Large-scale spanwise motions in shock wave–turbulent boundary-layer interactions over a $ 25^{\circ }$ compression ramp at Mach 2.95 are investigated using large-eddy simulations. Spectral proper orthogonal decomposition (SPOD) identifies coherent structures characterised by low-frequency features and a large-scale spanwise wavelength of $ O(15\delta _{0})$, where $ \delta _{0}$ is the incoming boundary-layer thickness. The dominant frequency is at least one order of magnitude lower than that of the shock motions. These large-scale spanwise structures are excited near the shock foot and are sustained along the separation shock. Global stability analysis (GSA) is then employed to investigate the potential mechanisms driving these structures. The GSA identifies a stationary three-dimensional (3-D) mode at a wavelength of $ 15\delta _{0}$ with a similar perturbation field, particularly near the separation shock. Good agreement is achieved between the leading SPOD mode and the 3-D GSA mode both qualitatively and quantitatively, which indicates that global instability is primarily responsible for the large-scale spanwise structures surrounding the shock. The reconstructed turbulent separation bubble (TSB) using the 3-D global mode manifests as spanwise undulations, which directly induce the spanwise rippling of the separation shock. Furthermore, the coupled TSB motions in the streamwise and spanwise directions are examined. The TSB oscillates in the streamwise direction while simultaneously exhibiting spanwise undulations. The filtered wall-pressure signals indicate the dominant role of the streamwise motions.

Fingering instabilities readily occur if a less viscous fluid displaces a more viscous fluid in a narrow gap due to the action of destabilising viscous forces. If the fluids are miscible, the instability can be suppressed in the limit of large advection as complicated flow structures are formed across the gap. Using a fluid to displace a monolayer of non-colloidal particles suspended in the same fluid, Luo et al. (2025 J. Fluid Mech. vol. 1011, A48) suppress the formation of the cross-gap structures and identify a new fingering mechanism which instead relies on long-range dipolar disturbance flows generated by the particle confinement.

In the rapidly rotating limit, we derive a balanced set of reduced equations governing the strongly nonlinear development of the convective wall-mode instability in the interior of a general container. The model illustrates that wall-mode convection is a multiscale phenomenon where the dynamics of the bulk interior diagnostically determine the small-scale dynamics within Stewartson boundary layers at the sidewalls. The sidewall boundary layers feedback on the interior via a nonlinear lateral heat-flux boundary condition, providing a closed system. Outside the asymptotically thin boundary layer, the convective modes connect to a dynamical interior that maintains scales set by the domain geometry. In many ways, the final system of equations resembles boundary-forced planetary geostrophic baroclinic dynamics coupled with barotropic quasi-geostrophic vorticity. The reduced system contains the results from previous linear instability theory but captured in an elementary fashion, providing a new avenue for investigating wall-mode convection in the strongly nonlinear regime. We also derive the dominant Ekman-flux correction to the onset Rayleigh number for large Taylor number, ${\textit {Ra}} \approx 31.8 \,{\textit{Ta}}^{1/2} - 4.43 \,{\textit{Ta}}^{5/12} + {\mathcal{O}}({\textit{Ta}}^{1/3})$ for no-slip boundaries. However, we find that the linear onset in a finite cylinder differs noticeably compared with a Cartesian channel. We demonstrate some of the reduced model’s nonlinear dynamics with numerical simulations in a cylindrical container.

