Flow Unsteadiness Research Articles

Stenosis to stented: decrease in flow disturbances following stent implantation of a diseased arteriovenous fistula.

The arteriovenous fistula (AVF) is commonly faced with stenosis at the juxta-anastomotic (JXA) region of the vein. Implantation of a flexible nitinol stent across the stenosed JXA has led to the retention of functioning AVFs leading to the resulting AVF geometry being distinctly altered, thereby affecting the haemodynamic environment within it. In this study, large eddy simulations of the flow field within a patient-specific AVF geometry before and after stent implantation were conducted to detail the change in flow features. Although the diseased AVF had much lower flow rates, adverse flow features, such as recirculation zones and swirling flow at the anastomosis, and jet flow at the stenosis site were present. Larger velocity fluctuations (leading to higher turbulent kinetic energy) stemming from these flow features were apparent in the diseased AVF compared to the stented AVF. The unsteadiness at the stenosis created large regions of wall shear stress (WSS) fluctuations downstream of the stenosis site that were not as apparent in the stented AVF geometry. The larger pressure drop across the diseased vein, compared to the stented vein, was primarily caused by the constriction at the stenosis, potentially causing the lower flow rate. Furthermore, the WSS fluctuations in the diseased AVF could lead to further disease progression downstream of the stenosis. The change in bulk flow unsteadiness, pressure drop, and WSS behaviour confirms that the haemodynamic environment of the diseased AVF has substantially improved following the flexible stent implantation.

Stabilizing two-dimensional turbulent Kolmogorov flow via selective modification of inviscid invariants

We stabilize 2D turbulent Kolmogorov flow by selectively altering the time rate of change of inviscid invariants (energy and enstrophy) of the flow. This method has earlier been demonstrated to modify the 2D unforced decaying turbulent flow to reach steady states. However, Kolmogorov flow exhibits flow unsteadiness over a range of spatial and temporal scales which are driven by constant external forcing at wave number kf. The energy injected at scale (k≈kf) is distributed to large (k>kf) and small (k<kf) wave numbers through interactions of different scales called direct and inverse energy cascading, respectively. The selective modification strategy autonomously identifies additional forcing inputs into the governing equations which results in the transformation of Kolmogorov flow into a non-trivial steady state. We demonstrate that this method is highly effective in altering the inverse energy cascading, a particularly intricate challenge in fluid dynamics. Intriguingly, we have also found that the steady states achieved through this approach resemble an invariant solution of the original Kolmogorov flow, highlighting the potential significance of our method.

Numerical Study on the Unusual Vibration Load Characteristics and Mechanisms of the Front Landing Gear Compartment

Civilian aircraft can experience noticeable vibrations in the cockpit and cabin due to mechanical faults during flight. To address this issue, a hybrid approach was utilized to investigate fluid-induced vibration load characteristics in the front landing gear compartment under different hatch opening angles. The results reveal that the root mean square (RMS) of cumulative pressure loads on both small and large hatches under different opening angles is largest at a 15°. For all the simulated cases (0°, 5°, 10°, 15°, 20°), the power spectral density (PSD) results of the chosen monitoring points on the inner wall of the large hatch exhibit broadband frequency characteristics, and the peak PSD values for the chosen monitoring points on the outer wall of the small hatch exhibit a significant concentration of energy at approximately 75 Hz. The peak PSD values for the selected monitoring points on the inner wall of the small hatch demonstrate a more uniform distribution of energy. Utilizing the iso-surface of Q-criterion, spatial streamlines, and streamlines at different cross-sections to analyze flow characteristics, the study investigates the fluctuating load mechanisms of the compartments. The results indicate that unsteady loads stem from the blunt edges of the hatches, which induce unsteady flow and spanwise flow. Geometric gaps between different locations cause flow separation, and the flows inside the compartment exhibit characteristics similar to those of a clean cavity. Furthermore, the mutual interference can be described using circulating flow and spanwise flow, resulting in flow unsteadiness. The flow separation zones enlarge and vortex intensity increases with the increase of the hatch opening angle from 0° to 15°; then, their values decrease as the hatch opening angle increases from 15° to 20°. These variations explain the maximum RMS of cumulative pressure loads at 15°.

