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A new method for fluid–structure interaction (FSI) diagnostics to simultaneously capture time-resolved three-dimensional, three-component (3D3C) velocity fields and structural deformations using a single light field camera is presented. A light field camera encodes both spatial and angular information of light rays collected by a conventional imaging lens that allows for the 3D reconstruction of a scene from a single image. Building upon this capability, a light field fluid–structure interaction (LF FSI) methodology is developed with a focus on experimental scenarios with low optical access. Proper orthogonal decomposition (POD) is used to separate particle and surface information contained in the same image. A correlation-based depth estimation technique is introduced to reconstruct instantaneous surface positions from the disparity between angular perspectives and conventional particle image velocimetry (PIV) is used for flow field reconstruction. Validation of the methodology is achieved using synthetic images of simultaneously moving flat plates and a vortex ring with a small increase in uncertainty under ~0.5 microlenses observed in both flow and structure measurement compared to independent measurements. The method is experimentally verified using a flat plate translating along the camera’s optical axis in a flow field with varying particle concentrations. Finally, simultaneous reconstructions of the flow field and surface shape around a flexible membrane are presented, with the surface reconstruction further validated using simultaneously captured stereo images. The findings indicate that the LF FSI methodology provides a new capability to simultaneously measure large-scale flow characteristics and structural deformations using a single camera. 

Plume-surface interactions (PSI) occur during the take-off and landing of interplanetary vehicles, leading to particle ejection and the formation of craters. This can be detrimental to the vehicle and any structures or infrastructure near the landing site. A major challenge in developing a comprehensive understanding of this three-dimensional phenomenon is the need to characterize the ejecta and cratering dynamics simultaneously. Here, experiments are conducted in a vacuum chamber at different nozzle heights and ambient pressure conditions using high-speed stereo-photogrammetry and planar particle tracking velocimetry to quantify the cratering and ejecta dynamics. Predictably, it was observed that the trajectory of ejecta with a large Stokes number was mostly unaffected by the nozzle flow after leaving the crater. Under rarefied conditions, the ejecta kinematics (velocity, ejection angle, range, and height) were significantly different compared to continuum conditions. Finally, the findings demonstrate a dependency between ejecta kinematics and crater topology for the current test cases, providing critical insights into particle ejection’s initial characteristics. 

This paper investigates the effect of smoothing operation in 3D reconstruction using a plenoptic camera. A plenoptic camera - also known as light field camera - features a commercial off the shelf camera with added microlens array (MLA) behind the imaging lens, directly in front of the sensor. The main lens focuses the light to the MLA plane, where each microlens then re-directs the light to small regions of pixels behind, each pixel corresponding to different angle of incident (T. Fahringer (2015)) (Adelson and Wang (1992)). Thus, MLA encodes angular information of incident light rays into the recorded image that assist to acquire 4D information (u,v,s,t) of light-field including both position and angular information of light rays captured by the camera (Ng et al. (2005)) (Adelson and Wang (1992)).