Photo of Samuel Grauer

232–233 Research East
Penn State
470-439-7599
sgrauer@psu.edu

Samuel Grauer’s Home Page

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Biography

I am an Assistant Professor in the Department of Mechanical Engineering at Penn State. My research group studies inverse problems in optical diagnostics and dynamical systems, with a focus on state and parameter estimation, non-destructive testing and evaluation, and uncertainty quantification for large-scale nonlinear systems.

We are interested in complex thermo-fluid systems that are difficult to measure and difficult to model, including turbulent boundary layers, particle-laden turbulence, compressible flows with shock waves, detonations, fluid–structure interactions, and multi-phase blast phenomena. Our group develops optical sensors to interrogate these systems and data assimilation (DA) methods to integrate experimental measurements with numerical simulations. We also study the theoretical limits of DA, with the goal of understanding when reconstruction problems transition from an ill-posed problem with many viable solutions to a well-posed one having a unique and stable solution. Such analyses reveal how the information content of different measurements depends on the measurement physics and the complexity of the target system’s dynamics. This knowledge then guides the design of sensors and DA algorithms to measure and reconstruct high-dimensional systems from experimental data.

Our work employs diagnostics such as PIV/PTV, BOS, and LAS, among others. And we use differentiable programming, scientific machine learning, Bayesian inference, and dynamical systems theory to reconstruct and analyze the systems mentioned above from limited data.

I earned a PhD from the University of Waterloo in 2018 and a BSc from the University of Manitoba in 2014. From 2018 to 2020, I was a postdoctoral fellow in the Ben T. Zinn Combustion Laboratory at Georgia Tech.

Curriculum Vitae – You can find a copy of my CV here.

Students

Underlined degrees were earned in my group.

Current Postdoctoral Associates

Current PhD Students

†Co-supervised with Prof Matthew Bross.
*Co-supervised with Prof Stefan Will and Dr Florian Bauer (FAU Erlangen-Nürnberg).

Current BS Students

Alumni

PhD Graduates

MS Graduates

BS Graduates

Prospective Students

If you are an aspiring graduate student with exceptional skills in programming, applied physics, or statistics, a passion for experimenting with laser beams and high-speed cameras, and an insatiable curiosity for tackling challenges at the intersection of physics, measurement, and uncertainty... I'd love to hear from you! Please send me an email to discuss opportunities in my research group.

Publications

Underlined authors were supervised by me and ‡ indicates that authors made an equal contribution.

Preprints (new work!)

  1. AK Singh, M Gomez, KY Cho, AW Skiba, and SJ Grauer, “Ultra-high-speed chemiluminescence tomography of spinning-mode detonation waves,” arXiv preprint, arXiv:2607.07971, 2026. doi:10.48550/arXiv.2607.07971

Book Chapters

  1. SJ Grauer, TA Sipkens, PJ Hadwin, and KJ Daun, “Statistical inversion, uncertainty quantification, and the optimal design of optical experiments,” in Optical Diagnostics for Reacting and Non-Reacting Flows: Theory and Practice, A Steinberg and S Roy, eds, 1st ed (AIAA, 2023), 1137–1202. doi:10.2514/5.9781624106330.1137.1202
  2. BR Halls, TR Meyer, SJ Grauer, and L Ma, “Tutorial: Tomographic imaging in combustion-related flows,” in Optical Diagnostics for Reacting and Non-Reacting Flows: Theory and Practice, A Steinberg and S Roy, eds, 1st ed (AIAA, 2023), 1089–1136. doi:10.2514/5.9781624106330.1089.1136
  3. H McCann, P Wright, K Daun, SJ Grauer, C Liu, and S Wagner, “Chemical species tomography,” in Industrial Tomography: Systems and Applications, M Wang, ed, 2nd ed (Woodhead Publishing, 2022), 155–206. doi:10.1016/B978-0-12-823015-2.00004-2

