Reverse Flow Conditions Research Articles

Evolving Dunes Under Flow Reversals: From an Initial Heap Toward an Inverted Dune

AbstractSand dunes are ubiquitous in nature, and are found in abundance on Earth and other planetary environments. One of the most common types are crescent‐shaped dunes known as barchans, whose mid‐line could be assumed to behave as 2D dunes. In this work, we (a) compare the morphology of the mid‐line of 3D barchans with 2D dunes; and (b) track the evolution of 3D barchans and 2D dunes while reversing flow conditions. We performed experiments on 2D dunes in a 2D flume and Euler‐Lagrange simulations of 3D bedforms. In all reversal experiments and simulations, the initial condition starts with a conical heap being deformed into a steady‐state dune, which is then perturbed by reversing the flow, resulting in an inverted dune. We show that during the reversal the grains on the lee side immediately climb back onto the dune while its internal part and toe remain static, forming a new lee face of varying angle on the previous stoss slope. We show that (a) the characteristic time for the development of 2D dunes scales with that for 3D barchans, (b) that the time for dune reversal is twice the time necessary to develop an initial triangular or conical heap to steady‐state, and (c) that a considerable part of grains remain static during the entire process. Our findings reveal the dynamics for dune reversal, and highlight that numerical computations of barchans based on 2D slices, which are more feasible in geophysical scales, predict realistic outcomes for the relevant time‐scales.

Theory for electrodiffusional wall shear stress measurement by directionally sensitive twin semicircular probe

This study investigates the theoretical aspects of mass transport at the surface of a twin semicircular electrodiffusion probe tailored to measure the magnitude and direction of near-wall fluid flows. A critical aspect of this research is the development of a theoretical framework that facilitates experimental measurements by analytically relating measured electric currents to the wall shear stress vector. Central to the study is the derivation of analytical expressions for the mass transfer coefficients of the front and rear segments of the probe, which are essential for quantifying near-wall hydrodynamics. Validation of these analytical relations is achieved through numerical solutions of the convection–diffusion equation, providing a robust confirmation of the underlying theory. A comprehensive procedure for experimental data processing is proposed, taking into account both frontal and reverse flow conditions across the probe. In addition, a sensitivity analysis of the twin semicircular probe is performed. This analysis focuses on the response of current ratios to changes in the flow direction, an aspect critical to understanding the operational performance of the probe. The results of this analysis are compared to the characteristics of two-segment strip probes, highlighting the distinct sensitivity nuances of the twin semicircular probe. Our findings provide insight into the optimal application of this probe in various fluid dynamics scenarios.

A Novel Leak-Proof Thermal Conduction Slot Battery Thermal Management System Coupled with Phase Change Materials and Liquid-Cooling Strategies

Electric vehicles (EVs) are experiencing explosive developments due to their advantages in energy conservation and environmental protection. As a pivotal component of EVs, the safety performance of lithium-ion batteries directly affects driving miles and even safety; hence, a battery thermal management system (BTMS) is especially important. To improve the thermal safety performance of power battery modules, first, a new leak-proof phase change material (PCM)-coupled liquid-cooled composite BTMS for large-scale battery modules is proposed in this research. Second, the numerical simulation analysis method was utilized to analyze the influences of the fluid flow channel shape, working fluid inlet temperature, inlet velocity, and reverse flow conditions on the BTMS. Eventually, the abovementioned performances were compared with the traditional PCM-coupled liquid-cooling strategy. The relative data indicated that the Tmax was reduced by 17.5% and the ΔTmax was decreased by 19.5% compared to the liquid-cooling approach. Further, compared with conventionally designed PCM composite liquid cooling, the ΔTmax was reduced by 34.9%. The corresponding data showed that, when using the e-type flow channel, reverse flow II, the inlet flow velocity was 0.001–0.005 m/s, and the inlet temperature was the ambient temperature of the working condition. The thermal performance of the anti-leakage system with a thermal conduction slot PCM-coupled liquid-cooling composite BTMS reached optimal thermal performance. The outcome proved the superiority of the proposed BTMS regarding temperature control and temperature equalization capabilities. It also further reduced the demand for liquid-cooling components, avoided the problem of the easy leakage of the PCM, and decreased energy consumption.

