Thermal fatigue on pistons induced by shaped high power laser. Part II: Design of spatial intensity distribution via numerical simulation

Abstract

In the laser induced thermal fatigue simulation test on pistons, the high power laser was transformed from the incident Gaussian beam into a concentric multi-circular pattern with specific intensity ratio. The spatial intensity distribution of the shaped beam, which determines the temperature field in the piston, must be designed before a diffractive optical element (DOE) can be manufactured. In this paper, a reverse method based on finite element model (FEM) was proposed to design the intensity distribution in order to simulate the thermal loadings on pistons. Temperature fields were obtained by solving a transient three-dimensional heat conduction equation with convective boundary conditions at the surfaces of the piston workpiece. The numerical model then was validated by approaching the computational results to the experimental data. During the process, some important parameters including laser absorptivity, convective heat transfer coefficient, thermal conductivity and Biot number were also validated. Then, optimization procedure was processed to find favorable spatial intensity distribution for the shaped beam, with the aid of the validated FEM. The analysis shows that the reverse method incorporated with numerical simulation can reduce design cycle and design expense efficiently. This method can serve as a kind of virtual experimental vehicle as well, which makes the thermal fatigue simulation test more controllable and predictable.

Numerical simulation of thermal loading produced by shaped high power laser onto engine parts

“…A reverse method based on finite element model (FEM) has been proposed to acquire the optimal design for pistons [4]. In this method two major steps were incorporated: validation of FEM and optimization of intensity distribution.…”

“…[1,2]. Recently high power laser was introduced to simulate the thermal loading on pistons [3,4]. Laser has been previously employed to study the thermal fatigue behavior of small material specimens cut from gas turbines, diesel engines, railroad steels, etc.…”

“…Laser has been previously employed to study the thermal fatigue behavior of small material specimens cut from gas turbines, diesel engines, railroad steels, etc. [4][5][6][7]. However, it is difficult to perform thermal fatigue test on large workpieces, since laser is typically characterized by extreme focusing and directional irradiation at high energy density.…”

“…However, it has been sampled that the instantaneous temperature fields on the top surfaces of both parts are roughly in circular patterns in the normal working condition [8]. The advantage of laser as the heat source is that it can be designed flexibly in both spatial and temporal domain in controllable manners [4]. Therefore firstly one needs to find the optimal intensity distributions for the shaped beam that can produce appropriate temperature fields and thermal loadings for pistons and cylinder heads, respectively.…”

Thermal fatigue on pistons induced by shaped high power laser. Part I: Experimental study of transient temperature field and temperature oscillation

“…The intensity distribution of the shaped beam was obtained through a reverse design method with the aid of finite element model (FEM), which is detailed in the accompanying paper [13]. In the simulation test, the shaped concentric multi-circular beam superimposed on the top surface of the piston, as illustrated in Fig.…”