Jianjun Wang

Bio: Jianjun Wang is an academic researcher from Beihang University. The author has contributed to research in topics: Finite element method & Vibration. The author has an hindex of 12, co-authored 38 publications receiving 454 citations.

Aerodynamic Modification of NACA 0012 Airfoil by Trailing-Edge Plasma Gurney Flap

Abstract: The effect of a novel plasma Gurney flap on the aerodynamic characteristics of a NACA 0012 airfoil is studied by solving the Reynolds-averaged Navier–Stokes equations The plasma actuator is simulatedwith a phenomenological model The results indicate that the plasma Gurney flap can increase the lift and nose-down pitching moment of the airfoil, and the mechanism is the same as that of the conventional Gurney flap The flowfield presents that the vonKarman vortex street disappears near the trailing edge of the airfoil with a plasmaGurney flap, which decreases the airfoil’s drag and thus increases the lift-to-drag ratio before stall By comparing the lift and nose-down pitching moment increments with the conventional Gurney flap and the jet Gurney flap, the equivalent height or jet blowing momentum coefficient of the plasma Gurney flap are estimated

Novel Signal Wave Pattern for Efficient Synthetic Jet Generation

Abstract: A novel signal wave pattern is proposed to generate a more efficient synthetic jet, and the unsteady and mean flow characteristics of the synthetic jet generated by different suction duty cycle factors k are examined by numerical simulation. The mean flowfields of the synthetic jet with different k have similar features to that exhibited in previous experiments, but they would have a stronger and larger scale vortex pair with a larger suction duty cycle factor k, when the two key parameters, the stroke length ratio L 0 /D and the Reynolds number Re U0 (based on the characteristic blowing velocity U 0 and the orifice scale D), are set to be constant. The suction duty cycle factor k affects the vortex strength formed during the blowing cycle only, and nearly does not influence the convection velocity and trajectory of the vortex. During the suction cycle, the entrainment effect of the actuator decreases with the increase of suction duty cycle factor k, so that the vortex pair can propagate farther and coalesce to synthesize a larger scale jet.

A stochastic model updating strategy-based improved response surface model and advanced Monte Carlo simulation

Abstract: To improve the accuracy and efficiency of computation model for complex structures, the stochastic model updating (SMU) strategy was proposed by combining the improved response surface model (IRSM) and the advanced Monte Carlo (MC) method based on experimental static test, prior information and uncertainties. Firstly, the IRSM and its mathematical model were developed with the emphasis on moving least-square method, and the advanced MC simulation method is studied based on Latin hypercube sampling method as well. And then the SMU procedure was presented with experimental static test for complex structure. The SMUs of simply-supported beam and aeroengine stator system (casings) were implemented to validate the proposed IRSM and advanced MC simulation method. The results show that (1) the SMU strategy hold high computational precision and efficiency for the SMUs of complex structural system; (2) the IRSM is demonstrated to be an effective model due to its SMU time is far less than that of traditional response surface method, which is promising to improve the computational speed and accuracy of SMU; (3) the advanced MC method observably decrease the samples from finite element simulations and the elapsed time of SMU. The efforts of this paper provide a promising SMU strategy for complex structure and enrich the theory of model updating.

Static/dynamic contact FEA and experimental study for tooth profile modification of helical gears

Abstract: With the development of high-performance computers, the contact finite element analysis (FEA) method has become more and more popular for studying both the static and dynamic behaviors of gear drives. In this paper, a precise tooth profile modification (TPM) approach of the helical gear pairs is presented first. The type and amount of the TPM are accurately determined by the static contact FEA results. Then dynamic contact simulations for the helical gear pairs with and without TPM are, respectively, carried out to evaluate the effect of the presented TPM approach on vibration reduction. No additional assumptions and simplifications are required for the static and dynamic contact analysis models. Vibration comparison experiments are also carried out on an open power flow test rig. Both the simulated and experimental results show that the presented precise TPM of helical gears is effective on vibration reduction around the working load, and the dynamic contact simulation is effective in estimating the effect of the TPM on vibration reduction in the designing stage.