This paper considers the propagation, arrest and recession of a planar hydraulic fracture in a porous elastic medium whose footprint is constrained to a growing or shrinking rectangular region with a constant height. Hydraulic fractures with large aspect ratio rectangular footprints are frequently referred to as PKN fractures in recognition of the original researchers (Perkins & Kern 1961 J. Petrol. Tech. 13, 937–949) and (Nordgren 1972 J. Petrol Technol. 1972, 306–314) who first analyzed models of such fracture geometries. We investigate the one-dimensional non-local PKN approximation to a fully planar rectangular hydraulic fracture model in a three-dimensional elastic medium. By analysing the tip behaviour of the non-local PKN model, a transformation procedure is established to render the asymptotic equations for the dynamics of the steady semi-infinite PKN and plane strain models formally identical, which implies that all the existing multiscale plane strain asymptotes can be converted directly to the PKN case by making use of this transformation. Using this transformation, it is shown that the appropriate PKN asymptotes for the average aperture $\bar {w}$ with distance $\hat {x}$ to the fracture front are $\bar {w}\sim \hat {x}^{1/2},\ \hat {x}^{5/8}\ {\textrm{and}}\, \ \hat {x}^{2/3}$ in the toughness, leak-off and viscous modes of propagation, respectively; as well as the linear elastic fracture mechanics tip asymptote $\bar {w}\sim \hat {x}^{1/2}$ for arrest, which transitions to the linear asymptote tip $\bar {w}\sim \hat {x}$ for a fracture driven to recede due to fluid leak-off. Both the arrest and recession tip asymptotes share the intermediate leak-off asymptote $\bar {w}\sim \hat {x}^{3/4}$. A scaling analysis yields the arrest time, length and aperture as functions of a dimensionless injection-cessation time $\omega$. An asymptotic analysis of the non-local PKN model is used to establish the fundamental decoupling between dynamics and kinematics, which leads to the emergence of a similarity solution – termed the sunset solution – close to the time of collapse of the fracture. The multiscale PKN numerical solutions agree well with those for a fully planar multiscale rectangular hydraulic fracture model in a three-dimensional elastic medium. The scaling laws and the emergence of the sunset solution are confirmed by the PKN numerical model. The sunset solution also emerges in the fully planar numerical model and persists beyond the collapse time of the PKN model, by which time its footprints have separated from the upper and lower constraining sedimentary layer boundaries and have assumed self-similar elliptic shapes that shrink as they approach collapse.

Natural fliers and marine swimmers twist and turn their lifting or control surfaces to manipulate the unsteady forces experienced in air and water. The passive deformation of such surfaces has been investigated by several researchers, but the aspect of controlled deformation has received comparatively less attention. In this paper, we experimentally measure the forces and the flow fields of a flat-plate wing (aspect ratio (AR) = 3), translating at a constant Reynolds number (Re) of 10 000, with a dynamically twisting span. We show that the unsteady forces can be dependably estimated by a three-dimensional discrete vortex model. In this model, we account for the leading-edge separation with the help of the leading-edge-suction parameter. Experiments are conducted for two angles of attack (AoAs), $5^\circ$ and $15^\circ$. In addition, two rates of twisting are implemented where part of the leading edge, closer to the tip region, is twisted away from the incoming flow, increasing the effective AoA. The results show that twisting away from the flow augments the lift forces in all cases, although the rate of increase of lift is higher for the highest twist rate. The act of twisting causes an increase in effective AoA beyond the static stall angle in the AoA $=15^\circ$ case. This is highlighted by a distinct dip in the force data following the initial rise after twisting is activated. The increase in effective AoA from the reference case (without twisting) causes separation of the flow below the mid-span. This, in turn, creates higher levels of vorticity in those regions and results in a leading-edge vortex with increased cross-section and strength when compared with the reference case without twisting. Finally, we apply force partitioning and reveal that dynamic twisting leads to a localised increase in vorticity-induced forces along the twisted part of the span, which is approximately twice that of the untwisted case.

Turbulent flows are strongly chaotic and unpredictable, with a Lyapunov exponent that increases with the Reynolds number. Here, we study the chaoticity of the surface quasi-geostrophic system, a two-dimensional model for geophysical flows that displays a direct cascade similar to that of three-dimensional turbulence. Using high-resolution direct numerical simulations, we investigate the dependence of the Lyapunov exponent on the Reynolds number and find an anomalous scaling exponent larger than that predicted by dimensional arguments. We also study the finite-time fluctuation of the Lyapunov exponent by computing the Cramér function associated with its probability distribution. We find that the Cramér function attains a self-similar form at large $\textit{Re}$.

In conventional hypersonic wind tunnels, tunnel noise is dominated by acoustic radiation from turbulent nozzle-wall boundary layers, which can directly influence the boundary-layer transition (BLT) over the model in the test section. To offer new insights into BLT in conventional ground facilities, direct numerical simulations (DNS) were performed to simulate the receptivity and transition processes of a Mach 8 boundary layer over a nearly sharp $7^\circ$ half-angle cone, with transition triggered by tunnel-like broadband free-stream acoustic disturbances radiated from the nozzle wall of the Sandia hypersonic wind tunnel at Mach 8 (Sandia HWT-8). The DNS captured all the stages of the transition to turbulence caused by tunnel noise, including the passage of broadband free-stream noise through the shock wave, the receptivity process leading to the generation of Mack’s second-mode waves, their nonlinear growth to saturation, the laminar breakdown to turbulence and the post-transitional, fully turbulent flow. The transition location predicted by DNS compared well with that of Pate’s theory and was also consistent with the locations of peak pressure fluctuations as measured in the Sandia HWT-8 facility. The computed skin friction and Stanton number distributions in the initial breakdown region showed an overshoot compared with the turbulent predictions by the van Driest II theory. The wall-pressure spectra in both the transitional and turbulent regions of the cone compared well with those measured in the Sandia HWT-8. The second-mode breakdown amplitude $A_{max}$ predicted by the DNS was also consistent with sharp-cone measurements from multiple conventional wind tunnels.

