Cavity Exit Research Articles

A fast quadrupole-based analytical model for solving transient heat transfer in ventilated double-skin walls and assessing their energy saving potential

This research proposes a fast and accurate method for modeling transient heat transfer in ventilated double-skin façades (VDFs) with forced ventilation to predict their energy-saving potential. Using the thermal quadrupole formalism, the method solves the VDF problem in the Laplace domain while considering the full transient nature of the heat transfer; the only approximation is in space. The solution involves obtaining a general transfer function that predicts heat transfer rates or air temperatures at ventilated cavity's exit. The quadrupole method is validated against computational fluid dynamic numerical simulations conducted under similar meteorological, design and boundary conditions. A very good agreement was found (less than 3 % average deviation) with a significant reduction in computation time (less than 3s against 6h for CFD calculations). The model is computationally efficient and can consider important factors such as the opacity of the walls, construction materials, and air cavity design parameters. Finally, the model allows the assessment of the energy-saving potential of VDFs under various scenarios compared to conventional systems, which helps contributing to more sustainable building design practices. The energy efficiency of a VDF configuration was compared against a conventional wall system. Energy savings of 8.4 and 5.2 % were obtained, in cold and hot climates respectively.

Numerical investigation of heat transfer and temperature distribution in a Microwave-Heated Heli-Flow reactor and experimental validation

Microwave-heated flow systems (MWFSs), offering improved process control, enhanced product yields, and the potential for scalable and sustainable manufacturing routes, have gained significant popularity in continuously manufacturing nanomaterials and their hybrids. Temperature control in a microwave zone can maintain fine control over the manufactured materials' properties; however, the current state-of-the-art designs lack monitoring of the temperature distribution throughout the flow reactor. Herein, a unique model of numerical estimations of temperature distribution in a microwave-heated system featuring a helical flow milli-reactor, Heli-Flow, is described and validated by experimentally acquired temperature profiles. The proposed numerical model accurately predicts the temperature profile along the Heli-Flow and the steady-state outlet temperature at the MW cavity's exit. The helical design of the reactor promotes homogeneous heating and eliminates orientation-related discrepancies. The maximum outlet temperatures achieved at different microwave powers and FRs align well with expected trends. The modeled temperatures closely match the experimental and analytical measurements, indicating the effectiveness of the simulation approach. This research contributes to understanding temperature distribution in MWFSs and offers insights for optimizing nanomaterial synthesis and other applications.

Design Optimization of Blade Tip in Subsonic and Transonic Turbine Stages—Part II: Flow Physics and Augmented Aerothermal Integral Objective Function

Abstract In Part I, a companion paper of the two-part article, a subsonic turbine stage and a transonic one conditioned at the same Reynolds number, flow coefficient, loading coefficient and reaction, but two different exit Mach numbers are designed to provide a direct contrast between a high-subsonic and a transonic flow conditioning for rotor blade squealer tips. In this paper as Part II, further analyses are carried out to address the main issues of interest arising from Part I: first, to identify the driving flow physical mechanisms for the contrasting aerodynamic efficiency sensitivities of the two stages; second to seek a more suitable heat transfer objective function for the tip aerothermal design optimization, given the seemingly strong conflicts among those conventionally adopted heat transfer objective functions. Two counter-rotating tip vortical structures, the pressure side vortex (PSV) and the casing-driven cavity vortex (CCV), are shown to impact the aero-performance differently between the two stages. For the subsonic stage, the leakage flow is strongly affected by a stronger residual PSV at the squealer cavity exit. For the transonic stage however, the tip choking in limiting the over tip leakage (OTL) mass flow and favorable pressure gradient in a transonic flow over a separation bubble led to a much stronger and more persistent CCV and thus lower aero-effectiveness of squealer tip for the transonic stage. The two vortices also show major heat transfer signatures on the cavity surfaces by impingement. For the PSV, the impingement impact is mainly on the cavity floor. For the CCV, on the other hand, its impact is mainly on the inner side-wall of the suction side rim. The latter is found to be mainly responsible for the overall linear variations of the heat load with the squealer height. Again, the relative strength between PSV and CCV serves as an effective differentiator in the heat transfer performance. The stronger and more persistent CCV in the transonic stage results in a strong signature on a large portion of the suction side cavity inner sidewall, thus a much higher increment in heat transfer with the squealer height than that for the subsonic stage. In seeking to establish a more consistent heat transfer objective function for combined aerothermal design and optimization, a coolability weighted nonuniformity parameter is proposed to integrate the local heat transfer and the coolability. The proposed objective function is shown to lead to consistent Pareto fronts for the combined aerothermal performance sensitivities, particularly for the present cases with strong heat transfer nonuniformity which are particularly challenging to those conventional treatments as shown in Part I. The coolability-augmented objective function should thus serve as an enabler to help practical applications of blade tip aerothermal design optimizations.

