Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations
<jats:title>Abstract</jats:title> <jats:p>The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex br...
| Main Authors: | , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | English |
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ASME International
2021
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| Online Access: | https://hdl.handle.net/1721.1/138758 |
| _version_ | 1826208701099278336 |
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| author | Gupta, Saarthak Shanbhogue, Santosh Shimura, Masayasu Ghoniem, Ahmed F Hemchandra, Santosh |
| author2 | Massachusetts Institute of Technology. Department of Mechanical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Mechanical Engineering Gupta, Saarthak Shanbhogue, Santosh Shimura, Masayasu Ghoniem, Ahmed F Hemchandra, Santosh |
| author_sort | Gupta, Saarthak |
| collection | MIT |
| description | <jats:title>Abstract</jats:title>
<jats:p>The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centerbody diameter (Dc) on the PVC in a nonreacting flow in a single nozzle swirl combustor. Time-resolved high-speed stereoscopic PIV measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm, and 0 (i.e., no centerbody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re∼20,000). The centerbody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centerbody, a coherent PVC is present in the flow as expected. The introduction of a centerbody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the VBB and centerbody wake recirculation zone regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the destabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centerbody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.</jats:p> |
| first_indexed | 2024-09-23T14:10:25Z |
| format | Article |
| id | mit-1721.1/138758 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T14:10:25Z |
| publishDate | 2021 |
| publisher | ASME International |
| record_format | dspace |
| spelling | mit-1721.1/1387582023-04-10T19:09:34Z Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations Gupta, Saarthak Shanbhogue, Santosh Shimura, Masayasu Ghoniem, Ahmed F Hemchandra, Santosh Massachusetts Institute of Technology. Department of Mechanical Engineering <jats:title>Abstract</jats:title> <jats:p>The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centerbody diameter (Dc) on the PVC in a nonreacting flow in a single nozzle swirl combustor. Time-resolved high-speed stereoscopic PIV measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm, and 0 (i.e., no centerbody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re∼20,000). The centerbody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centerbody, a coherent PVC is present in the flow as expected. The introduction of a centerbody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the VBB and centerbody wake recirculation zone regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the destabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centerbody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.</jats:p> 2021-12-21T15:20:30Z 2021-12-21T15:20:30Z 2021 2021-12-21T15:17:44Z Article http://purl.org/eprint/type/JournalArticle https://hdl.handle.net/1721.1/138758 Gupta, Saarthak, Shanbhogue, Santosh, Shimura, Masayasu, Ghoniem, Ahmed F and Hemchandra, Santosh. 2021. "Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations." Journal of Engineering for Gas Turbines and Power, 144 (2). en 10.1115/1.4052144 Journal of Engineering for Gas Turbines and Power Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf ASME International ASME |
| spellingShingle | Gupta, Saarthak Shanbhogue, Santosh Shimura, Masayasu Ghoniem, Ahmed F Hemchandra, Santosh Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title | Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title_full | Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title_fullStr | Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title_full_unstemmed | Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title_short | Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations |
| title_sort | impact of a centrebody on the unsteady flow dynamics of a swirl nozzle intermittency of pvc oscillations |
| url | https://hdl.handle.net/1721.1/138758 |
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