A wall-modelled large eddy simulation approach is proposed in a discontinuous Galerkin (DG) setting, building on the slip-wall concept of Bae et al. (J. Fluid Mech., vol. 859, 2019, pp. 400–432) and the universal scaling relationship by Pradhan and Duraisamy (J. Fluid Mech., vol. 955, 2023, A6). The effect of the order of the DG approximation is introduced via the length scales in the formulation. The level of under-resolution is represented by a slip Reynolds number and the model attempts to incorporate the effects of the numerical discretization and the subgrid-scale model. The dynamic part of the new model is based on a modified form of the Germano identity -- performed on the universal scaling parameter -- and is coupled with the dynamic Smagorinsky model. A sharp modal cutoff filter is used as the test filter for the dynamic procedure, and the dynamic model can be easily integrated into any DG solver. Numerical experiments on channel flows show that grid independence of the statistics is achievable and predictions for the mean velocity and Reynolds stress profiles agree well with the direct numerical simulation, even with significant under-resolution. When applied to flows with separation and reattachment, the model also consistently predicts one-point statistics in the reverse flow and post-reattachment regions in good agreement with experiments. The performance of the model in accurately predicting equilibrium and separated flows using significantly under-resolved meshes can be attributed to several aspects that work synergistically: the optimal finite-element projection framework, the interplay of the scale separation and numerical discretization within the DG framework, and the consistent dynamic procedures for subgrid and wall modelling.

The influence of compressibility on shear flow turbulence is investigated within a self-preservation framework. This study focuses on the axisymmetric jet to examine compressibility effects in a slowly spatially evolving flow, unlike mixing layers, where the convective Mach number remains constant. Revisiting self-preservation, an a priori description of the compressible scaling for Reynolds stresses and higher-order velocity moments is developed. Turbulence moments are found to scale with powers of the spreading rate, suggesting Reynolds stress anisotropy results from compressibility effects consistent with self-preservation of the governing equations. Particle image velocimetry measurements for Mach 0.3 and perfectly expanded Mach 1.25 jets confirm the scaling predictions. The attenuation function, $\varPhi (M_c)$, describing the relationship between the convective Mach number, $M_c$, and the spreading rate, follows a similar trend in jets and mixing layers, where a higher $M_c$ results in reduced spreading rates. In the jet where $M_c$ decays, the relationship between the local $M_c$ and turbulence attenuation remains captured through $\varPhi (M_c)$, which scales proportionally with the spreading rate. A new scale is introduced, where the pressure in the mean momentum equation is substituted. The difference between the streamwise and radial-Reynolds-normal stresses was found to be a scale which is independent of Mach number and spreading rate. Further analysis of the Reynolds-stress-transport budget shows that internal redistribution of energy occurs within the Reynolds-normal stresses, and the role of pressure modification in turbulence attenuation supports previous observations. These findings confirm that the compressible axisymmetric jet exhibits self-preservation, with scaling extending into supersonic regimes.

Standing acoustic waves in a channel generate time-mean Eulerian flows. In homogeneous fluids, these streaming flows have been shown by Rayleigh to result from viscous attenuation of the waves in oscillatory boundary (i.e. Stokes) layers. However, the strength and structure of the mean flow significantly depart from the predictions of Rayleigh when inhomogeneities in fluid compressibility or density are present. This change in mean flow behaviour is of particular interest in thermal management, as streaming flows can be used to enhance cooling. In this work, we consider standing acoustic wave oscillations of an ideal gas in a differentially heated channel with hot- and cold-wall temperatures respectively set to $T_* + \Delta \varTheta _*$ and $T_*$. An asymptotic analysis for a normalised temperature differential $\Delta \varTheta _*/T_*$ comparable to the small acoustic Mach number is performed to capture the transition between the two documented regimes of Rayleigh streaming ($\Delta \varTheta _*\,{=}\,0$) and baroclinic streaming ($\Delta \varTheta _* =O(T_*)$). Our analytical solution accounts for existing experimental and numerical results and elucidates the separate contributions of viscous torques in Stokes layers and baroclinic forcing in the interior to driving the streaming flow. The analysis yields a scaling estimate for the temperature difference $\Delta \varTheta _{c_*}$ at which baroclinic driving is comparable to viscous forcing, signalling the smooth transition from Rayleigh to baroclinic acoustic streaming.