Examining the Quasi-Steady Airflow Assumption in Irregular Vocal Fold Vibration

The quasi-steady flow assumption (QSFA) is commonly used in the field of biomechanics of phonation. It approximates time-varying glottal flow with steady flow solutions based on frozen glottal shapes, ignoring unsteady flow behaviors and vocal fold motion. This study examined the limitations of QSFA in human phonation using numerical methods by considering factors of phonation frequency, air inertance in the vocal tract, and irregular glottal shapes. Two sets of irregular glottal shapes were examined through dynamic, pseudo-static, and quasi-steady simulations. The differences between dynamic and quasi-steady/pseudo-static simulations were measured for glottal flow rate, glottal wall pressure, and sound spectrum to evaluate the validity of QSFA. The results show that errors in glottal flow rate and wall pressure predicted by QSFA were small at 100 Hz but significant at 500 Hz due to growing flow unsteadiness. Air inertia in the vocal tract worsened predictions when interacting with unsteady glottal flow. Flow unsteadiness also influenced the harmonic energy ratio, which is perceptually important. The effects of glottal shape and glottal wall motion on the validity of QSFA were found to be insignificant.

Laminar post-stall wakes of tapered swept wings

While tapered swept wings are widely used, the influence of taper on their post-stall wake characteristics remains largely unexplored. To address this issue, we conduct an extensive study using direct numerical simulations to characterize the wing taper and sweep effects on laminar separated wakes. We analyse flows behind NACA 0015 cross-sectional profile wings at post-stall angles of attack $\alpha =14^\circ$ – $22^\circ$ with taper ratios $\lambda =0.27$ – $1$ , leading-edge sweep angles $0^\circ$ – $50^\circ$ and semi aspect ratios $sAR =1$ and $2$ at a mean-chord-based Reynolds number of $600$ . Tapered wings have smaller tip chord length, which generates a weaker tip vortex, and attenuates inboard downwash. This results in the development of unsteadiness over a large portion of the wingspan at high angles of attack. For tapered wings with backward-swept leading edges, unsteadiness emerges near the wing tip. On the other hand, wings with forward-swept trailing edges are shown to concentrate wake-shedding structures near the wing root. For highly swept untapered wings, the wake is steady, while unsteady shedding vortices appear near the tip for tapered wings with high leading-edge sweep angles. For such wings, larger wake oscillations emerge near the root as the taper ratio decreases. While the combination of taper and sweep increases flow unsteadiness, we find that tapered swept wings have more enhanced aerodynamic performance than untapered and unswept wings, exhibiting higher time-averaged lift and lift-to-drag ratio. The current findings shed light on the fundamental aspects of flow separation over tapered wings in the absence of turbulent flow effects.

Pressure gradient and an upstream cylinder on nanofluid flow around a heated cylinder: Heat transfer and entropy analysis

This study numerically investigates the nanofluid flow around a long heated cylinder of square cross-section (DSC) with height placed parallel to a cold wall at a fixed gap height The incident flow is Couette–Poiseuille (C–P) flow. Another cylinder of rectangular cross section (UREP) is placed on the upstream side in an inline arrangement with different gap spacings between the cylinders. The base fluid is chosen as the water and ethylene glycol–water mixture. Numerical experiments are made using staggered grid arrangement on non–uniform grid, finite volume methods, and Semi–Implicit Method for Pressure Linked Equations algorithm. Impact of pressure gradient at the inlet (due to C–P flow), position and shape (square/rectangular) of the UREP, nanoparticle concentration, and base fluid on the crowding of isotherms around edges of the DSC and hence to the heat transfer characteristics (Nusselt number and entropy generation rate density) is investigated. Bejan number is used to ratify that the irreversibility due to heat transfer is the major constituent of the total system irreversibility here. A reduction of heat transfer and entropy generation from the values of an isolated DSC is natural here due to the inline arrangement. An effort is made to improve the heat transfer by reducing the height of the UREP or/and by generating unsteadiness in the incoming flow to the DSC using a bluffer UREP or/and an increased pressure gradient. Finally, some scenarios are reported where the heat transfer decrement is less in comparison to that of the total system irreversibility.

