Gas Mass Flux Research Articles

Full-scale experimental and numerical study of smoke spread and temperature distribution in a room-corridor structure building

This paper aims to study the smoke spread and temperature distribution inside a full-scale room-corridor structure building. A series of experiments and simulations with different fuel properties and fuel configurations (crib and pool fires) were carried out. There was a barrier at the top of the left end of the corridor, and the end wall was on the right side. The fire source was located in the room. The evolution of the smoke spread process, pressure distribution, and temperature distribution in rooms and corridors were obtained and analyzed. The results indicate that the barrier and the end wall hinder the smoke spread and make it to accumulate below the corridor ceiling. This causes the smoke layer height of the corridor to be lower than the top of the door, which changes the pressure distribution inside and outside the room and also affects the temperature distribution. Based on the changes of pressure distribution, some correction formulas for the gas flow rate and mass flux at the opening are proposed. Under the effect of the barrier and the end wall, the smoke temperature in the room and the corridor increases. A smoke temperature decaying model along the corridor direction is proposed. Some methods are used and compared to calculate the smoke layer height based on the vertical temperature distribution. The smoke layer height determined by the buoyancy frequency method is most consistent with the experimental observation values.

Effect of water film evaporation on the shale gas transmission in inorganic nanopores under viscosity.

Shale gas reservoirs generally have ultra-low water saturation, and the water in reservoirs is closely bound to the walls of inorganic nanopores, forming a water film structure on the hydrophilic surface. When shale gas enters the inorganic nanopores, the water films in the inorganic pores will be removed by evaporation instead of being driven away by the gas, which increases the difficulty of predicting production during shale gas extraction. Based on molecular dynamics simulations, a water film evaporation model is proposed, considering the evaporation of water films during shale gas transport and the influence of water film evaporation on the shale gas transport mechanism. The Green-Kubo method is employed to calculate the viscosity of the water film. The evaporation flux of the water film under the influence of viscosity is discussed in the evaporation model. The transport mechanisms of shale gas in nanopores and the effect of water film evaporation on shale gas transport mechanisms are analyzed in detail. The result indicates that the water films in the inorganic nanopores are constrained on the hydrophilic surface, and the viscosity normal to the surface of the water film of 4Å is 0.005 26 Pa⋅S, which is 6.12 times the reference value of viscosity at 298K. In the process of water film evaporation, the evaporation flux of the water film is influenced by viscosity. In the study of the shale gas transport mechanism, water films in inorganic nanopores can hinder the surface diffusion of the methane molecules adsorbed on boundary and significantly reduce the mass flux of shale gas.

Evaluation of Mixing Effect on Coupled Heat Release and Transfer Performance of a Novel Segregated Solid Rocket Motor

The effect of mixing on coupled heat release and transfer performance of a novel segregated solid motor is numerically evaluated with a transient two-dimensional combustion model. The results show that vortex structures are formed and evolved in the combustion chamber. Quantitative calculation of the mixing effect shows the inhomogeneous distribution of oxidant and fuel species. The well-mixing area is located in a narrow belt-like coupled combustion region near the burning surface of the propellant. Heat transfer coefficient decreases greatly due to lower combustion reaction rate and enlarged flow channel area. Heat transfer coefficients near the two ends of the propellant grain are higher than other parts due to the influence of vortex mixing. Raising the inlet mass flow rate leads to enhanced mixing and heat transfer, which results in a lower temperature and regression rate of the propellant with combustion time. Temperature and oxidation rates of H2 and CO are unevenly distributed in the boundary layer of coupled combustion. Increasing the mass flux of inlet oxidizer gas leads to a higher combustion heat release rate. Therefore, the gas-phase temperature increases significantly. The heat release rate reaches the maximum near the ends of the propellant grain, where vortex mixing strengthens the coupled combustion process in the motor.

FRACTAL STUDY ON THE INFLUENCE OF SURFACE MORPHOLOGY ON SEEPAGE CHARACTERISTICS IN THE ROUGH FRACTURE NETWORK

In the fracture network, the surfaces of fracture are frequently rough. In this article, a binary tree fractal model for curved capillaries has been established based on the fractal theory. The expression of the mass flux rate of the fluid in the rough fracture network has been derived following the Hagar-Poiseuille formula, and the term of the gas mass flux rate has been obtained by using the gas plane radial flow binomial law. The two have been combined to obtain a fracture network permeability model. The correctness and availability of the model have been demonstrated by comparing it with the experimental data. Furthermore, the sensitivity of the model parameters has been analyzed.