A Surge/Stall-Capable Dynamic Performance Simulation Methodology for a Turbojet Engine

Abstract A lumped-parameter dynamic performance model for a single-spool turbojet engine is presented in this paper. This model can handle pre and poststall transients under forward and reverse-flow conditions. The inter-component volume technique is employed instead of the standard matching technique to be able to handle high-frequency transients and reverse-flow conditions. Inspired by Greitzer's lumped-parameter surge model, momentum (duct) and volume elements are placed within the flow path to handle surge dynamics. Compressor and turbine maps are extended to low-flow and reverse-flow regions using a combination of the guidelines presented by Kurzke, the cubic axisymmetric characteristics of Moore and Greitzer, and a quadratic function guess for in-stall characteristics. Combustor efficiency, stability limits, and delay are taken from the literature. Poststall behavior of the model is validated using the data available in the literature for a Rolls-Royce Viper engine. A good match is observed with a correct prediction of poststall behaviors, which transition from surge after locked stall to multiple surge cycles around 80% speed and multiple surge cycles to surge after flameout around 95% speed. The effects of different modeling choices and modeling parameters on the obtained results are discussed. The produced model can be calibrated for a specific engine with surge tests, and it can be used for hard-to-test scenarios like surge after shaft breakage. Different surge/stall-causing events, such as fuel spiking, in-bleeding, and shaft breakage, are simulated to see the capabilities of the model.

Effects of hydraulic conditions on biofilm detached in drinking water distribution system

It is well documented that after the water has been treated in the treatment plant, the quality of drinking water is degraded during transport to consumers inside the drinking water distribution system (DWDS). One of the critical reasons for altering drinking water quality is the biofilm detached from the pipe wall to the bulk water. In this paper, the effects of hydraulic conditions such as flow velocity and flow direction, on the biofilm were investigated. The results show that, compared with other flow conditions, the biofilm is the thickest (267.4 μm) and the adhesion force is the lowest under the fluctuant flow velocity. The fluctuant flow velocity increased the relative abundance of Sphingobium and Blastomonas, decreased the relative abundance of Dechloromonas and Sediminibacterium. The Sphingobium with strong environmental adaptability and metabolic capacity could accelerate the growth of biofilm under fluctuant flow velocity conditions. The abundance of functional genes that could reflect microbial metabolic capacity in the biofilm under fluctuant flow velocity conditions is significantly higher than that under other hydraulic conditions. The total number of bacteria in the biofilm under reverse flow conditions was 31.48 %–32.01 % and 47.97 %–71.38 % lower than that under low and high flow conditions, respectively, indicating that the shear force generated by the reverse flow had resulted in biofilm detachment. This study improved our understanding of the influence of different hydraulic conditions on biofilms in the DWDS and helped us understand how to operate the DWDS without causing additional biofilm detachment.

Deep learning predictions of unsteady aerodynamic loads on an airfoil model pitched over the entire operating range

For the design and certification of wind turbines, it is essential to provide fast and accurate unsteady aerodynamic load prediction models for the whole operational range of angle of attack, up to 180° for vertical-axis and 90° for horizontal-axis wind turbines. This work describes a computationally efficient unsteady forces prediction model based on a deep learning approach, namely the bidirectional long short-term memory (BiLSTM) algorithm, for an airfoil pitched over the full operational range of angles of attack up to 180°. No model has been developed to capture the unsteady forces at high angles of attack. Novel features based on operating conditions and the steady polars of the airfoil are used as inputs for the BiLSTM model. Direct measurements of steady and unsteady forces on a NACA 0021 airfoil model were conducted at reduced frequencies up to 0.075 and a Reynolds number of 120 000 in an open-jet wind tunnel for model learning and testing. The unsteady forces vary significantly from the steady values at high pitching amplitudes and post-stall angles, which, if not accounted for when simulating wind turbine performance, would result in inaccurate predictions. Furthermore, measurements revealed the effect of unsteady vorticity development and shedding on aerodynamic forces under forward and reverse flow conditions. The BiLSTM model is capable of capturing the underlying physics of unsteady aerodynamic forces under extreme operating conditions.

