SVC nozzle and an aero-engine was studied, and a new balance relationship between the improved SVC nozzle and an aero-engine was established. Results shows that (1) with the assistance of bypass injection, the jet penetration and the capability of vector control are largely improved, resulting in a vector efficiency (η) of 1.98 deg/%-ω at the designed NPRD = 13.88; (2) in a wide range of operating conditions, larger vector angle (δp), higher thrust coefficient (Cfg), and higher vector efficiency (η) of the improved SVC nozzle were obtained, (3) in the coupling process of the improved SVC nozzle and an aero-engine, a δp of 18.1 deg was achieved at corrected secondary flow ratio of 10% and corrected bypass ratio of 6.98%, and the change of the thrust and the specific fuel consumption (SFC) were within 12%, which is better than the coupling performance of a SVC nozzle and an aero-engine.

Serpentine nozzles have been used in stealth fighters to increase their survivability. For real turbofan aero-engines, the existence of the double ducts (bypass and core flow), the tail cone, the struts, the lobed mixers, and the swirl flows from the engine turbine, could lead to complex flow features of serpentine nozzle. The aim of this paper is to ascertain the effect of different inlet configurations on the flow characteristics of a double serpentine convergent nozzle. The detailed flow features of the double serpentine convergent nozzle including/excluding the tail cone and the struts are investigated. The effects of inlet swirl angles and strut setting angles on the flow field and performance of the serpentine nozzle are also computed. The results show that the vortices, which inherently exist at the corners, are not affected by the existence of the bypass, the tail cone, and the struts. The existence of the tail cone and the struts leads to differences in the high-vorticity regions of the core flow. The static temperature contours are dependent on the distributions of the x-streamwise vorticity around the core flow. The high static temperature region is decreased with the increase of the inlet swirl angle and the setting angle of the struts. The performance loss of the serpentine nozzle is mostly caused by its inherent losses such as the friction loss and the shock loss. The performance of the serpentine nozzle is decreased as the inlet swirl angle and the setting angle of the struts increase.

Shock Vector Controlling (SVC) nozzle is one of the most effective ways to obtain the thrust vector for the advanced engine. The SVC nozzle has the advantages of simple structure, light weight and fast response. Numerous analytical, numerical and experimental studies have been carried out on SVC nozzle in recent years. While these studies mainly focus on the nozzle and ignore the influence between SVC nozzle and engine. In fact, the secondary flows of fluidic thrust vectoring nozzle are all extracted from the engine fan or high pressure compressor, no matter it is based on SVC or others. The extraction and injection of the secondary flow both influence the components matching and engine performance. And the mass flow and pressure of secondary flow are constrained by engine working condition in turn. So the SVC nozzle should be installed in the engine environment for evaluation. The influence of SVC nozzle secondary flow on engine thermodynamic cycle and performance is in two major ways. First, when the secondary flow extracts from the fan or HPC, the operating point of the engine will change. It results in the thermodynamic parameters at each engine stations and the performance of engine change. The reason for this change is that the bleeding of secondary flow broke the mass flow balance equations between the engine components. Second, the injection of secondary flow in the expansion section of nozzle also leads to engine performance change, while the engine operating point remains normal. The characteristic of certain SVC nozzle is obtained by computational fluid dynamics method. Then the Response Surface Method (RSM) model based on the design of experiment is employed to build the relations of performance parameters and design variables of SVC nozzle. Combining basic engine performance simulation model with SVC nozzle RSM model, the model for engine with SVC nozzle is built. To evaluate the performance of the engine with SVC nozzle, the conceptual design of double bypass variable cycle engine with SVC nozzle is given. The influence of the secondary flow extracting from the fan outlet, CDFS outlet and the first stage of HPC is discussed. And its performances such as vector angle, thrust coefficient, thrust and specific fuel consumption are obtained by employing the engine simulation model built by this paper.

Shock vector controlling (SVC) nozzle, based on confined transverse injection and shock wave/boundary layer interaction, offers an alternative for future aircraft thrust vectoring (TV) exhausting system, due to its simple structure, low weight, and quick vector response. In the paper, the flow mechanism of SVC nozzle was studied by numerical simulation after the validation of computational fluid dynamics (CFD) models was confirmed. Then, the influence of substantial affecting factors, including injection configurations and injection angles, on the confined transverse injection flowfield characteristics and vector performance was investigated numerically. The results show that the “λ” shock wave induced by the jet injection causes unbalanced side force for the primary flow deflecting, and under larger secondary pressure ratio (SPR), the induced shock wave interacts with upper wall, weakening the thrust vector efficiency; with the increase of injection orifice numbers, the vector angle of SVC nozzle rises and is less than that of slot injection configuration; under smaller SPR, the thrust vector angle increases with the injection angle. For the case of SPR = 1.0 and 1.2, there exist optimal injection angles at which the maximum TV angle achieved.

This study was aimed to analyze the efficiency and influence factors of PBSC collection by an automatic (AutoPBSC procedure) and a semiautomatic apheresis procedure ( MNC procedure) of COBE Spectra cell separators. According to the different objects, A total of 109 apheresis cases were divided into autologous cohort (patient) and allogeneic cohort (donor). The quantity and quality of the collections and the characteristics of apheresis procedure were compared, the yields and influence factors of two cohorts with two kinds of procedures were analyzed respectively. The results showed that the collections of two procedure in patients and donors which processed the similar blood volumes were insignificantly different in MNC%, CD34⁺ %, CD34⁺ cell counts and Hb concentration (P0.05) ; the collections by AutoPBSC procedure had got fewer platelets, less product volumes whereas more ACD-A used, longer apheresis time in comparison with MNC procedure (P0.05). Correlation analysis indicated that MNC (r = 0.314,P = 0.015) , CD34⁺ cell counts (r = 0.922, P = 0.000) in collections were positively correlated with preahperesis in the autologus cohort by two procedures, CD34⁺ cell counts were correlated with WBC (r = 0.369, P = 0.004) and MNC (r = 0.495,P = 0.000) in collections; MNC (r = 0.896, P = 0.000) was positive correlated with preahperesis by AutoPBSC procedures and CD34⁺ cell counts also (r = 0.666,P = 0.000) by MNC procedure in the allogeneic cohort. Male had got more MNC and CD34⁺ cell counts than female (P0.05), age ≤ 40 had got more MNC and CD34⁺ cell counts than age40 (P0.05) in patients by AutoPBSC procedure; age40 had got more CD34⁺ cell counts than age ≤ 40 by MNC procedure(P0.05). Only male had got more MNC and CD34⁺ cell counts than female (P0.05) by MNC procedure in donors. It is concluded that with same amount of blood processing, the PBSC collections from autologous patients and allogeneic donors had got a high degree of uniformly in purity of MNC and purity and concentration of CD34(+) cell counts by two procedure, whereas sex and age imposed more influence on PBSC collection in autologous.