Application of Artificial Neural Networks for Mathematical Modelling of Horizontal Jet Fires

Aim: This article focuses on the use of artificial neural networks to mathematically describe the parameters that determine the size of a jet fire flame. To teach the neural network, the results of a horizontal propane jet fire, carried out experimentally and using CFD mathematical modelling, were used. Project and methods: The main part of the work consisted of developing an artificial neural network to describe the flame length and propane-air mixing path lengths with good accuracy, depending on the relevant process parameters. Two types of data series were used to meet the stated objective. The first series of data came from field tests carried out by CNBOP-PIB and from research contained in scientific articles. The second type of data was provided by numerical calculations made by the authors. The methods of computational fluid mechanics were used to develop the numerical simulations. The ANSYS Fluent package was used for this purpose. Matlab 2022a was used to develop the artificial neural network and to verify it. Results: Using the nftool function included in Matlab 2022a, an artificial neural network was developed to determine the flame length Lflame and the length of the Slift-off mixing path as a function of the diameter of the dnozzle and the mass flux of gas leaving the nozzle. Using Pearson’s correlation coefficient, a selection was made of the best number of neurons in the hidden layer to describe the process parameters. The neural network developed allows Lflame and Slift-off values to be calculated with good accuracy. Conclusions: Artificial neural networks allow a function to be developed to describe the parameters that determine flame sizes in relation to process parameters. For this purpose, the results of the CFD simulations and the results of the jet fire experiments were combined to create a single neural network. The result is a ready-made function that can be used in programmes for the rapid determination of flame sizes. Such a function can support the process of creating scenarios in the event of an emergency. A correctly developed neural network provides opportunities for the mathematical description of jet fires wherever experimental measurements are not possible. Solution proposed by the authors does not require a large investment in ongoing calculations, as the network can be implemented in any programming language. Keywords: computational fluid mechanics, artificial neural networks, jet fire

Numerical analysis of inlet flows at different altitudes in the upper atmosphere

A comprehensive numerical study is performed to investigate gas flows inside the inlet of an atmosphere-breathing electric propulsion (ABEP) system operating in the upper atmosphere ranging from 120 to 300 km using the direct simulation Monte Carlo method. Gas pressure, mass flux, and aerodynamic drag are analyzed in depth in order to gain a deep understanding of the effects of operation altitude and the assumption of free molecular flow (FMF) on gas flows within the inlet. Computational results show that both the gas pressure and mass flux in the compression and ionization sections decrease with increasing altitude, indicating weaker compression and collection performances at higher altitudes. Therefore, careful attention should be paid to compression and collection performances of the inlet when it operates at higher altitudes. At altitudes smaller than 180 km, gas flows within the inlet are fully or partly characterized by transitional flows, so the FMF assumption tends to overestimate the gas pressure and underestimate the mass flux within the inlet resulting from the neglect of the collisions between the oncoming and reflected molecules. However, FMFs predominate within the inlet and even fill the entire inlet at altitudes larger than 180 km, so it is fairly reasonable to assume an FMF in the aerodynamic design of the inlet of an ABEP system.

What Sets the Star Formation Rate of Molecular Clouds? The Density Distribution as a Fingerprint of Compression and Expansion Rates

We use a suite of 3D simulations of star-forming molecular clouds, with and without stellar feedback, magnetic fields, and driven turbulence, to study the compression and expansion rates of the gas as functions of density. We show that, around the mean density, supersonic turbulence promotes rough equilibrium between the amounts of compressing and expanding gas, consistent with continuous gas cycling between high- and low-density states. We find that the inclusion of protostellar jets produces rapidly expanding and compressing low-density gas. We find that the gas mass flux peaks at the transition between the lognormal and power-law forms of the density probability distribution function (PDF). This is consistent with the transition density tracking the post-shock density, which promotes an enhancement of mass at this density (i.e., shock compression and filament formation). At high densities, the gas dynamics are dominated by self-gravity: the compression rate in all of our runs matches the rate of the run with only gravity, suggesting that processes other than self-gravity have little effect at these densities. The net gas mass flux becomes constant at a density below the sink formation threshold, where it equals the star formation rate. The density at which the net gas mass flux equals the star formation rate is one order of magnitude lower than our sink threshold density, corresponds to the formation of the second power-law tail in the density PDF, and sets the overall star formation rates of these simulations.

