Spinning Mode Research Articles

Mode Analysis for the Rotating Aerodynamic Disturbance of a Transonic Fan

Abstract The non-synchronous blade vibration induced by a rotating aerodynamic disturbance is encountered for the fan of a turbofan engine working at 65% speedline. To analyze the unsteady characteristics, two methods based on the phase analysis and the compressive sensing (CS) for spatially-undersampled data are proposed and applied to obtain the circumferential mode order of the aerodynamic disturbance, and their performance has been carefully examined at various parameters. It was shown that when there are sufficient probes, i.e., 7–8 in the present study, both the two methods can give a correct prediction to the dominant mode order (the highest is 26 in this work) for all non-engine-order (EO) frequencies. However, if less probes are used, the deterioration of accuracy can be observed for both the two methods and a better performance can be observed for the CS method. In order to suppress the blade vibration, the fan blade is trimmed to alter its solid eigenfrequencies and avoid the resonance, which is proved to be an effective anti-vibration design. The existence of the aerodynamic disturbance after the blade is trimmed also suggests that the vibration is not self-excited but induced by the resonance of the flow excitation and the structure. For the cases with and without vibration, the origin of these non-EO frequencies can be well explained by the spinning mode theory and the interaction between the blade vibration and a high-order blade passing frequency has been observed in this study.

High-frequency transverse acoustic interactions between two lean-premixed hydrogen combustors connected with cross-fire and cross-talk sections

Large-scale inter-combustor thermoacoustic interactions occur frequently in modern can-annular gas turbine combustion systems due to the presence of an annular cross-talk section upstream of the first stage turbine stator vanes. Although the whole system's modal dynamics depend on the relative dominance of low-frequency planar or high-frequency transverse acoustic waves, the majority of prior studies have chiefly focused on longitudinal mode instabilities. Motivated by the paucity of detailed information, here we examine high-frequency transverse acoustic interactions between two adjacent lean-premixed hydrogen combustors connected via two different pathways, known as cross-fire (XF) and cross-talk (XT) sections. We observe that the dual-combustor system undergoes high-frequency spinning mode in the clockwise direction, manifested as well-defined limit cycles with peak-to-peak amplitude of around 10 kPa. The transverse pressure oscillations, in contrast to the well-established low-frequency mutual synchronization dynamics, are not fully synchronized even in the presence of cross-talk communication. This situation leads to the formation of two closely-spaced 1T modes at 4.76 and 4.86 kHz in the respective hydrogen combustors, accompanied by the beating of the pressure fluctuations solely in the XF tube section. Remarkably, the pressure waves induced near the XF tube section tend to lag behind the pressure waves spinning in the injector face, demonstrating the existence of the angular shift characteristically connected to the high-frequency transverse combustion dynamics.

Non-synchronous vibration of rotor blade in a six-stage transonic compressor

This paper presents an experimental study on the Non-Synchronous Vibration (NSV) in a six-stage transonic compressor. The first part of the paper describes the NSV phenomenon of Rotor 1, which occurs when both Stator 1(S1) and Stator 2(S2) or S1 only are closed. Detailed measurements and analysis are carried out for the former case through the unsteady wall pressure and the Blade Strain (BS). The spinning mode theory used in the rotor/stator interaction noise is employed to explain the relation between the circumferential wave number of the aerodynamic disturbance and the Nodal Diameter (ND) of the blade vibration. The variations of the vibration amplitudes of different blades and the Inter-Blade Phase Angles (IBPAs) at different moments suggest that the evolution of NSV is a highly nonuniform phenomenon along the circumferential direction. In addition, the difference between the wall-pressure spectra generated by the NSV and the classic flutter has been discussed. In the second part, the variations of aerodynamic loading due to the adjustment of the staggers of the Inlet Guide Vane (IGV), S1 and S2 have been investigated. It is found that closing S1 only can result in a great fluctuation to the performance of the front stages, which might be detrimental to the flow organization and increase the risk of NSV. In contrast, the effect of closing S2 only on the performance of the first two stages appears to be slighter relatively.