In the present study, we investigate the relation between temperature ($T^{\prime}$) and streamwise velocity ($u^{\prime}$) fluctuations by assessing the state-of-the-art Reynolds analogy models. These analyses are conducted on three levels: in the statistical sense, in spectral space and via the distribution characteristics of temperature fluctuations. It is observed that the model proposed by Huang et al. (HSRA) (1995 J. Fluid Mech. 305, 185–218), is the only model that works well for both channel flows and turbulent boundary layers in the statistical sense. In spectral space, the intensities of $T^{\prime}$ at small scales are discovered to be larger than the predictions of these models, whereas those at scales corresponding to the energy-containing eddies and the large-scale motions are approximately equal to and smaller than the predictions of the HSRA, respectively. The success of the HSRA arises from this combined effect. In compressible turbulent boundary layers, the relationship between the intensities of positive temperature and negative velocity fluctuations is found to be well described by a model proposed by Gaviglio (1987 Intl J. Heat Mass Transfer, 30, 911–926), whereas that between negative temperature and positive velocity fluctuations is accurately depicted by the HSRA. The streamwise length scale, rather than the spanwise length scale, is found to be more suitable for characterising the scale characteristics of the $u^{\prime}-T^{\prime}$ relation in spectral space. Combining these observations and a newly proposed modified generalised Reynolds analogy (Cheng & Fu 2024 J. Fluid Mech. 999, A20), models regarding the relations in spectral space for both compressible channel flows and turbulent boundary layers are developed, and a strategy for generating more reliable temperature fluctuations as the inlet boundary condition for simulations of compressible boundary layers is also suggested.

Turbulence–chemistry interaction in a Mach-7 hypersonic boundary layer with significant production of radical species is characterised using direct numerical simulation. Overriding a non-catalytic surface maintained as isothermal at 3000 K, the boundary layer is subject to finite-rate chemical effects, comprising both dissociation/recombination processes as well as the production of nitric oxide as mediated by the Zel’dovich mechanism. With kinetic-energy dissipation giving rise to temperatures exceeding 5300 K, molecular oxygen is almost entirely depleted within the aerodynamic heating layer, producing significant densities of atomic oxygen and nitric oxide. Owing to the coupling between turbulence-induced thermodynamic fluctuations and the chemical-kinetic processes, the Reynolds-averaged production rates ultimately depart significantly from their mean-field approximations. To better characterise this turbulence–chemistry interaction, which arises primarily from the exchange reactions in the Zel’dovich mechanism, a decomposition for the mean distortion of finite-rate chemical processes with respect to thermodynamic fluctuations is presented. Both thermal and partial-density fluctuations, as well as the impact of their statistical co-moments, are shown to contribute significantly to the net chemical production rate of each species. Dissociation/recombination processes are confirmed to be primarily affected by temperature fluctuations alone, which yield an augmentation of the molecular dissociation rates and reduction of the recombination layer’s off-wall extent. While the effect of pressure perturbations proves largely negligible for the mean chemical production rates, fluctuations in the species mass fractions are shown to be the primary source of turbulence–chemistry interaction for the second Zel’dovich reaction, significantly modulating the production of all major species apart from molecular nitrogen.

We analyse the pressure-driven radial flow of a shear-thinning fluid between two parallel plates. Complex fluid rheology may significantly affect the hydrodynamic features of such non-Newtonian flows, which remain not fully understood, compared with Newtonian flows. We describe the shear-thinning rheology using the Ellis model and present a theoretical framework for calculating the pressure distribution and the flow rate–pressure drop relation. We first derive a closed-form expression for the pressure gradient, which allows us to obtain semi-analytical expressions for the pressure, velocity and flow rate–pressure drop relation. Specifically, we provide the corresponding asymptotic solutions for small and large values of the dimensionless flow rates. We further elucidate the entrance length required for the radial velocity of a shear-thinning fluid to reach its fully developed form, showing that this length approximates the Newtonian low-Reynolds-number value at low shear rates, but may strongly depend on the fluid’s shear-thinning rheology and exceed the Newtonian value at high shear rates. We validate our theoretical results with finite-element numerical simulations and find excellent agreement. Furthermore, we compare our semi-analytical, asymptotic and finite-element simulation results for the pressure distribution with the experimental measurements of Laurencena & Williams (Trans. Soc. Rheol. vol. 18, 1974, pp. 331–355), showing good agreement. Our theoretical results using the Ellis model capture the interplay between the shear-thinning and the zero-shear-rate effects on the pressure drop, which cannot be explained using a simple power-law model, highlighting the importance of using an adequate constitutive model to accurately describe non-Newtonian flows of shear-thinning fluids.

