@article{zheng_kuznetsov_roberts_paxson_2011, title={Influence of Geometry on Starting Vortex and Ejector Performance}, volume={133}, ISSN={["0098-2202"]}, DOI={10.1115/1.4004082}, abstractNote={For many propulsion devices, the thrust may be augmented considerably by adding a passive ejector, and these devices are especially attractive for unsteady propulsion systems such as pulse detonation engines and pulsejets. Starting vortices from these unsteady devices dominate the flowfield and control to a great extent the level of the thrust augmentation. Therefore, it is of fundamental interest to understand the geometric influences on the starting vortex and how these manifest themselves in augmenter/ejector performance. An unsteady Reynolds averaged Navier–Stokes calculation was used to study the physics of a starting vortex generated at the exit of a pulsed jet and its interaction with an ejector. A 50 cm long pulsejet (typical hobby scale, allowing comparison with experimental data) with a circular exit was modeled as the resonant driving source and used to suggest an optimal ejector geometry and relative position. Computed limit-cycle thrust augmentation values compared favorably to experimentally obtained values for the same ejector geometries. Results suggest that the optimal diameter of the ejector is related to its relative position, dictated by the trajectory of the vortex toroid. The effect of the length of the ejector (which determines the natural frequency of the ejector, related to the acoustic processes occurring in the ejector) on overall performance was also investigated and shown to be less important than the ejector diameter.}, number={5}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Zheng, Fei and Kuznetsov, Andrey V. and Roberts, William L. and Paxson, Daniel E.}, year={2011}, month={May} }
 @article{geng_zheng_kuznetsov_roberts_paxson_2010, title={Comparison Between Numerically Simulated and Experimentally Measured Flowfield Quantities Behind a Pulsejet}, volume={84}, ISSN={["1573-1987"]}, DOI={10.1007/s10494-010-9247-6}, abstractNote={Pulsed combustion is receiving renewed interest as a potential route to higher performance in air breathing propulsion and ground based power generation systems. Pulsejets offer a simple experimental device with which to study unsteady combustion phenomena and validate simulations. Previous computational fluid dynamics (CFD) simulations focused primarily on pulsejet combustion and exhaust processes. This paper describes a new inlet sub-model which simulates the fluidic and mechanical operation of a valved pulsejet head. The governing equations for this sub-model are described. Sub-model validation is provided through comparisons of simulated and experimentally measured reed valve motion, and time averaged inlet mass flow rate. The updated pulsejet simulation, with the inlet sub-model implemented, is validated through comparison with experimentally measured combustion chamber pressure, inlet mass flow rate, operational frequency, and thrust. Additionally, the simulated pulsejet exhaust flowfield, which is dominated by a starting vortex ring, is compared with particle imaging velocimetry (PIV) measurements on the bases of velocity, vorticity, and vortex location. The results show good agreement between simulated and experimental data. The inlet sub-model is shown to be critical for the successful modeling of pulsejet operation. This sub-model correctly predicts both the inlet mass flow rate and its phase relationship with the combustion chamber pressure. As a result, the predicted pulsejet thrust agrees very well with experimental data.}, number={4}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Geng, Tao and Zheng, Fei and Kuznetsov, Andrey V. and Roberts, William L. and Paxson, Daniel E.}, year={2010}, month={Jun}, pages={653–667} }