Numerical Analysis of High Frequency Transverse Instabilities in a Can-Type Combustor

Abstract Dry low emissions (DLE) systems are well-known to be susceptible to thermoacoustic instabilities. In particular, transverse, spinning modes of high frequency may appear, and lead to severe damage in a matter of seconds. The thermoacoustic response of an engine is usually specific to the combustor geometry, operating conditions and difficult to reproduce at the lab-scale. In this work, details of high frequency dynamics (HFD) observed during the early development phase of a new DLE system are provided, where a multipeaked spectrum was noticed during testing. Beginning with an analysis of the measured pressure spectra from three different concepts, an analytical model of the clockwise and anticlockwise transverse waves was fitted to the experimental data using a nonlinear curve fitting approach to produce a simple yet useful understanding of the phenomena. A flamelet-based large eddy simulation (LES) of the entire combustion system was used to complement this analysis and confirm the mode shapes using dynamic mode decomposition (DMD). Both approaches independently identified a spinning second-order mode as the dominant one in the high frequency regime. The LES indicates the coupling of a distortion of swirl profile with a precessing vortex core as a possible cause for the onset of instability. With regard to modeling sensitivities, it is shown that subgrid scale combustion modeling has a strong impact on predicted amplitudes. Ultimately, a thickened-flame model with a modified efficiency function provided consistent results.

Large Eddy Simulation and Acoustic Analysis of Combustion Instability in an Annular Combustor with Low-Swirl Flames.

Self-excited combustion instability in an annular combustor with low-swirl flames is studied with a combination of large eddy simulation (LES) and acoustic solvers. Acoustic analysis with a Helmholtz solver provides an estimate of frequencies and modal structures in the annular combustor. LES gives detailed modal dynamics for specific instability modes. Combustion instabilities in the annular combustor including longitudinal, spinning, and standing modes are successfully captured in a single LES. Numerical results show that the instability modes are not constant; they switch among these modes randomly and rapidly. The flow oscillates back and forth in phase with the largest pressure amplitude located near the outlet of the injectors for the longitudinal mode. The azimuthal instability oscillates in the 1A2L mode of the annular system. In the spinning mode, the pressure antinodes move forward while the modal structure keeps constant. For the standing mode, the locations of pressure antinodes are fixed in the annular combustor and the fluctuations at the pressure antinodes keep out of phase. The near-zero value of the mean spin ratio indicates that the dominant azimuthal mode is the standing mode. The azimuthal modes captured by LES are in good agreement with that predicted by Helmholtz solver in terms of frequency and modal structure. The maximum deviation of the predicted frequency is less than 5%. This adds values before the low-swirl injector is placed into the actual annular combustor.

Multi-Passage harmonic balance method for flutter prediction in multi-row configurations

A multi-passage harmonic balance method is presented for flutter prediction in multi-row configurations, and particular focus is on simulation of more than two blade rows. The unsteady flows in such configurations contain two kinds of multiple perturbations: one refers to those who have different frequencies and the other one refers to those who have the same frequency but different inter-blade phase angles (IBPAs). Most of current harmonic balance methods only consider the former one and the applications have been restricted to two-blade-row configurations. In the few studies that consider more rows, a one-to-one correspondence assumption between frequency and IBPA is usually made putting extra limitation on the used modes. This motivates our work, and a simple but effective idea is proposed by adding passages adopted per row. The theoretical basis of this work is provided by the spinning mode analysis. The present method is developed based on the time-spectral and multi-frequential form of harmonic balance. The treatment of pitchwise and inter-row boundary conditions in the case of multi passages are particularly addressed. A recently-developed Jacobian-free Newton-Krylov method with a simplified LU-SGS preconditioner is employed to solve the resultant harmonic balance equations. For validation, two typical multi-row flutter cases are investigated. The numerical results show the validity and accuracy of the developed method.

Acoustic Streaming-Induced Multimodal Locomotion of Bubble-Based Microrobots.

Acoustically-driven bubbles at the micron scale can generate strong microstreaming flows in its surrounding fluidic medium. The tunable acoustic streaming strength of oscillating microbubbles and the diversity of the generated flow patterns enable the design of fast-moving microrobots with multimodal locomotion suitable for biomedical applications. The acoustic microrobots holding two coupled microbubbles inside a rigid body are presented; trapped bubbles inside the L-shaped structure with different orifices generatevarious streaming flows, thus allowing multiple degrees of freedom in locomotion. The streaming pattern and mean streaming speed depend on the intensity and frequency of the acoustic wave, which can trigger four dominant locomotion modes in the microrobot, denoted as translational and rotational, spinning, rotational, and translational modes. Next, the effect of various geometrical and actuation parameters on the control and navigation of the microrobot is investigated. Furthermore, the surface-slipping multimodal locomotion, flow mixing, particle manipulation capabilities, the effective interaction of high flow rates with cells, and subsequent cancerous cell lysing abilities of the proposed microrobot are demonstrated. Overall, these results introduce a design toolbox for the next generation of acoustic microrobots with higher degrees of freedom with multimodal locomotion in biomedical applications.