Analysis of fluid-structure interaction in a directional permeability membrane in pressure-driven flow

Finite volume and finite element analysis of fluid-structure interaction is performed to understand the behavior of a directional permeability membrane in pressure-driven flow. The membrane is comprised of two flexible porous sheets separated by a spacer. The porous sheets each have a different thickness with pores that are offset from each other. The design allows flow when the thicker sheet is on the high pressure side, but prevents flow if the pressure gradient is reversed. Flow through the membrane is studied for a pressure range of 0.01–0.1 m H2O in forward flow to understand the complex fluid motion and dependence of membrane deformation on sheet thickness, downstream pore diameter, and initial gap between the sheets. In forward flow, maximum mass flow rate of 0.2 g s−1 (or flow rate of 12.024 ml min−1) can be obtained at 0.1 m H2O pressure head. Reverse flow conditions are modeled to study the effect of design parameters on the required closing pressure, indicating that as little as 0.0325 m H2O of pressure head is required for closing.

Wind tunnel tests of a wing at all angles of attack

Tailsitters have complex aerodynamics that make them hard to control throughout the entire flight envelope, especially at very high angle of attack (AoA) and reverse flow conditions. The development of controllers for these vehicles is hampered by the absence of publicly available data on forces and moments experienced in such conditions. In this paper, wind tunnel experiments are performed under different flap deflections and throttle settings at all possible AoA. The dataset is made open access. Our analysis of the data shows for the tested wing, flap deflections greatly affect the lift coefficient and stall occurs at [Formula: see text] AoA as well as [Formula: see text]. Wing-propeller interaction is studied by analyzing the propeller induced force in the axis orthogonal to the thrust axis, which is dependent on AoA, airspeed, flap deflections and thrust in a nonlinear and coupled manner. The influence of inverse flow on the wing is also discussed: The data confirm that when the airflow over the wing is reversed, flap deflections will affect the pitch moment in an opposite way compared to the non-reversed case, but this opposite effect can be avoided by increasing the throttle setting. The data show the exact relationship between flap deflections and forces in this condition. Moreover, it is found that the flap control effectiveness for a wing with or without spinning propellers is usually higher around zero degrees AoA than at [Formula: see text] and it is more effective to change the flaps from [Formula: see text] to [Formula: see text] than from [Formula: see text] to the respective [Formula: see text].

On the prediction of the reverse flow and rotating stall characteristics of high-speed axial compressors using a three-dimensional through-flow code

This paper presents the development of a low-order three-dimensional through-flow code created at Cranfield University in the UK, named ACROSS (Axial Compressor Rotating Stall and Surge simulator), and its application to create the reverse flow and rotating stall characteristics of a modern high-speed compressor. The compressor modelled is a six-stage axial-flow machine, representative of a modern aero-engine high-pressure compressor. The tool has been previously validated using experimental data from two low-speed compressor rigs. This article describes how the tool's robustness and computational speed have been improved by introducing higher-order schemes to model the circumferential fluxes and the rigid movement of the flow in the rotating blade rows. Further improvements include variable axial discretization, an algorithm to introduce random flow perturbations in the flow field and an improved plenum model. The compressor is first modelled in reverse flow conditions to create its reverse-flow characteristics and these are then compared against results from high-fidelity 3D CFD simulations. Results obtained suggest that despite the presence of three-dimensional flow features, 2D axi-symmetric simulations are adequate to generate the full range of reverse flow characteristics of the compressor. The rotating stall characteristics at 77% and 100% corrected rotational speed are created by modelling several steady rotating stall cases in 3D. Using the code ACROSS, the complete map of the compressor modelled, comprising of forward flow, reverse flow and rotating stall characteristics, was created in only 5 days using 3 desktop workstations. For comparison, state-of-the-art high-fidelity 3D CFD requires several days to simulate a single rotating stall case on a high performance computing facility.

Simulation of a counter-current horizontal gas-liquid flow experiment at the WENKA channel using a droplet entrainment model

Usually droplet formation mechanisms are missing in standard fluid dynamics codes. However, for self-generating waves and slugs, the interfacial momentum exchange and the turbulence parameters ought to be modelled adequately. Furthermore, knowledge and thinking about the mechanism of droplet entrainment for heat and mass transfer processes is of high importance in the nuclear industry.Consequently a step of progress of modelling liquid/gas interfaces is the consideration of droplet entrainment model. The suggested model assumes that due to liquid turbulence the interface gets uneven and wavy leading to the creation of droplets. The model is validated against existing horizontal two-phase flow data from the WENKA (Water ENtrainment Channel KArlsruhe) channel. Experiments were taken out for an air/water system at ambient pressure and temperature. High speed videometry was used to get velocities from flow pattern maps of the counter current flow. In the horizontal part of the channel with partially reversed flow the fluid velocities were conducted by planar particle image velocimetry. An experiment with droplet generation at the reversed flow conditions was utilized to compare it with the simulation data. The agreement of the experimental findings and CFD results is more than satisfactory. Also the droplet mass flow was compared and showed the applicability of the droplet entrainment model. Further work is necessary to validate the model for different flow conditions.