Numerical study on transient regression rate and combustion characteristics of segregated AP-based oxidizer/TAGN-based fuel

In the present study, a two-dimensional combustion model is established to simulate transient flow and combustion characteristics of a segregated oxidizer/fuel solid motor (SOFSM). A detailed gas-phase reaction kinetic mechanism with 35 species and 190-step reactions is developed to describe the gas-phase combustion process between AP-based oxidizer and TAGN-based fuel. The effects of mass flux and initial temperature of inflow oxidizer gas on the transient flow and combustion characteristics of the TAGN-based fuel are numerically investigated. With the mass flux of inflow oxidizer gas increasing from 249 kg·m−2·s−1 to 995 kg·m−2·s−1, the maximum spatially averaged regression rate of the burning surface of TAGN-based fuel increases by almost 200 % and the combustion efficiency first increases and then decreases with a maximum combustion efficiency of 94.3 % at the mass flux of 442 kg·m−2·s−1. With the initial temperature of inflow oxidizer gas increasing from 1000 K to 1750 K, the maximum average regression rate of the burning surface of TAGN-based fuel increases by around 10 %. Meanwhile, the combustion efficiency increases from 88.38 % to 95.8 %. During the combustion process (almost 3 s), the spatially averaged regression rate remains basically stable from 0.5 s to 2 s and increases slightly from 2.0 s to 3.0 s for given mass flux and initial temperature, indicating the combustion process is basically stable under the studied conditions. The results also show that during the transient combustion process, a large vortex first appears and then is split into a major vortex and a small one in the post-combustion chamber. With the increase of the mass flux and initial temperature of inflow oxidizer gas, the size of the vortex increases while the center position of the vortex moves towards the burning surface, which significantly enhances the mixing process and increases combustion efficiency.

Apparent permeability of organic matter in shale considering pore size distribution

The gas flow in shale nanopores is a crucial factor for shale gas exploitation. Organic matter in shale is an important constituent of gas shale reservoirs because of its gas storage ability. Current apparent permeability (Kapp) models focus on permeability calculations derived from pores with a given diameter or given mathematical distribution instead of pore size distribution. We confirmed the gas mass flux in organic matter by modifying the molecular diffusion coefficient and adsorption amount related to surface diffusion and flow regime transformation critical conditions such as pore size and pressure. Then, Kapp was calculated by coupling the mass flux with the pore size distribution. Our research shows that steps occur in the Kapp curves of organic matter owing to the flow regime transformation from transition flow to slip flow. Additionally, porosity, dominant pore diameter and frequency were the main factors affecting the Kapp of organic matter.

Effect of non-condensable gas on submerged steam jet condensation in a narrow pipe

A visualization study was performed to investigate the effect of non-condensable gas on stable submerged steam jet condensation in water flow in a narrow pipe. The direct contact condensation (DCC) characteristics including jet plume shapes, dimensionless penetration length and average heat transfer coefficient were analyzed in a wide range of water flow subcooling, Reynolds number of water flow and steam–air mixture flow rates. As four different steam plume shapes for pure steam jet in subcooled water flow in a pipe were reported in the previous research, the effect of non-condensable gas on the four steam plume shapes was investigated by introducing a certain amount of air into steam. In the current study, the submerged steam–air mixture jet behavior was investigated through direct visualization techniques. The effect of non-condensable gas on jet plume shapes was recorded by using a high speed camera. The gas–liquid interface and the dimensionless penetration length was obtained by digital image processing method implemented by a MATLAB subroutine. Then the average heat transfer coefficient was calculated based on thermal equilibrium of gas–liquid interface. In the experiment, the gas mass flux at nozzle exit was within 320–780 kg/m2/s, with no more than 1 % non-condensable gas. The results indicated that the non-condensable gas plays an important role on the gas–liquid interface, jet penetration length and heat transfer coefficient. It was found that when 1 % non-condensable gas was mixed with steam jet, the dimensionless penetration length was extended by 16–70 %, and the average heat transfer coefficient decreased by 12–50 %. Based on the force-balance of jet plume, a new quantitative correlation for the steam–air mixture jet penetration length was proposed. The predicted jet penetration length agrees well with the experimental measured values.