Self-sustained azimuthal aeroacoustic modes. Part 1. Symmetry breaking of the mean flow by spinning waves

In this paper, we study the aeroacoustic instability which occurs in a deep axisymmetric cavity in a turbulent pipe flow. This phenomenon is the axisymmetric counterpart of the classical whistling of a rectangular deep cavity subject to a grazing flow. The whistling of such axisymmetric cavity originates from the interaction of the coherent fluctuations of the vorticity at the cavity's opening with one of its trapped azimuthal or radial acoustic modes. We focus here on the situation involving the first pure azimuthal mode, which is trapped in the cavity. As a consequence of the rotational symmetry of the configuration, azimuthal modes are actually pairs of degenerate eigenmodes, or almost degenerate in the presence of small asymmetries. Therefore, the aeroacoustic instabilities exhibit more complex mechanisms than in the case of a rectangular deep cavity. In particular, we show that self-sustained spinning modes induce a symmetry breaking of the mean flow and we will elucidate the details of this phenomenon. To that end, simultaneous acoustic and time-resolved stereoscopic particle image velocimetry (PIV) measurements are performed. They reveal that when large-amplitude aeroacoustic waves spin around the cavity, a quasi-steady mean flow starts whirling slowly in the opposite direction to the wave propagation. A linear perturbation analysis around an axisymmetric mean flow confirms the experimental observations: although the incoming pipe flow is not swirling, the hydrodynamic component of the aeroacoustic wave induces such whirling motion of the mean flow because of the forcing from the steady part of the coherent Reynolds stress tensor.

Realization of spinning mode with maximum chirality in photonic-crystal defect cavity at exceptional point

Optical modes spinning with maximum chirality in cavities at the chip level are essential for quantum and biomedical applications. The coalescent chiral mode at the exceptional point (EP) due to non-Hermicity is the one in demand. Yet, approaching EPs require fine balances between the loss/gain and the dielectric perturbation, which are typically nontrivial. In this paper, by elevating the reliability of fine-tuning, we realize circularly-polarized-like lasing modes with maximum chirality at the EP of photonic-crystal one-hole cavities. Such an EP is of intracavity type in the subwavelength scale and reaching it requires more reliable strategies than those for its forerunners. We adopt the in-plane tunneling loss that is well controlled with the layer number of air holes in the photonic-crystal slab. By removing and relocating holes in blocks, we systematically elevate the chirality of the radiation field. The collective variations of holes render the EP robust against the uncertainty in fabrications. Without auxiliary non-Hermitian and chiral structures, our works promote coherent chiral light sources at the chip level.

A three-dimensional solver for simulating detonation on curvilinear adaptive meshes

A generic solver in a parallel Cartesian adaptive mesh refinement framework is extended to simulate detonations on three-dimensional structured curvilinear meshes. A second-order accurate finite volume method is used with grid-aligned Riemann solvers for thermally perfect gas mixtures. Detailed, multi-step chemical kinetic mechanisms are employed and numerically incorporated with a splitting approach. The adaptive mesh refinement technique is applied to a mapped mesh using modified prolongation and restriction operators. The flux along the coarse-fine interface is considered in a correction procedure to ensure the conservation of the solver. The numerical accuracy, conservation and robustness of the simulations are verified and validated with suitable benchmark tests. The new solver is then used to simulate detonation problems in non-Cartesian geometries. A simulation is conducted of the three-dimensional detonation propagation in a 90-degree pipe bend. A detonation in a round tube is also simulated in a Galilean frame of reference. Both a rectangular mode and a spinning mode are observed in the simulations. In addition, the fundamental problem of detonation wave/boundary layer interaction is studied. The results show that the new solver can simulate high-speed reactive flows efficiently by the combined use of a curvilinear mapping with mesh adaptation.