Influence of reversing currents on the erosion stability and bed degradation of widely graded grain material

Physical model tests were done in a recirculating flume to investigate the overall erosion stability of widely graded bed material in estuarine and coastal conditions by means of simulating tidal flow conditions with reversing currents. As a result of the reversing flow conditions, previously protected sediment eventually became exposed again, leading to bidirectional displacement processes depending on the flow direction. Furthermore, eroded sediment fractions were slightly finer due to flow in the initially applied direction rather than under the subsequently applied flow in the reverse direction. This indicates higher critical shear stresses, and, thus, erosion stability for the initial flow direction. In comparison to the erosional pattern found when subjecting the material to unidirectional currents, this study finds an even higher erosional stability for sediment fractions smaller than the median (d50) diameter of the parent bed material under reversing current conditions. Overall, no significant damage or failure of the bed was observed after subjecting the material to reversing currents, indicating only a small amount of bed degradation, and, thus, high potential for scour and bed protection under the tested flow conditions.

太陽光発電設備の出力変動が逆潮流対応型SVRの自律制御に与える影響

太陽光発電設備の出力変動が逆潮流対応型SVRの自律制御に与える影響

Interactions Between Parallel Unevenly Heated Minichannels During Flow Boiling of R134A

Transient pressure drop of individual channels during flow boiling of R134a in four 0.54 mm square parallel minichannels was experimentally studied in this work. The design of the test section enabled the experimenter to control and to vary heat flux independently in each channel in the range from 3.82 to 18.66 kW/m2 at five different overall flow rates from 86 to 430 kg/m2-s. Flow rate fluctuation in parallel channels due to the formation of bubbles under the nonuniform heat flux conditions caused significant oscillations in local pressure drop. Statistical analysis indicated that the pressure drop signal was normally distributed when boiling was stable with no incoming flow disturbance. Pressure drop distribution was highly skewed and multimodal when significant evaporation rate at low mass fluxes led to rapid annular flow formation, reducing the free flow of incoming fluid. Cross-correlation analysis revealed a strong interaction between minichannels having the highest heat flux difference among the set of channels. The least heated channel was more sensitive to the fluctuations in other channels. Cross-correlation between the most heated channel and the adiabatic one was estimated to be 39% when the total flow rate was the lowest, 86 kg/m2-s. The power of the relationship between channels dropped significantly as the flow rate increased. Less than 5% of data points could be considered cross-correlated at the highest flow rate of 430 kg/m2-s. Increasing the two-phase pressure drop across each channel caused higher resistance to the incoming disturbances and led to less interchannel interaction. This study of the channels interaction in a system of parallel, nonuniformly heated minichannels can be used as a tool to identify and quantify instabilities and reversed flow conditions.

Mechanisms of Amplified Arteriogenesis in Collateral Artery Segments Exposed to Reversed Flow Direction.

Collateral arteriogenesis, the growth of existing arterial vessels to a larger diameter, is a fundamental adaptive response that is often critical for the perfusion and survival of tissues downstream of chronic arterial occlusion(s). Shear stress regulates arteriogenesis; however, the arteriogenic significance of reversed flow direction, occurring in numerous collateral artery segments after femoral artery ligation, is unknown. Our objective was to determine if reversed flow direction in collateral artery segments differentially regulates endothelial cell signaling and arteriogenesis. Collateral segments experiencing reversed flow direction after femoral artery ligation in C57BL/6 mice exhibit increased pericollateral macrophage recruitment, amplified arteriogenesis (30% diameter and 2.8-fold conductance increases), and remarkably permanent (12 weeks post femoral artery ligation) remodeling. Genome-wide transcriptional analyses on human umbilical vein endothelial cells exposed to reversed flow conditions mimicking those occurring in vivo yielded 10-fold more significantly regulated transcripts, as well as enhanced activation of upstream regulators (nuclear factor κB [NFκB], vascular endothelial growth factor, fibroblast growth factor-2, and transforming growth factor-β) and arteriogenic canonical pathways (protein kinase A, phosphodiesterase, and mitogen-activated protein kinase). Augmented expression of key proarteriogenic molecules (Kruppel-like factor 2 [KLF2], intercellular adhesion molecule 1, and endothelial nitric oxide synthase) was also verified by quantitative real-time polymerase chain reaction, leading us to test whether intercellular adhesion molecule 1 or endothelial nitric oxide synthase regulate amplified arteriogenesis in flow-reversed collateral segments in vivo. Interestingly, enhanced pericollateral macrophage recruitment and amplified arteriogenesis was attenuated in flow-reversed collateral segments after femoral artery ligation in intercellular adhesion molecule 1(-/-) mice; however, endothelial nitric oxide synthase(-/-) mice showed no such differences. Reversed flow leads to a broad amplification of proarteriogenic endothelial signaling and a sustained intercellular adhesion molecule 1-dependent augmentation of arteriogenesis. Further investigation of the endothelial mechanotransduction pathways activated by reversed flow may lead to more effective and durable therapeutic options for arterial occlusive diseases.