Influence of Internal Structural Parameters on the Inner Flow and Outer Spray Characteristics for Feedback-Free Fluidic Oscillator

Feedback-free fluidic oscillators, relying on the interaction of jets to oscillate, have a wide range of operation frequencies and no moving parts, which is promising for future applications. In this paper, the sweep angle, oscillation frequency, and volume flow rate of the feedback-free fluidic oscillator with a cavity width of 4.6 mm were measured experimentally, and the sweeping mechanism was analyzed based on the internal flow simulation. The influence of the impact angle, cavity exit width, and shoulder radius on the internal flow and external spray characteristics was analyzed by the numerical method. The results show that the sweep angle and oscillation frequency are affected throughout the increase in impact angle from 80° to 120°. However, only when the SR is greater than 0.88 mm does the internal flow and spray state change significantly. The volume flow rate is mainly affected by the cavity exit width and increases linearly from 5.3 mL/s to 9.3 mL/s as the width increases from 0.45 mm to 0.85 mm. It can be surmised that the sweep angle is approximately linear with the distance between the hit point and the impact cavity centerline.

Numerical Study of the Purge Flow’s Effect on the Loss Mechanism of the Blocking and Shear Effects

The loss mechanism of shear and upstream blockage caused by the interaction of the purged flow and ingested gas needs to be systematically studied to optimize the flow near the rim. In order to study the causes and influence factors of blocking and shearing effects and quantify their losses reasonably, the three-dimensional unsteady numerical method validated by the experiment data was adopted to study the turbine with three kinds of sealing structures. The block and shear loss are quantified by integrating the dissipation coefficient in the volume where the specific aerodynamic loss occurs. The result indicated that there was a larger radial velocity and smaller tangential velocity of the purged flow relative to the main flow caused the blocking effect. Therefore, its loss is affected by the seal flow and seal structure. The shear effect is mainly affected by the tangential velocity gradient and the axial velocity gradient near the cavity exit. The contribution of the tangential velocity gradient to shear loss is increased with the enlarged sealing efficiency. Through research, it is clear that increasing the purge flow’s tangential velocity is beneficial to reducing the shear loss and has a positive significance for weakening the blocking effect in the main flow channel. Furthermore, the influence of sealing structure on blocking and shear effect must be particularly considered since both are related to sealing efficiency.

Numerical study on heat and mass transfer characteristics in a confined enclosure with variable buoyancy ratio

This numerical study was conducted to investigate the ventilation and airflow in a confined enclosure undergoing rapid inclusion of heat and contaminants representing air quality changes in working environments. A flow of air is passing inside a square enclosure with a heat source and a pollutant source on the right and bottom wall, creating double-diffusion, as well as two ventilation ducts on the upper sides asserting mixed convection. The Galerkin weighted residual method is implemented, which is based on the finite element method. For fixed values of Lewis number, Le = 0.5, Richardson number, Ri = 1, Reynolds number, Re = 100, and Prandtl number, Pr = 1.01, simulations were done with Buoyancy Ratio, Br = −10, 1, 10 and 20 over dimensionless time, τ = 0.1, 0.5, and 1.0. The results have been shown with the streamline, isothermal lines, iso-concentration lines, average Nusselt and Sherwood number, average fluid temperature, average mass concentration, and the average temperature at the square cavity's exit port plots. The findings have been discussed to ensure understanding of the changes in parameters, and an enhancement in heat as well as mass transfer was seen with the rapid change in dimensionless time. This specific study could be a guide for designing air conditioning and ventilation systems.