Journal Papers

  1. K Zhou and SJ Grauer, “On the joint estimation of flow fields and particle properties from Lagrangian data,” J Fluid Mech (Accepted), 2026. doi:10.48550/arXiv.2510.00479
  2. R Tang, K Zhou, J Tan, and SJ Grauer, “Neural inference of fluid–structure interactions from sparse off-body measurements,” Phys Rev Fluids 11, 074901, 2026. doi:10.1103/k48m-pmjz
  3. NB Frank, JL Pughe-Sanford, and SJ Grauer, “Degree-of-freedom and optimization-dynamic effects on the observability of Kuramoto–Sivashinsky systems,” J Comput Phys 563, 115114, 2026. doi:10.1016/j.jcp.2026.115114
  4. JP Molnar, AK Singh, CJ Clifford, JD Thayer, SJ Peltier, GC Jones, and SJ Grauer, “Open-source BOS tomography dataset of high-speed flow over a flight body,” Exp Fluids 67(4), 44, 2026. doi:10.1007/s00348-026-04189-z
  5. M Bundy, E Warner, JP Molnar, SJ Grauer, and KT Lowe, “Physics-informed filtered Rayleigh scattering applied to compressible jets,” Meas Sci Technol 37(13), 135201, 2026. doi:10.1088/1361-6501/ae540c
  6. BE Schmidt, BF Bathel, SJ Grauer, MJ Hargather, JT Heineck, and M Raffel, “Twenty-five years of background-oriented schlieren: Advances and novel applications,” AIAA J 63(12), 5028–5058, 2025. doi:10.2514/1.J065669
  7. JP Molnar‡, J Xia‡, R Zhang, SJ Grauer, and C Liu, “Unsupervised neural-implicit laser absorption tomography for quantitative imaging of unsteady flames,” Combust Flame 279, 114298, 2025. doi:10.1016/j.combustflame.2025.114298
  8. AI Masker‡, K Zhou‡, JP Molnar, and SJ Grauer, “Neural optical flow for planar and stereo PIV,” Exp Fluids 66(6), 120, 2025. doi:10.1007/s00348-025-04058-1
  9. N Schmidt, PAB Braeuer, MM Pereira, SJ Grauer, FJ Bauer, and Stefan Will, “Development of a high-speed temperature sensor based on ratiometric NIR water emission for hydrogen and methane flames,” Appl Energy Combust Sci 23 , 100336, 2025. doi:10.1016/j.jaecs.2025.100336
  10. Y Bin, XIA Yang, SJ Grauer, and RF Kunz, “Data-enabled reduction of the time complexity of iterative solvers,” J Comput Phys 529, 113859, 2025. doi:10.1016/j.jcp.2025.113859
  11. JP Molnar, EJ LaLonde, CS Combs, O Léon, D Donjat, and SJ Grauer, “Forward and inverse modeling of depth-of-field effects in background-oriented schlieren,” AIAA J 62(11), 4316–4329, 2024. doi:10.2514/1.J064095
  12. JL Suazo Betancourt, SJ Grauer, J Bak, AM Steinberg, and MLR Walker, “Bayesian plasma model selection for Thomson scattering,” Rev Sci Instrum 95, 043004, 2024. doi:10.1063/5.0158749
  13. Y Bin, X Hu, J Li, SJ Grauer, and XIA Yang, “Constrained re-calibration of two-equation Reynolds-averaged Navier–Stokes models,” Theor Appl Mech Lett 14(2), 100503, 2024. doi:10.1016/j.taml.2024.100503
  14. FJ Bauer‡, PAB Braeuer‡, MWR Wilke, S Will, and SJ Grauer, “2D in situ determination of soot optical band gaps in flames using hyperspectral absorption tomography,” Combust Flame 258, 112730, 2023. doi:10.1016/j.combustflame.2023.112730
  15. K Zhou, J Li, J Hong, and SJ Grauer, “Stochastic particle advection velocimetry (SPAV): theory, simulations, and proof-of-concept experiments,” Meas Sci Technol 34(6), 065302, 2023. doi:10.1088/1361-6501/acc049
  16. JP Molnar, L Venkatakrishnan, BE Schmidt, TA Sipkens, and SJ Grauer, “Estimating density, velocity, and pressure fields in supersonic flows using physics-informed BOS,” Exp Fluids 64, 14, 2023. doi:10.1007/s00348-022-03554-y
  17. TA Sipkens, JC Corbin, SJ Grauer, and GJ Smallwood, “Tutorial: Guide to error propagation for particle counting measurements,” J Aerosol Sci 167, 106091, 2023. doi:10.1016/j.jaerosci.2022.106091
  18. SJ Grauer‡, K Mohri‡, T Yu, H Liu, and W Cai, “Volumetric emission tomography for combustion processes,” Prog Energy Combust Sci 94, 101024, 2023. doi:10.1016/j.pecs.2022.101024
  19. SJ Grauer, KM Rice, JM Donbar, NJ Bisek, JJ France, BA Ochs, and AM Steinberg, “Optimization of tunable diode laser arrays for inlet mass capture measurement,” AIAA J 60(10), 5854–5867, 2022. doi:10.2514/1.J061774
  20. JP Molnar and SJ Grauer, “Flow field tomography with uncertainty quantification using a Bayesian physics-informed neural network,” Meas Sci Technol 33(6), 065305, 2022. doi:10.1088/1361-6501/ac5437