Effect of Unsteady Fan-Intake Interaction on Short Intake Design

Abstract The next generation of ultrahigh bypass ratio civil aero-engines promises notable engine cycle benefits. However, these benefits can be significantly eroded by a possible increase in nacelle weight and drag due to the typical larger fan diameters. More compact nacelles, with shorter intakes, may be required to enable a net reduction in aero-engine fuel burn. The aim of this paper is to assess the influence of the design style of short intakes on the unsteady interaction under crosswind conditions between fan and intake, with a focus on the separation onset and characteristics of the boundary layer within the intake. Three intake designs were assessed, and a hierarchical computational fluid dynamics (CFD) approach was used to determine and quantify primary aerodynamic interactions between the fan and the intake design. Similar to previous findings for a specific intake configuration, both intake flow unsteadiness and the unsteady upstream perturbations from the fan have a detrimental effect on the separation onset for the range of intake designs. The separation of the boundary layer within the intake was shock driven for the three different design styles. The simulations also quantified the unsteady intake flows with an emphasis on the spectral characteristics and engine-order signatures of the flow distortion. Overall, this work showed that is beneficial for the intake boundary layer to delay the diffusion closer to the fan and reduce the preshock Mach number to mitigate the adverse unsteady interaction between the fan and the shock.

Mean flow and turbulence in unsteady canopy layers

Non-stationarity is the rule in the atmospheric boundary layer (ABL). Under such conditions, the flow may experience departures from equilibrium with the underlying surface stress, misalignment of shear stresses and strain rates, and three-dimensionality in turbulence statistics. Existing ABL flow theories are primarily established for statistically stationary flow conditions and cannot predict such behaviours. Motivated by this knowledge gap, this study analyses the impact of time-varying pressure gradients on mean flow and turbulence over urban-like surfaces. A series of large-eddy simulations of pulsatile flow over cuboid arrays is performed, programmatically varying the oscillation amplitude $\alpha$ and forcing frequency $\omega$ . The analysis focuses on both longtime-averaged and phase-dependent flow dynamics. Inspection of longtime-averaged velocity profiles reveals that the aerodynamic roughness length $z_0$ increases with $\alpha$ and $\omega$ , whereas the displacement height $d$ appears to be insensitive to these parameters. In terms of oscillatory flow statistics, it is found that $\alpha$ primarily controls the oscillation amplitude of the streamwise velocity and Reynolds stresses, but has a negligible impact on their wall-normal structure. On the other hand, $\omega$ determines the size of the region affected by the unsteady forcing, which identifies the so-called Stokes layer thickness $\delta _s$ . Within the Stokes layer, phase-averaged resolved Reynolds stress profiles feature substantial variations during the pulsatile cycle, and the turbulence is out of equilibrium with the mean flow. Two phenomenological models have been proposed that capture the influence of flow unsteadiness on $z_0$ and $\delta _s$ , respectively.

Dynamic mode decomposition for the tip unsteady flow analysis in a counter-rotating axial compressor

Counter-rotating axial compressor (CRAC) is a promising potential technology to improve the thrust-to-weight ratio of aero-engines, but its special aerodynamic layout usually causes more pronounced flow unsteadiness. Understanding the unsteady flow features and mechanism in the CRAC contributes to the aerodynamic optimization design and flow control strategy organization. A data-driven dynamic mode decomposition method is introduced to investigate the tip flow unsteadiness in a CRAC, and the unsteady features of the tip flow at the design point (DP) and near-stall point (NSP) conditions are revealed. The results show that the 1.0 times blade passage frequency (BPF) and its multi-order harmonic frequency are the dominant frequencies for both rotors at the DP condition. At the NSP condition, the 1.0 BPF is no longer the dominant frequency causing the tip flow unsteadiness, and the low frequency fluctuation of the tip leakage flow becomes the dominant frequency to induce the flow unsteadiness. In the front rotor R1, the unsteady dominant frequency is 1.0 BPF, whereas in the rear rotor R2, the frequency (0.801 BPF and 0.803 BPF) of the tip leakage flow is the dominant frequency. By reconstructing the flow field under the NSP condition, the spatiotemporal evolution of the tip flow during the unsteady stable manifests that the interference effect between the rotors is an important source of the tip flow unsteadiness. The increase in flow unsteadiness leads to an increase in the reconstruction error, indicating that more modes are required to obtain a more accurate reconstruction flow field.