Modeling of diffusion kinetics during gas adsorption in a coal seam with a dimensionless inversion method

Modeling gas diffusion kinetics in a coal seam plays an essential role in predicting performance of both coalbed methane production and its enhanced recovery. Throughout the diffusion period, not only does there exist a large deviation between the analytical solution of the classical Fickian unipore diffusion model (UDM) and experimental measurements, but also constant diffusion coefficients calculated with the inversion of the simplified empirical/semi-empirical correlations are still not accurate enough. In this paper, we proposed a free gas density gradient model (FGDGM) to characterize the gas adsorption and transport properties in a coal seam. Experimentally, isothermal experiments were performed using a high-temperature and high-pressure gas adsorption analyzer with methane gas. Theoretically, a Langmuir gas concentration was derived and improved as a function of free gas density, and then we correlated a numerical inversion model to determine the effective diffusion coefficients by combining dimensionless variables and empirical correlations. Finally, the developed models were validated with the measured gas adsorption isotherms. The numerical solution curves based on the FGDGM are found to be basically consistent with the measured data in the entire time scale, while the developed inversion method is accurate as well as efficient in computational expenses. On the basis of the ideal gas assumption, the actual density gradient and diffusion coefficient will be underestimated and overestimated, respectively. By incorporating real gas behaviour into the improved FGDGM, both gas mass flux and effective diffusion coefficient can be determined more accurately to model gas diffusion kinetics and gas flow patterns in a coal seam.

Structure and extinction of reverse smolder waves in the presence of heat losses: A premixed-flame perspective

A reverse smolder wave is structurally analogous to a premixed flame in the sense that the solid fuel and the gaseous oxidizer enter the reaction zone in a co-current manner. Such structural similarity is explored in this work to analytically examine the structural characteristics and extinction properties of planar reverse smolder waves that are driven by a forced oxidizer flow, based on the activation-energy asymptotic method. The analysis covers both the adiabatic condition and the non-adiabatic condition resulting from an external heat loss. Within the framework of the adopted diffusive-thermal model, two distinct reaction regimes are identified, namely the fuel-rich regime and the fuel-lean regime, separated in between by a stoichiometric state, which corresponds to a critical gas mass flux (for the adiabatic condition) or a critical heat loss coefficient (for the non-adiabatic condition). It is found that, under both adiabatic and non-adiabatic conditions, extinction occurs exclusively in the near-stoichiometric fuel-lean regime, in the sense that the values of characteristic quantities at the extinction limit are at most O(ε) away from those at the corresponding stoichiometric state, where ε is a small parameter inversely proportional to the activation energy. It is then demonstrated how this near-stoichiometric character can be exploited to seek a series-form representation of all the quantities characterizing the extinction limit, where the normalized initial oxygen mass fraction and the oxygen Lewis number are identified as two primary control parameters. A close examination of the differences between reverse smolder waves and premixed flames identifies a mechanism that may account for why reverse smolder waves are generally more robust than premixed flames when subjected to heat losses. Further, it is justified that limiting kinetics as a unified bottom-level mechanism can provide a uniform characterization of the extinction conditions of non-adiabatic reverse smolder waves.

A General Model for the Longevity of Super-Hydrophobic Surfaces in Under-Saturated, Stationary Liquid

Abstract We perform a numerical study of the longevity of a super-hydrophobic surface (SHS) in under-saturated, stationary liquid. We numerically solve the spatial-temporal evolution of the gas concentration in the liquid, the time-variation of mass flux of gas out of the plastron, as well as the time required for the gas in the plastron to be fully dissolved (i.e., the plastron lifetime). We find that the profiles of gas concentration at different times are self-similar, and the mass flux reduces with time (t) at a rate of 1/t0.5. In addition, we examine the impact of texture parameters, including pitch, gas fraction, texture height, and advancing contact angle, on the diffusion process. Our results show that both plastron lifetime and diffusion length increase with increasing the gas fraction or increasing the texture height and are independent of the advancing contact angle and pitch. We propose simple analytical models for plastron lifetime and diffusion length. We show that the model has a fair agreement with the experimental data reported in the literature, and can predict the longevity for SHS with various texture geometries, texture sizes, and under different degrees of under-saturations. Our models could guide the design of long-life SHS for underwater applications such as reducing skin-friction drag and preventing biofouling.