Unsteady Numerical Investigation on Vortex Interaction between Rim Seal Purge Flow and Upstream Stator

To assess unsteady vortex interaction between rim seal purge flow and upstream stator, numerical ‎investigations were conducted under different purge flow rates. The vortex distributions for the stator and ‎cavity were investigated and the interaction processes near the cavity exit, in particular the vorticity ‎change resulting from the ingress and egress, were analyzed. Results show the intensity of hub passage ‎vortex (HPV) and hub trailing shedding vortex (HTSV) at stator exit is decreased as a consequence of ‎enhancing blockage effects caused by the egress flow. However, when the purge flow rate increases, ‎from stator exit to downstream of cavity exit, the reduction in the intensity of two vortices is weakened as ‎the extrusion of egress flow thins their vortex tubes. The vortex inside the cavity is generated as the ‎combined effect of relative rotation of cavity walls and non-uniform circumferential pressure mainly ‎imposed by upstream stator. The ingress leads the positive axial vorticity near the stator hub to ingest into ‎the cavity and eject into the main passage due to the blockage of purge flow. Furthermore, the interaction ‎between the ingress of the mainstream and purge flow produces local negative axial vorticity. The egress ‎flow carries negative axial vorticity mainly originated from the rotational cavity wall, and enters into the ‎main flow passage near the rotating hub, then locations of HPV and HTSV move to the mid-span slightly ‎with the extrusion of egress flow‎.

Investigations on the interaction between the front and aft purge flow and the downstream vane of 1.5-stage turbine

Abstract The present work reports the influence of the 1.5-stage turbine flow field by the front and aft rim seal flow. The interaction between the front and aft purge flow and the mainstream of a 1.5-stage turbine was numerically simulated, and the influence of the front and aft purge flow on the downstream vane was analyzed separately. The results show that the front purge flow is distributed at the higher radius of second vane inlet, which changes the position of the blade hub secondary flows, and the aft purge flow is distributed at the low radius. The purge flow at different locations in the aft cavity exit forms shear induced vortex, pressure and suction side legs of the egress, which converges with the suction and pressure side legs of the horse vortex to form vane hub passage vortex. The increased purge flow rate in both the front and aft cavities significantly increases the sealing effectiveness of the rim seal, but also causes a reduction in turbine efficiency. The combined effect of the front and aft purge flow reduces the turbine efficiency of the end-wall structure by 0.3619, 0.9062, 1.5004, 2.0188 and 2.509% at IR = 0, IR = 0.5%, IR = 0.9%, IR = 1.3% and IR = 1.7%.

A Sector-Cascade Test Rig for Measurements of Heat Transfer in Turbine Center Frames

Abstract The turbine center frame (TCF) is an inherent component of turbofan aircraft engines and is used for connecting the high-pressure turbine (HPT) to the low-pressure turbine (LPT). Its position immediately downstream of the HPT makes it susceptible to the extremely high temperatures of future engines. Despite this, fundamental knowledge of heat transfer in TCFs and the influencing factors is still missing. This paper presents a new 45-deg sector-cascade test rig specifically designed for fundamental studies of film cooling effectiveness and heat transfer coefficient in TCFs and the development and validation of a measurement technique involving infrared thermography and heating foils. Measurements of heat transfer coefficient in the TCF were taken for two purge-to-mainstream mass flow ratios corresponding to the case of no purge and nominal (to engine operation) purge. The magnitude of the heat transfer coefficients on the hub and strut surfaces was highly influenced by the various flow structures in the passage and by the velocity variation of the mainstream flow due to the “aggressive” design of the TCF. Heat transfer on the surface of the strut was mainly governed by boundary layer behavior (laminar near the leading edge and turbulent for the rest of the strut) augmented by the effect of the secondary flow structures. Measurements of film cooling effectiveness were also taken for the single case of the nominal purge. A region of high film cooling effectiveness was observed, extending from the purge cavity exit to about 40% of the passage axial length. In this region, the effectiveness decreased with increasing axial length. On the surface of the struts and fillet radii, the film cooling effectiveness was found to be zero. This was attributed to the effect of the horseshoe vortex that sweeps the purge flow away from the strut surface and dilutes it by continuously entraining hot mainstream flow.