Dynamic Behavior of a Spinning Exponentially Functionally Graded Shaft With Unbalanced Load

Abstract The dynamic behaviors of a pinned–pinned spinning exponentially functionally graded shaft with unbalanced loads are investigated. The shaft is simulated in the Rayleigh beam model considering rotary inertia and gyroscopic effects. The governing equation for the flexural vibration of the shaft is derived via the Hamilton principle. Based on the boundary conditions, both the exact and approximate whirl frequency equations of the system are obtained analytically. Also, the validity of the proposed model is confirmed by comparing it with the results reported in the literature. Finally, a numerical study on the basis of the analytical solutions is performed to evaluate the main parameters, including slenderness ratio (α), gradient index (β), mass ratio (μ), and eccentric distance (γ) on the whirl frequency, critical spinning speed, mode shapes, and stability of the system. The results reveal that the vibration and instability of the spinning shaft are strongly dependent on the unbalanced load and material gradient.

Numerical investigation of azimuthal thermoacoustic instability in a gas turbine model combustor

Self-excited spinning mode azimuthal instability in an annular combustor with non-swirling flow is investigated using large eddy simulation (LES). Compressible Navier–Stokes equations are solved with a flamelet combustion model to describe the subgrid chemistry-turbulence interactions. Two flamelet models, with and without heat loss effects, are compared to elucidate the non-adiabatic wall effects on the thermoacoustic instability. The azimuthal modes are captured well by both models with only marginal differences in the computed frequencies and amplitudes. By comparing with the experimental measurements, the frequencies given by the LES are approximately 10% higher and the amplitudes are well predicted. Further analysis of the experimental and LES data shows a similar dominant anti-clockwise spinning mode, under which a good agreement is observed for the phase-averaged heat release rate fluctuations. Dynamic mode decomposition (DMD) is applied to shed more light on this spinning mode. The LES and experimental DMD modes reconstructed for their azimuthal mode frequencies agree very well for the heat release fluctuations. The DMD mode structure for the acoustic pressure from the LES shows a considerable non-zero profile at the combustor outlet, which could be essential for azimuthal modes to establish in this annular combustor. Finally, a low-order modelling study was conducted using an acoustic network combined with the flame transfer function extracted from LES. The results show that the dominant mode is associated with the plenum showing a first longitudinal and azimuthal mixed mode structure. By tuning the plenum length to match the effective volume, the predicted frequency becomes very close to the measured value.

Symmetry Breaking in an Experimental Annular Combustor Model With Deterministic Electroacoustic Feedback and Stochastic Forcing

AbstractIn this study, we use an annular combustor experimental model with electroacoustic feedback to investigate systematically the effect of stochastic forcing and nonuniform flame response distribution on azimuthal thermoacoustic modes. We break the symmetry of a nominally degenerate mode of azimuthal order m by imposing a nonzero 2m Fourier component of the flame gain, b2m, and of the time-delay, ε2m. Various orientations between the gain and the time-delay staging patterns are considered. In addition, stochastic forcing is introduced. First, all experiments are performed without noise, as well as at the maximum noise intensity. We observe that the mode nature that dominates in the presence of intense noise may be far from the one observed in noise-free conditions. To better understand the effect of noise in the presence of asymmetries, we repeat some of the experiments at various noise intensities. Although our results confirm that for the axisymmetric configuration and some asymmetric configurations pure spinning modes are never reached, we also observe some radically different behaviors. For a noise-free experiment leading to a purely standing mode, the introduction of a sufficient amount of noise can lead to beating. We also observe that, for a mode that is nearly standing in the absence of noise, an increase in the noise intensity leads to the predominance of mixed modes with a clearly favored spinning direction. We explain our experimental results with the aid of low-order models.

Numerical analysis of self-excited tangential combustion instability for an MMH/NTO rocket combustor