 @article{zheng_ordon_scharton_kuznetsov_roberts_2008, title={A new acoustic model for valveless pulsejets and its application to optimization thrust}, volume={130}, ISSN={["0742-4795"]}, DOI={10.1115/1.2900730}, abstractNote={Due to its simplicity, the valveless pulsejet may be an ideal low cost propulsion system. In this paper, a new acoustic model is described, which can accurately predict the operating frequency of a valveless pulsejet. Experimental and computational methods were used to investigate how the inlet and exhaust area and the freestream velocity affect the overall performance of a 50cm pulsejet. Pressure and temperature were measured at several axial locations for different fuel flow rates and different geometries. Computer simulations were performed for exactly the same geometries and fuel flow rates using a commercial CFD package (CFX) to develop further understanding of the factors that affect the performance of a valveless pulsejet. An acoustic model was developed to predict the frequency of these valveless pulsejets. The new model treats the valveless pulsejet engine as a combination of a Helmholtz resonator and a wave tube. This new model was shown to accurately predict geometries for maximum thrust. The model was further extended to account for the effect of freestream velocity. Evidence is provided that valveless pulsejet generates the highest thrust when the inherent inlet frequency matches the inherent exhaust frequency.}, number={4}, journal={JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, author={Zheng, F. and Ordon, R. L. and Scharton, T. D. and Kuznetsov, A. V. and Roberts, W. L.}, year={2008}, month={Jul} }
 @article{geng_zheng_kiker_kuznetsov_roberts_2007, title={Experimental and numerical investigation of an 8-cm valveless pulsejet}, volume={31}, ISSN={["0894-1777"]}, DOI={10.1016/j.expthermflusci.2006.06.005}, abstractNote={This paper investigates the performance of a small scale pulsejet whose overall length is approximately 8 cm, the smallest pulsejet ever reported to the author's knowledge. Gas dynamics, acoustics and chemical kinetics were modeled to gain an understanding of various physical phenomena affecting pulsejet operation, scalability, and efficiency. Numerical simulations were performed utilizing CFX to model 3-D compressible vicious flow in the pulsejet using the integrated Westbrook–Dryer single step combustion model. The simulation results were validated with experimental data and provide physical insight into the pulsejet operation. The pulsejet was run in valveless mode on hydrogen fuel with either a forward-facing inlet or a pair of rearward-facing inlets. Pressure, temperature, thrust, and frequency were measured as a function of valveless inlet and exit lengths and different geometries. As expected, the rearward-facing inlet produced considerably more net thrust, although still not very efficient, with a TSFC of 0.02 kg/N-h. The operating frequency was found to scale with inlet length to the negative 0.22 power, in addition to the inverse of the overall length for valved pulsejet.}, number={7}, journal={EXPERIMENTAL THERMAL AND FLUID SCIENCE}, author={Geng, T. and Zheng, F. and Kiker, A. P. and Kuznetsov, An. and Roberts, W. L.}, year={2007}, month={Jul}, pages={641–647} }
 @article{zheng_basciano_li_kuznetsov_2007, title={Fluid dynamics of cell cytokinesis - Numerical analysis of intracellular flow during cell division}, volume={34}, ISSN={["1879-0178"]}, DOI={10.1016/j.icheatmasstransfer.2006.09.005}, abstractNote={Intracellular flow of cytoplasmic fluid during cell cytokinesis is investigated. The intercellular bridge connecting two daughter cells is modeled as a cylindrical microchannel whose squeezing causes cytoplasmic flow inside the bridge itself and into the daughter cells. An equation from recent experimental measurements by Zhang and Robinson [W. Zhang, D.N. Robinson, Balance of actively generated contractile and resistive forces controls cytokinesis dynamics, Proceedings of the National Academy of Sciences of the United States of America 102 (2005) 7186–7191.] that governs the dynamics of bridge thinning is implemented in this model. The purpose of this research is to compute intracellular flow induced by the bridge thinning process. Two different types of boundary conditions are compared at the membrane–cytoplasm interface; these are a no-slip condition and a no tangential stress condition. Pressure and flow velocity distributions in the daughter cells and the force exerted by this flow on the daughter cell nucleus are computed. It is established that the pressure difference between the daughter cell and the intercellular bridge increases as time progresses. It is also observed that a region of stagnation develops on the downstream side of the nucleus as the bridge thins.}, number={1}, journal={INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER}, author={Zheng, F. and Basciano, C. and Li, J. and Kuznetsov, A. V.}, year={2007}, month={Jan}, pages={1–7} }