# Effect of Dissolved CO2 on the Hydraulic Performance of a Centrifugal Pump with Inducer under Cavitating Conditions

Nanbol Keza Bongdap, Victor Gentis, Michaël Pereira, Florent Ravelet, Farid Bakir, Liza Abtroun, Loïc Pora, Petar Tomov

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Nanbol Keza Bongdap, Victor Gentis, Michaël Pereira, Florent Ravelet, Farid Bakir, et al.. Effect of Dissolved CO2 on the Hydraulic Performance of a Centrifugal Pump with Inducer under Cavitating Conditions. 10th IAHR Meeting of the WorkGroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, Oct 2025, Brno (Rép. Tchèque), Czech Republic. pp.012016, 10.1088/1755-1315/1561/1/012016 . hal-05398076

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# Effect of Dissolved CO2 on the Hydraulic Performance of a Centrifugal Pump with Inducer under Cavitating Conditions

To cite this article: Nanbol Keza Bongdap et al 2025 IOP Conf. Ser.: Earth Environ. Sci. 1561 012016

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# Effect of Dissolved CO2 on the Hydraulic Performance of a Centrifugal Pump with Inducer under Cavitating Conditions

Nanbol Keza BONGDAP¹, Victor GENTIS¹, Michaël PEREIRA¹,
Florent RAVELET¹, Farid BAKIR¹, Liza ABTROUN², Loïc PORA²,
Petar TOMOV²

¹Arts et Metiers Institute of Technology, Cnam, LIFSE, Paris, France

²Safran Aircraft Engines, Moissy-Cramayel, France

E-mail: farid.bakir@ensam.eu

**Abstract.** This experimental study investigates the impact of dissolved gases specifically carbon dioxide (CO₂) on the hydraulic performance of a centrifugal pump equipped with an inducer. Tests were conducted at constant temperature in a closed-loop test rig using both degassed water and water containing 300 ppm in mass of dissolved CO₂, corresponding to the maximum solubility of the gas at 0.2 bars. The experimental setup included a transparent test section and a high-speed camera operating at 1000 Hz, allowing detailed visualization of vapor cavity dynamics under cavitating flow regimes. The results demonstrate that the presence of dissolved CO₂ significantly impairs pump performance, especially at low flow rates, where head degradation occurs earlier and more gradually. In contrast, degassed water delays cavitation onset but results in a more abrupt performance drop once cavitation develops. These findings underscore the critical role of fluid quality and gas content in cavitation behavior and confirm previous observations made on the inducer- only configuration.

## 1 Introduction

Cavitation and degassing are at the origin of complex hydrodynamical phenomena that can dramatically affect the pumping systems performances, particularly in rotating turbomachinery such as centrifugal pumps. Cavitation occurs when the local pressure of the fluid falls below its saturated vapor pressure, resulting in the formation of vapor cavities. At the same time, dissolved gases may be released by degassing when the fluid pressure falls below the gas saturation pressure, or gaseous inclusions in the form of microbubbles or clusters may be present in the fluid, which alters the flow behavior. These phenomena, when combined, can interact to amplify certain effects, such as performance degradation, vibrations, noise, or even premature wear of internal components. However, in certain specific cases, this coupling can also improve the stability and efficiency of the system (Deng et al., 2021; Fanjie et al., 2022).

Recent experimental investigations on centrifugal pumps operating under gas-liquid two-phase flow have shown that even small amounts of free gas can exacerbate cavitation effects or alter their onset and dynamics. Wang et al., 2021 have demonstrated that the simultaneous presence of free gas and cavitation

<figure><img src="image_3.png" /></figure>

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can significantly increase vibration amplitudes, particularly in the low-frequency domain, and provoke rapid performance degradation due to gas-locking phenomena. These results highlight the importance of considering coupled gas-vapor effects on pump instability.

To limit the effects of cavitation, high-performance centrifugal pumps are often equipped with an inducer, a helical device placed upstream of the main impeller, on the same shaft. The inducer plays a key role in reducing the required Net Positive Suction Head (NPSH) and stabilizing the flow at the suction, thus delaying the onset of cavitation and improving the hydraulic performance of the pump (Cui & Li, 2023; Fu et al., 2018).