This study presented the numerical simulation of the tangential combustion instability in a hypergolic liquid bipropellant rocket thrust chamber, which applied fuel liquid film cooling method and unlike impinging injectors. The liquid spray was modeled using Lagrangian approach, while the gas was regarded as Euler phase. Stress-blended eddy simulation and finite rate/eddy–dissipation model were adopted to simulate the turbulent combustion process. Consistent with the experiment results, this work successfully simulated the transformation of tangential combustion instability from standing mode to spinning mode. The mean pressure, amplitude and frequency of limit cycle oscillation were in good agreement with the experiment. There was a detailed analysis about the flow field, Rayleigh index, and driving mechanism of the combustion instability. It was found that the oscillation began with hot spots of heat release rate due to the interaction between the spray of impinging injectors and cooling fuel jet. More than that, cooling fuel jet also contributed to drive the oscillation. In the standing mode, injectors in the inner and outer rings drive the oscillation together, while the spinning mode is mainly driven by injectors in the outer ring. The pressure wave is subsonic and its Mach number is close to 1. It was shown that the pressure wave contained a complex structure divided into three parts. This led to the in-phase of the pressure along the axial direction and the double-peak characteristic of the downstream pressure signal. Besides, a positive feedback closed-loop system associated with periodic oxidizer/fuel ratio was believed to sustain the combustion instability. The oscillation can be maintained when pressure, heat release and oxidizer/fuel ratio are coupled together. The analysis results indicate that rotating detonation is an implication to tangential combustion instability.

Tomographic reconstruction of an azimuthally forced flame in an annular chamber

Azimuthally forced spinning modes on a single ethylene-air swirl flame in an annular combustor were investigated using phase-averaged three-dimensional (3D) Computed Tomography of Chemiluminescence. Strongly spinning azimuthal modes in the clockwise (CW) and anticlockwise (ACW) directions were introduced by means of carefully controlled acoustic forcing. Tomographic reconstructions were calculated based on 25 independent views for an unforced, and CW and ACW forced cases. Using only a single flame in an annular enclosure resulted in a flame shape that differed from previous multi-flame investigations. The flame experiences significantly less flame-wall and no flame-flame interactions. Results at high and low equivalence ratio indicate that in the absence of significant enclosure effects, the global heat release rate (HRR) response is the same for both forcing directions. The 3D HRR oscillation distributions were investigated in detail, and the local flame response to modes with opposite spin direction was shown to feature 180∘ rotational symmetry. High magnitude HRR oscillations are formed close to the flame base, but due to the combined azimuthal and axial excitation the response on one side of the flame is significantly higher in magnitude, and concentrations of HRR oscillations are seen close to the inner or outer annular walls during CW or ACW excitation respectively. Swirl also causes these high magnitude structures to rotate slowly with downstream distance, although the spatial redistribution of HRR oscillations through this effect is subtle. This improves our physical understanding of previous observations of differing global flame responses to CW and ACW azimuthal excitation.

Duct mode identification in a statistical model via the Iterative Bayesian Focusing

The measurements of aero-engine fan noise are crucial to engine-noise reduction and silent-turbofan design. The duct mode identification is adpoted to decompose inner duct noises into spinning modes from acoustic pressure measured by a microphone array. However, modes identification of the aero-engine fan are difficult cause the number of modes is usually much larger than the number of microphones and leading to an ill-posed problem during the inverse process. A mode identification method based on Iterative Bayesian Focusing is used to solve this problem. The in-duct sound field is described by a statistical model, and the inverse problem of mode identification is expressed in a Bayesian framework. The sparsity of the target acoustic modes is applied as a priori condition, and a Mode Aperture Function (MAF) is developed. The aperture width of the MAFis automatically updated and contracted through iterations, after which mode coefficients are contracted to a sparsest solution. The used mode identification method is firstly validated through numerical simulations, and the effects of the number of microphones and SNR on mode identification results are discussed. Then the Iterative Bayesian Focusing-based mode identification method is experimentally verified through a well designed Spinning Mode Synthesizer. Both numerical and experimentalresults indicate that target modes can be accurately identified when the number of microphones are much less than the number of all propagating modes.

Symmetry-breaking in thermoacoustics: Theory and experimental validation on an annular system with electroacoustic feedback

In this study, we investigate experimentally the linear and nonlinear thermoacoustic response of an annular combustor model with electroacoustic feedback to study the effects that various types of asymmetric modifications have on the system’s eigenvalue degeneracy, and on its self-sustained oscillations. The baseline configuration has a nominal rotational symmetry of degree N=12 and a mirror symmetry. First, we break the symmetry by modifying the downstream boundary condition, using lids with multiple holes. Some lids reduce the degree of rotational symmetry of the entire system, and may retain or break the mirror symmetry, depending on their orientation; other lids completely break the rotational symmetry but preserve the mirror symmetry. Second, for an axisymmetric downstream boundary condition, we break only the mirror symmetry by modelling for the first time flames for which the centre of heat release is not aligned with the burner axis. This leads the clockwise and counterclockwise spinning modes to have distinct frequencies and growth rates. The effect of all above-mentioned types of asymmetries is investigated over a broad range of flame gain values, which allows assessing how the sensitivity to asymmetries depends on the flame gain. The experimental results are then interpreted with the aid of low-order models and a 3D Helmholtz solver. This experimental study complements recent theoretical and numerical analyses on the effect of asymmetries on the nature of the thermoacoustic spectrum in annular combustors.