Sensitivity analysis on the impact of geometrical and operational variations on turbine hub cavity modes and practical methods to control them

This paper presents an experimental investigation on the impact of different design and operational variations on the instabilities induced at the hub cavity outlet of a turbine. The experiments were conducted at the “LISA” test facility at ETH Zurich. The axial gap at the 2nd stage hub cavity exit was varied, and also three different flow deflectors were implemented at the cavity exit to control the cavity modes (CMs). Furthermore, the turbine pressure ratio was altered to mimic the off-design condition and study the sensitivity of the CMs to this parameter. Measurements were performed using pneumatic, and Fast Response Aerodynamic Probes (FRAP) at stator and rotor exit. In addition, unsteady pressure transducers were installed at the cavity exit wall to measure the characteristic parameters of the CMs. For the small axial gap, distinct and strong CMs were generated, which actively interacted with stator and rotor hub flow structures. Increasing the gap damped the fluctuations; however, a broader range of frequencies was amplified. The flow deflectors successfully suppressed the CMs by manipulating the shear layer velocity profile and blocking the growing instabilities. Eventually, the increase in the turbine pressure ratio strengthened the CMs and vice versa.

Injection-rolling nozzle in an imprint system with continuous injection direct rolling for ultra-thin microstructure guide light plate

A novel Injection-rolling Nozzle (IRN) in an imprint system with continuous injection direct rolling (CIDR) for ultra-thin microstructure polymer guide light plates was developed to achieve uniform flow velocity and temperature at the width direction of the cavity exit. A novel IRN cavity was designed. There are eight of feature parameters of cavity were optimized by orthogonal experiments and numerical simulation. Results show that the flow velocity at the width direction of the IRN outlet can reach uniformity, which is far better than that of traditional cavity. The smallest flow velocity difference and temperature difference was 0.6 mm/s and 0.24 K, respectively. The superior performance of the IRN was verified through a CIDR experiment. Several 0.35-mm thick, 340-mm wide, and 10-m long microstructural Polymethyl Methacrylate (PMMA) guide light plates were manufactured. The average filling rates of the microgrooves with the aspect ratio 1:3 reached above 93%. The average light transmittance is 88%.

Turbine Hub Cavity Modes and Their Impact on Efficiency

Abstract Non-synchronous pressure and temperature fluctuations at the hub cavity of a turbine stage are the main focus of this study. Cavity modes are unsteady fluctuations generated at the cavity exit due to instabilities in this region. The cavity modes carried into the main flow impose an unsteady flow field in the rotor passages, which varies the passage-wise flow parameters considerably. A two-stage axial turbine was designed and tested in the “LISA” test facility at ETH Zurich. A reference case with baseline geometry and a modified case with an axial deflector at the hub cavity exit were tested. Comprehensive unsteady pressure and temperature measurements were performed using fast response aerodynamic (FRAP) and entropy probes (FENT), respectively. In addition, 12 fast response unsteady pressure transducers were mounted on the stationary wall of the cavity exit to measure the main characteristic parameters of the cavity modes. Full annular unsteady simulations were also carried out for both cases to support the experiments. Computational fluid dynamics (CFD) successfully predicted the effect of cavity modes on both frequency and amplitude of the fluctuations. The cavity modes indicated fluctuation amplitudes up to eight times of the blade passing fluctuations at the cavity exit. The analysis shows that the convected cavity modes alter the efficiency of different rotor passages by redistributing the mass flow and the losses resulting in a drop in overall efficiency. This work suggests that implementing a small axial deflector at the hub cavity exit would completely eliminate the cavity modes leading to a reduced pressure unsteadiness and enhanced efficiency.

Flight Tests of Passive Flow Control for Suppression of Cavity Aeroacoustics

This research focused on furthering the current understanding of the flowfield inside a cavity under typical flight conditions. The flight envelope included altitudes of up to 40,000 ft and maximum Mach number of 1.28 and included several test points between Mach 0.9 and 1.1, which are challenging to isolate in wind tunnel testing due to tunnel wall interference. The pod was instrumented to collect aeroacoustic pressures and qualitative flowfield imaging for a cavity with a length-to-depth ratio of four. Test missions were flown with several different passive flow control configurations, and their respective effect on acoustic properties and flow patterns were collected. Flow control comprising a rod-in-a-crossflow or a traditional sawtooth spoiler was generally found to reduce sound pressure level, though the extent of effectiveness varied with flight condition. The flow control devices installed at or below the cavity exit plane were found to have little influence. Tuft-based flow visualization complemented the effort, for one example, by demonstrating the outward flow near the cavity lip for the sawtooth spoiler.