Large-eddy simulation of non-isothermal flow and heat transfer in an enclosed rotor–stator cavity

This paper presents a numerical study of non-isothermal flow and heat transfer in an enclosed rotor–stator disk cavity. Wall-resolved large-eddy simulation is implemented with attention focused on the Reynolds number effect (Reϕ=105 and 5×105) and non-isothermal effects, including different thermal Rossby numbers (βΔT=0.05–0.25) and heat convection types (axial heat convection, axial and radial heat convection). Verification and validation are implemented by comparing with available experimental data and examining the resolution of the present LES. Although the Batchelor flow type is unchanged, the non-isothermal effect is found to be responsible for the acceleration of flow in both disk boundary layers and cavity core. Temperature in the cavity is negatively correlated with the Rayleigh number. The radial inward temperature gradient is found to be responsible for destabilizing the flow near the cylinders, due to the effect of centrifugal buoyant force. Transition from laminar to turbulent is shown in the rotor boundary layer for Reϕ=5×105 conditions. The non-isothermal effect increases flow unsteadiness in both rotor and stator boundary layers, but it has little to no effect on the transition position, as well as the kinematic and thermal boundary layer thicknesses, which are mainly controlled by Reϕ. Spectral proper orthogonal decomposition is implemented to explore the Reynolds number effect. Analyzing the most energetic mode and its energy spectra provides some insights into the understanding of non-isothermal rotor–stator disk cavity flows.

Effects of Flow Unsteadiness on the Transport of Bimodal Bed Material

The grain size distribution of the transported bed load was experimentally investigated under unsteady flow conditions with bimodal mixture of sand and gravel in a laboratory flume. Five various triangular hydrographs were generated. A clockwise behavior for the total bed load versus shear velocity was observed meaning that the bed load during rising limb was higher than that of falling limb. It was found that the percent finer at the plateau of bimodal sediment size distribution curve had higher values during the initial and final phases compared to those obtained during the peak time. At all plateaus, the percent finer values related to the hydrograph peak discharge were in the same order of magnitude with that of the bed material. The sand content of the transported bed material initially decreased, then maintained a constant value during a certain time interval and finally returned to its original value. The sand percent of the bed load decreased in the falling limb showing a counterclockwise loop and the duration of the hydrograph did not affect the results considerably. The greater the peak flow rate of the hydrograph, the greater was the hysteresis. The bimodality index was calculated for all transported sediment samples and it was revealed that its initial and final values were less than that of the bed material but it was approximately the same elsewhere. The 5% finer sediment amount was nearly equal during rising and falling limbs. It was revealed that D50 value of the bed load decreased in the rising limb showing a clockwise loop. The hysteresis was not considerably changed according to the hydrograph characteristics. The clockwise type hysteresis was also observed for the size group of D95. The lag increased as the peak flow rate increased. A strong relation was found between the dimensionless total bed load Wt* and the total work index Wk as well as Wk and the ratio WR/WF. The correlations between the dimensionless total bed load and the unsteadiness parameters P, and Pmod were very weak, whereas a high value of determination coefficient was obtained with the unsteadiness parameter Pgt, implying an appreciable interdependence.

Dynamic mode characteristics of flow instabilities in a centrifugal compressor impeller

Centrifugal compressors are key parts of medium and small aircraft engines, the flow instabilities of centrifugal compressors have become the bottleneck of the developments of engines. It is vital to investigate the dynamic mode characteristics of flow instabilities in centrifugal compressors for solving the issues. In this study, unsteady full annular simulations of the centrifugal compressor flow are firstly implemented. It is found that the flow instability of the compressor primarily arises in the impeller. To capture the dominant transient modes in process of flow instabilities and accurately describe their temporal evolutions, a modified dynamic mode decomposition method (DMD-TC) is adopted to analyze the dynamic mode characteristics, which was proposed in our previous study. The results show that perturbations in the impeller can be mainly classified into three categories: impeller-diffuser interactions, self-excited perturbations, and vortex-induced perturbations. In detail, the modes induced by the impeller-diffuser interactions and self-excited perturbations are intrinsic modes, and they reflect the inherent flow unsteadiness in the impeller. On the one hand, the vortex-induced perturbations couple with the self-excited ones, which affect the spatial structures of modes induced by self-excited perturbations. The coupling effects enhance with the reduced mass flow rate, and the “resonance” effect might be excited. As a result, the mode of 4 RF (rotor frequency) grows during rotating stall process (RSP), which is a typical characteristic of rotating stall in the impeller. On the other hand, the vortex-induced perturbations emerge as different characteristic modes, due to the variant vortex structures with the mass flow rate. During the RSP, the growth of low-frequency characteristic modes is another typical feature of rotating stall in the impeller.

