Zhanxue Wang

Experimental and computational investigation of double serpentine nozzle

Infrared radiation signatures of gas turbine engine exhaust are suppressed markedly when equipped with a serpentine nozzle compared to an axisymmetric nozzle. The aim of this paper is to research more detailed flow characteristics of the serpentine nozzle, and to this end a double serpentine nozzle cold fluid test was conducted in this paper, static pressures on the nozzle walls surface were measured, and schlieren flow visualizations downstream of the nozzle exit were observed. Then numerical simulations of the experimental model were carried out using CFD software with k-ɛ turbulence model adopted. And the effects of geometric design parameters (the length ratio of first S length to second S length and the centerline distributions) on serpentine nozzle performance were investigated numerically. Detailed flow characteristics were presented including the distributions of static pressure, Ma number (streamlines), wall shear stress (limited streamlines), and the total pressure. Results show good agreement between the experimental data and computation. Static pressure distributions on the upper and down walls surface of double serpentine nozzle are completely different compared to the traditional axisymmetric nozzle. The rapid turning and steep passage slope of the serpentine nozzle would result in high friction loss and strong secondary flow loss, hence the value of the length ratio of first S passage to second S passage is recommended to be chosen from 2:5 to 2:3. The centerline distributions are crucial to the nozzle design for its influence on air acceleration inside the nozzle. The centerlines with a rapid turning at the exit would result in a high Ma number, which brings on high friction loss and secondary loss at the turnings. For maximum efficiency of centerline distributions, it is recommended that curves with a gentle turning at each serpentine passage exit should be chosen.

Investigation on Influence of Design Parameters for Tandem Cascades Diffuser Using DOE Method

Abstract The tandem cascade can be used as an efficient way to improve the compressor load. As for the interaction parameters between two rows of the tandem diffuser, it is known that the relative circumferential position, radial gap between two rows, ratio of chord length of two rows, difference of the stagger angle between the front row and rear row blades have significant impact on the performance of the tandem cascade diffuser. In the literature, there is a lack of references for evaluating quantitatively the influence of important tandem design parameters on the tandem diffuser, and thus the adjustment ranges of the tandem parameters cannot be determined accurately. In order to investigate the influences of the tandem design parameters on the compressor performance, in an economically affordable manner, the influences of the design parameters for the tandem cascades diffuser were investigated by Design of Experiments (DOE) method. The orthogonal experimental designs are performed for the radial gap R between the front row and rear row, inlet stagger angle θ of the rear row and relative circumferential position L between the front row and rear row of the tandem diffuser. The DOE analysis results demonstrate that the inlet stagger angle θ of the rear row has significant influence on the response value of total pressure ratio and isentropic efficiency. The relationship between the design parameters of the tandem diffuser and the compressor performance is obtained from the DOE method. The design parameters are adjusted and determined according to the DOE analysis, and then the validation calculations are carried out. The parameter selection capacity of DOE method has been validated by the results. The design parameters determined from DOE analysis can be effectively used in the design process of the tandem diffuser, with notably reduced amount of simulation of each parameter.

Multidisciplinary Design Optimization on Conceptual Design of Aero-engine

Abstract In order to obtain better integrated performance of aero-engine during the conceptual design stage, multiple disciplines such as aerodynamics, structure, weight, and aircraft mission are required. Unfortunately, the couplings between these disciplines make it difficult to model or solve by conventional method. MDO (Multidisciplinary Design Optimization) methodology which can well deal with couplings of disciplines is considered to solve this coupled problem. Approximation method, optimization method, coordination method, and modeling method for MDO framework are deeply analyzed. For obtaining the more efficient MDO framework, an improved CSSO (Concurrent Subspace Optimization) strategy which is based on DOE (Design Of Experiment) and RSM (Response Surface Model) methods is proposed in this paper; and an improved DE (Differential Evolution) algorithm is recommended to solve the system-level and discipline-level optimization problems in MDO framework. The improved CSSO strategy and DE algorithm are evaluated by utilizing the numerical test problem. The result shows that the efficiency of improved methods proposed by this paper is significantly increased. The coupled problem of VCE (Variable Cycle Engine) conceptual design is solved by utilizing improved CSSO strategy, and the design parameter given by improved CSSO strategy is better than the original one. The integrated performance of VCE is significantly improved.

Numerical study of passive cavity control on high-pressure ratio single expansion ramp nozzle under over-expansion condition

Single expansion ramp nozzle (SERN) is widely used in the propulsion system of hypersonic vehicle; it has good effect on weight loss, and also can reduce the nozzle base drag and friction loss effectively. But under the condition of transonic region, the flow is severely over-expanded in the SERN, and the corresponding performance of SERN is sharply declined. In order to improve the SERN performance under over-expansion condition, the passive flow control technique application of passive cavity on SERN is investigated numerically by solving Reynolds average Navier–Stokes equations, and with standard two-equation k-ɛ turbulent models adopted. The influences of major geometric parameters of passive cavity on the flow field and performance of passive cavity SERN are deeply explored. Results show passive cavity structure has active influence on the performance of SERN under the over-expansion condition. The shock position moves upstream and separation region increases in the passive cavity SERN. The number of the shock train in the passive cavity SERN decreases. And the second peak of the pressure distribution is obviously higher than that it has for the baseline SERN. The performance of passive cavity SERN is related to the size of separation zone and its starting position, which is determined by the position of the first hole in the passive cavity. Percent of porosity has a dominant influence on the flow field of passive cavity SERN. The position of the first hole in the passive cavity changes with the variation of percent of porosity, and the corresponding starting position of the flow blowing out from the passive cavity is different, resulting in the different position and intensity of the anterior oblique compression shock wave. The axial thrust coefficient of passive cavity SERN decreases with the increase in percent of porosity accordingly. The flow structures of passive cavity SERN change little with variety of aperture and cavity depth when percent of porosity remains constant, the axial thrust coefficient of passive cavity SERN are almost tantamount at this case. Compared to the effect of percent of porosity, the influence of aperture and cavity depth on flow field are much smaller. The influence of aperture and cavity depth on the performance of the passive cavity SERN can be ignored in the design.

Investigation on Fluidic Throat Control of Fixed Geometric Nozzle and Coupling Performance With Aero-Engine

Fluidic throat control is one key technology of fixed geometry thrust vectoring nozzle. Based on CFD numerical simulation, the flow characteristics of fluidic throat control by high pressure secondary flow injected into throat of nozzle, and performance of nozzle were investigated. The coupling method of nozzle with fluidic throat control and aero-engine was proposed. Firstly, the approximate model of nozzle with fluidic throat control was established by combining the design of experiment and response surface methodology. Then the aero-engine simulation model with air extraction was established. And by mass flow balance and pressure balance relationship, the approximate model of fluidic throat control nozzle and aero-engine simulation model with air extraction were combined into coupling model. Simulation results show that, due to the high pressure secondary flow injected into nozzle throat, there exist obvious high and low speed layers near nozzle throat, and the secondary injection made the nozzle flow over expand. Through the check of validation of approximate model, it shows good precision and can be used for the coupling model. For coupling performance, under different air extraction ratios from fan, the operating point on compressor map did not move obviously, the change of throat area affects the fan operating points greatly, and made it move to the surge boundary. And in the simulation, at the air extraction ratio of 12%, the throat control ratio of 17.8% was achieved.Copyright