Synergistic Integration and Pharmacomechanical Function of Enzyme-Magnetite Nanoparticle Swarms for Low-Dose Fast Thrombolysis.

Magnetic micro-/nanoparticles are extensively explored over the past decade as active diagnostic/therapeutic agents for minimally invasive medicine. However, sufficient function integration on these miniaturized bodies toward practical applications remains challenging. This work proposes a synergistic strategy via integrating particle functionalization and bioinspired swarming, demonstrated by recombinant tissue plasminogen activator modified magnetite nanoparticles (rtPA-Fe3 O4 NPs) for fast thrombolysis in vivo with low drug dosage. The synthesized rtPA-Fe3 O4 NPs exhibit superior magnetic performance, high biocompatibility, and thrombolytic enzyme activity. Benefiting from a customized magnetic operation system designed for animal experiments and preclinical development, these agglomeration-free NPs can assemble into micro-/milli-scale swarms capable of robust maneuver and reconfigurable transformation for on-demand tasks in complex biofluids. Specifically, the spinning mode of the swarm exerts focused fluid shear stresses while rubbing on the thrombus surface, constituting a mechanical force for clot breakdown. The synergy of the NPs' inherent enzymatic effect and swarming-triggered fluid forces enables amplified efficacy of thrombolysis in an in vivo occlusion model of rabbit carotid artery, using lower drug concentration than clinical dosage. Furthermore, swarming-enhanced ultrasound signals aid in imaging-guided treatment. Therefore, the pharmacomechanical NP swarms herein represent an injectable thrombolytic tool joining advantages of intravenous drug therapy and robotic intervention.

Analysis of Tangential Combustion Instability Modes in a LOX/Kerosene Liquid Rocket Engine Based on OpenFOAM

Self-excited high frequency combustion instability (HFCI) of first-order tangential (1T) mode was observed in a staged-combustion LOX/Kerosene liquid rocket engine numerically. Two different kinds of 1T patterns, standing wave mode and traveling wave mode, were captured in the present work. In the nominal operation condition, the ratio of oxygen-to-fuel (O/F) was 2.5. Propellant was evenly distributed in all injectors and no HFCI occurred. The chamber pressure obtained from the numerical simulation and experiment showed a good agreement, which validated the numerical model. When the mass flow of fuel for two injectors was modified, severe HFCI occurred. The pressure wave node was located at a fixed diameter, showing a 1T standing wave mode. As the O/F was set 4.4 and the propellant distribution was completely uniform, the numerical result yielded a 1T wave node featured a spinning behavior, which was a traveling 1T wave mode. Once the HFCI arose, no matter what standing mode or spinning mode, the pressure and heat release oscillated totally in phase temporally and coupled spatially. The heat release from combustion was fed into the resonant acoustic mode. This was the thermoacoustic coupling process that maintained the HFCI.

Controlling the rotation modes of hematite nanospindles using dynamic magnetic fields.

The magnetic field-induced actuation of colloidal nanoparticles has enabled tremendous recent progress towards microrobots, suitable for a variety of applications including targeted drug delivery, environmental remediation, or minimally invasive surgery. Further size reduction to the nanoscale requires enhanced control of orientation and locomotion to overcome dominating viscous properties. Here, control of the coherent precession of hematite spindles via a dynamic magnetic field is demonstrated using nanoscale particles. Time-resolved small-angle scattering and optical transmission measurements reveal a clear frequency-dependent variation of orientation and rotation of an entire ensemble of non-interacting hematite nanospindles. The different motion mechanisms by nanoscale spindles in bulk dispersion resemble modes that have been observed for much larger, micron-sized elongated particles near surfaces. The dynamic rotation modes promise hematite nanospindles as a suitable model system for field-induced locomotion in nanoscale magnetic robots.