Study and comparison of different drying processes of porous particle at high temperature

This work presents a comparative study of four drying processes of a porous media: superheated steam drying at atmospheric pressure (APSSD), humid air (HA), low pressure superheated steam drying (LPSSD) and vacuum drying (VD). A single porous particle model has been developed to simulate the four drying processes. The model is based on the method of averaging volume. Spherical porous particles of coal are used as the model material in this paper. The evaporation rates are equal for these processes in point called the inversion temperature. This temperature was calculated during the constant rate period (CRP) and the falling rate period (FRP). A variation in the values of inversion temperature was observed (363-503 K). The effect of drying parameters such as: particle radius, gas mass flux, permeability, porosity and operating pressure were investigated. Several researchers have reported the noticeable variation of the inversion temperature values according to the drying period used to calculate this key parameter. Our results are compared with those obtained from a front model reported in the literature. A good agreement is found.

Experimental Investigation on Turbulent Flow Deviation in a Gas-Particle Corner-Injected Flow

An experimental model of a corner-injected flow is built to investigate the turbulent flow behavior by employing the PIV technique. The influences of the ideal tangential circle, the additive particles and the initial gas mass flux on the corner-injected flow are analyzed systematically. To be specific, the flow deviation, the velocity profile, the vortex evolution and the turbulent flow development are discussed quantitatively. The influences of the increasing ideal tangential circle on the turbulent jet deviation are shortened gradually, and the impinging circles are obviously narrowed with the injection of particles. The gas-particle corner-injected flow can obtain a good rotation when the ideal tangential circle is 0.25 times the width of the impinging chamber. The momentum decay of the corner-injected flow diminishes with the increasing ideal tangential circle and the decreasing initial gas velocity. The rotation strength of the vortex is more affected by the injection of laden particles, while the angular distortion enhances when increasing the ideal tangential circle. The increasing initial gas mass flux plays a dominant role in the development of the corner-injected flow, secondly the increasing ideal tangential circle, and last the injection of particles. All these findings can provide theoretical support in the design of a corner-fired furnace.

Sensitivity of PM2.5 and O3 pollution episodes to meteorological factors over the North China Plain

The Comprehensive Air-quality Model with extensions (CAMx) was used to explore the sensitivity of PM2.5 and O3 concentrations to four selected meteorological factors: wind speed, temperature, water vapor mixing ratio (Q), and planetary boundary layer height (PBLH) during two pollution episodes over the North China Plain (NCP). We also investigated the impact pathways of different meteorological factors on the formation of PM2.5 and O3. It is found that PM2.5 was more sensitive to the selected meteorological factors in the southeastern NCP, where high anthropogenic emissions and severe air pollution occur. Large variations were observed along the Taihang Mountains, where the height of the terrain changes dramatically. The sensitivity of O3 to wind speed, PBLH, temperature, and Q was mainly determined by the inhibition effects of PM2.5 in winter, while in summer, the complex chemical reactions were dominant. Significant diurnal variations of process analysis (PA) results were observed under various meteorological conditions. Higher temperature generally enhance heterogeneous chemistry and transport of NO3− through the top boundary layer during night-time in winter, however, in summer, the heterogeneous chemistry of NO3− and NH4+ during daytime were the major pathways to the increased PM2.5 due to increased temperature. Moreover, temperature alter PM2.5 concentrations through affecting vertical diffusivity and relative humidity, and alter O3 concentrations by affecting the gas phase chemistry and mass fluxes through the top boundary layer. Q mainly affects the rate of chemical reactions of PM2.5 and O3. The different impact pathways suggest that it is essential to consider variations in meteorological factors, in addition to the direct impacts of wind speed and PBLH, more attention should be paid to the complex impacts of temperature and Q, when developing emission control strategies.

Experimental investigation of gas-liquid flow in a vertical venturi installed downstream of a horizontal blind tee flow conditioner and the flow regime transition

A venturi device is commonly used as an integral part of a multiphase flowmeter (MPFM) in real-time oil-gas production monitoring. Partial flow mixing is required by installing the venturi device vertically downstream of a blind tee pipework that conditions the incoming horizontal gas-liquid flow (for an accurate determination of individual phase fraction and flow rate). To study the flow-mixing effect of the blind tee, high-speed video flow visualization of gas-liquid flows has been performed at blind tee and venturi sections by using a purpose-built transparent test rig over a wide range of superficial liquid velocities (0.3–2.4 m/s) and gas volume fractions (10–95%). There is little ‘homogenization’ effect of the blind tee on the incoming intermittent horizontal flow regimes across the tested flow conditions, with the flow remaining intermittent but becoming more axis-symmetric and predictable in the venturi measurement section. A horizontal (blind tee) to vertical (venturi) flow-pattern transition map is proposed based on gas and liquid mass fluxes (weighted by the Baker parameters). Flow patterns can be identified from the mean and variance of a fast electrical capacitance holdup measured at the venturi throat.