In a previous study, the authors of the present paper have examined the influence of dissolved gas on the cavitating performances of an isolated inducer (Magne et al., 2020). These studies have shown that the presence of dissolved gas significantly modifies the critical cavitation number and the shape of the gaseous structures. This results moreover in a great impact on both the inducer efficiency and its stability. Furthermore, Jiang et al., 2022 have experimentally demonstrated that the cavitation performance of low-specific-speed centrifugal pumps can be affected in non-trivial ways by the inlet gas volume fraction (IGVF). Their study shows that a small amount of entrained gas (IGVF = 1%) may in some cases enhance cavitation resistance at low flow rates, while higher gas contents rapidly lead to increased pressure pulsations and degradation of the pump head. These findings underline the complex interaction between degassing, cavitation, and operating conditions.

However, to the best of our knowledge, no study has been yet reported that deals with the effect of dissolved gas in cavitating regimes on a full-stage pump with a coupled inducer and centrifugal impeller. This configuration is often used in applications such as propulsion or fuel supply systems (Hong et al., 2013). Particularly in the aeronautics sector, the aviation-fuel is known to contain large amounts of dissolved air (Dunn et al., 2010) and cavitation can overlap with the phenomenon of fuel degassing, caused by the drop in pressure at altitude, a phenomenon that has not yet been sufficiently studied.

The present experimental study aims to explore the impact of dissolved CO₂ on the hydraulic performance of a full-stage centrifugal pump. The pump is built for exploration purposes for the aviation industry. The aircraft engine fuel pumps are subjected to a degassing phenomenon when a aircraft is climbing and cruising. The decrease in the ambient pressure with the increase of altitude makes the jet fuel pressure in the tanks to decrease, which can potentially result in a cavitation and degassing coupling. As a result and in order to avoid security constraints, a closed loop is being built, which uses water and CO₂. As suggested by the results of Magne et al., 2020, the injection of CO₂ in water may lead to similar behaviors as the one observed for dissolved air in jet fuel regarding the degassing phenomenon. The tests are carried out in a closed loop at constant temperature with water containing an amount of 300 ppm of dissolved CO₂ representing the maximum solubility of this gas in water at 0.2 bar. The results are compared with the one reported by Gentis et al., 2025 that were obtained for totally degassed water. The evolution of pressure rise with the cavitation number is explored for 5 flow rates extending from very partial ones to close to nominal flow rates. A high-speed visualization device is also used to monitor the cavity dynamics in detail.

## 2 Experimental setup and protocol

The full-stage pump consisting in an axial inducer of specific speed $\Omega_{ind} \simeq 2$ and a centrifugal impeller of specific speed $\Omega_{imp} \simeq 0.4$ mounted on the same shaft is illustrated in Fig. 1. The main geometrical characteristics of the pump are reported in Tab. 1. The radial gap between the inducer and the tube is 0.75% of the tube diameter $D$. The impeller is of closed-type, the blades being covered at the shroud, with a labyrinth seal at the impeller inlet. The flow is discharged in a volute of exit diameter $d \simeq 0.3D$.

The pump is driven by a 30 kW Dietz motor. The rest of the test bench consists of an upstream tank with a free surface that is connected to an Edwards nXDS15i vacuum pump. Downstream of the pump, a manual valve and a motorized valve with position control are mounted to adjust the flow rate. The rest of the loop is composed of a tube of diameter 0.62D, a booster pump used to compensate for the pressure losses and to help controlling the flow rate and a large buffer tank. The flow rate measurement