Cilia exist ubiquitously in nature, and they are very effective in generating flow in a low Reynolds number environment. Inspired by nature, various artificial cilia have been invented for microfluidic applications, and a nature-mimicking tilted conical motion was often used for flow generation due to its simplicity and effectiveness. However, the current theoretical model for predicting the net flow rate generated by the tilted conical motion fails when the cilia are in close confinement, i.e. when the tips of the cilia are close to the ceiling of their channel or chamber, which is, in reality, the most practical way to enhance flow rate generation. Moreover, numerical simulations are very expensive for optimisation of such designs. In this study, we derive a new theoretical model, taking into account the tilting and opening angles of the cone, the height of the chamber and the length of the cilia. The results differ significantly from when the ceiling is not considered, and counter-intuitively in some cases the flow can even reverse. These unexpected results have important implications for artificial cilium design and applications. We validate the model with both numerical simulations and experiments using magnetic artificial cilia, and show that the flow optimisation based on tilted conical cilium motion can now be performed accurately in a realistic and practical manner. This study not only offers a simple tool for optimising designs of artificial cilium-based systems for microfluidic applications, but it also provides fresh insights for understanding natural cilium-driven flows.

Numerical studies on the statistical properties of irregular waves in finite depth have to date been based on models founded on weak nonlinearity; as a consequence, only lower-order (usually third-order) nonlinear interactions have thus far been investigated. The present study performs numerical simulations with a fully nonlinear, spectrally accurate model to investigate the statistics of irregular, unidirectional wave fields in finite water depth initially given by a Texel, Marsen and Arsloe spectrum. A series of random unidirectional wave fields are considered, covering a wide range of water depth. The wave spectrum and statistical properties, including the probability density function of the surface elevation, exceedance probability of wave crests and occurrence probability of extreme (rogue) waves, are investigated. The importance of full nonlinearity in comparison with third-order results is likewise evaluated. The results show that full nonlinearity increases kurtosis and enhances the occurrence probability of large wave crests and rogue waves substantially, in both deep water and finite water depth. Therefore, we propose that full nonlinearity may contribute significantly to the formation of rogue waves. Furthermore, to account for the effects of higher-order nonlinearity on modulational instability, we analyse the relationship between the Benjamin–Feir index (BFI) and maximal excess kurtosis. Our results show a strong linear relationship i.e. $({\mathcal{K}}_{max}-3)\propto {\textrm{BFI}}$, in contrast to $({\mathcal{K}}_{max}-3)\propto {\textrm{BFI}}^2$ based on the assumptions of weak nonlinearity, a narrow-banded spectrum and deep-water conditions. Above, $\mathcal{K}_{max}$ is the maximal kurtosis.

The dynamics of self-excited shock train oscillations in a back pressured axisymmetric duct was investigated to deepen the understanding of the isolator/combustor coupling in high-speed propulsion systems. The test article consisted of an internal compression inlet followed by a constant area isolator, both having a circular cross-section. A systematic back pressure variation was implemented by using a combination of aerodynamic and physical blockages at the isolator exit. High bandwidth two-dimensional pressure field imaging was performed at $8\,{\rm kHz}$ repetition rate within the isolator for different back pressure settings. The acquisition rate was considerably higher than the dominant frequency of the shock train oscillations across the different back pressure settings. The power spectral density of the pressure fluctuations beneath the leading shock foot exhibited broadband low frequency oscillations across all back pressures that resembled the motions of canonical shock–boundary layer interaction units. A node in the vicinity of reattachment location that originated the pressure perturbations within the separation shock was also identified, which further ascertained that the leading shock low frequency motions were driven by the separation bubble pulsations. Above a threshold back pressure, additional peaks appeared at distinct higher frequencies that resembled the acoustic modes within the duct. However, none of the earlier expressions of the resonance acoustic frequency within a straight duct agreed with the experimentally observed value. Cross-spectral analyses suggested that these modes were caused by the shock interactions with upstream propagating acoustic waves that emanate from the reattachment location, originally proposed for transonic diffusers by Robinet & Casalis (2001) Phys. Fluids 13, 1047–1059. Feedback interactions described using one-dimensional stability analysis of the shock perturbations by obliquely travelling acoustic waves (Robinet & Casalis 2001 Phys. Fluids 13, 1047–1059) made favourable comparisons on the back pressure threshold that emanated the acoustic modes as well as the acoustic mode frequencies.