Insight into chemical reaction kinetics effects on thermal ablation of charring material

Thermal ablation plays an important role in the aerospace field. In this paper, to study the chemical kinetics effects on heat transfer and surface ablation of the charring ablative material during aerodynamic heating, a charring ablation model was established using the finite element method. The AVCOAT 5026-39H/CG material, one typical thermal protection material used in thermal protection system, was employed as the ablative material and heated by aerodynamic heating condition experienced by Apollo 4. The finite element model considers the decomposition of the resin within the charring material and the removal of the surface material, and uses Darcy?s law to simulate the fluid-flow in the porous char. Results showed that the model can be used for the ablation analysis of charring materials. Then effects of chemical kinetics on ablation were discussed in terms of four aspects, including temperature, surface recession, density distribution, and mass flux of pyrolysis gas. The pre-exponential factor and activation energy have different effects on ablation, while the effect of the reaction order is little. This paper is helpful to understand the heating and ablation process of charring ablative materials and to provide technical references for the selection and design of thermal protection materials.

Shale Gas Transport in Nanopores: Contribution of Different Transport Mechanisms and Influencing Factors

The classical Darcy’s law cannot effectively describe the microscopic flow rules of shale gas. In addition, conducting gas transport experiments in nanopores is difficult, and the correctness of the simulation results is not guaranteed. Studies on the flow and transmission of shale gas in microscopic nanopores can effectively guide the macroscopic numerical simulation of shale gas reservoirs, which is of great significance to the economical and efficient development of such reservoirs. In this work, the dimensionless relaxation time expression is modified, and the Peng–Robinson equation of state (P–R EOS) is introduced to the microscale gas flow lattice Boltzmann model. The influences of viscous flow, slippage effect, boundary Knudsen layer, adsorbed gas layer, and surface diffusion are considered, and the results are combined with the real isothermal adsorption experimental data of shale samples collected from the Longmaxi formation in Sichuan Basin. Finally, the contributions of various transport mechanisms to shale gas flow in nanopores and their influencing factors are studied. Results show that the gas velocity and mass flux (Q) obtained using the ideal gas EOS are higher than those obtained using P–R EOS under high pressure. When the effective pore diameter (He) is less than 5 nm, surface diffusion and its induced free flow are the main transport mechanisms of shale gas flow in nanopores. Viscous flow becomes the main transport mechanism when He exceeds 20 nm. He, pressure, and shale adsorption capacity significantly affect the contribution rate of each transport mechanism to the total Q of shale gas. By comparison, the influence of temperature on the Q of shale gas is relatively small and can be neglected under high pressure.

Large-Eddy Simulations of Rim Seal Flow in a One-Stage Axial Turbine

The flow field in a one-stage axial flow turbine with 30 stator and 62 rotor blades including the wheel space is investigated by large-eddy simulation (LES). The Navier-Stokes equations are solved using a massively parallel finite-volume solver based on a Cartesian mesh with immersed boundaries. The strict conservation of mass, momentum, and energy is ensured by an efficient cut-cell/level-set ansatz, where a separate level-set solver describes the motion of the rotor. Both solvers use individual subsets of a shared Cartesian mesh, which they can adapt independently. The focus of the analysis is on the flow field inside the rotor stator cavity between the stator and rotor disks. Two cooling gas mass flow rates are investigated for the same rim seal geometry. First, the time averaged flow field for both simulations is compared, followed by a detailed investigation of the unsteady flow field. The results for the cooling effectiveness are compared to experimental data. Both cases show good agreement with experimental data. It is shown that for the lower cooling gas mass flux several of the wheel space’s acoustic waves are excited. This is not observed for the higher cooling gas mass flux. The excited waves lead to stable, i.e., bounded, fluctuations inside the wheel space and result in a significantly higher hot gas ingestion.