<table><caption>Table 1: Main geometrical characteristics of the studied inducer and impeller</caption><thead><tr><td>Geometrical parameter</td><td>Inducer</td><td>Impeller</td></tr></thead><tbody><tr><td>Number of blades</td><td>3</td><td>9</td></tr><tr><td>Inlet hub/tip radius ratio</td><td>0.35</td><td>0.38</td></tr><tr><td>Outlet radius (mm)</td><td>40</td><td>68</td></tr></tbody></table>
<figure><img src="image_4.png" /><figcaption>Figure 1: Top left part: picture of the full-stage pump: the inducer appears in orange, while the centrifugal impeller appears in yellow (top cover with labyrinth seal) and green (blades, hub and rear side). Top right part: CAD of the pump with its volute the and upstream vein. The positions of the pressure sensors are displayed in the figure: sensor $P_1$ is situated 31D upstream of the inducer nose with D the diameter of the upstream vein, while $P_7$ is 10d downstream of the exit from the volute with diameter $d \approx 0.3D$. Bottom part: photo of the pump showing the transparent upstream vein, the volute and the motor.</figcaption></figure>
is conducted using a Krohne Waterflux 3000 electromagnetic flowmeter just before the returning of the fluid into the tank. The signals from 6 absolute and differential static pressure sensors, the flowmeter and a PT100 temperature probe are recorded with a National Instruments data acquisition system. The absolute static pressure $P_1$ is measured 31D upstream of the pump and this value is taken as the reference value for defining the cavitation number. Downstream of the pump, the outlet absolute pressure $P_7$ is measured at 10d. In the present study, the pressure is also monitored 2D upstream of the inducer at $P_2$ and between the inducer and the impeller at $P_5$.

The concentration of carbon dioxide is monitored with a CO2NTROL RS485 120 sensor (Hamilton Process Analytic) in the return part of the loop with a pre-Sens optical probe. The solubility of CO2 in water is indeed fairly high. Carbon dioxide is slowly injected in the upstream tank in previously degassed water while maintaining a small flow rate in the hydraulic loop. The target concentration is 300 ppm (part per million in mass). The gas and its concentration have been chosen as representative of the natural concentration of air in kerosene at atmospheric pressure. Please see the work of Magne et al., 2020 for details. In the present experiments, the concentration of dissolved carbon dioxide is kept constant within ±10 ppm.

All data are presented in dimensionless form. The static pressure rises between sensors $P_x$ and $P_y$ is presented as pressure coefficients $\Psi_{y-x}$:

$$ \Psi_{y-x} = \frac{P_y - P_x}{\rho\omega^2 R_i^2} $$

with $\rho$ the specific mass, $\omega$ the angular velocity and $R_i = 68$ mm the impeller outlet radius. In the present experiment, the Reynolds number based on the impeller radius and angular velocity is of the order of $2 \times 10^6$.

The flow rate is presented as percentage of the reference flow rate $Q_{ref}$ which corresponds to the design point of the impeller.

Finally, the cavitation number $\sigma$ is based on the impeller tip speed and on the (infinite) upstream absolute pressure $P_1$:

$$ \sigma = \frac{2(P_1 - P_v)}{\rho\omega^2 R_i^2} $$

with $P_v$ the vapor pressure of water at the temperature of the experiment.

The flow rate measurement are accurate within ±0.5% of $Q_{ref}$, and the propagated uncertainties are respectively ±3 × 10⁻³ for flow coefficient $\Psi$ and ±1 × 10⁻³ for cavitation number $\sigma$.

Five flow rates were selected for the study. They correspond to 4%, 16%, 39%, 58% and 78% of the reference flow rate. These flow rates correspond to quite unusual very partial values. However, they represent critical operating points that are linked to different regimes associated with the flight phases of an aircraft. Similarly, the cavitation curves are examined up to very large pressure drop as high as 15%, for this peculiar application purposes.

### 3 Comparison of the cavitating behavior of the full-stage pump between degassed water and water with dissolved carbon dioxide

In this section, the static pressure rises $\Psi_{7-1}$, $\Psi_{5-1}$ and $\Psi_{2-1}$ are presented for each constant flow rate as a function of the cavitation number $\sigma$ for degassed water and water with 300 ppm of dissolved CO2.

