Resonant interactions between runaway electrons (REs) and whistler waves in a tokamak may lead to pitch angle scattering of the REs. An increase in RE pitch angles may give rise to the energy dissipation of the runaways via synchrotron radiation. DIII-D experiments on whistler waves have indicated a possibility of intentionally launching whistler waves to mitigate the deleterious effects of REs on the plasma facing components via resonant interactions with whistlers [1,2]. In present work, we have use the coupled KORC-AORSA model to numerically analyze the complex nature of the interactions between whistler waves and runaway electrons in DIII-D. In this framework, we follow full orbit trajectories of large RE ensembles using the Kinetic Orbit Runaway Electron (KORC) code in the presence of whistler wave fields calculated by All Orders Spectral Algorithm (AORSA) code in a DIII-D experimental equilibrium. The nature of RE transport (diffusive/non-diffusive) [3] is analyzed in the presence of whistler fields and the impact of whistler field amplitudes and frequencies is observed on the pitch angle scattering of REs. Our findings indicate a significant increase in RE energy and scattering of the runaways to large pitch angles for whistler fields exceeding a threshold amplitude. The coupled KORC-AORSA simulation model can be further used to get physical insights into tokamak experiments on whistler waves- REs interactions. [1] D. A. Spong et al., Phys. Rev. Lett., 120, 155002 (2018). [2] W. W. Heidbrink at al., Plasma Phys. Control. Fusion, 61, 14007 (2019). [3] D. del-Castillo-Negrete, Phys. Plasmas, 13, 082308 (2006). This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award(s) DE-AC05-00OR22725, DE-FC02-04ER54698, DE-FG0289ER54297, DE-AC02-09CH11466.