Characteristics and Genesis of Loess High Slope on the West Side of Shuiliandong Colliery in Binxian County

The loess high-slope on the west side of water curtain cave colliery is an old landslide debris back-wall. There is an old landslide debris deposit at bottom of the slope. Surface water can infiltrate into the slope through loess uprightness joints and cranny. The groundwater flow gradually causes the formation of water cavities in the upper slope region. The slope further has loess stratification, obliquity (from 5° to 10°) and paleosols place. Surface water infiltrates into paleosols and induce water cavity exit with the top water cavity transfixion. The paleosols ideally prevents water. The loess stratification leans to ravine. The slope is unstable and will fail under the action of precipitations.

Design and beam dynamic simulation of the thermionic RF electron gun with external resonant cavity for transverse emittance reduction

Abstract The accelerator components and radiation production systems at the PBP-CMU Electron Linac Laboratory of the Plasma and Beam Physics Research Facility are currently being developed and upgraded to make it possible for generation of the mid-infrared free-electron laser (MIR FEL) and the coherent intense terahertz (THz) radiation via transition radiation and superradiant undulator radiation. To generate a high brightness radiation, a high quality electron beam is crucially required. One of the important keys for this issue is the good performance and reliable electron source . Development of a new thermionic radio-frequency (RF) electron gun is foreseen at our facility. The design of the new RF gun was conducted with the aim to reduce transverse emittance while keeping the longitudinal phase space distribution that is suitable for the bunch compression with the alpha magnet. The present design of the PBP-CMU RF electron gun, which has 1-1/2 cell TM 010 reentrant cylindrical standing-wave resonant cavities and a side-coupling cavity, was used as the starting model for this work. The shape and dimensions of the new RF gun were optimized and the electromagnetic field distribution was simulated by using the program CST Microwave Studio 2016. Electron beam dynamic simulations were done with program ASTRA. The initial particle distribution from thermionic emission process was created by using the self-developed MATLAB script that provides the thermal emittance values corresponding well to the theoretical values. The results of this work suggest that by adding an external resonant cavity with a rounded pill-box shape to the present RF gun model can reduce the transverse emittance. This additional cavity has an optimal length of 25 mm and is connected to the present RF gun at the position 13 mm downstream the second cavity exit. The RF wave is coupled from the second cavity to the external cavity via the second side-coupling cavity. The entire structure finally has a resonant frequency of 2856.03 MHz, an unloaded quality factor of 15623 and a shunt impedance of 1.18 M Ω . The maximum electric field values in the first, the second and the external cavity are 32.8, 65.0 and 29.8 MV/m, respectively. The results from beam dynamic simulations show that this new design RF gun should be able to produce electron bunches with a charge of 170 pC per bunch, a maximum kinetic energy of 2.72 MeV and an energy spread of 540 keV. The simulated horizontal and vertical normalized emittances of 90% beam were respectively reduced by 11.6% and 4.5% compared to the values obtained from the original PBP-CMU RF gun. Furthermore, it was found that the transverse emittance is conserved at the distance longer than 60 cm downstream the external cavity exit.

Unsteady measurement of core penetration flow caused by rotating geometric non-axisymmetry in a turbine rotor-stator disc cavity

The existence and causes of the deep ingress into the core region of a turbine rotor-stator disc cavity, or core penetration flow, generated by a rotating non-axisymmetric geometry have been investigated experimentally. In a low-speed, low-expansion ratio, single-stage, cold turbine test facility, time-resolved tangential and radial velocities in the cavity have been measured with 2-D hot-wire anemometers. In addition, time-resolved static pressures on the stator disc have been measured with fast response pressure transducers, and unsteady cavity velocity field in the absolute frame has been measured using Particle Image Velocimetry (PIV). Rotating geometric non-axisymmetry leads to an unsteady radial pressure gradient in the disc cavity. A time lag in the tangential velocity adjustment to the variation in the radial pressure gradient results in a net radial force, causing core penetration flow. A first-harmonic rotating geometric non-axisymmetry makes the core penetration flow to occur three times per revolution (twice when the cavity exit pressure increases and once when the cavity exit pressure decreases) and to revolve at the disc’s rotational speed. Core penetration flow due to the rotating geometric asymmetry is not affected by variations in the annulus flow coefficient or rotational Reynolds number but is weakened by increasing purge air flow rate.