The static pressure rise $\Psi_{7-1}$ is taken between the volute discharge and the infinite upstream. A total pressure rise of the pump would include the dynamic pressure rise of the pump. This contribution is not taken into account here, as it represents 12% of the static pressure rise at the highest flow rate under study (78% of the reference flow rate) and decreases with the flow rate. The static pressure rise $\Psi_{5-1}$ gives informations on the wall static pressure at the interface between the inducer and impeller. Finally, the static pressure rise $\Psi_{2-1}$ is taken between a position 2D upstream of the pump and the infinite upstream position. It is linked to the inhomogeneity of the flow and pressure fields upstream of the pump. Numerical evidences reported by Fanning et al., 2019; Gentis et al., 2022 have shown that the upstream wall pressure rise is mainly linked to a large pre-rotation that takes place at partial flow rates and to a large backflow in the radial gap between the inducer and the casing.

A selection of pictures taken at different cavitation numbers are also systematically shown in order to compare the gaseous structures that are present upstream of the inducer between the two different fluids.
<figure><img src="image_5.png" /><figcaption>Figure 2: Static pressure coefficients $\Psi_{7-1}$, $\Psi_{5-1}$ and $\Psi_{2-1}$ as a function of the cavitation number $\sigma$ at a flow rate corresponding to 78% of $Q_{ref}$ for degassed water and water with a concentration of 300 ppm of dissolved carbon dioxide. The pictures in the right part presents captures from high-speed camera at the same $\sigma$ for the two fluids.</figcaption></figure>
## 3.1 Flow rate equal to 78% of the reference one

The results are plotted in Fig. 2 for 78% $Q_{ref}$. One can first notice that at high cavitation numbers (high upstream pressures) the three different pressure rises are the same for degassed water and water with $CO_2$. The wall pressure rise upstream of the inducer $\Psi_{2-1}$ is very low, below 0.005: the pre-rotation and the backflow close to the blade tip are negligible at this flow rate. The static pressure rise at the interface between the inducer and impeller is of the order of $\Psi_{5-1} \simeq 0.110$, while the static pressure rise of the full-stage pump is of the order of $\Psi_{7-1} \simeq 0.330$.

When decreasing the upstream absolute pressure, i.e. decreasing the cavitation number $\sigma$, no cavities are observed above $\sigma \gtrsim 0.100$ as can be seen in the rightest picture in the bottom part in Fig. 2 where small bubbly tip vortices are visible. No differences are seen between the two fluids, with similar pressure rises. A similar trend is observed for $0.050 \lesssim \sigma \lesssim 0.100$ though few more cavities are developing upstream of the inducer in the case of water with dissolved gas compared to degassed water. Then, the three pressure rise coefficients start to decrease simultaneously. A decrease of 5% of $\Psi_{7-1}$ is obtained at $\sigma_{5\%} \simeq 0.030$ for the degassed water and $\sigma_{5\%} \simeq 0.031$ for the water with 300 ppm of dissolved $CO_2$ which could be considered as being within the uncertainty of the measurements. At this stage, similar cavitating structures are observed for the two fluids, with backflow vortices (see pictures at $\sigma = 0.029$ in the right part of Fig. 2).

The pump behavior when pumping the two different fluids starts to be different once the cavitation has already strongly developed. At $\sigma = 0.022$, the pictures taken upstream of the inducer reveal the presence of a pre-rotating cavitating vortex for the case of water with dissolved gas, that is not yet present with dissolved water. The critical cavitation number corresponding to a 15% decrease in $\Psi_{7-1}$ is obtained at

<figure><img src="image_6.png" /><figcaption>Figure 3: Static pressure coefficients as a function of the cavitation number and pictures at a flow rate corresponding to 58% of $Q_{ref}$.</figcaption></figure>
$\sigma_{15\%} \approx 0.016$ for the degassed water and $\sigma_{15\%} \approx 0.018$ for the water with 300 ppm of dissolved CO$_2$. Finally, the critical cavitation at which the pump fails to pressurize the fluids and to maintain the flow rate is significantly different for the two fluids, with a value of $\sigma_{breakdown} \approx 0.011$ for degassed water and $\sigma_{breakdown} \approx 0.015$ for water with gas.

## 3.2 Flow rate equal to 58% of the reference one

The cavitation curves for this flow rate are plotted in Fig. 3. First, at high pressure, i.e. in monophasic flow, the wall pressure rise upstream of the inducer $\Psi_{2-1}$ at 58% $Q_{ref}$ is greater than at 78% $Q_{ref}$ with a value around $\Psi_{2-1} \approx 0.010$: the pre-rotation and the backflow close to the blade tip are more developed at this partial flow rate. The static pressure rise at the interface between the inducer and impeller is of the order of $\Psi_{5-1} \approx 0.130$, while the static pressure rise of the full-stage pump is of the order of $\Psi_{7-1} \approx 0.410$.