Hydraulic modelling of closed pipes in loop equations of water distribution networks

Zero flows in closed pipes in pressurised water supply networks require additional computational boundary constraints, which can result from two different operational states for pipe appurtenances. Static closed pipes are produced by turning off the isolation valves to undertake inspections/repairs of related pipe segments or to separate adjacent pressure zones. In addition, closed pipes can occur dynamically due to shutdowns of check valves and pressure/flow regulating facilities equipped with non-return valves. In this study, a generalised solution approach is developed to solve the nonlinear loop equations of the network flow problem involving closed pipes, which is integrated directly into hydraulic simulations of water distribution systems. The iterative approach uses the Newton–Raphson method based on the energy equations. The head loss across closed pipes is estimated using a novel computational technique called the unknown hydraulic function to avoid the singularity of the Jacobian matrix. The flow corrections of the related loops are performed locally using the Hardy-Cross technique, which allows small amounts of the flow rates to vary within lower (εmin) and upper (εmax) bounds during the iteration process. As an additional convergence criterion, the upper limit (εmax ≤ 0.020 l/s) is allowed to vary in both flow directions for static closed pipes, whereas this is permitted only under reverse flow conditions for closed pipes of unidirectional control devices. The reliability and efficiency of the proposed algorithm are demonstrated using some example network applications. The results obtained after many computer runs demonstrated that the iteration process is robust and efficient, thereby ensuring consistent convergence in a rapid manner. The flow correction magnitude was reduced to negligible small values for the related loops after executing a Hardy-Cross step, which significantly helped to stabilise the direction of the solution matrix.

Lessons learned from geotextile filter failures under challenging field conditions

This paper reviews sixty-nine (69) field failures involving geotextile filters which performed unsatisfactorily and are categorized herein as failures. They are grouped into four categories; inadequate design, atypical soils, unusual permeants, and improper installation. In the first category are poor fabric selection, poor fabric design, socked drainage pipe and reversing flow conditions. In the second category are fine grained soils, gap-graded soils, dispersive clays and ochre. In the third category are sludges, turbid water, alkaline water, leachates and agricultural waste liquids. In the fourth category are lack of intimate contact and completely adhesive clogging of surfaces. While not the topic of the paper, it should be noted that, most of these same conditions are known to be troublesome to sand filters as well as to geotextile filters.

Numerical and experimental characterization of the 2D vertical average-velocity plane at the center-profile and qualitative air entrainment inside a gully for drainage and reverse flow

Gullies are devices that connect the surface system to the sewer allowing the drainage of water during a rainfall event. During severe flooding, the sewer might become pressurized and water may gush out of the sewer onto the surface, in what is termed reverse flow. Experimental and numerical studies of gullies are rare because of the high computational time and the experimental facilities costs. In this paper we aim to characterize the average velocity inside a gully at the center profile and discuss the qualitative air-entrainment structure for both drainage and reverse flow conditions. The experimental facility termed the Multiple-Linking-Element experiment (MLE) is located at the University of Coimbra. OpenFOAM™ v.1.7.1 is used with the Large Eddy Simulation (LES) Smagorinsky model to simulate turbulence. Numerical and experimental results show reverse flow with a strong jet at the center and an anticlockwise vortex on the left side of the gully box, and drainage flow with a large clockwise vortex located above and slightly to the left of the bottom outlet. Reverse flow shows few traces of air-entrainment, unlike drainage flow that exhibits large quantities of air-entrainment caused by a hydraulic jump formed on the surface flow.