Unsteady numerical investigation on viscous shear loss caused by rim seal purge flow

One of the most important loss sources is viscous shear caused by interaction between the turbine stator-rotor cavity rim seal purge flow and main flow and has not yet been studied systematically. To assess viscous shear loss, numerical simulations under different purge flow rate are presented. Results show that interaction between the purge flow and main flow causes three high viscous dissipation regions: two regions are located in the main passage resulting from interaction between egress flow and main flow and a third region is situated inside the cavity, mainly induced by the mixing between ingress main flow and purge flow. For both ingress and egress, the circumferential velocity difference between the purge flow and main flow is responsible for most of the viscous dissipation. Furthermore, the velocity difference and viscous shear loss increase as purge flow rate is increased. On average, relative to the design condition, viscous shear loss increases by approximately 127% per 1% increase in purge flow rate. Viscous dissipation continues to decrease as the swirl ratio is increased. Moreover, the influence on viscous shear loss of cavity angle of inclination, cavity location, and cavity exit width are negligible because these three parameters do not significantly affect the circumferential velocity difference.

Energetics of Storage and Diffusion of Water and Cyclo-Octasulfur for a Nonpolar Cavity of RHCC Tetrabrachion by Molecular Dynamics Simulations

Tetrabrachion forms the key component of the S-layer of Staphylothermus marinus. Molecular dynamics simulations have been used to study the energetics of occupancy of cavity 3 of the right-handed coiled-coil stalk of tetrabrachion by both water molecules and cyclooctasulfur S8 crowns, as well as to determine possible pathways and free energy barriers for the diffusion of both water and cyclooctasulfur through the peptide walls of RHCC tetrabrachion between cavity 3 and bulk solvent. Calculations of the transfer free energy from solvent to cavity show that clusters of six, seven and eight water molecules are marginally stable in cavity 3, but that occupancy of the cavity by a cyclooctasulfur ring is favoured significantly over water clusters of all sizes. Thermal activation simulations at T = 400K revealed that water molecules diffusing through the wall pass through a sequence of metastable configurations where they are temporarily immobilized by forming networks of hydrogen bonds with specific wall residues. Calculations of the free energy of these metastable configurations using multi-configurational thermodynamic integration yielded a free energy profile with a principal free energy maximum ∆G~50 kJ/mol and a slight activation asymmetry in favour of the direction from cavity to solvent. Potential exit pathways for cyclooctasulfur were investigated with the methods of steered molecular dynamics and umbrella sampling. The cyclooctasulfur was steered through a gap in the tetrabrachion wall along a linear path from cavity 3 into the solvent and the resulting trajectory was subdivided into 22 sampling windows. The free energy profile created for the trajectory by umbrella sampling showed a sharp principal maximum as a function of the reaction coordinate with asymmetric free energy barriers ∆Gexit~220 kJ/mol and ∆Gentrance~100 kJ/mol for cavity exit and entrance, respectively.

Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM110 mode for ultrafast electron microscopy

We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM110 mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM. This is confirmed by charged particle tracking simulations using a realistic cavity geometry, including fringe fields at the cavity entrance and exit apertures.

Modulation and Radial Migration of Turbine Hub Cavity Modes by the Rim Seal Purge Flow

In the present paper, the results of an experimental and numerical investigation of the hub cavity modes and their migration into the main annulus flow are presented. A one-and-a-half stage, unshrouded and highly loaded axial turbine configuration with three-dimensionally shaped blades and cylindrical end walls has been tested in an axial turbine facility. Both the blade design and the rim seal purge flow path are representative to modern high-pressure gas turbines. The unsteady flow field at the hub cavity exit region has been measured with the fast-response aerodynamic probe (FRAP) for two different rim seal purge flow rates. Furthermore, fast-response wall-mounted pressure transducers have been installed inside the cavity. Unsteady full-annular computational fluid dynamics (CFD) simulations have been employed in order to complement the experimental work. The time-resolved pressure measurements inside the hub cavity reveal clear cavity modes, which show a strong dependency on the injected amount of rim seal purge flow. The numerical predictions provide information on the origin of these modes and relate them to pronounced ingestion spots around the circumference. The unsteady probe measurements at the rim seal interface show that the signature of the hub cavity induced modes migrates into the main annulus flow up to 30% blade span. Based on that, an aerodynamic loss mechanism has been found, showing that the benefit in loss reduction by decreasing the rim seal purge flow rate is weakened by the presence of turbine hub cavity modes.