Concerning the cavitation curves, the general trends for a flow rate corresponding to 58% $Q_{ref}$ are similar to those observed for 78% $Q_{ref}$. The three pressure rises coefficients start to decrease simultaneously at a cavitation number $\sigma \approx 0.045$. The critical values of the cavitation numbers for the head drop are a little bit lower than in the previous case, with a value slightly higher for water with dissolved gas than for degassed water. For instance, the critical value for a drop of 5% of $\Psi_{7-1}$ is $\sigma_{5\%} \approx 0.014$ for degassed water, $\sigma_{5\%} \approx 0.017$ for water with CO$_2$, while the breakdown occurs at $\sigma_{breakdown} \approx 0.009$ and $\sigma_{breakdown} \approx 0.011$ respectively.

## 3.3 Flow rate equal to 39% of the reference one

The results at a flow rate of 39% of the reference one are plotted in Fig. 4. At high pressures, the wall static pressure rise upstream of the impeller is more pronounced than at higher flow rates, with a value close to $\Psi_{2-1} \approx 0.016$. The main difference with the two previous higher flow rates is that the upstream static pressure rises $\Psi_{2-1}$ start to differ between the two fluids at $\sigma \lesssim 0.06$ while the pressure rises $\Psi_{5-1}$ and $\Psi_{7-1}$ remain close in both fluids until $\sigma \lesssim 0.04$ and then follow similar trends. The inlet pre-rotation vortex indeed becomes visible at $\sigma = 0.046$ for the water with dissolved gas while it is not the case for degassed water, as can be seen in the pictures in Fig. 4. Moreover, once cavitation is further developed, micro-cavities are visible in the inter-blades channel for the water with dissolved gas at $\sigma = 0.022$ but not in the case of degassed water. As a result, the differences in critical cavitation numbers between the two fluids are enhanced, with, respectively, $\sigma_{5\%} \approx 0.011$ & $\sigma_{breakdown} \approx 0.008$ for degassed water, and $\sigma_{5\%} \approx 0.016$ & $\sigma_{breakdown} \approx 0.011$ for water with CO$_2$. Finally, one can mention that the large scale surge cavitation instability that was reported by Gentis et al., 2025 in degassed water at this flow rate for $\sigma \lesssim 0.017$ is not clearly observed for water with dissolved CO$_2$. The analysis of time signals in that case shows low-frequency intermittent bursts instead of a clear periodic cycle.

## 3.4 Flow rate equal to 16% of the reference one

The results corresponding to this very partial flow rate are plotted in Fig. 5. At 16% of the reference flow rate, the upstream pressure rise is still larger with a value around $\Psi_{2-1} \approx 0.026$. This time, all three pressure rises do not start to decrease at the same cavitation number for the two fluids. The upstream pressure rise $\Psi_{2-1}$ starts to decrease for $\sigma \lesssim 0.09$ in the case of water with dissolved gas concurrently with the development of the pre-rotating vortex, while the decrease and the concomitant pre-rotating vortex starts for $\sigma \lesssim 0.08$ in the case of degassed water. For the pressure rise between the infinite upstream and the interface between the inducer and the impeller $\Psi_{5-1}$, the decrease starts for $\sigma \lesssim 0.08$ in both fluids, and the full-stage pump pressure rise $\Psi_{7-1}$ starts to decrease for $\sigma \lesssim 0.066$, with a faster decrease for the water with dissolved gas. As a result, the differences in critical cavitation numbers between the two fluids become significant with for instance $\sigma_{5\%} \approx 0.021$ for degassed water, and $\sigma_{5\%} \approx 0.028$ for water with CO$_2$. Finally, in the case of degassed water, a low-frequency instability is observed in the range $0.016 \lesssim \sigma \lesssim 0.018$ and the breakdown of the pump occurs around $\sigma_{breakdown} \approx 0.014$. This dynamical regime seems to be linked to the strong backflow that forms upstream of the inducer at these very partial flow rate, coupled to high prerotation of the fluid, and has been deeper analyzed in the work of Gentis et al., 2025. In the case of water with dissolved gas, for $\sigma \lesssim 0.020$ at which the drop in full-stage pressure rise is 15%, the system is very unsteady, with randomly distributed periods when the pump pressurizes the fluid and periods when it seems stalled.