Particle suspensions in confined geometries can become clogged, which can have a catastrophic effect on function in biological and industrial systems. Here, we investigate the macroscopic dynamics of dense suspensions in constricted geometries. We develop a minimal continuum two-phase model that allows for variation in particle volume fraction. The model comprises a ‘wet solid’ phase with material properties dependent on the particle volume fraction, and a seepage Darcy flow of fluid through the particles. We find that spatially varying geometry (or material properties) can induce emergent heterogeneity in the particle fraction and trigger the abrupt transition to a high-particle-fraction ‘clogged’ state.

Waves transport particles in the direction of wave propagation with the Stokes drift. When the Earth’s rotation is accounted for, waves induce an additional (Eulerian-mean) current that reduces drift and is known as the anti-Stokes drift. This effect is often ignored in oceanic particle-tracking simulations, despite being important. Although different theoretical models exist, they have not been validated by experiments. We conduct laboratory experiments studying the surface drift induced by deep-water waves in a purpose-built rotating wave flume. With rotation, the Lagrangian-mean drift deflects to the right (counterclockwise rotation) and reduces in magnitude. Compared with two existing steady theoretical models, measured drift speed follows a similar trend with wave Ekman number but is larger. The difference is largely explained by unsteadiness on inertial time scales. Our results emphasise the importance of considering unsteadiness when predicting and analysing the transport of floating material by waves.

Drops in a shear flow experience shear-induced diffusion due to drop–drop interactions. Here, the effects of medium viscoelasticity on shear-induced collective diffusivity are numerically investigated. A layer of viscous drops suspended in a viscoelastic fluid was simulated, fully resolving each deforming drop using a front-tracking method. The collective diffusivity is computed from the spreading of the drop layer with time, specifically a one-third scaling, as well as using an exponentially decaying dynamic structure factor of the system of drops. Both methods led to matching results. The surrounding viscoelasticity was shown to linearly reduce the diffusion-led spreading of the drop layer, the effect being stronger for less deformable drops (low capillary number). Because of the competition between the increasing effect with capillary number (Ca) and the decreasing effect with Weissenberg number (Wi), collective diffusivity vanishes at very low Ca and high enough Wi. The physics behind the hindering effects of viscoelasticity on shear-induced diffusion is explained with the help of drop–drop interactions in a viscoelastic fluid, where shear-induced interaction leads to trapping of drops into tumbling trajectories at lower Ca and higher Wi due to viscoelastic stresses. Using the simulated values, phenomenological correlations relating the shear-induced gradient diffusivity with Wi and Ca were found.

Elastoviscoplastic (EVP) fluid flows are driven by a non-trivial interplay between the elastic, viscous and plastic properties, which under certain conditions can transition the otherwise laminar flow into complex flow instabilities with rich space–time-dependent dynamics. We discover that under elastic turbulence regimes, EVP fluids undergo dynamic jamming triggered by localised polymer stress deformations that facilitate the formation of solid regions trapped in local low-stress energy wells. The solid volume fraction $\phi$, below the jamming transition $\phi\lt\phi_J$, scales with $\sqrt {\textit{Bi}}$, where $\textit{Bi}$ is the Bingham number characterising the ratio of yield to viscous stresses, in direct agreement with theoretical approximations based on the laminar solution. The onset of this new dynamic jamming transition $\phi \geqslant \phi _J$ is marked by a clear deviation from the scaling $\phi \sim \sqrt {\textit{Bi}}$, scaling as $\phi \sim \exp {\textit{Bi}}$. We show that this instability-induced jamming transition – analogous to that in dense suspensions – leads to slow, minimally diffusive and rigid-like flows with finite deformability, highlighting a novel phase change in elastic turbulence regimes of complex fluids.