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Galindo, JAuthorTiseira, AAuthorNavarro, RAuthorEchavarria, JdCorresponding Author
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Numerical Analysis of the Effects of Different Rotor Tip Gaps in a Radial Turbine Operating at High Pressure Ratios Reaching Choked Flow

Publicated to:Energies. 15 (24): 9449- - 2022-12-01 15(24), DOI: 10.3390/en15249449

Authors: Galindo, Jose; Tiseira, Andres; Navarro, Roberto; Benjamin Inhestern, Lukas; David Echavarria, Juan

Affiliations

Tech Univ Berlin, Inst Luft & Raumfahrt, Marchstr 12-14 - Author
Univ Politecn Valencia, CMT Motores Term, Camino Vera S-N - Author

Abstract

To operate, radial turbines used in turbochargers require a minimum tip gap between the rotor blades and the stationary wall casing (shroud). This gap generates leakage flow driven by the pressure difference between the pressure and suction side. The tip leakage flow is largely unturned, which translates into a reduction of the shaft work due to the decrease in the total pressure. This paper investigates the flow through the rotor blade tip gap and the effects on the main flow when the turbine operates at a lower and higher pressure ratio with the presence of supersonic regions at the rotor trailing edge for two rotational speeds using computational fluid dynamics (CFD). The rotor tip gap has been decreased and increased up to 50% of the original tip gap geometry given by the manufacturer. Depending on the operational point, the results reveal that a reduction of 50% of the tip gap can lead to an increase of almost 3% in the efficiency, whereas a rise in 50% in the gap penalty the efficiency up to 3%. Furthermore, a supersonic region appears in the tip gap just when the flow enters through the pressure side, then the flow accelerates, leaving the suction side with a higher relative Mach number, generating a vortex by mixing with the mainstream. The effects of the vortex with the variation of the tip gap on the choked area at the rotor trailing edge presents a more significant change at higher than lower speeds. At a higher speed, the choked region closer to the shroud is due to the high relative inlet flow angle and the effects of the high relative motion of the shroud wall. Furthermore, this relative motion forces the tip leakage vortex to stay closer to the tip suction side, generating a subsonic region, which increases with the tip gap height. The leakage flow at lower and higher rotational speed does not affect the main flow close to the hub. However, close to the shroud, the velocity profile changes, and the generated entropy increases when the flow goes through the tip gap.

Keywords
BladeCfdChoked flowClearanceComputational fluid dynamicsDesignEfficiencyHigh pressure effectsHigh pressure ratioLeakage flowModelPressure profilePressure profilesRadial turbinesRotor tipScraping flowSonic conditionsSuction sideTip gapTip leakageTurbine componentsTurbocharger turbineTurbomachine bladesVortex flow

Quality index

Bibliometric impact. Analysis of the contribution and dissemination channel

The work has been published in the journal Energies due to its progression and the good impact it has achieved in recent years, according to the agency Scopus (SJR), it has become a reference in its field. In the year of publication of the work, 2022, it was in position , thus managing to position itself as a Q1 (Primer Cuartil), in the category Engineering (Miscellaneous).

Independientemente del impacto esperado determinado por el canal de difusión, es importante destacar el impacto real observado de la propia aportación.

Según las diferentes agencias de indexación, el número de citas acumuladas por esta publicación hasta la fecha 2025-05-03:

  • Scopus: 1
Impact and social visibility

From the perspective of influence or social adoption, and based on metrics associated with mentions and interactions provided by agencies specializing in calculating the so-called "Alternative or Social Metrics," we can highlight as of 2025-05-03:

  • The use of this contribution in bookmarks, code forks, additions to favorite lists for recurrent reading, as well as general views, indicates that someone is using the publication as a basis for their current work. This may be a notable indicator of future more formal and academic citations. This claim is supported by the result of the "Capture" indicator, which yields a total of: 4 (PlumX).

With a more dissemination-oriented intent and targeting more general audiences, we can observe other more global scores such as:

    It is essential to present evidence supporting full alignment with institutional principles and guidelines on Open Science and the Conservation and Dissemination of Intellectual Heritage. A clear example of this is:

    • The work has been submitted to a journal whose editorial policy allows open Open Access publication.
    Leadership analysis of institutional authors

    This work has been carried out with international collaboration, specifically with researchers from: Germany.

    There is a significant leadership presence as some of the institution’s authors appear as the first or last signer, detailed as follows: First Author (Galindo Lucas, José) and Last Author (ECHAVARRIA OLAYA, JUAN DAVID).

    the author responsible for correspondence tasks has been ECHAVARRIA OLAYA, JUAN DAVID.