## 3.5 Flow rate equal to 4% of the reference one

The results for the lowest flow rate are plotted in Fig. 6. The differences are the most marked among the previously studied flow rates. The curves of the upstream pressure rises $\Psi_{2-1}$ for degassed water and
<figure><img src="image_7.png" /><figcaption>Figure 4: Static pressure coefficients as a function of the cavitation number and pictures at a flow rate corresponding to 39% of $Q_{ref}$.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 5: Static pressure coefficients as a function of the cavitation number at a flow rate corresponding to 16% of $Q_{ref}$.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Figure 6: Static pressure coefficients as a function of the cavitation number at a flow rate corresponding to 4% of $Q_{ref}$.</figcaption></figure>
water with dissolved CO₂ start to exhibit differences from $\sigma \lesssim 0.120$. In the case of water with CO₂, the pre-rotating hub vortex cavitation is clearly visible at $\sigma = 0.098$ while only tip vortices can be noticed on the picture in the case of degassed water, and at this cavitation number, the pressure coefficient drops from $\Psi_{2-1} \simeq 0.031$ in degassed water to $\Psi_{2-1} \simeq 0.026$ with dissolved gas, which corresponds to a drop of 16%. The hub vortex cavitation appears in degassed water around $\sigma \simeq 0.075$. The intermediate pressure rise $\Psi_{5-1}$ decreases rapidly by a relative amount of $\simeq 10\%$ and shows a plateau for dissolved gas in the range $0.060 \lesssim \sigma \lesssim 0.085$, while the same drop is observed only from $\sigma \lesssim 0.060$ in degassed water. However, this does not seem to have an impact on the full-stage pump static pressure rise $\Psi_{7-1}$ that remains almost equal and greater than 95% of the high-pressure value for $\sigma \gtrsim 0.060$ in both fluids. The two curves for $\Psi_{7-1}$ then separate and the critical cavitation numbers are very different, with respectively, $\sigma_{5\%} \simeq 0.049$ & $\sigma_{breakdown} \simeq 0.014$ for degassed water, and $\sigma_{5\%} \simeq 0.057$ & $\sigma_{breakdown} \simeq 0.023$ for water with CO₂.

## 4 Conclusion and perspectives

<figure><img src="image_10.png" /><figcaption>Figure 7: Critical cavitation numbers corresponding to a decrease of 5%, 10% and 15% of the static pressure coefficient $\psi_{7-1}$ for the 5 selected flow rates, for degassed water, and water with an amount of 300 ppm of dissolved carbon dioxide.</figcaption></figure>

The presence of dissolved gas in water has a noticeable impact on the performances of the full-stage pump under low inlet pressure conditions. Figure 7 presents the critical cavitation numbers corresponding to 5%, 10%, and 15% drops in the static pressure coefficient $\Psi_{7-1}$, for five selected flow rates and for both degassed water and water containing 300 ppm of dissolved CO₂.

The first clear observation is that dissolved CO₂ increases the critical cavitation numbers associated with various head drop thresholds compared to degassed water. This effect is negligible at the highest tested flow rate (78% of the reference), but it becomes increasingly significant as the flow rate decreases. The most pronounced impact occurs at 4% of the reference flow rate, where the critical cavitation number corresponding to a 5% head drop increases by 16%, and the cavitation number at full breakdown rises by as much as 64%.

Additionally, the low-frequency surge instability previously observed at intermediate flow rates with degassed water appears to be strongly mitigated—or even completely suppressed—when dissolved gas
is present. This suggests that gas content could be a key parameter in stabilizing the system's behavior under cavitating conditions. However, further dedicated investigations are required to fully understand this phenomenon.

