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!
|
| _version_ | 1850059415867097088 |
|---|---|
| author | Francisco C. Martins José C. F. Pereira |
| author_facet | Francisco C. Martins José C. F. Pereira |
| author_sort | Francisco C. Martins |
| collection | DOAJ |
| description | 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. |
| format | Article |
| id | doaj-art-c6eafabdb07740819bde368589de8f01 |
| institution | DOAJ |
| issn | 2311-5521 |
| language | English |
| publishDate | 2024-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Fluids |
| spelling | doaj-art-c6eafabdb07740819bde368589de8f012025-08-20T02:50:53ZengMDPI AGFluids2311-55212024-12-0191229210.3390/fluids9120292Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio RegimeFrancisco C. Martins0José C. F. Pereira1LAETA, IDMEC, Mechanical Engineering Department/LASEF, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisbon, PortugalLAETA, IDMEC, Mechanical Engineering Department/LASEF, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisbon, PortugalThe 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.https://www.mdpi.com/2311-5521/9/12/292jet in crossflowcircular and square jetscounter-rotating vortex pairlow jet-to-crossflow velocity ratiothree-dimensionality flow topologyvorticity dynamics |
| spellingShingle | Francisco C. Martins José C. F. Pereira Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime Fluids jet in crossflow circular and square jets counter-rotating vortex pair low jet-to-crossflow velocity ratio three-dimensionality flow topology vorticity dynamics |
| title | Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime |
| title_full | Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime |
| title_fullStr | Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime |
| title_full_unstemmed | Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime |
| title_short | Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime |
| title_sort | numerical study of laminar unsteady circular and square jets in crossflow in the low velocity ratio regime |
| topic | jet in crossflow circular and square jets counter-rotating vortex pair low jet-to-crossflow velocity ratio three-dimensionality flow topology vorticity dynamics |
| url | https://www.mdpi.com/2311-5521/9/12/292 |
| work_keys_str_mv | AT franciscocmartins numericalstudyoflaminarunsteadycircularandsquarejetsincrossflowinthelowvelocityratioregime AT josecfpereira numericalstudyoflaminarunsteadycircularandsquarejetsincrossflowinthelowvelocityratioregime |