  21. M Gomez, SJ Grauer, J Ludwigsen, AM Steinberg, SF Son, S Roy, and TR Meyer, “Megahertz-rate background-oriented schlieren tomography in post-detonation blasts,” Appl Opt 61(10), 2444–2458, 2022. doi:10.1364/AO.449654
  22. TA Sipkens, SJ Grauer, AM Steinberg, SN Rogak, and P Kirchen, “New transform to project axisymmetric deflection fields along arbitrary rays,” Meas Sci Technol 33(3), 035201, 2021. doi:10.1088/1361-6501/ac3f83
  23. NP Brown, SJ Grauer, JA Deibel, MLR Walker, and AM Steinberg, “Bayesian framework for THz-TDS plasma diagnostics,” Opt Express 29(4), 4887–4901, 2021. doi:10.1364/OE.417396
  24. SJ Grauer and AM Steinberg, “Linear absorption tomography with velocimetry (LATV) for multiparameter measurements in high-speed flows,” Opt Express 28(22), 32676–32692, 2020. doi:10.1364/OE.408588
  25. RB Miguel, J Emmert, SJ Grauer, J Thornock, and KJ Daun, “Optimal filter selection for quantitative gas mixture imaging,” J Quant Spectrosc Radiat Transfer 254, 107208, 2020. doi:10.1016/j.jqsrt.2020.107208
  26. SJ Grauer and AM Steinberg, “Fast and robust volumetric refractive index measurement by unified background-oriented schlieren tomography,” Exp Fluids 61(3), 80, 2020. doi:10.1007/s00348-020-2912-1
  27. J Emmert, SJ Grauer, S Wagner, and KJ Daun, “Efficient Bayesian inference of absorbance spectra from transmitted intensity spectra,” Opt Express 27(19), 26893–26909, 2019. doi:10.1364/OE.27.026893
  28. SJ Grauer‡, J Emmert‡, ST Sanders, S Wagner, and KJ Daun, “Multiparameter gas sensing with linear hyperspectral absorption tomography,” Meas Sci Technol 30(10), 105401, 2019. doi:10.1088/1361-6501/ab274b
  29. SJ Grauer, A Unterberger, A Rittler, KJ Daun, AM Kempf, and K Mohri, “Instantaneous 3D flame imaging by background-oriented schlieren tomography,” Combust Flame 196, 284–299, 2018. doi:10.1016/j.combustflame.2018.06.022
  30. TA Sipkens, PJ Hadwin, SJ Grauer, and KJ Daun, “Predicting the heat of vaporization of iron at high temperatures using time-resolved laser-induced incandescence and Bayesian model selection,” J Appl Phys 123(9), 095103, 2018. doi:10.1063/1.5016341
  31. SJ Grauer, BC Conrad, RB Miguel, and KJ Daun, “Gaussian model for emission rate measurement of a heated plume using hyperspectral data,” J Quant Spectrosc Radiat Transfer 206, 125–134, 2018. doi:10.1016/j.jqsrt.2017.11.005
  32. TA Sipkens, PJ Hadwin, SJ Grauer, and KJ Daun, “General error model for analysis of laser-induced incandescence signals,” Appl Opt 56(30), 8436–8445, 2017. doi:10.1364/AO.56.008436
  33. SJ Grauer, PJ Hadwin, TA Sipkens, KJ Daun, “Measurement-based meshing, basis selection, and prior assignment in chemical species tomography,” Opt Express 25(21), 25135–2514, 2017. doi:10.1364/OE.25.025135
  34. SJ Grauer, RW Tsang, and KJ Daun, “Broadband chemical species tomography: Measurement theory and a proof-of-concept emission detection experiment,” J Quant Spectrosc Radiat Transfer 198, 145–154, 2017. doi:10.1016/j.jqsrt.2017.04.030
  35. SJ Grauer, PJ Hadwin, and KJ Daun, “Improving chemical species tomography of turbulent flows using covariance estimation,” Appl Opt 56(13), 3900–3912, 2017. doi:10.1364/AO.56.003900
  36. SJ Grauer, PJ Hadwin, and KJ Daun, “Bayesian approach to the design of chemical species tomography experiments,” Appl Opt 55(21), 5772–5782, 2016. doi:10.1364/AO.55.005772
  37. KJ Daun, SJ Grauer, and PJ Hadwin, “Chemical species tomography of turbulent flows: Discrete ill-posed and rank deficient problems and the use of prior information,” J Quant Spectrosc Radiat Transfer 172, 58–74, 2016. doi:10.1016/j.jqsrt.2015.09.011
  38. SJ Grauer, EJFR Caron, NL Chester, MA Wells, and KJ Daun, “Investigation of melting in the Al–Si coating of a boron steel sheet by differential scanning calorimetry,” J Mater Process Technol 216, 89–94, 2015. doi:10.1016/j.jmatprotec.2014.09.001

Gallery

Bowling, Spring 2026

Photo of Grauer Lab

Boal City Brewing, Summer 2024

Photo of Grauer Lab

Bowling, Spring 2024

Photo of Grauer Lab

Links

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