Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime
The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The analysis fo...
Saved in:
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-12-01
|
| Series: | Fluids |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2311-5521/9/12/292 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The analysis focuses on jets in crossflow with moderate Reynolds numbers (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>200</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>300</mn></mrow></semantics></math></inline-formula>) based on the jet velocity the characteristic length of the nozzle and low jet-to-cross-flow velocity ratios, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>0.25</mn><mo>≤</mo><mi>R</mi><mo>≤</mo><mn>1.4</mn></mrow></semantics></math></inline-formula>, where the jets are absolutely unstable. In this regime, the flow becomes periodic and laminar, and three distinct wake flow configurations were identified: (1) symmetric shedding of hairpin vortices at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>200</mn></mrow></semantics></math></inline-formula>; (2) the formation of toroidal vortices as the legs of hairpin vortices merge and the vortices roll up at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>300</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><mo>≤</mo><mn>0.67</mn></mrow></semantics></math></inline-formula>; (3) asymmetric shedding of hairpin vortices in the square jet at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>300</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><mo>≥</mo><mn>0.9</mn></mrow></semantics></math></inline-formula>, where higher-frequency hairpin vortex shedding combines with a low-frequency spanwise oscillation in the counter-rotating vortex pair. The dynamics of each of these flow states were analyzed. Power spectral density plots show a measurable increase in the shedding frequencies in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>R</mi><msub><mi>e</mi><mi>j</mi></msub><mo>=</mo><mn>300</mn></mrow></semantics></math></inline-formula> jets with <i>R</i>, and that these frequencies are consistently larger in circular jets. |
|---|---|
| ISSN: | 2311-5521 |