Effect of aspect ratio and inclined angle on the fluid flow and heat transfer past two parallel flat plates

The flow past two parallel flat plates is undoubtedly one of the most classic problems in fluid mechanics, as the aerodynamic and heat transfer performance can be significantly affected by the geometry of the flat plate. In this work, using the open-source package OpenFOAM, we first performed a numerical investigation on the fluid flow and heat transfer past two parallel flat plates with different aspect ratios (AR) and inclined angles (α). The representative vortex structures and instantaneous flow patterns were presented and analyzed. We then discussed the local force characteristics and heat transfer rate on the plate walls, as well as the velocity and temperature distributions near the wake. The global flow unsteadiness and heat transfer characteristics were obtained. The numerical results revealed that larger AR and α enhanced the flow unsteadiness and increased the fluid force. The global heat transfer performance increased with increasing α, but first decreased and then increased with increasing AR. The objective of this work was to further achieve a more effective flat plate application and to provide theoretical support for its improvement.

Mixed Convective Flow Past Reverse Doublet like Rotating Side by Side Cylinders

The flow unsteadiness and the consequent evolution of the vortex shedding for flows around bluff objects are significantly important in fluid dynamics. Rotating the bluff objects may help in controlling such flow instabilities. Depending on the rotational speed, the unsteady flow may be transfigured into a steady pattern. On the other hand, multiple objects placed transverse to the incoming flow have destabilizing wake interactions. The instability even gets amplified with the introduction of thermal buoyancy. Under such conditions, the rotation plays an important role in stabilizing the wake dynamics. In view of the above, the present study aims to numerically investigate the wake and the thermal characteristics around a pair of circular cylinders arranged in side-by-side fashion in an unconfined medium. The top and the bottom cylinders are rotated in the counterclockwise and the clockwise directions, respectively, replicating a reverse doublet like configuration. The Reynolds and the Prandtl numbers are fixed at 100 and 0.71, respectively. The effect of the rotation on the flow instability is studied for Richardson number 0 to 1. The computations are performed using a finite volume method for the dimensionless cylinder spacings 0.7, 1.5, 3.0, and 5.0. The unsteady and the steady attributes are examined using the vorticity, isotherm-streamline contours, and lift signals. Finally, a regime diagram is constructed to exhibit the critical rotational speeds at which the flow becomes steady for various cylinder spacings.

Experimental and numerical investigation on the metering and diffuser length effects of a laidback fan-shaped film cooling hole

In this study, the metering and diffuser length effects of a laidback fan-shaped (LBF) hole on the film cooling effectiveness (FCE) were investigated. The FCE was measured using the pressure sensitive paint (PSP) technique, with a density ratio (DR) of 2.0 and five blowing ratios (BR). The experimental results indicated that the FCE increased as the diffuser length increased. However, when the metering length ratio increased beyond the critical length, the coolant was shifted to a specific side of the diffusion section, resulting in a lower FCE. A computational analysis was performed to investigate the coolant shift at longer metering lengths. Numerical results indicate that the center velocity of the cylinder section is higher for the longer metering length cases, which leads to a large separation bubble in the diffusion section, these resulted in the increase of the flow unsteadiness and instability at the hole exit.

Flow structures and unsteadiness in hypersonic shock wave/turbulent boundary layer interaction subject to steady jet

Flow structures and unsteadiness in hypersonic shock wave/turbulent boundary layer interaction subject to steady jet