Experimental Study of Plasma Flow Control on Highly Swept Delta Wing

Abstract: A ERODYNAMIC flow control based on plasma actuators is now in expansion, because plasma actuators are fully electronic with nomoving parts; they have an extremely fast response, very low mass, low input power, and the easy ability to simulate their effect in numerical flow solvers [1] In particular, they areflexible, so that they can be formed to various shapes and located on the air vehicles with relative ease There are no other known actuators that have such flexibility [2] There are many different plasma actuators, including dielectric barrier discharge (DBD), direct current glow discharge, radio frequency glow discharge, and filamentary arc discharges Suchomel et al [3] provided an overview of different plasma generation technologies currently under investigation for aeronautical applications The actuator used here is based on surface DBD This new discharge was invented by Roth et al and protected by a US patent since 1995 [4] The surface plasma has considerably influenced research on airflow control by plasmas, because the simplicity of its use allowed many researchers in aerodynamics to work on this subject (without necessarily being specialists in plasma generation [5]) Velocity measurements indicate that theprimary result of the averagedplasmainduced body forces is the formation of a wall jet that imparts momentum to the fluid [1] The plasma actuators for aerodynamic flow control can be applied for different purposes Examples include boundary layer control [6], lift augmentation and separation control for airfoils [7,8], and control of the dynamic stall vortex on oscillating airfoils [9] More recently, the plasma actuator has been demonstrated on application in three-dimensional vortical flow controls on delta wings and unmanned aerial vehicle (UAVs) [2,10–12] Patel et al [10] used the DBD plasma actuators for hingeless flow control over the 1303 unmanned combat air vehicle wing Control was implemented at the wing leading edge to provide longitudinal control without the hinged control surfaces Force balance results showed considerable changes in the lift characteristics of thewing for the plasma-controlled cases, when comparedwith the baseline cases Compared with the conventional traditional trailing-edge devices, the plasma actuators were demonstrated to have a significant improvement in the control authority in the 15 to 35 deg angle-ofattack range, thereby extending the operational flight envelope of the wing In addition to the lift modification, Nelson et al [11] studied the plasma actuator to provide roll control at high angles of attack on a scaled 1303 UAV configuration It was found to have excellent roll control capability, which was very responsive Greenblatt et al [2] investigated the DBD plasma actuator active control of a leadingedge vortex on a semispan delta wing at typical micro aerial vehicle Reynolds numbers The plasma actuator produced a plasma-induced jet inward from the leading edge The maximum CL ( 36 deg) increased by 02 in the poststall region at the optimum reduced frequency F 1 1 Visbal and Gaitonde [12] deployed asymmetric DBD plasma actuators on the apex of a 75 deg swept delta wing to control the vortical flows by numerical simulation The actuator was placed at x=c 0:08 and extended in a spanwise direction The strength of the plasma actuator was chosen to be Dc 2400 The changes near the apex of the wing, induced by the plasma, resulted in significant downstream displacements of the vortex breakdown location This effect could be potentially beneficial for roll control authority at high angles of attack Following actuation, the unsteady shear layer evolved into a steady pattern, characterized by stationary helical subvortices The origin of these steady substructures appeared to be linked to the increase in axial velocity within the secondary vortex, induced by the momentum injection of the actuator In this technical note, the configurations of the plasma actuator on the delta wing, similar to that used in Visbal and Gaitonde’s simulation [12], are used The plasma actuators are mounted in different chordwise locations on the leeward side of the delta wing The effect of the location of the plasma actuator on the aerodynamic performance of the delta wing is studied by the balanced force measurement in the wind tunnel At last, the smokewire visualization is used to present the flow structure variation induced by the plasma actuator

Recent developments in DBD plasma flow control

Abstract: Flow control using DBD (dielectric-barrier-discharge) plasma actuators is a relatively new, but rapidly expanding area of research. There are a number of review papers available on this subject, but few discuss on their latest developments. The purpose of the present article is to “fill the gap” by reviewing the recent trend of plasma actuator design and to summarise aerodynamic control techniques. Here, we review new plasma actuators, such as plasma synthetic jet actuators, plasma spark jet actuators, three-dimensional plasma actuators and plasma vortex generators, which can induce three-dimensional flows away from the wall. We also review the starting vortex that leads to formation of a plasma wall jet. This is an important subject not only for a better understanding of the flow induced by DBD plasma actuators, but also as a database that can be used to calibrate the numerical models for plasma flow control. Design of DBD plasma actuators to obtain turbulent skin-friction reduction is shown and the modifications to near-wall turbulence structures are summarised. Novel applications of DBD plasma actuators for aerodynamic control are then discussed, including pitch and roll control, plasma jet vectoring, circulation control and plasma flap, showing a potential of DBD plasma actuators for replacing movable, aircraft control surfaces. Finally, vortex shedding control techniques by a number of different plasma actuators are surveyed.

