The Study of Turbulent Fluctuation Characteristics in a Small Rotary Engine with a Peripheral Port Based on the Improved Delayed Detached Eddy Simulation Shear-Stress Transport (IDDES-SST) Method
Abstract
:1. Introduction
2. Mathematical Model
2.1. Improved Delayed Detached Eddy Simulation (IDDES) Model
2.2. Flow-Field Decomposition
2.3. Velocity Circulation
2.4. Q-Criterion
3. Geometric Model and Dynamic Meshing
3.1. Geometric Model
3.2. Dynamic Meshing
4. Boundary Conditions and IDDES Model Validation
4.1. Determination of Time Step Size
4.2. Computing Model and Boundary Condition
4.3. Experimental Results
5. Results and Discussion
5.1. Velocity Field
5.2. Coherent Structure
5.3. Velocity Fluctuation
5.4. Velocity Circulation
6. Conclusions
- (1)
- In the initial phase of the intake stroke, two reverse vortices with the same radius form at one side of the intake port. With the operation of the engine, the radius of the clockwise vortices keeps increasing and several small vortex structures without dominant flow direction occur at different positions.
- (2)
- At 15,000 r/min, the large-scale vortex structures with high intensity mainly gather in the center of the chamber and go through deformation and are broken during the intake process. At 135° BTDC, lots of small vortex structures distribute throughout the whole space of the chamber. Most of the vortices disappear at the end of the compression stroke.
- (3)
- Flow stability of the X direction increases from the leading to the trailing. The calculated results show the maximum fluctuation velocity RMS at the X direction is mostly four times larger than its minimum at 450° BTDC. The distribution of Y velocity RMS is like a paraboloid and the peak position moves from the mid-back to the middle of the chamber.
- (4)
- In the intake phase, two vortices occur at the cross section parallel to the covers and are located at the leading and trailing of the cross section, respectively. Compared to the intake process, more vortices occur at cross sections which are far away from the central section during the compression process.
Author Contributions
Conflicts of Interest
Nomenclature
N | cycle number |
mean velocity | |
transient fluctuation velocity | |
fluctuation velocity | |
velocity circulation | |
fluctuation velocity magnitude at X, Y | |
X, Y coordinate X, Y coordinate | |
vorticity | |
J | vortex intensity |
mean strain rate tensor | |
tensor of stress | |
turbulent kinetic energy | |
t | time |
L | a certain close curve |
IDDES length scale | |
RANS length scale | |
LES length scale | |
grid scale | |
empirical constant | |
factor of length scale | |
distance to the nearest wall | |
empirical delay function | |
elevating function | |
F1 | first blending function of the SST |
Greek Letters | |
density | |
molecular viscosity | |
turbulent viscosity | |
blending function | |
constant value | |
Acronyms | |
LES | large eddy simulation |
RNS | Reynolds-average Navier Stoke |
LDV | laser doppler velocimetry |
BTDC | before top dead center |
ATDC | after top dead center |
RNG | renormalization group |
CA | crank angle |
DES | mean strain rate tensor |
IDDES | improved delayed detached eddy simulation |
TKE | turbulent kinetic energy |
SST | shear-stress transport |
PIV | particle image velocimetry |
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Parameter | Value |
---|---|
Generating radius | 21 mm |
Eccentricity | 3 mm |
Displacement | 5 mL |
Compression ratio | 8.5 |
Width | 14.5 mm |
Intake phase | Advanced angle, 459° BTDC; Delay angle, 220° ATDC |
Exhaust phase | Advanced angle, 198° BTDC; Delay angle, 486° ATDC |
CA/° | Experimental Results | Simulation Results |
---|---|---|
730 | ||
820 | ||
910 | ||
1000 |
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Zhang, Y.; Liu, J.; Zuo, Z. The Study of Turbulent Fluctuation Characteristics in a Small Rotary Engine with a Peripheral Port Based on the Improved Delayed Detached Eddy Simulation Shear-Stress Transport (IDDES-SST) Method. Energies 2018, 11, 642. https://doi.org/10.3390/en11030642
Zhang Y, Liu J, Zuo Z. The Study of Turbulent Fluctuation Characteristics in a Small Rotary Engine with a Peripheral Port Based on the Improved Delayed Detached Eddy Simulation Shear-Stress Transport (IDDES-SST) Method. Energies. 2018; 11(3):642. https://doi.org/10.3390/en11030642
Chicago/Turabian StyleZhang, Yan, Jinxiang Liu, and Zhengxing Zuo. 2018. "The Study of Turbulent Fluctuation Characteristics in a Small Rotary Engine with a Peripheral Port Based on the Improved Delayed Detached Eddy Simulation Shear-Stress Transport (IDDES-SST) Method" Energies 11, no. 3: 642. https://doi.org/10.3390/en11030642