Instability of the optimal edge trajectory in the Blasius boundary layer

In the context of linear stability analysis, considering unsteady base flows is notoriously difficult. A generalisation of modal linear stability analysis, allowing for arbitrarily unsteady base flows over a finite time, is therefore required. The recently developed optimally time-dependent (OTD) modes form a projection basis for the tangent space. They capture the leading amplification directions in state space under the constraint that they form an orthonormal basis at all times. The present numerical study illustrates the possibility to describe a complex flow case using the leading OTD modes. The flow under investigation is an unsteady case of the Blasius boundary layer, featuring streamwise streaks of finite length and relevant to bypass transition. It corresponds to the state space trajectory initiated by the minimal seed; such a trajectory is unsteady, free from any spatial symmetry and shadows the laminar–turbulent separatrix for a finite time only. The finite-time instability of this unsteady base flow is investigated using the 8 leading OTD modes. The analysis includes the computation of finite-time Lyapunov exponents as well as instantaneous eigenvalues, and of the associated flow structures. The reconstructed instantaneous eigenmodes are all of outer type. They map unambiguously the spatial regions of largest instantaneous growth. Other flow structures, previously reported as secondary, are identified with this method as relevant to streak switching and to streamwise vortical ejections. The dynamics inside the tangent space features both modal and non-modal amplification. Non-normality within the reduced tangent subspace, quantified by the instantaneous numerical abscissa, emerges only as the unsteadiness of the base flow is reduced.

On the flow unsteadiness and operational characteristics of a novel supersonic fluidic oscillator

A novel supersonic jet oscillating method is investigated both experimentally and numerically. A rectangular primary supersonic jet is issued into a confined chamber with sudden enlargement. Secondary control jets are issued from the top and bottom backward-facing step regions formed due to sudden enlargement. The primary jet is oscillated in the transverse direction by blowing the secondary jets in the streamwise direction in a pulsating manner with a phase shift. The out-of-phase secondary jet blowing causes the primary jet to periodically adhere to the upper and lower part of the confined chamber, causing flapping of the primary jet and acting as a supersonic fluidic oscillator. The supersonic jet oscillation characteristics are experimentally investigated using shadowgraph type flow visualization technique and steady and unsteady pressure measurements. Quantitative analysis of the shadowgraph images using the construction of y – t and y – f plots reveals the presence of periodic jet oscillation with a discrete dominant frequency similar to the secondary jet excitation frequency. The existence of linearity between the excitation frequency and the flapping jet frequency on the low-frequency (0.66–6.6 Hz) side is first proven experimentally. Later, the high-frequency (16.67–5000 Hz) operation extent of the supersonic fluidic oscillator is further demonstrated using unsteady computational studies owing to the existing experimental facility's limitations. A reduced-order analytical framework has also been proposed to investigate the limiting oscillation frequency. It is found that the limiting frequency predicted from the proposed analytical model shows fairly good agreement with the computationally predicted results (5 kHz).

Design Optimization of Lambda-Wing Planform and Vortex Generators for Longitudinal Instability Alleviation

This paper focuses on optimizing the planform and vortex generators (VGs) to improve longitudinal stability of the lambda-wing aircraft by alleviating pitchup. The optimizations are performed in two stages using a Reynolds-averaged Navier–Stokes (RANS) solver that can accurately capture the vortical flow structure, affecting the pitchup. First, the planform configuration is optimized to minimize the rise in the pitching moment while maintaining aerodynamic and stealth performances. The designed planform delays the pitchup by 4 deg and increases the usable lift by 31% due to the leading-edge vortex (LEV) flow over the outboard wing. Second, the VGs are installed and optimized to reduce the sudden increase in the pitching moment at high angles of attack. The designed VGs partially eliminate the separated flow and recover the LEV on the outboard wing, suppressing the radical change in the pitching moment by 75%. Some quantitative difference in aerodynamic coefficients is observed in unsteady RANS computations, but the vortical flow unsteadiness minimally affects the flow structure, and the stability improvement remains over 80%. Overall, the generation and sustainability of the LEV are critical aerodynamic factors to secure longitudinal stability in designing the lambda-wing aircraft.

Reheat effect on the improvement in efficiency of the turbine driven by pulse detonation

Due to the strong unsteadiness of pulse detonation, large flow losses are generated when the detonation wave interacts with the turbine blades, resulting in low turbine efficiency. Considering that the flow losses are dissipated into the gas as heat energy, some of them can be recycled during the expansion process in subsequent stages by the reheat effect, which should be helpful to improve the detonation-driven turbine efficiency. Taking this into account, this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine, and a stoichiometric hydrogen-air mixture was used. The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine. The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation, which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled, so that the efficiency of the two-stage turbine was improved. At a 95% confidence level, the efficiency improvement was stable at 4.5%–5.3%, demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.