Mechanical model development of rolling bearing-rotor systems: A review

Abstract: The rolling bearing rotor (RBR) system is the kernel of many rotating machines, which affects the performance of the whole machine Over the past decades, extensive research work has been carried out to investigate the dynamic behavior of RBR systems However, to the best of the authors' knowledge, no comprehensive review on RBR modelling has been reported yet To address this gap in the literature, this paper reviews and critically discusses the current progress of mechanical model development of RBR systems, and identifies future trends for research Firstly, five kinds of rolling bearing models, ie, the lumped-parameter model, the quasi-static model, the quasi-dynamic model, the dynamic model, and the finite element (FE) model are summarized Then, the coupled modelling between bearing models and various rotor models including De Laval/Jeffcott rotor, rigid rotor, transfer matrix method (TMM) models and FE models are presented Finally, the paper discusses the key challenges of previous works and provides new insights into understanding of RBR systems for their advanced future engineering applications

An improved analytical method for mesh stiffness calculation of spur gears with tip relief

Abstract: Due to the effects of gear flexibility, the extended tooth contact (ETC) can appear, which is the phenomenon that the incoming tooth pair gets into contact ahead of the theoretical start of contact and the outgoing tooth pair is out of contact later than the theoretical end of contact. A large calculation error for the time-varying mesh stiffness (TVMS) calculation can be caused if the effects of ETC are ignored, especially under the larger torques. In this paper, an improved analytical method (IAM) suitable for gear pairs with tip relief is established to determine time-varying mesh stiffness (TVMS), where the effects of ETC, nonlinear contact stiffness, revised fillet-foundation stiffness, and tooth profile modification are considered. Based on the improved analytical model, TVMS under different torques, lengths, and amounts of profile modification is compared with that obtained from analytical finite element approach [29] and from FE method. The results show that TVMS obtained from the IAM agrees well with that from FE method and from analytical FE approach [29], and the computational efficiency of the IAM is also much higher than that of FE method.

An Introduction to the Design and Behavior of Bolted Joints

Abstract: Although the title of this book includes the word “introduction”, the treatment of the subject is extensive and complete. The material goes well beyond the coverage of bolted joint design received in a typical undergraduate machine design course. The easy-to-read text begins with the fundamentals of bolt strength, deformation, and material selection and proceeds to cover the topics of preload, torque, and stretch control. The emphasis is on practical considerations for the efficient design of joints, including cost, ease of assembly, inspection, and disassembly. This second, revised edition has expanded the coverage of corrosion, fatigue, gaskets, and ultrasonic measurement of bolt strain. Also included are discussions of the failure modes and mechanisms of bolted joints. Case histories from industry are presented throughout the text to illustrate key points. Many up-to-date references are presented at the end of each chapter to allow the reader to pursue individual topics further, if desired. The text contains several appendices with useful tables and formulas for quick reference. The author has broad experience in the subject area from many years as a consultant to the power generation and nuclear industry, active participation on society working groups such as ASME and PVRC, as well as the presentation of numerous seminars on the topic. This book would serve as a valuable desk reference for engineers concerned with the design and performance of bolted joints.

Fault features analysis of cracked gear considering the effects of the extended tooth contact

Abstract: Owing to the effect of gear flexibility, the extended tooth contact occurs, which is a phenomenon that the incoming tooth pair enters contact earlier than the theoretical start of contact, and the outgoing tooth pair leaves contact later than the theoretical end of contact. Considering the effects of the extended tooth contact and tooth root crack on the time-varying mesh stiffness (TVMS), a finite element (FE) model of a spur gear pair in mesh is established by ANSYS software. TVMS under different crack depths at constant rated torque (60 Nm) are calculated based on the FE model. Then, a FE model of a geared rotor system is developed by MATLAB software. Frequency-domain features, statistical features (Kurtosis and RMS) and instantaneous energies based on empirical mode decomposition (EMD) under different crack depths are calculated at 1000 rev/min and the corresponding measured results are also performed by model experiment. The results show that considering the effect of extended tooth contact, TVMS of crack gear pair becomes smooth from double-tooth engagement to single-tooth engagement; the gear crack has reduced the gear body rigidity, which leads to the reduction of stiffness of the healthy teeth and has little effect on the vibration response. The instantaneous energy can be chosen as a distinguishing indicator to qualitatively diagnose the gear cracks with different levels.