Computational Analysis of a Three-Dimensional High-Velocity Oxygen Fuel (HVOF) Thermal Spray Torch
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Computational Analysis of a Three-Dimensional High-Velocity Oxygen Fuel (HVOF) Thermal Spray Torch B. Hassan, A.R. Lopez, and W.L. Oberkampf (Submitted 11 November 1996; in revised form 14 June 1997) An analysis of a high-velocity oxygen fuel thermal spray torch is presented using computational fluid dynamics (CFD). Three-dimensional CFD results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco diamond jet rotating wire torch, but wire feed is not simulated. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Argon is injected through the center of the nozzle. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled assuming instantaneous chemistry. A standard, two-equation, k-ε turbulence model is employed for the turbulent flow field. An implicit, iterative, finite volume numerical technique is used to solve the coupled conservation of mass, momentum, and energy equations for the gas in a sequential manner. Computed flow fields inside and outside the aircap are presented and discussed.
Keywords
computational fluid dynamics, gas dynamics, HVOF
1. Introduction High-velocity oxygen fuel (HVOF) thermal spraying employs a combustion process to heat the gas flow and melt the coating material. The two-phase gas and particle flow is then accelerated to high velocities. The combustion process produces temperatures in the range of 3000 K inside the thermal spray device and high pressure sufficient enough to produce a supersonic stream exterior to the device. In contrast, plasma spray devices typically attain temperatures in the range of 10,000 K, where significant ionization of the gas mixture can occur. These high temperatures typically produce lower density, subsonic flows with lower velocities as compared to HVOF. During the last few years, advances in computational fluid dynamics (CFD) have made their way into thermal spray modeling. Modern CFD incorporates detailed modeling of such physical phenomena as turbulence, chemical reactions, and multiphase flows to provide an in-depth understanding of the spray process and fundamentally aid in torch design. CFD simulations have been computed in two dimensions, primarily on axisymmetric thermal spray devices both with and without powder injection. The first CFD simulation of the HVOF process was conducted by Power et al. (Ref 1,2) and Smith et al. (Ref 3). They modeled the internal and external flow of the Metco diamond jet torch (Sulzer-Metco, Westbury, NY) with a powder feeder. Since the flow was choked at the exit of the nozzle, the internal flow was solved separately from the external flow. A
B. Hassan, A.R. Lopez, and W.L. Oberkampf, Aerosciences and Compressible Fluid Mechanics Department, Sandia National Laboratories, Albuquerque, NM 87185-0825, USA.
Journal of Thermal Spray Technology
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