High Yttria-Zirconia and Yttria Ceramics for Petrochemical Reverse-Flow Reactor Applications

Reverse-flow reactors achieve the desired hydropyrolysis reaction of natural gas and other hydrocarbon feeds at very high temperatures of up to 2000°C, which enables the production of many high-value chemicals. To identify refractory ceramic materials suitable for constructing key components of the reactor, the full range of solid solutions between zirconia and yttria having 18 to 100 mol% yttria have been tested in a laboratory reactor. Conventional yttria-stabilized zirconia (YSZ) materials having 8 mol% Y2O3 appear to accommodate reactor thermal severity, but are prone to a new form of corrosion termed ceramic dusting that is observed when pyrolysis and oxidation cycles are alternated under reverse-flow conditions. Yttria and high yttria–zirconia ceramics having ~80 mol% or more yttria suppress ceramic dusting corrosion in steam-free pyrolysis environments. The addition of low levels of steam of ~5% to the pyrolysis gas stream increases the stability of YSZ materials substantially, so that the stability threshold is closer to 40 mol% Y2O3 in the yttria–zirconia system. The two approaches can be combined to optimize reactor performance. Key experimental results are presented and discussed taking into account the thermodynamic phase stability of the different phases.

Regenerative reverse-flow reactor system for cracking of producer gas tars

The gas produced in a biomass gasifier contains high amounts of tars which have to be removed prior to downstream utilization. Calcined dolomite is catalytically active for tar cracking reactions and resistant to sulfur poisoning. In this study, calcined dolomite was used as bed material in a reverse-flow reactor for cracking of tars in a model synthesis gas. 1-methylnaphthalene was used as model tar compound at a concentration of 15,000 mg/Nm3. The reactor system was operated at temperatures between 700 and 850 °C in the active zone. Total tar conversion was over 95 % for the system under reverse-flow conditions at the highest temperature. Already at the lowest temperature, up to 78 % of the 1-methylnaphthlene was converted, but mainly to other more stable tar compounds such as naphthalene and benzene, reaching a total tar conversion of only 23 %. To produce tar-free gas, higher temperatures are thus needed. The use of very high temperatures does, however, lead to a significant decrease in the specific area of the dolomite, as shown by BET surface measurements. The dolomite was further characterized with x-ray diffraction and energy dispersive spectroscopy.

Aeroelasticity at Reversed Flow Conditions—Part III: Reduction of Surge Loads by Means of Intentional Mistuning

Compressor surge consists of four phases: (i) pressure rise, (ii) flow breakdown, (iii) blow-down, and (iv) flow recovery. During the blow-down phase reversed flow conditions exist, where a blade may accumulate hundreds of vibration cycles, depending on the surge volume and the vibration frequency. High vibration amplitudes and blade damages were observed in the past. In Part I (GT2011-45034) a compressor cascade was analyzed experimentally and analytically at steady reversed flow conditions. It has been shown that (i) the steady flow field can be predicted well by CFD analysis, (ii) the overall damping coefficient calculated by unsteady CFD compares reasonably well with measurements, and (iii) a blade may become unstable at certain reversed flow conditions. In Part II (GT2011-45035) the analytical procedures used in Part I were applied to the front part of a multistage HPC for reversed flow conditions. It was found that surge loads consist in reality of two physically different phenomena (i) the pressure wave during the flow breakdown leading to rather low blade stresses and (ii) flutter during the blow-down phase which may lead to very high blade stresses and damages during surge for some stages. As it is well known that intentional mistuning is a way to mitigate flutter, intentional mistuning is investigated in Part III of the paper at reversed flow conditions. At first, a CFD study of a single airfoil is presented showing the dependency of aerodynamic damping upon flow angle and pressure ratio over the airfoil at reversed flow conditions, including intentional mistuning studies. Secondly, an investigation is presented which shows experimentally and analytically that surge stresses can be reduced significantly by the use of intentional mistuning. In a multistage compressor test rig, one rotor stage, which experienced very high stresses during surge, was subjected to a cutback on every second blade, leading to significantly reduced surge stresses. Analytically, an aeroelastic eigenvalue analysis showed the same behavior.