Turbulent mixing and combustion in non-premixed and premixed colorless distributed combustion (CDC) systems are simulated with a hybrid large-eddy simulation/filtered mass density function (LES/FMDF) model. The CDC systems have low (NOx and hydrocarbon) emissions, stable combustion, and low-pressure drop and noise. They are also characterized by distributed combustion as opposed to thin flamelets, seen in ordinary combustion systems. The two parts of hybrid LES/FMDF model, i.e., the Eulerian gas dynamics finite-difference solver and the Lagrangian stochastic FMDF solver are shown to be fully consistent and computationally robust and accurate for both nonreacting and reacting flows. The LES/FMDF results are also shown to be in good agreement with the available experimental data. The numerical results show that the variation in inflow air temperature or the air to fuel jet momentum ratio has a significant effect on the turbulent flow, mixing, and combustion. They also indicate the importance of the flow configuration in the CDC combustors.

Development of efficient and low-emission colorless distributed combustion (CDC)systems for gas turbine applications require careful examination of the effects of various parameters on the fuel-air mixing and combustion in these systems. These effects are systematically studied by experimental and numerical simulations of turbulent flow, mixing and combustion in a laboratory-scale CDC system. The high air temperature CDC has shown to significantly reduce the NOx and hydrocarbon emissions while improving the reaction pattern factor and stability with low pressure drop and noise without using any flame stabilizer. Numerical simulations conducted in this study are based on the large eddy simulation (LES) and high order numerical methods. The main objective is to investigate the flow field and fuel-air mixing within the combustor by LES for the same conditions as experiments. The numerical results establish the reliability of the computational model for the CDC simulations. They also indicate the importance of fuel injector configuration and show the effects it has on the velocity, scalar and temperature fields within the combustor.HE Colorless Distributed Combustion (CDC) has been demonstrated to provide ultra-low NOx and CO emissions, improved pattern factor and reduced combustion noise in stationary gas turbine combustors. 1-3 The flame in the CDC is homogeneous and is formed in the entire combustion volume instead of a limited reaction zone. [1][2][3][4] The key factor to achieve CDC is the controlled flow distribution, reduce ignition delay, and rapid injection and mixing of fuel and air jets to promote the distributed reaction in the entire combustion volume without any flame stabilizer. 1-3 Large gas recirculation and high turbulent mixing rates are desirable and helpful for achieving the distributed reaction and for avoiding hot spot zones in the flame. 9 Air and fuel jets are normally injected separately to prevent the formation of thin reaction zones between the heated air stream and the fuel jet. Both air and fuel jets entrain hot and diluted burned gases to a desirable degree and with controlled shear layer mixing, to establish "complete" mixing of fuel and oxygen and suitable fuel-air mixture temperature in the entire combustor priori to autoignition 1 . The CDC may be established by various fuel and air injection configurations. The performance of non-premixed CDC for various geometries and fuel-air injection configurations has been studied experimentally at the University of Maryland (UMD). The focus of this study was to develop CDC for stationary gas turbine combustors, operating in the thermal intensity range of 5-85 MW/m 3 -atm. The thermal load was scaled with volume as well as the operating pressure. 7,8 The present work uses the LES model for detailed and systematic study of the turbulent flow pattern and fuel-air mixing in the UMD CDC system. The numerical predictions are first compared with the available experimental data for the case without fuel jet injection. The CDC system is then simulated...

Aerodynamics of vehicles account for nearly 80% of fuel losses on the road. Today, the use of the Intelligent Transport System (ITS) allows vehicles to be guided at a distance close to each other and has been shown to help reduce the drag coefficients of the vehicles involved. In this article, the aim is to investigate the effect of distances between a three car platoons, to their drag and lift coefficients, using computational fluid dynamics. To that end, a computational fluid dynamics (CFD) simulation was first performed on a single case and platoon of two Ahmed car models using the STAR-CCM+ software, for validation with previous experimental studies. Significant drop in drag coefficients were observed on platoon models compared to a single model. Comparison between the k-w and k-e turbulence models for a two car platoon found that the k-w model more closely approximate the experimental results with errors of only 8.66% compared to 21.14% by k-e turbulence model. Further studies were undertaken to study the effects of various car gaps (0.5L, 1.0L and 1.5L; L = length of the car) to the aerodynamics of a three-car platoon using CFD simulation. Simulation results show that the lowest drag coefficient that impacts on vehicle fuel savings varies depending on the car's position. For the front car, the lowest drag coefficient (CD) can be seen for car gaps corresponding to X1 = 0.5L and X2 = 0.5L, where CD = 0.1217, while its lift coefficient (CL) was 0.0366 (X1 and X2 denoting first to second and second to third car distance respectively). For the middle car, the lowest drag coefficient occurred when X1 = 1.5L and X2 = 0.5L, which is 0.1397. The lift coefficient for this car was -0.0611. Meanwhile, for the last car, the lowest drag coefficient was observed when X1 = 0.5L and X2 = 1.5L, i.e. CD = 0.263. The lift coefficient for this car was 0.0452. In this study, the lowest drag coefficient yields the lowest lift coefficient. The study also found that for even X1 and X2 spacings, the drag coefficient increased steadily from the front to the last car, while the use of different spacings were found to decrease drag coefficient of the rear car compared to the front car and had a positive impact on platoon driving and fuel-saving.