The chosen concentration of 300 ppm of dissolved CO₂ was selected based on earlier experiments, with the aim of approximating cavitation behavior observed in single-inducer tests with kerosene containing naturally dissolved air at atmospheric pressure. Building on these promising results, future work will include tests with kerosene on a full-stage configuration, as well as experiments using higher concentrations of dissolved CO₂ in water, up to the solubility limit at atmospheric pressure and room temperature (approximately 1500 ppm). Deeper analyzes are needed to confirm and characterize the supposed mitigation by dissolved gas of the instabilities observed at partial flow rates and very low pressures. These studies will help refine our understanding of how dissolved gases influence cavitation dynamics and pump stability, especially in critical aerospace applications.

## References

Cui, B., & Li, C. (2023). Influence of axial matching between inducer and impeller on energy loss in high-speed centrifugal pump. *Journal of Marine Science and Engineering, 11*, 940. https://doi.org/10.3390/jmse11050940

Deng, F., Yuan, J., Liao, M., Chen, M., Zhu, H., & Si, Q. (2021). Variations of performance and pressure pulsation during cavitation in centrifugal pumps with entrained air. *E3S Web of Conferences*, 321, 04017. https://doi.org/10.1051/e3sconf/202132104017

Dunn, P. F., Thomas, F. O., Davis, M. P., & Dorofeeva, I. E. (2010). Experimental characterization of aviation-fuel cavitation. *Physics of Fluids*, 22, 117102. https://doi.org/10.1063/1.3490051

Fanjie, D., Jianping, Y., Song, Y., Biaobiao, W., & Qiaorui, S. (2022). Investigation on the influence of entrained air to internal flow of centrifugal pumps under cavitation condition. *International Journal of Fluid Machinery and Systems*, 15, 56–63. https://doi.org/10.5293/IJFMS.2022.15.1.056

Fanning, D. T., Gorrell, S. E., Maynes, D., & Oliphant, K. (2019). Contributions of tip leakage and inlet diffusion on inducer backflow. *Journal of Fluids Engineering*, 141 (12), 121102. https://doi.org/10.1115/1.4043770

Fu, Y., Fan, M., Pace, G., Valentini, D., Pasini, A., & d'Agostino, L. (2018). Experimental and numerical study on hydraulic performances of a turbopump with and without an inducer. *Fluids Engineering Division Summer Meeting, FEDSM2018-83506*. https://doi.org/10.1115/FEDSM2018-83506

Gentis, V., Pereira, M., Ravelet, F., Bakir, F., Pora, L., & Tomov, P. (2022). Etude numérique des interactions entre un rouet centrifuge et un inducteur. *Congrès Français de Mécanique*. https://hal.science/hal-03708443

Gentis, V., Pereira, M., Ravelet, F., Bakir, F., Tomov, P., Pora, L., & Brun, G. (2025). Experimental comparison of hydrodynamic behavior under partial flowrates and cavitation in three configurations of a centrifugal pump with inducer and impeller. *Journal of Fluids Engineering*, 147, 091204. https://doi.org/10.1115/1.4068132

Hong, S.-S., Kim, D.-J., Kim, J.-S., Choi, C.-H., & Kim, J. (2013). Study on inducer and impeller of a centrifugal pump for a rocket engine turbopump. *Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science*, 227, 311–319. https://doi.org/10.1177/0954406212449939

Jiang, L., Liu, H., Wang, Y., Mao, Y., Zhou, R., & Gu, J. (2022). Experimental study on the effect of gas volume fraction on the cavitation performance of a low-specific-speed centrifugal pump. *Water*, 14, 798. https://doi.org/10.3390/w14050798

Magne, T., Paridaens, R., Khelladi, S., Bakir, F., Tomov, P., & Pora, L. (2020). Experimental study of the hydraulic performances of two three-bladed inducers in water, water with dissolved CO₂, and jet fuel. *Journal of Fluids Engineering*, 142, 111210. https://doi.org/10.1115/1.4048143

Wang, C., Zhang, Y., Zhu, J., Yuan, Z., & Lu, B. (2021). Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump. *Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy*, 235, 440–453. https://doi.org/10.1177/0957650920939343